I’ve just done a legtimate 425 mile solar powered round trip which is the culmination of many things I will explain below. I can now effectively drive anywhere in a 225 mile radius and back for about $10 total cost and on 100% solar power.
I have a two complete solar systems on my house the first one was 10.98kW AC installed 4 years ago with the panels facing south. The second was just installed a few days ago and is a 9.9kW AC with the panels facing east/west. Combined the system will produce over 20MWh of power per year. Both systems are grid tied used EnPhase microinverters and are now combined together for monitoring in one site.
I have an EnPhase IQ EV Charger. This has a mode where it communicates with the solar system, understands how much power is being produced and consumed in the house and then adjusts the EV charger output to match the excess solar production.
I have an EV with the largest battery that is available. The Chevy Silverado EV truck has 24 battery modules with a total gross capacity of slightly over 200kWh. The efficiency on road trips at high speeds is about 2.1miles per kWh. I have verified this with a real world road trip of over 400 miles.
The cost of the solar is around 5 cents per kWh over the 25+ year lifespan of the system.
Another less commonly discussed option is community solar (also called offsite solar). It's especially attractive if the roof line of your house isn't ideal for solar panels or if you expect to be replacing your roof within the lifespan of your panels. (Or if you have a historic association like I do that makes almost every home project impossible.)
You still purchase and own the panels, but often a third party maintains them for you and they are installed as part of a large, offsite array. Since they're usually installed at ground level, they can also do more interesting things like follow the sun. The way it works is the power your panels produce is subtracted from your energy usage via an arrangement made with your utility provider.
Like any solar purchase, the cost of your panels can be financed over time and charged against your energy production. So the net effect is your power bill just goes down until the panels are paid for. At that point all the power you generate is deducted from your power bill. To me, it's most all the upside of owning panels on my roof.
The described version of community solar is nice. How it is usually implemented like in Maine ends up sucking.
The root cause is that they wanted community solar customers to be able to opt-in and opt-out any time. As such it isn’t really what you describe which is owning panels offsite, you are more or less doing a short term rental on them. As such you don’t get the full benefit from them but simply a 15% discount on the current residential rate.
I very much think that proper community solar would be a larger upfront investment just like panels on your roof are. With a small monthly cost to maintain the grounds and pay taxes on the real estate where the panels exist. All power generated would be metered for the specific panels you own using microinverters.
I don't understand the purpose of consumers owning individual solar panels in a large array. How is that better than a single entity owning the whole array, and what function does the consumer provide?
> I don't understand the purpose of consumers owning individual solar panels in a large array. How is that better than a single entity owning the whole array, and what function does the consumer provide?
I don't now if it's better, but it is different.
The benefit to the utility in this case is much lower capex - it's basically like the restaurant franchise model, but for power.
But like you imply, there's a tradeoff that can be made between capex and opex - in this case, the utility could own everything and consumers could pay for electricity on an ongoing basis. IMO, this model is superior due to reduced principal-agent problems.
Just to be clear you're talking about variable costs not total costs. Total costing include time value of money, amortization etc. (I'm no hater I also drive an EV).
> I have an EV with the largest battery that is available. The Chevy Silverado EV truck has 24 battery modules with a total gross capacity of slightly over 200kWh. The efficiency on road trips at high speeds is about 2.1miles per kWh. I have verified this with a real world road trip of over 400 miles.
This is interesting. While it has the most storage capacity, the range is not good for that much battery.
I don’t think the Silverado is optimized for driving range, but rather - can it do typical “truck” stuff. For example hauling and/or towing. For this workload, having more towing capacity in a slightly less aerodynamic package is probably a good trade off. You don’t get a truck for the efficiency, you get one so you can do stuff with it.
Still, having a 400 mile range also makes this more useful for the middle of the country where there are wide open spaces between towns for charging. Also, having a legitimate truck EV makes it more likely for traditional truck buyers to think of getting an EV.
I'm looking at doing similar stuff right now. I already have a house battery.
However, looking at getting an EV - were you able to get bidirectional charging going?
I saw a few places mentioning demos of it over the past 5 years, but I can't find any v2x charger/car configurations I can buy and use in the UK.
Before looking at any of this stuff, I didn't realise how large and cheap the battery in an EV is compared to house batteries. Now I'm struggling to justify getting an EV if I can't do at least V2H bidirectional charging.
Interesting thanks! It looks like most of the GM vehicles that v2x works with are... uh... not really something a European would consider an option (not even sure if some of them will fit on our roads). Ford UK makes no mention anywhere of anything to do with v2x though.
There's a few places that apparently offered it here, but when I've contacted them, they've all explained it was a tech demo, or trial, or some other PR type thing which means they didn't take it any further and regular humans can't buy it. I think there's some nuance or regulation around the UK power network which is stopping any progress with bidirectional charging here.
Over here though, if you don't have old electric heating, or an electric shower, 9.6kw is very much more than enough for the average household. I have a relatively high usage, and a 6kw inverter can power my house in a powercut, as long as I don't use the electric shower. The various retired people in my life tend to use 2 - 4kwh /day, the peak draw is the kettle which uses 3kw for a minute or so.
> Thier max output is only 9.6kW so it can’t do a whole home backup and the car can only run in backup mode when the grid is out.
9.6kW should be enough to backup your entire house, that's 87A... Lots of people only have a 100A supply in general. Depending on your setup you may have to limit what you use at one time but even in a large house that will be more than enough for AC, lights and electronic devices.
9.6kW is 40A at 240V, and a 240V 100A single-phase residential service is 24kW.
Still, 9.6kW should be more than enough to run a fridge, lights, receptacles, sump pump, a 2-3 ton A/C unit, and a furnace fan. It would be challenging to impossible to back up a home with electric (resistive) furnace and electric (resistive) water heater with only 9.6kW.
That’s peak production, without battery storage the fluctuation during the year will likely be too much to keep the “lights on”. Would be cool to have a smart home that prioritizes the electricity supply to different systems based on how much is available.
>This has a mode where it communicates with the solar system,
I just find this so cool. We have projects like SETI where the solar system tries to communicate with us. Here, you, just one person, have set up a machine talking with outer space and the solar system. Space is talking and we are listening. Amazing. Rock on space cowboy.
I assume you're on a pretty attractive net metering agreement? That's a huge system.
Unless you're consuming a significant portion of that, the payback rate is going to be pretty badly impacted by having such a large system for most people.
I consume about 17MWh a year between two EVs and a large heat pump for winter heating.
I will have overproduction now with the 2nd array. We do have net metering at about 80% of the cost on NEM 2.0. Our bill is split by transmission, generation, distribution and fees. We get 100% on transmission and generation and 25% on distribution.
$0.05 is the rate we pay in BC at night. I was still debating whether to add solar or not, I guess your post answers the question.
Until we can get to $0.01 there is no point in solar in BC at least.
From an efficiency standpoint, we should probably be building grid-scale solar in Alberta and pumped storage in BC. There's more sunshine on the east side of the Rockies.
As a resident of Alberta, I pay $0.205/kWh for energy and delivery, which I largely attribute to bad decisions made by our provincial government. Even still, my 10 kW rooftop solar install is barely financially viable at those rates.
With that said, it would help if the Canadian government didn't have enormous tariffs on solar panels. Canada levies taxes such that solar panels here cost nearly triple what they cost elsewhere.
The article is about installing solar panels on vehicles. Your truck has no solar panels installed on it. What is the relevance of your anecdote to this discussion?
I built my own electric cars and calculated if this would be worth it. Roof of car is curved and you get the conversion losses (needs to be bumped to 400V to charge batteries).
You add a lot of complexity for marginal gains. Peak time you get maybe 500W which doesn't go very far.
I have a 100w solar panel on top of my car...to tend a 12v battery. It's got a Dewalt battery charger, mikrotik ltap, and raspberry pi hooked up to it. Little hotspot with multiple sims and resource server(mainly just for fun). Anyone that can do basic math should immediately realize there's just not enough area to make an appreciable difference in regards to mileage.
The Prius Prime solar panel roof I think can net 3-6 miles a day under ideal conditions (which we're probably close to here in Arizona). I think that's a little more than people would expect, but still only applicable in niche conditions (tiny daily commute, or a longer non-daily commute). I think the math works out to ~4-6 years to break even for the cost of adding the solar roof assuming $0.15 per kwh, which isn't terrible.
If solar tech gets more efficient or cheaper, I think it starts becoming a much more attractive option in some areas. If you get into the 10+ miles per day range, that would cover a lot of peoples commutes in certain areas.
13.6 kWh battery. 39mile EPA range. Equals 2.87 miles of range per kWh. Leaving it out for 8 hours straight, on a sunny day, in LA, netted 915 Wh. Or, 2.86 miles. [0] Not 3-6, 2.86.
2.86 miles of charge, but only if left outside, uncovered, in full sun, on a fully sunny day, for a full 8 hours, in a place that gets effectively the maximum amount of solar radiation per day out of anywhere in the entire country.
Now, do the same experiment anywhere else in the country, that doesn't get max solar radiation, or that can't get full sunlight for full 8 hours, or where it's cloudy at all, or rainy at all.
2.86 miles per day is the practical MAXIMUM, given perfect conditions. For the average scenario it'd be some fraction of that.
The 6 miles figure is what they said you'd get if, in addition to perfect conditions, "if the sun shifted its orbit" (?) and gave perfect sunlight for 12 hours straight. Which is a number which should obviously not be thrown around as if it's obtainable.
The fact that they're quoting numbers about what range you'd get if the solar system was constructed differently also makes me doubt the impartiality of their experiment and the numbers they provided.
> 2.86 miles per day is the practical MAXIMUM, given perfect conditions
In your particular setup.
A typical car can expose about 3 square meters of lateral area for those same 8 hours, and receive 3 kW of irradiance. multijunction cells can exceed 50% efficiency, so we're talking about a theoretical upper limit of 12 kWh electric per day.
That would require a vehicle totally covered in cells, including the windows, so not very practical, but adding up to 30 miles/50 km per day
is nothing to sneeze at.
We could also imagine all sorts of solar receivers that engage during parking and inflate the apparent surface within the limits available, track the sun etc. to maximize energy.
The maximum demonstrated efficiency of a multijunction cell, in a lab, WITH CONCENTRATION is less than 50%. Commercially available cells are lower.
Concentration is an important caveat for two reasons:
First, it implies that you are collecting light from a larger area than the PV panel itself. Second, efficiency grows with increased irradiance (so efficiency will be lower without concentration).
> 3 square meters of lateral area
Lateral area is meaningless. It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck, there is zero probability that you can put 3 kW of irradiance on your panels. Neither of those vehicles will achieve kWh/mile numbers anywhere close to a Prius.
In practice, you need to halve the efficiency and more than halve the collection area you quoted. You also need to account for conversion losses.
This is a theoretical exploration of the hard limits, not an engineering design.
The multijunction theoretical efficiency limit is 87% with infinite junctions, and over 50% with a practical number of junctions. There's nothing stopping you from creating a miniatural concentrating solar device that focuses the light from a 10 cm^2 area onto a 0.5cm^2 cell, we haven't seen such devices because the cost and extra mass exceed what you get from the efficiency gains when you can simply increase area; a very area constrained application with high power requirements might change that.
> It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck
Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the sun, perhaps even unfurl additional area? what about the area of the doors and windows?
Current solar cars can drive 1000 km per day with an average speed approaching 100km/h. It doesn't seem completely out of the realm of the possible to achieve 50km in an hour for a passenger car that can expose similar area while parked.
> This is a theoretical exploration of the hard limits, not an engineering design
You replied to (and even quoted) a comment explaining the practical limits, then doubled-down and said multi junction cells can exceed a number which has never been experimentally demonstrated.
And here you are again saying that multifunction cells can achieve 87% efficiency.
An ICE engine can achieve 100% thermal efficiency with the right Th and Tc. That has about as much relevance to the discussion at hand as 87% efficient solar panels.
Let me be clear: the most efficient cells that have ever been experimentally demonstrated under any conditions are less efficient than the number you originally stated. In real world conditions the number is half of what you originally.
> Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the
EPA range tends to be pessimistic for EVs as it assumes you are always traveling at highway speeds. Even small reductions in speeds can make EVs much more efficient since drag is quadratic. A quick google search shows Prius prime owners reporting 4-5.5 miles/kwh, so the 3-6 mile range is entirely plausible.
> EPA range tends to be pessimistic for EVs as it assumes you are always traveling at highway speeds.
EV EPA range historically has been overstated. However, the water is muddied because the EPA doesn't really force the manufacturers to give an accurate number. A manufacturer can choose a highway only test, but then also arbitrarily decide to derate the value (EPA example is 70%). A manufacturer can choose to include city driving in the rating and weigh it accordingly and also derate the value (if they want).
Tesla traditionally (still the vast majority of new and used EV market share) has been the only manufacturer that uses the highway + city driving tests. People then get surprised when the car cannot do the full range at 85 MPH.
All in all, this is the EPAs fault. For EVs they really need two numbers, city driving range and highway driving range. EVs are so much more efficient than ICE that speed makes a huge difference given there substantially smaller energy density.
If we're picking nits, the usable capacity is only 10.5 kWh (11.5 kWh with AC-to-DC losses), so it should be 3.40 miles. Not 2.86, or even 2.62 (= 39/13.6 * 0.915).
Everyone is also glossing over the distinction that regardless of the actual amount, it's not at an actual voltage that can charge the battery to add mileage. You can hypothetically say that because it's offsetting the power usage from the AC that it could theoretically be saving that battery usage...but there's so many gross assumptions being made that it's a pointless statement to make, and it's all out the window the second the car starts the ICE side of the hybrid drive system for even an instant.
> Everyone is also glossing over the distinction that regardless of the actual amount, it's not at an actual voltage that can charge the battery to add mileage.
Neither is the voltage when you plug it in at home. The car has a unit specifically to convert the voltage.
If you're saying they didn't connect the right wires for that, that sucks but is easily fixed.
> it's all out the window the second the car starts the ICE side of the hybrid drive system for even an instant
Nah, doing a drive where it's 99% solar power and 1% "burned an ounce of gas to maintain the engine for the month" is fine.
That article sure has 49 pictures, none of which show more than the very edge of the solar panel.
But looking at some proper pictures, it covers most of the midroof with 7x8 tiles of solar. But you could fit a good percentage, even sticking with a design where a huge amount of the roof into the trunk is all glass. And there are no panels on the hood. So that's an easy doubling right there, more with an average car roof shape.
I wonder how much extra range you would get if one leaves the car in the shade so that it doesn't get super hot and there is no need to turn on the AC hard? I bet it's more than 2.86 miles.
I believe having a carport and house roof covered with solar panels + (PH)EV is the best option.
The initial use of solar on the Prius was to power a ventilation fan while the car was parked, and the current version seems to specifically be designed to provide power to the air conditioner while driving. But, I also can't imagine the difference between cooling down the cabin is much different from parking in the sun or in the shade - you'd be running it continually to achieve "room temperature" during the entire drive either way.
You can't imagine that air conditioning power draw varies with the heat load that it is working against? As a heat-pump, it takes more energy to move more energy.
In the old days, they used duty cycle to adapt to the changing load. Modern ones do things like varying compressor displacement or compressor speed to adapt to the load. Variable frequency inverters are used to efficiently drive electric compressors.
The variable displacement trick is used in ones mechanically linked to internal combustion engines. It can vary the compression stroke to account for different load as well as different engine speed.
Watching power draw on my Leaf with LeafSpy, the AC seems to use between 500-1000W (maybe more sometimes, but that's just off the top of my head from a few times running it while driving).
At the low end maybe achievable with a full rooftop covered in solar panels, but probably not adequate at 1kW+.
What kind of European cities are you talking about lol, no offence but I hate this generalisation of "European" anything as if Southern Spain has the same culture and architecture as Poland or Lithuania.
To my thinking, the best use of a solar panel on a car is running a low power AC unit all the time whenever the car is in the sun. Parking in the shade often isn't possible.
I don’t think you’d have to run the AC any more aggressively with the solar panels than with a traditional steel roof?
If you’re suggesting it wouldn’t work in a garage, that’s obviously true (and another factor in whether car solar makes sense) but many (most?) people park their cars outside during the day anyway. I for one can’t remember the last time I parked under cover
That's still 3-6 fewer miles worth of charging to do from more expensive sources. Even if it can't come close to covering your full use it's still covering something
It may still lose on this, but you would also want to include the externality costs that the consumer doesn't themselves bear for whether it is worth it overall.
There is going to be a parasitic drag loss to figure into it as well. I think the only way to accurately calculate that would be in a wind tunnel or maybe an amp meter with a before and after installation under identical conditions.
The Prius Prime solar roof is a $610 option available only on the top XSE trim level, so a hypothetical buyer is paying ~$7500 to access this effectively negligible amount of energy.
ETA: and the fact that this option is tied to the significantly less efficient 19" wheel package, instead of the standard 17" wheels, means that this will never, ever be a net benefit.
I just started doing this with my car, mostly to add a camera/temp monitoring for when I leave my dog in the kennel in the car (she's well watched over, please don't fret over it).
I'm hooking it up via starlink specifically so it works in remote areas with no cell coverage too.
Monitoring and proxying everything via an RPI as well. Victron DC-DC inverter to keep the bluetti battery pack charged with bluetooth relay boards so we can turn loads (camera/starlink/others) on/off programmatically (it only turns the starlink on when there's no good/known wifi for example).
Fun project, combines software dev (which I'm fairly good at) with hardware work (which I'm less) and my dogs (which I'm a big fan of).
The maths says that the *mean* number of miles driven by a vehicle is surprisingly low, and that tiling the surface of a car can get to about 80% of that *mean* in places where the car is just left out on the street and not shaded parking.
But!
That's a practical consideration at the level of "should a government require EV makers to design the roof, bonnet, doors etc. to be tiled in PV in order to reduce, but not eliminate, the induced extra demand on the grid" and definitely not "should I personally bolt a small, fixed, PV panel and inverter into my EV as an aftermarket DIY job?"
The former gets wind-tunnel tests for efficiency, QA, designed around all the other safety concerns cars have e.g. crash safety.
> You add a lot of complexity for marginal gains. Peak time you get maybe 500W which doesn't go very far.
The complexity should not be overlooked. The PV panels add a lot of things that can fail: An additional layer that must be adhered or fastened the roof. Transparent panel covers that can become damaged in ways that aren’t as easy to repair as a rock chip in paint. Extra wiring that runs into the vehicle. A charging regulator. Systems to monitor that it’s all working and give the appropriate diagnostic codes if it fails.
Having worked on a lot of older and newer cars when I was younger, I’ve come to appreciate a degree of simplicity in vehicles. Modern electronics and vehicle systems are more reliable, but when the number of motors, sensors, and functions in a car goes up by 10X with all of the new features, a lot of little things start to fail in annoying ways as cars age out.
With solar I imagine old car owners would just ignore the system when it stopped working, but you’re still hauling all of that extra weight around for the lifetime of the car. That extra weight subtracts from your efficiency.
The simplicity of EVs is one of their big strengths! Compare all the cooling, transmission, lubrication and fuel systems of an ICE car to the simple Electric Motor of an EV. Vastly simpler. As an end user, I see it to, my EV has no scheduled maintenance, whereas the ICE wants me to take it to the dealer every 20k miles.
But most of that electronic complexity is just as present in ICEs as in EVs, no? It’s not like most of it is in the drivetrain. All those auxiliary systems.
That's the problem. I don't need or want any of that extra nonsense. You can't replace the radio in these contraptions. The only thing a car needs is: drive-line control, braking/ABS/ESP, steering, HVAC. Electronics wise dump the lame glued on tablet look and just give me a single up front dash display and a double DIN cutout in the dash. HVAC only needs knobs. I hope a Chinese auto maker comes out with an EV that dumps all of this stupidity and just gives us cars again.
Backup cameras (and the associated display in the dash) are a significant safety improvement. I wouldn't want to buy a car without one at this point, despite the increase in tech that it necessitates.
To be fair, modern PV cells are purely solid state (no moving parts, no lubricants or coolants), so a solar system shouldn't add a scheduled maintenance burden, just add to potential unscheduled maintenance costs in worst case scenarios.
There was some car which used a small solar panel to pass fresh, cooler air into the cabin during sunny days. This both made the car more pleasant to enter and lowered the initial AC surge. I don't know if it also trickle charged the starter battery so it never could get completely depleted from just standing for longer periods. Both these things seemed worthwile.
The 2010 Prius IV had this as an option - one of my favorite cars due to low maintenance (the lowest maintenance visits per year for its era). The solar panel air vent circulation is a nice feature (even if slightly gimmicky) and I suspect extends the hybrid battery life as well by preventing some marginal battery heat death while parked.
The newest (2023+) Prius brought back the solar roof as an option - and this time it charges the battery (albeit marginally / but not bad for those that drive minimally).
This is a perfect nerd snipe. I can't imagine any car owning (esp ev owning) engineer hasn't or wouldn't eventually think about "why can't I charge my car from my car".
You might like the series by youtuber 'Power of Light' where he packs solar panels in his car to charge his car to do a solar cannonball run from New York to California on those solar panels alone: https://m.youtube.com/playlist?list=PL9nfj0jfPXYBF8FO7sckzvV...
Can't remember how long it took, think a couple weeks at least?
he planned for 30 days and it wound up taking 60. he didn't strategize to minmax it, though? there was a lot of up and down and he stopped mostly at places where there were fun public camping parks. also he went solar -> battery -> ac -> tesla with an alternator to a standard tesla house plug iirc? whoo.
i think there was an interview later where he said, "yeah never doing that again" or something to that effect.
Agreed. Using solar to power vehicles is great, but there's little benefit in the panels being on the vehicle. Put panels on your house, charge your EV, and you've got a solar powered vehicle (and house).
Not sure if I've slipped a 0 here but 500w taken over the year, at say a 10% capacity factor, is still over 3500 miles of range per year. A fair bit short of the average mileage (in the UK somewhere around 10k) but still more significant than I expected. Of course 500w is a lot of solar for a car and 4 miles / kWh is also quite efficient.
I think this is a flawed comparison. You only care about speed when driving, but charging we care about whenever the car gets sunlight. I would argue for most people car in sunlight time is a multiple of car driving time. Still pretty abysmal, but less bad than 2 mph.
Range isn't a unit though, so it isn't actually telling you anything technical. Since range is a distance unit, it would still be "miles per hour" or "kilometers per hour" or "meters per second" or anything to let you know how long it will take to top up to full range.
Could be "%/minute" maybe, but that is less useful if you know you need to go 45 miles, you would want to know how many hours (or fraction there of) that would take.
Same dimensions, same units. Sure it can be expressed more specifically e.g. "miles of nominal range per hour". But it's still miles per hour to facilitate mental calculation.
People don't seem to talk about Watt hours per mile much but when you're generating the power yourself it really matters. Tesla's model 3 is AFAIK one of the more efficient EVs and gets ~260 Watt hours per mile. With solar a good rule of thumb is to take the nominal rating for the panels you can point south and multiply it by 4 to get the approximate daily energy you'll generate in watt hours. If you could optimally park a car and let's assume you could cover it in a couple 100 Watt panels that would give you about four extra miles of daily range.
Maybe it's interesting if you live in a city and drive once a week.
I wonder if it would be OK-ish to build a very lightweight, very long, low powered solar "bus" (or a tram like chain). Just enough to roam around a city at 15-20mph for free.
There have been solar car competitions that colleges have been doing for decades. Here's a YouTube compilation of one that ran last week: https://www.youtube.com/watch?v=ZBin-oXBJzM
I think it can help calibrate people's intuitions about what you can expect out a pure-solar car.
You also need to remember that inside those shells is basically nothing but a driver. No AC, no seats for people beyond the bare minimum. And that's broad daylight. So you need to look at them doing 20-30mph and bear in mind that it's still not comparable to a street-legal sedan of a similar size doing 20-30mph... those cars are essentially as close to "a mobile cardboard box" as the competitors can make them.
You might be able to build something that people would agree is "a bus" that moves with a couple of people on board, but it probably will stop moving once it enters shadow. Anything that we'd call "a bus" is going to need a lot more physical material per unit solar input than those cars have. I'm not sure that even "moves with a couple of people on board" will necessarily end up being faster than those couple of people walking, either. It's effectively impossible to power a vehicle with its own solar footprint in real time. It also ends up difficult to use them to power batteries because having to move the additional mass of the batteries eats up the advantages of being able to gather power for larger periods of time. It's possible, because of course you can hook a car up to solar panels and eventually charge it, but you don't get very many miles-per-day out of it for what fits on the car itself alone if you work the math.
Yup, was just going to link something like that— here's the University of Waterloo's solar car team's vehicles: https://www.uwmidsun.com/our-cars
And even those IIRC don't drive continuously. They drive for part of the day, then park them angled into the sun for the other part of the day to top up the batteries.
It's pretty hard to beat fixed panels + fast charging + parking your vehicle in a garage where it doesn't see the sun anyway (or get super hot).
It's an interesting idea. I did some napkin math based on the Solaris Urbino 18 bus. The buses have about 45 square meters of ceiling area (18m by 2.5m). Assuming efficient solar panels you could get 250w/sqm. That works out to 11.25 kwh/hour. The bus advertises with 600km of range with 800kwh of batteries so that is 1.33 kwh/km. Hence it could do ~8km/h on average when it is sunny.
The math does not really work out to a viable product with this bus, but it is not too far off. A city bus that has been purpose-built for low speed in urban areas without other traffic may work as it can make some sacrifices. For instance, since it runs much slower on average it would need smaller engines. It could also use more light-weight material since it won't need to handle high speed collisions. If it is just used for short distances within a city center it could also do away with seats. Lower speed should also lead to lower consumption.
The Solaris Urbino 18 weighs 17.5 tons curb weight. Assuming fuel consumption is pretty linearly related with weight and you could get it down to less than half, you could get a bus with a range of 10 miles per hour of charging. If it drove for 6 hours a day, but got charged for 12, 20 miles on average per hour is possible.
Yeah I wasn't clear enough but I was really thinking about the most limited form of "transportation", low speed, low weight, so minimal frame and no protections really. Basically a string of bus stops on wheels. Maybe an average speed of 13mph would be enough. That's 3 three times the average walking speed.
Why bother? Put the charge station in the bus stop instead. They have a longer runtime to charge and the bus does not have to be slow.
Potentially easier to maintain too.
Why bother ? Have the solar panels on top of the tram warehouse, use the tram batteries for storage, swap empty ones for full ones when needed. If the solar array is down use the grid. That way you divid points of failure instead of multiplying them
> I'm sure they must exist somewhere, but battery-powered trams are not popular.
Yes, they do exist. The Alstom Citadis at Rio de Janeiro, which I take often, uses a supercapacitor for small pieces of its route (mostly crossings where the third rail would be damaged too often by vehicle traffic, or be impractical); according to the Wikipedia article (https://en.wikipedia.org/wiki/Alstom_Citadis), the Alstom Citadis at Nice uses batteries for parts of its route (https://www.railway-technology.com/projects/nice-trams/). I'm sure there are others.
I suspect the lightweight, and hence low power requirements, are the correct part of the hypothesis. But making the vehicle as big as a bus implicates a lot of weight. Maybe a solar charging cargo bike fairing would have some benefit, but that's an expensive bike and it will tend to get stored indoors.
Maybe an electric assisted pedal bus with a solar roof would make sense.
Very location specific, might do wonders in Cancun or San Francisco or Vegas, not so much in Gatlinburg or Seattle or anywhere where there is not a lot of tourism or where there is a lot of rain or that has a long snowy season.
Well, if you have a fixed route you are not limited by space on the vehicle to put solar on, but can provide electricity via a rail or wire or something and then gather energy on some larger Solarstation or from wind turbines or what else comes to mind.
Then you can reduce rolling resistance by using steel tracks and steel wheels ...
... and oh, you have invented the tram/light rail ;)
(But even with solar you need to finance the construction and maintenance, even the slow vehicle need some ... thus either tax finance or charge fares or mix income)
Yep. A solar car ceiling seems great to make EVs more reliable on the hands of people that only charge them rarely or may travel to the middle of nowhere and can get surprised by battery faults.
Those are a very small share of car owners, and EVs are nowhere close to the market penetration to care abut them. But it will eventually make sense.
I agree on this. Using the pvwatts calculator for a very rough estimate of cumulative kWh produced per *month*, a theoretical 380W panel on top of a car that is in perfect sunshine from sunrise to sunset, never shaded or obstructed, on a car in the sunny climate of San Diego CA will produce the following:
61 kWh per month in the best month of the year (August)
39 kWh per month in the worst month of the year (December)
As you can see from this, the kWh per day is quite minuscule, not enough to charge a car to go any appreciable distance.
I believe that solar panels were an option on the Maybach 62S, and they would run the ventilation fan while you were parked so you wouldn't return to a hot car after going to the store.
Like everyone else has said - there just isn't enough area on the top surfaces of a car to do any noticeable charging.
If you were to theoretically have a perfect 400W PV panel on top of a car, and left in direct sunlight, it might be enough to run a medium sized peltier/TEC cooling unit to somewhat cool down the car while you leave it parked. Or a very small heat pump. Would definitely add a lot of extra cost in manufacturing and complexity.
Or just keep the car fan running and use the existing AC system (in ventilation mode, no compressor) to keep the car just as hot as outside (instead of much hotter). If you have some spare power maybe even run the AC when the key gets back in range.
The rough estimate calculation for the theoretical 39 to 61 kWh per month are for a perfectly mounted, south facing, 15 degree tilted PV panel such as might be on the roof of a warehouse, or in a field somewhere. With no buildings or trees or shade obstructions around it. And perfectly exposed to sunlight from the moment of sunrise all the way to sunset. That's the 'default' assumptions built into pvwatts for calculating a fixed installation PV site.
On an actual car that parks under trees, in parking garages, beside buildings in the shade, etc, the actual production would be much less. Not to mention the panel would be 'flat' on the roof and rarely if ever angled facing south, unless you happened to park on a hill with the roof of the car angled south...
It's also not possible to say that a theoretical 39kWh can be turned into so many miles at 270Wh/mile because it's not a perfectly efficient system, I'd guess at least 15-20% would be lost to heat in charging the battery and DC-DC conversion.
The math is biased towards when you are using the vehicle. The solar panels also work when you aren't using the vehicle. They work from when the sun comes up until it goes down. And actually most people don't actually use their cars most of the time. It's just sitting there parked doing nothing well over 90 percent of the time. And especially hybrids have tiny batteries to begin with. Instead of charging those burning petrol, you could be partially charging those with solar.
If you get 400W watt performance for a few hours per day, that's maybe a couple of kwh per day. 2 would be alright. 4 would be amazing. 6 probably not that likely unless you live in a very sunny place. Most decent EVs do at least 3 miles per kwh. So, you get maybe 6-12 "free" miles per day. Maybe more with an efficient one. Up to 20 miles even.
Most commute round trips aren't that long. You are might need more power than that. But not a lot. You could be cutting how often you charge by some meaningful percentage. It's not going to be that useful on a long journey. But most people don't do those all the time but they drive small distances on a daily basis. Imagine you drive to work, and back maybe covering 20 miles. You go to sleep, and the car is back at 100% charge. Because you only used a few kwh driving there and back and the car had plenty of time parked to collect those back because the weather is nice. Or maybe it got to 95%. The difference is meaningless because you only use a few percent on a given day. Basically you'd be charging a bit less often and stretch existing charges a bit longer.
If you have a 60kwh battery and you get 2kwh per day from the sun, that's 1 full charge per month. Most people would charge maybe 2-4 times per month. So that's a meaningful amount. Cutting them amount of power that you have to pay for by 25 or more percent can be interesting. I think for most the savings aren't going to be dramatic. But it's nice that the car just sits there slowly topping its battery up without you having to worry about it. That's convenient.
Can you comment more on the complexity? Like, is it running wire harnesses everywhere, is it the power electronics, cooling, mechanical mounting, something else, all of the above?
Of course. It is an intriguing idea, but a local maximum.
- The panel sits at open-circuit voltage of 48V
- That then needs to be converted/boosted to 400V (conversion loss)
- The converter needs to talk to the BMS to make sure batteries can be charged at this moment (component that is live all the time and is a current draw)
- Need to think about it, but you want another set of contactors between panel and HV-Bus where the battery sits (current draw)
1km of driving is 150Wh so 1kWh gets you 6.6km or 4.1 mi
Let's be generous and say you have a 500W panel(punchy) for 8 hours at full blast (doesn't happen), you get 500W x 8 hrs = 4kWh. Lets say isolated converter loses you 10% so you are at 3.6kWh Thats 24km or 15mi of driving in perfect conditions.
2x Gigavac contactors, keep them closed costs you 24W, so that lowers the input further to 476W * 8hrs = 3.8kWh, less 10% = 3.42kWh ...
Someone who studied EE might be able to make this more accurate.
Back of the napkin math, not totally impossible, but not worth adding it for a trickle charge. Adding components that can break, adding weight etc.
There are interesting solar cars out there where you reduce the weight heavily and fold out big solar sails. Then you are getting somewhere, for a city car you don't have enough surface. For an SUV or American Style Flatbed truck you have so much weight it's not worth it either.
I don't drive 24km per day, and don't have a good way to get to the train station other than by car. The bus is too tight, they miss each other often. Cycling isn't safe between towns, you have to basically go on a highway without any separation (yes that's legal in Germany to cycle on, as there is no other way than perhaps a farmer's grass path to go between towns, so they don't call them highways but cars drive highway speeds - or more, if they don't stick to the limit). I also don't have charging infrastructure or a driveway. A vehicle that does those couple km a few times per week without needing to drive elsewhere to charge gets me a long way. Charge me up, Scotty
I've looked into this and the moment the Aptera ships (probably never but here's for hoping) I'm buying my first car. I've looked critically at the range they assume you get at my latitude and it would keep topped up for enough months of the year that it's totally worth it (maybe it was even year-round because they're so efficient, I don't remember now, but I'm also okay charging it thrice a year)
But 24 km per day is under ideal conditions (perfectly sunny day, mid-latitude, panels angled southward) and 500W requires 2 square meters of panels[1].
Unless you own a big American pickup truck, it's hard to see where those panels fit on the car. And if you do own a big American pickup truck, you will not achieve the 150 Wh/km assumed by the GP (it will be more like double that). GP also used quite optimistic loss figures for conversion.
It begs the question: Why not a Nissan Leaf and solar panels on your (home) roof?
[1] Only 1000 W of solar energy falls on each square meter of the earth's surface at noon. The best commercially available solar panels have about 25% efficiency converting light to low voltage DC. This means you need a flat surface of about 2 square meters directly facing the sun to collect 2000 W of light, which will achieve 500 W of electrical power.
Why not on your home roof: because I don't have a home roof or a place to run the cable to the car. I could ask the landlord if they'll allow me to pay for solar panels on their building but I still don't have a driveway as mentioned
Why doesn't the Leaf have it: afaik the leaf is a normal car, not like the Aptera that I'd be looking to buy. Even the Lightyear One was claiming to be more efficient than normal but pretty disappointing in how much range you get from the solar roof. Still more than zero though, so yeah ask them why they don't sell that variant ¯\_:|_/¯ While we're at it, let's find out why there isn't a smartphone that fits my niche (modern chipset with dual frequency GNSS for less than twice the price that competitors charge for it, operable with one average-sized hand, sdcard slot, and ideally a headphone jack but at this point I'd settle just for a bit of storage and really don't feel like it should be a hard-to-find device) or a laptop that makes sense (arrow keys and no annoying tapered edges that don't fit a network port, for example, already limits your options to a tiny percentage of the available systems)
Maybe an RV could be covered with solar? The top is much bigger, and if it isn’t charging fast enough you can always pull over and have lunch while the battery catches up.
RV panels make sense for the boondocking use case, where you want to charge computers or power a satellite internet terminal or something, but I can't imagine actually trying to drive on that trickle of juice.
Agreed. There’s an EV camper van with rooftop solar. IIRC it gets about 1000W peak, which isn’t bad for the home batteries but is basically nothing for the high voltage drive system
How about charging your house batteries, which power fans and lights and perhaps cooking and A/C? This kind of solar setup can be rather cheap and quite effective.
Yes, that's what I'm meaning. AIUI off-grid camping tends to be more limited by the drinking water supply more than electricity, but if collecting solar power lets you avoid running the generator quite as often, that sounds like a win.
It’s always going to be anecdotal. I reckon a mid size RV (say upper class B) will have 1500-2000W of solar capacity, if it’s really boxy. It’s going to have the aerodynamics of a brick. Meaning you’ll be lucky to get 1mi/kwh at highway speed, maybe 2~2.5 if you keep under 30.
So you’ll be charging at 2~5mi/h, if the sun is shining straight overhead.
It’ll count for something if you park the RV in the sun for a week as you camp somewhere, but on the road it gives you some limping ability and that’s about it. The main benefit is not running the AC off of the engine.
It doesn't make sense to power any vehicle with onboard solar. There are no electric RVs yet because the batteries required to have any amount of range are cost prohibitive and heavy.
I put 1800W on my RV and that's covering the roof end to end. I'd guess it'd be enough for something like 1-2 miles a day on an electric drive train, assuming you don't use power for anything else.
> I'd guess it'd be enough for something like 1-2 miles a day on an electric drive train
It's probably more 10~20, possibly as much as 30, if it's a long and sunny summer day FWIW.
For references:
- the F150 lightning gets close to 2 miles / kWh on average, ~1.5 at highway speeds but as much as 3~4 at consistent low speeds
- on the other side of an RV, Volvo markets their FH Electric (cabover semi) for 1.1kWh/km — 0.7 mi/kWh — at 80km/h (50mph), DAF/Innovate UK's Battery Electric Truck Trial yielded similar results (1.08kWh/km over 287000 km), it's also close to the numbers of the electric trucker in their very recent MAN eGTX video (0.83 kWh/km = 0.75 mi/kWh)
It averages something like 12mpg diesel. This is a 25' long, 16k lb vehicle. There's no way it would get 2mi/kWh. 0.7 mi/kWh sounds closer to what it'd be.
But that's assuming you use no power. When I was living in it I was using 50% to 100% of the solar output a day.
Even better to get a fixed structure such as a garage or carport, that keeps the vehicle safe and out of the sun, and cover that in Solar.
It has larger surface area, doesn't weight the vehicle down at all even if it's built in a less weight-efficient way, and the vehicle doesn't need to be exposed to the elements.
Who lunches for several days/weeks? logically you would charge high speed through a plug with energy generated by panels that are much more efficiëntly (money+yield) placed and not have to carry around.
People are absolutely starting to populate their RVs with solar. What I've seen so far is just a few panels - around 600 watts. Usually connected to a battery separated from the RV wiring.
One can now get (flexible-ish) multi-junction PV (say 29% efficiency) from the factory for under $1/W. Still a higher price than the $0.2/W, lower efficiency panels, but when I messed with panels I felt like we were living in the future.
Anyway, one could also set up the panel to output a much higher voltage by having the factory wire cells in series (though how well that trades off with partial shading for a car roof I have no idea, and I have no idea the minimum quantity required to get that).
... but I agree, even with all that, it seems like a stretch to make it work.
They're not wrong but if you stick a solar panel on a car that's almost constantly going to be in less than perfect conditions to gather power the EROEI for the panel is going to struggle to be above 1.
Stick a panel on the bloody roof of a house or building and use that to charge the car. It'll do orders of magnitude more good.
My last EV used 22 MWh over 6.5 years. That works out to 390W.
My solar array is located at high latitudes (northern Minnesota), the mounting angle isn't great, it's occasionally covered in snow, etc. In these conditions, I need 6.3 solar panels to produce 22 MWh over 6.5 years.
The area used by 6.3 solar panels -- enough PV to cover _all_ my EV's energy needs -- works out to be a parking spot large enough to fit the vehicle but not large enough to fully open any of the doors.
Only thing holding off my EV purchase is that I want proper V2G support. If I'm paying for 100kWh of lithium battery capacity I damn well want to use it as a backup for my house.
My understanding is that V2G (vehicle to grid) requires transfer switches etc to be installed to your home electrical setup so you don't accidentally backfeed electricity into the grid. So it's never going to be a simply a matter of getting a better EV.
Why exactly do you want a backup? If you're looking to maintain a few key appliances or internet during a grid outage a vehicle with V2L like an MG4 or BYD might be sufficient.
You probably already know this, but for the sake of providing context to other readers: V2G - vehicle to grid, providing power to the grid from your car battery like is common for home solar batteries; V2L - vehicle to load, a power outlet using energy from your car battery.
Transfer switches are trivial to have installed. I already have a manual, interlocked one for a portable generator.
I have a 13kW array on the roof and live in a place where ice storms make power outages a thing most years. My solar inverter is grid following. Even if I can't get grid forming from a car I'd only have to pay for a small battery and grid forming inverter to cold start the whole operation rather than $10K of extra batteries for them to do the grid forming. Then I can let the solar and vehicle do their thing and follow the islanded grid during the outage.
> Only thing holding off my EV purchase is that I want proper V2G support.
I always find this argument strange and it just feels like an excuse people use to sound informed while also dumping on EVs.
Do you have frequent enough power outages that you need a backup power solution? Why don't you have that solution already? Did the lack of ability to use an ICE vehicle as a generator for your home stop you from purchasing ICE vehicles? What's your definition of "proper V2G support" and why don't current EVs with V2G suffice?
V2G has a number of downsides. The most glaring is that you're stranded at home during a power outage or your house is without power while you go out. It requires to your EV to be plugged in, and won't automatically kick in when the power fails.
The power needs of a home are minimal compared to an EV, if having power during power outages is important then you're far better off investing in a whole home battery backup system. They're significantly cheaper than an EV because they aren't optimized for density and portability.
My understanding is that the only vehicle for which both the vehicle and the necessary house-side equipment are _currently_ available on the market is the Ford Lightning. Several other manufacturers have promised that their vehicles will support it, but there isn't yet any available source of the house side yet.
I assume this means that no one is using open standards or else you could conceivably just use the Ford Lightning equipment with any other vehicle.
The Quasar 2 bi-directional charger has been on the verge of coming out for years now but still isn't ready to just go out and buy it.
I agree with you though. I work from home and so my EV sits in front of my house for the vast majority of the time, and the battery is more than 2x my total usage during high cost hours. I don't have solar, but I do have time of use rating, so if I could use the giant battery to demand shift, that would save me a ton of money every year.
I suspect the main issue is the north american 2 split phases+neutral design.
Specifically, without the neutral, the car can already generate that with the onboard charger. A bidirectional charger costs no more than a unidirectional one if you are designing it.
But generating that neutral is expensive. You either need a hundred lbs of transformer, or some expensive power electronics.
Honestly we should consider giving generous tax benefits so that every open air parking lot in any city in America that has more than 50,000 residents would be stupid to not have solar installed that covers the front of the cars in the parking lot and the walkways between the lot and the stores.
That's so much real estate available that would lower electricity costs, decrease the amount of AC used to cool cars down, and make going to malls and similar places a little nicer for everyone.
You’ve made an assumption - that the owner of the car has a roof, and can charge the car from there. People who don’t live in a place with off street parking to install a cable need a slightly different solution.
Exactly. Maybe just because I live in a city and almost everyone I know with a car will just find street parking somewhere within walking distance of their apartment.
So .. it would make sense to make a law that requires new parking spaces to have a solar roof which can charge the cars which park there for a few. This would spread rather quickly, I think.
I have solar panels at home and can charge a car .. but I'm mostly parked elsewhere when the sun is shining the most.
So do we, but you can't produce the electricity at one location and consume it in another. In the non-practical sense where our government decided that this is not possible.
>it would make sense to make a law that requires new parking spaces to have a solar roof... This would spread rather quickly, I think.
"If we threaten people with the state monopoly on violence, they'll do that thing I want."
Sure, probably true!
If solar parking lots are such a great idea, why do you need the threat? It seems like businesses or environmental groups would already be clamoring to install them.
PV parking is a highly visible status symbol and good PR signal for your community or company (hence the few installations), but actually it isn't a great RoI either financially or for the environment.
Sorry - I wasn’t explicit enough. The vast majority of existing and new developments where I live have on street parking - it’s not allocated, there’s no bays.
The panels themselves would be more efficient, but in terms of getting that power into the car you might be better off having inefficient panels that work everywhere you go rather than optimized panels that only work when you go to a charging station
The big issue tends to be complex logic for going to sleep often getting stuck. Ie. "oh, I was trying to use the LTE connection to poll for updates, but the connection got reset so I kept the CPU awake forever whilst retrying every 5 minutes rather than going to sleep mode".
Older cars had this too - I had a bunch of cars which would kill their own batteries if not locked - the engineers assumed that all owners lock the car when walking away, which often isn't the case in your own garage.
It's not, but older cars tried to keep their batteries fully charged. Newer cars with the so-called "smart" alternators never keep the battery full, they always leave some empty capacity to recover energy while moving.
I had this same problem in my 2005-ish Lexus! I got a cheap switch[1] on Amazon and put it in-line with my battery. If I’m going to leave the car undriven for more than a week, I just disconnect the battery with the switch. It’s been great, no complaints so far.
Doesn't anti-theft precautions kick in when you do this? On my Honda, if the battery goes completely dead or when I replace it, I have to enter a code in after, and IIRC all my radio stations reset, so it would be really inconvenient to do this often.
My way around this, which is also somewhat inconvenient- is that I pop the hood and connect a trickle charger if I have a feeling I won't be driving for a few weeks. I have a garage so this is the lesser evil.
Hmm I do have to put the key in the door when I’m reconnecting the battery, or else the car alarm will go off. That’s the only thing I’ve noticed though — maybe it’s just too old to have more complex features? I never listen to radio, so the stations may be reset and I just don’t notice.
My accord is a 2007 so not much newer than yours. We can Uber around for most trips but find it very convenient to have a car at times. If it works for you great, I thought that was a fairly common thing- particularly in cars of that era, because radio theft used to be so common.
I use a PV trickle charger, the panel is barely 1 square foot or so. Would be nice if it was integrated instead of having to connect/disconnect it constantly. Although, and I'm just guessing, many vehicles that are so seldomly driven are being kept indoors/garaged? (Mine is)
I haven't found any appreciable drain on my EV's primary battery over the longest period I've left it sitting so far (a little over a week, so not that long, admittedly), but the car _does_ do a very bad job of keeping the 12V battery charged and I've already had to replace it once in <2 years of ownership, plus I bought one of those small jump start packs in case it ever dies not at home (luckily, for an EV, it barely requires any power at all to turn everything on and get it started, so the very smallest, cheapest, jump packs are way more than sufficient). A built in trickle charger to combat that would indeed be nice, if the car companies are incapable of figuring out the logic necessary to do it off of the massive primary battery.
Alternator delete is a very common hack in the ecomodder community (usually coupled with LiFePo or Lithium battery instead of the regular lead-acid). It reduces the complexity and load on the engine, and does give a few percentage better fuel efficiency. But if you mostly ride at night, yeah ...
Everyone except you has approached this discussion with the intent of using the solar power to drive the car, but they should actually be thinking of using it to power the cars electrical system, and thus negating the need for the alternator.
A current gen 2.5L petrol Camry has a 12v 80A alternator. That 80amps likely covers driving at night in the rain (ie headlights on, window wipers going, HVAC fan blowing, etc). Normal daytime driving would be much less demanding, say 50A load, thus 600W power. Then you have to factor in the alternators inefficiencies, which could raise that demand to 1kW.
Next consider what the engine is having to generate whilst cruising, which could be 20kW for the Camry. In this scenario, that 1kW of alternator load is responsible for 5% of the engines load. So ditching the alternator would give 5% fuel efficiency increase on this Camry. A smaller car that only needs 12kW to cruise would see an 8% improvement (8% of a low consumption value though), whilst a much bigger car that needs 50kW to cruise would only see a 2% gain (but that's 2% of a high consumption value).
So if "solar body panels" could generate 500W like people have already guessed in this thread, then that would be close to offsetting the normal day-time electrical load. In this scenario it's probably a good idea to power the vehicles electrical system from a lithium battery, which wouldn't mind the gradual draw-down, because that could then be offset by parking the car in the sun (and possibly even by regenerative braking). Then there could still be an isolated lead-acid battery that is purely for starting the engine (because that needs high cranking amps), and that could be DC to DC charged from the vehicle circuit.
That 12v 80A alternator can generate almost 1kW at max effort. So even if you drive all night in the rain, that's still less than 1/5th of the energy in a Tesla or BYD vehicle battery. So this alternator-less car could get away with a much smaller battery, and it might even be smaller in area than the cars boot!
ICE Vehicle is hiding a major category division here, hybrid vs. traditional ICE. I think in the case of the latter this would only make sense as a bandaid to deal with parasitic battery drainage on a vehicle that is usually parked outside.
The cyclic nature of the sun actually makes for way better maintenance of lead acid batteries in practice than float chargers. Basically everyone with a boat, RV or rarely used heavy equipment has switched over at this point.
Float chargers do fairly frequently kill batteries by evaporating the fluid over time. It's like the difference between a battery being dead in a month or two of non-use vs 3-6 on a conventional float. It's hard to get the charge current just right. By contrast a charger that's voltage naturally decreases in proportion with what the battery is willing to suck up and tapers its charging and turns off overnight has the effect of more or less just "topping off" the battery without boiling much/any of the fluid. If you don't have a parasitic draw in excess of what the solar charger can make up for a battery is likely to be good for 6+mo without being touched. I can go 6mo on cars and other stuff that has digital electronics that draw a little bit and I can go 12+ for heavy equipment that has a hard cutoff switch.
And yet I know quite some people who report to be very happy with their plugin hybrid, doing max 40 km they hardly have to use fuel anymore and some can charge off their own PV setups (in summer).
I guess it’s a testament to the Netherlands being very compact.
I went the plugin hybrid route. The added complexity caused a lot of maintenance and reliability issues. I ended up having to dump the vehicle at a loss.
Something to keep in mind: A full EV doesn't require oil changes, which you still need to do with a plugin hybrid.
If you're able to do all your daily driving on battery only, then why bother with a gas engine that you aren't using? High speed charging works very well for the occasional road trip; it's at the point where if you take your bathroom breaks at high-speed chargers, you don't even need to "think" about charging.
I'm sure; it's certainly intuitive that a hybrid could do quite a lot with a PV setup. I just don't see PV doing much for a non-hybrid ICE vehicle outside of acting as a battery tender.
I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon. Even though the sun doesn't really shine all that much there, he still got enough power out of it, to never have to charge his car for his 20kmish daily commute.
No he didn't. Sweden gets ~2.6kWh/day per kW of solar panels. Malmö is at 55N latitude. If he put the panels on the car I hope he had a decent anti reflection coating because at that latitude he could be looking at 25% reduction in performance from the incident angle.
A purpose built EV gets something like 270Wh/mile in near perfect conditions little alone in a colder climate like Sweden.
12.5 * 270 = 3,375
So we've made absolutely every assumption greatly in his favor and we're already 750Wh short.
I don't remember the exact details, it's possible that he charged it over the weeked (or just didn't use it, thus getting 2 extra day of charge).
You can play around with assumptions, like what if it was driven in stop-and-go traffic at very low speeds? Then your quoted 270Wh figure might be lower.
But anyways, with these general conditions, with the numbers you quoted, and with a 10 kwh battery (aspull), you'd be looking at a net loss of 775Wh/day, which means you could go 13 days between charges.
The point I tried to make, is that solar panels on hybrids/EVs add a lot of practical value to people who can't charge at home/work, and it's not just meaningless greenwashing.
Also that 2.6kWh figure is a yearly average probably, sunlight varies greatly over the year.
> I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon.
I want to see a picture of that.
Apparently 1 kw fits on an extended box van [1]. But I don't now how you'd do it on a wagon without making it look like some sort of Burning Man art car.
My exact numbers might be off (which is kind of a problem it seems on HN), but the point still stands - you can add practical amounts of range by having the car just sitting there, even in places where there's not that much sunlight.
Besides, I just checked out panels, and there's a lot of 500w ones that are appx 1mx2m, these station wagons are huge, easily 2m wide and 5m long, half of it a flat roof, so its not outrageous.
Won't work for most cars in cities, as they will be parked in indoor/underground garages, so no solar to speak of for their parking time, and the bit of solar you get while driving will maybe power the lights/electronics/audio system at most.
(Driving a full EV, but needing to charge 30+kwh/week, and my small (but larger than a car could fit) home-solar only provides max 20kwh/week in spring/summer.
A lot of car parks have chargers. Wiring up low wattage chargers is no big deal, considering AC chargers are just wiring+breakers. Considering cars will spend a long time here, large wattages are not needed, you could wire up a multi-story parking lot for chump change, and the entire wattage would be still less than a DC fast charger serving half a dozen cars.
Even the Aptera, which is designed to be super lightweight, can only regen about 10% of the battery (40 mi vs. 400 mi total capacity) with rooftop solar (https://aptera.us/)
Good reminder with respect to the CAFE standards (rip) that sometimes engineering doesn't trend towards what is "good" with respect to SWaP-C but rather what games the current regulatory environment best.
But the average American drives less than 40 miles per day (33 is the current estimate). The relative charge doesn't matter, because what this suggests is that most Americans would be able to go most days without spending any effort or money at all on charging.
America also loves reserving vast swathes of the road for on-street parking, as well as endless fields of parking lots, not to mention that an enormous number of homeowners would rather park in their driveway and use their garage for storage.
I'm not trying to say solar roofs on cars make sense as a default option, but focusing on "percentage of battery charged" is the wrong metric. Most Americans would get by just fine on a relatively modest amount of charge per day, especially if we got over our range anxiety of insisting on massively oversized batteries for the average EV, which drastically increases weight and decreases efficiency.
Double an ioniq 5's miles per kw/h to 8m/kWh, use the maximum possible insolation (1kw/m^2) and theoretical PV efficiency (70%, reality is 30% btw) and you get... 8kw/h@12hrs a day generated and 3.75kwh needed. about double what this impossibly optimistic calculation gives. Half all the inputs and double the consumption and you get a quarter of the power needed.
It's interesting how much people expect an EV battery to be at 100% charged at all times but have you met the sort of person that tries to keep an ICE vehicle 100% fueled at all times? (It's costly and wasteful and a logistics nightmare, before also getting into questions of how dangerous it can be.)
10% of the battery per day, which would cover all of my driving other than the rare long road trip. I have plenty of weekends where I drive 200 miles, but then the battery would recharge over the week when I drive less than 40 miles a day
Maybe I am missing something but this feels like a study for the sake of a study? Has this not been solved for a long time. The complexity cost and the potential losses from drag make this fairly pointless. You would be better off with a fixed solar installation.
I don’t believe the primary cost is so much the physical panel but the cost to engineer and design it into a roof, also the additional systems needing to hook it into the wiring harness. It’s a fun toy for some but has no real benefit for the many.
But even stipulating this, with the way solar is improving, it may very well not be the case for much longer.
If you can guarantee that, in moderately sunny weather, the solar panel on your car's roof can provide enough power to keep the car going at, say, 30mph indefinitely, that's no longer just a fun toy.
Now, that level of utility may still be a long way off—or may even never be possible!—but I'm not willing to write it off for good, given solar's curve.
ETA: sorry, realized I should unpack a bit why I think this is worth mentioning: Your GP post was expressing confusion over why people would study this; I think it's very valuable to continue studying it as solar continues to improve, so that we can understand just where we are in relation to that utility curve.
For larger utility vehicles you can cover 80% or more of the top, almost doubling the numbers of the study. Depending on the region, this seems to be an obvious way to extend range without adding larger batteries.
For most of my own commutes, this would mean I’d almost never have to plug the vehicle in. While abundant stationary chargers without stupid mobile app requirements would be preferable, this sounds like a perfectly fine plan B.
Huh? This paper is about the economics or gain from adding solar powers to vehicles hence my statement that it’s a gimmick and it adds complexity (cost) for a gain that is not beneficial. Now if we were talking about marketing the vehicle, sure it perhaps drives a fun idea for buyers.
From an economic standpoint solar panels on vehicles are a gimmick.
One thing the paper does is introduce a mathematical model that allows us to decide when it's a gimmick and when it actually becomes useful. As PV panels get more efficient and lighter, there is a point it'll start to make sense despite conversion losses. It's very unlikely to make much sense in Sweden (or even in Ireland, where I live), but different locations, with different infrastructure and, most important, solar exposure, will drive different economics.
It was a cool trip but everyone needs to understand how much downtime they had waiting for their batteries to charge. They had to deploy their solar while stopped, not while driving.
It appears they didn't cover cargo transportation in the analysis. Curious if it may be worth for large trucks, over 20m long, as there is a large area available to install panels, and cargo transport is a hard to decarbonize sector. In long routes that extend east-west, I also imagine one coud try to adjust timing so the truck travels along the sun while it's day, and against it while it's night, so days in the local frame are slightly lenghtened, and nights are slightly shorter, improving light availability.
20m by 3m is 60m^2, with 300W/m^2 solar panels, it's less than 20kW.
A truck departs NY at the crack of dawn on the longest day of the year and cannonball-runs west at 100mph without hitting a single red light. The sun covers 15 degrees per hr. Denver is 30 degrees west of NY. The truck doesn't quite make it to Denver though, the sun sets on it somewhere in the middle of Nebraska. By chasing the sun, instead of 1700 miles, it gained a whole 1hr40mins of extra sunlight. That 20kW array turns that into 36kWh of extra power. By doing this chasing the sun instead of west-to-east, our truck turned a 1700 mile trip into something like 1718 miles.
On any 'typical' daily long-haul of 600 miles, we're looking at something more like an extra 3000-4000 feet. On something not as perfectly east-to-west like 900 miles NY to Atlanta, we're in the extra 100-200 feet, as long as it's not overcast.
Good idea! The AC in my Nissan Leaf uses about 3kw so I assume it'd be about the same in my Corsa. However the Corsa disables auto-start stop and keeps the engine idling whenever the AC is on, negating any fuel savings!
I've wondered if there could be a way to make it so that internal combustion cars don't need lead acid batteries w/ a few solar panels and a setup like a scaled version of a solar watch. But that wouldn't be about big efficiency gains, just dropping a little space and the annoyance of them going dead every three years.
When I looked at the title, I immediately thought that even if this makes sense from an engineering standpoint, psychology is going to be the bigger problem. For some reason many people are hell-bent on burning fossil fuels, almost in a sect-like belief kind of way. I do not understand it, but the backlash against anything electric for example is real.
Burning fossil fuels is relatively simple and well understood by general public. Modern business strategies to squeeze every cent out of a customer that involves subscriptions, planned obsolescence, adding bizarre complexity for marginal gains are not helping.
Buying a very expensive black box with questionable reliability, possible dependency on a manufacturer provided internet services (APIs for updating etc), questionable availability of parts and probably not really fixable by yourself or your local shop with rednecks with wrenches is not very appealing when you are living paycheck to paycheck.
A friend of my family is a carpenter who came from a very bad family situation, and is just climbing out of poverty. He has an old Chevy K1500 that gets him to and from work, with all his tools.
His transmission went, but he was able to find one at a local junkyard and swap it in over the course of a day and be back on the road for a few hundred dollars.
If you proposed this guy get a F-150 Lightning (or god forbid, a Cybertruck) to reduce his carbon emissions, he'd keel over laughing.
Top Gear, one of the most popular car shows of all time, was responsible for a lot of this. They spent years spreading myths about electric cars being worse for the environment and doing things like filming fake segments where they were pushing an EV claiming the battery had died.
They did come around in later years, changing their tune to be more pro-EV. A lot of the damage was done, though.
Or maybe you are just blind to the realities of normal people. Most people are not hell-bent on burning fossil fuels. There are numerous valid reasons for people to continue to choose ICE. I want an EV. I want to dump every piece of outdoor equipment with an ICE for something with an electric motor. I very much prefer the pieces I have switched to electric. I've been wanting to make the switch for years. It just does not make sense for me at this time.
And that’s exactly why we added 1000 watts of solar to any vehicles’ roof rack here at DartSolar. We created and aftermarket roof rack so any car can add solar. More details at https://dartsolar.com
"significant increase in the range of 10.7-42.2% for lightweight and aerodynamic efficient vehicles" shout out to aptera motors https://aptera.us/vehicle/ that's currently vapor ware "Designed with ~700 watts of integrated solar cells, drive up to 40 miles per day completely off the grid and enjoy 400 miles of range per full charge"
> [ ... ] by adding on-board PVs to cover less than 50% of the projected horizontal surface area of a typical mid-size vehicle (e.g., Toyota Camry or Nissan Leaf), up to 50% of total daily miles traveled by an average U.S. person could be driven by solar energy.
This is nonsense and would easily be proven false except that the article's technical content is paywalled. But common sense says that, if the claim were true, simple economics would make it a reality.
The publishing journal, the "SAE International Journal of Alternative Powertrains", appears to be one of thousands of online-only journals meant to provide a fee-based publication opportunity for authors who have no chance to publish in a reputable journal. In short, the authors pay, then the readers pay -- quite a system.
For a moment I thought this was somehow about putting solar PV panels inside an engine and getting energy from the light from the detonation.... I need a cup of coffee
Since the title said "internal combustion" my first thought, too, was could they make an engine a bit more efficient with some electrical process that increases the efficiency. The actual article was much more nonsensical than this take.
I’ve just done a legtimate 425 mile solar powered round trip which is the culmination of many things I will explain below. I can now effectively drive anywhere in a 225 mile radius and back for about $10 total cost and on 100% solar power.
I have a two complete solar systems on my house the first one was 10.98kW AC installed 4 years ago with the panels facing south. The second was just installed a few days ago and is a 9.9kW AC with the panels facing east/west. Combined the system will produce over 20MWh of power per year. Both systems are grid tied used EnPhase microinverters and are now combined together for monitoring in one site.
I have an EnPhase IQ EV Charger. This has a mode where it communicates with the solar system, understands how much power is being produced and consumed in the house and then adjusts the EV charger output to match the excess solar production.
I have an EV with the largest battery that is available. The Chevy Silverado EV truck has 24 battery modules with a total gross capacity of slightly over 200kWh. The efficiency on road trips at high speeds is about 2.1miles per kWh. I have verified this with a real world road trip of over 400 miles.
The cost of the solar is around 5 cents per kWh over the 25+ year lifespan of the system.
Another less commonly discussed option is community solar (also called offsite solar). It's especially attractive if the roof line of your house isn't ideal for solar panels or if you expect to be replacing your roof within the lifespan of your panels. (Or if you have a historic association like I do that makes almost every home project impossible.)
You still purchase and own the panels, but often a third party maintains them for you and they are installed as part of a large, offsite array. Since they're usually installed at ground level, they can also do more interesting things like follow the sun. The way it works is the power your panels produce is subtracted from your energy usage via an arrangement made with your utility provider.
Like any solar purchase, the cost of your panels can be financed over time and charged against your energy production. So the net effect is your power bill just goes down until the panels are paid for. At that point all the power you generate is deducted from your power bill. To me, it's most all the upside of owning panels on my roof.
I have always liked this idea, it is such a neat middle ground between massive grid scale systems and the hassle of individual system maintenance.
The described version of community solar is nice. How it is usually implemented like in Maine ends up sucking.
The root cause is that they wanted community solar customers to be able to opt-in and opt-out any time. As such it isn’t really what you describe which is owning panels offsite, you are more or less doing a short term rental on them. As such you don’t get the full benefit from them but simply a 15% discount on the current residential rate.
https://www.wabi.tv/2025/02/18/maine-public-advocate-claims-...
I very much think that proper community solar would be a larger upfront investment just like panels on your roof are. With a small monthly cost to maintain the grounds and pay taxes on the real estate where the panels exist. All power generated would be metered for the specific panels you own using microinverters.
I don't understand the purpose of consumers owning individual solar panels in a large array. How is that better than a single entity owning the whole array, and what function does the consumer provide?
> I don't understand the purpose of consumers owning individual solar panels in a large array. How is that better than a single entity owning the whole array, and what function does the consumer provide?
I don't now if it's better, but it is different.
The benefit to the utility in this case is much lower capex - it's basically like the restaurant franchise model, but for power.
But like you imply, there's a tradeoff that can be made between capex and opex - in this case, the utility could own everything and consumers could pay for electricity on an ongoing basis. IMO, this model is superior due to reduced principal-agent problems.
Just to be clear you're talking about variable costs not total costs. Total costing include time value of money, amortization etc. (I'm no hater I also drive an EV).
> I have an EV with the largest battery that is available. The Chevy Silverado EV truck has 24 battery modules with a total gross capacity of slightly over 200kWh. The efficiency on road trips at high speeds is about 2.1miles per kWh. I have verified this with a real world road trip of over 400 miles.
This is interesting. While it has the most storage capacity, the range is not good for that much battery.
I don’t think the Silverado is optimized for driving range, but rather - can it do typical “truck” stuff. For example hauling and/or towing. For this workload, having more towing capacity in a slightly less aerodynamic package is probably a good trade off. You don’t get a truck for the efficiency, you get one so you can do stuff with it.
Still, having a 400 mile range also makes this more useful for the middle of the country where there are wide open spaces between towns for charging. Also, having a legitimate truck EV makes it more likely for traditional truck buyers to think of getting an EV.
Thanks for the perspective
Part of it is the weight of a battery this size but the bigger issue is the aerodynamics of the large frontal area.
The Lucid Gravity has a 450 mile range with a 123kWh pack. It’s the only other vehicle with a range close to the GM large packs.
I'm looking at doing similar stuff right now. I already have a house battery.
However, looking at getting an EV - were you able to get bidirectional charging going?
I saw a few places mentioning demos of it over the past 5 years, but I can't find any v2x charger/car configurations I can buy and use in the UK.
Before looking at any of this stuff, I didn't realise how large and cheap the battery in an EV is compared to house batteries. Now I'm struggling to justify getting an EV if I can't do at least V2H bidirectional charging.
You can do bidirectional with most GM vehicles now with the GM energy solution. I don’t have this but I did have a call with them.
Thier max output is only 9.6kW so it can’t do a whole home backup and the car can only run in backup mode when the grid is out.
https://gmenergy.gm.com/
Interesting thanks! It looks like most of the GM vehicles that v2x works with are... uh... not really something a European would consider an option (not even sure if some of them will fit on our roads). Ford UK makes no mention anywhere of anything to do with v2x though.
There's a few places that apparently offered it here, but when I've contacted them, they've all explained it was a tech demo, or trial, or some other PR type thing which means they didn't take it any further and regular humans can't buy it. I think there's some nuance or regulation around the UK power network which is stopping any progress with bidirectional charging here.
Over here though, if you don't have old electric heating, or an electric shower, 9.6kw is very much more than enough for the average household. I have a relatively high usage, and a 6kw inverter can power my house in a powercut, as long as I don't use the electric shower. The various retired people in my life tend to use 2 - 4kwh /day, the peak draw is the kettle which uses 3kw for a minute or so.
> Thier max output is only 9.6kW so it can’t do a whole home backup and the car can only run in backup mode when the grid is out.
9.6kW should be enough to backup your entire house, that's 87A... Lots of people only have a 100A supply in general. Depending on your setup you may have to limit what you use at one time but even in a large house that will be more than enough for AC, lights and electronic devices.
9.6kW is 40A at 240V, and a 240V 100A single-phase residential service is 24kW.
Still, 9.6kW should be more than enough to run a fridge, lights, receptacles, sump pump, a 2-3 ton A/C unit, and a furnace fan. It would be challenging to impossible to back up a home with electric (resistive) furnace and electric (resistive) water heater with only 9.6kW.
That’s peak production, without battery storage the fluctuation during the year will likely be too much to keep the “lights on”. Would be cool to have a smart home that prioritizes the electricity supply to different systems based on how much is available.
>This has a mode where it communicates with the solar system,
I just find this so cool. We have projects like SETI where the solar system tries to communicate with us. Here, you, just one person, have set up a machine talking with outer space and the solar system. Space is talking and we are listening. Amazing. Rock on space cowboy.
I assume you're on a pretty attractive net metering agreement? That's a huge system.
Unless you're consuming a significant portion of that, the payback rate is going to be pretty badly impacted by having such a large system for most people.
I consume about 17MWh a year between two EVs and a large heat pump for winter heating.
I will have overproduction now with the 2nd array. We do have net metering at about 80% of the cost on NEM 2.0. Our bill is split by transmission, generation, distribution and fees. We get 100% on transmission and generation and 25% on distribution.
https://www.energy.nh.gov/sites/g/files/ehbemt551/files/inli...
$0.05 is the rate we pay in BC at night. I was still debating whether to add solar or not, I guess your post answers the question. Until we can get to $0.01 there is no point in solar in BC at least.
From an efficiency standpoint, we should probably be building grid-scale solar in Alberta and pumped storage in BC. There's more sunshine on the east side of the Rockies.
As a resident of Alberta, I pay $0.205/kWh for energy and delivery, which I largely attribute to bad decisions made by our provincial government. Even still, my 10 kW rooftop solar install is barely financially viable at those rates.
With that said, it would help if the Canadian government didn't have enormous tariffs on solar panels. Canada levies taxes such that solar panels here cost nearly triple what they cost elsewhere.
The article is about installing solar panels on vehicles. Your truck has no solar panels installed on it. What is the relevance of your anecdote to this discussion?
The relevance is readily apparent to people who aren’t grumpy yahoos.
I built my own electric cars and calculated if this would be worth it. Roof of car is curved and you get the conversion losses (needs to be bumped to 400V to charge batteries).
You add a lot of complexity for marginal gains. Peak time you get maybe 500W which doesn't go very far.
I haven't made video about solar yet, but I am sharing what I know on https://www.youtube.com/@foxev-content
I have a 100w solar panel on top of my car...to tend a 12v battery. It's got a Dewalt battery charger, mikrotik ltap, and raspberry pi hooked up to it. Little hotspot with multiple sims and resource server(mainly just for fun). Anyone that can do basic math should immediately realize there's just not enough area to make an appreciable difference in regards to mileage.
The Prius Prime solar panel roof I think can net 3-6 miles a day under ideal conditions (which we're probably close to here in Arizona). I think that's a little more than people would expect, but still only applicable in niche conditions (tiny daily commute, or a longer non-daily commute). I think the math works out to ~4-6 years to break even for the cost of adding the solar roof assuming $0.15 per kwh, which isn't terrible.
If solar tech gets more efficient or cheaper, I think it starts becoming a much more attractive option in some areas. If you get into the 10+ miles per day range, that would cover a lot of peoples commutes in certain areas.
13.6 kWh battery. 39mile EPA range. Equals 2.87 miles of range per kWh. Leaving it out for 8 hours straight, on a sunny day, in LA, netted 915 Wh. Or, 2.86 miles. [0] Not 3-6, 2.86.
2.86 miles of charge, but only if left outside, uncovered, in full sun, on a fully sunny day, for a full 8 hours, in a place that gets effectively the maximum amount of solar radiation per day out of anywhere in the entire country.
Now, do the same experiment anywhere else in the country, that doesn't get max solar radiation, or that can't get full sunlight for full 8 hours, or where it's cloudy at all, or rainy at all.
2.86 miles per day is the practical MAXIMUM, given perfect conditions. For the average scenario it'd be some fraction of that.
The 6 miles figure is what they said you'd get if, in addition to perfect conditions, "if the sun shifted its orbit" (?) and gave perfect sunlight for 12 hours straight. Which is a number which should obviously not be thrown around as if it's obtainable.
The fact that they're quoting numbers about what range you'd get if the solar system was constructed differently also makes me doubt the impartiality of their experiment and the numbers they provided.
[0] https://www.motortrend.com/features/the-2023-toyota-prius-pr...
> 2.86 miles per day is the practical MAXIMUM, given perfect conditions
In your particular setup.
A typical car can expose about 3 square meters of lateral area for those same 8 hours, and receive 3 kW of irradiance. multijunction cells can exceed 50% efficiency, so we're talking about a theoretical upper limit of 12 kWh electric per day.
That would require a vehicle totally covered in cells, including the windows, so not very practical, but adding up to 30 miles/50 km per day is nothing to sneeze at.
We could also imagine all sorts of solar receivers that engage during parking and inflate the apparent surface within the limits available, track the sun etc. to maximize energy.
This is all wrong.
> multijunction cells can exceed 50% efficiency
The maximum demonstrated efficiency of a multijunction cell, in a lab, WITH CONCENTRATION is less than 50%. Commercially available cells are lower.
Concentration is an important caveat for two reasons:
First, it implies that you are collecting light from a larger area than the PV panel itself. Second, efficiency grows with increased irradiance (so efficiency will be lower without concentration).
> 3 square meters of lateral area
Lateral area is meaningless. It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck, there is zero probability that you can put 3 kW of irradiance on your panels. Neither of those vehicles will achieve kWh/mile numbers anywhere close to a Prius.
In practice, you need to halve the efficiency and more than halve the collection area you quoted. You also need to account for conversion losses.
This is a theoretical exploration of the hard limits, not an engineering design.
The multijunction theoretical efficiency limit is 87% with infinite junctions, and over 50% with a practical number of junctions. There's nothing stopping you from creating a miniatural concentrating solar device that focuses the light from a 10 cm^2 area onto a 0.5cm^2 cell, we haven't seen such devices because the cost and extra mass exceed what you get from the efficiency gains when you can simply increase area; a very area constrained application with high power requirements might change that.
> It’s all about area perpendicular to the solar axis. Unless you are driving a box van or a big pickup truck
Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the sun, perhaps even unfurl additional area? what about the area of the doors and windows?
Current solar cars can drive 1000 km per day with an average speed approaching 100km/h. It doesn't seem completely out of the realm of the possible to achieve 50km in an hour for a passenger car that can expose similar area while parked.
> This is a theoretical exploration of the hard limits, not an engineering design
You replied to (and even quoted) a comment explaining the practical limits, then doubled-down and said multi junction cells can exceed a number which has never been experimentally demonstrated.
And here you are again saying that multifunction cells can achieve 87% efficiency.
An ICE engine can achieve 100% thermal efficiency with the right Th and Tc. That has about as much relevance to the discussion at hand as 87% efficient solar panels.
Let me be clear: the most efficient cells that have ever been experimentally demonstrated under any conditions are less efficient than the number you originally stated. In real world conditions the number is half of what you originally.
> Again, what stops the top hood and engine cover of a Prius from raising at an angle and tracking the
I guess I’m just feeding the trolls here.
EPA range tends to be pessimistic for EVs as it assumes you are always traveling at highway speeds. Even small reductions in speeds can make EVs much more efficient since drag is quadratic. A quick google search shows Prius prime owners reporting 4-5.5 miles/kwh, so the 3-6 mile range is entirely plausible.
> EPA range tends to be pessimistic for EVs as it assumes you are always traveling at highway speeds.
EV EPA range historically has been overstated. However, the water is muddied because the EPA doesn't really force the manufacturers to give an accurate number. A manufacturer can choose a highway only test, but then also arbitrarily decide to derate the value (EPA example is 70%). A manufacturer can choose to include city driving in the rating and weigh it accordingly and also derate the value (if they want).
Tesla traditionally (still the vast majority of new and used EV market share) has been the only manufacturer that uses the highway + city driving tests. People then get surprised when the car cannot do the full range at 85 MPH.
All in all, this is the EPAs fault. For EVs they really need two numbers, city driving range and highway driving range. EVs are so much more efficient than ICE that speed makes a huge difference given there substantially smaller energy density.
https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-...
EPA's city cycle speed is an average 19.6 mph, highway speed is an average of 48.3 mph. City range weighted at 55% and the highway range at 45%.
I don't think it's that simple. IIRC you don't have to do the city testing.
https://www.epa.gov/greenvehicles/fuel-economy-and-ev-range-...
Regardless, the EPA test cycles have unrealistically low speed profiles.
Everyone is also glossing over the distinction that regardless of the actual amount, it's not at an actual voltage that can charge the battery to add mileage. You can hypothetically say that because it's offsetting the power usage from the AC that it could theoretically be saving that battery usage...but there's so many gross assumptions being made that it's a pointless statement to make, and it's all out the window the second the car starts the ICE side of the hybrid drive system for even an instant.
> Everyone is also glossing over the distinction that regardless of the actual amount, it's not at an actual voltage that can charge the battery to add mileage.
Neither is the voltage when you plug it in at home. The car has a unit specifically to convert the voltage.
If you're saying they didn't connect the right wires for that, that sucks but is easily fixed.
> it's all out the window the second the car starts the ICE side of the hybrid drive system for even an instant
Nah, doing a drive where it's 99% solar power and 1% "burned an ounce of gas to maintain the engine for the month" is fine.
That article sure has 49 pictures, none of which show more than the very edge of the solar panel.
But looking at some proper pictures, it covers most of the midroof with 7x8 tiles of solar. But you could fit a good percentage, even sticking with a design where a huge amount of the roof into the trunk is all glass. And there are no panels on the hood. So that's an easy doubling right there, more with an average car roof shape.
I wonder how much extra range you would get if one leaves the car in the shade so that it doesn't get super hot and there is no need to turn on the AC hard? I bet it's more than 2.86 miles.
I believe having a carport and house roof covered with solar panels + (PH)EV is the best option.
Does the extra 3-6 miles factor in the need to now run the AC much more aggressively because the car will be hot from sitting in the sun all day?
If this quoted number comes from the manufacturer itself, then I think the answer is "no".
The initial use of solar on the Prius was to power a ventilation fan while the car was parked, and the current version seems to specifically be designed to provide power to the air conditioner while driving. But, I also can't imagine the difference between cooling down the cabin is much different from parking in the sun or in the shade - you'd be running it continually to achieve "room temperature" during the entire drive either way.
You can't imagine that air conditioning power draw varies with the heat load that it is working against? As a heat-pump, it takes more energy to move more energy.
In the old days, they used duty cycle to adapt to the changing load. Modern ones do things like varying compressor displacement or compressor speed to adapt to the load. Variable frequency inverters are used to efficiently drive electric compressors.
The variable displacement trick is used in ones mechanically linked to internal combustion engines. It can vary the compression stroke to account for different load as well as different engine speed.
Watching power draw on my Leaf with LeafSpy, the AC seems to use between 500-1000W (maybe more sometimes, but that's just off the top of my head from a few times running it while driving).
At the low end maybe achievable with a full rooftop covered in solar panels, but probably not adequate at 1kW+.
> Does the extra 3-6 miles factor in the need to now run the AC much more aggressively because the car will be hot from sitting in the sun all day?
Most cars are already sitting in the sun all day.
Not here in European cities where they’re either within a multi story park or in the side of a half day shaded tiny street.
Yah, it's a great point that the whole scheme is predicated on very questionable land use policy...
You are not getting the 3-6 mile per day boost if your car is parked in the shade.
That's his point. You won't get any reasonable charge because you (mostly avoid parking your car in direct sunlight
What kind of European cities are you talking about lol, no offence but I hate this generalisation of "European" anything as if Southern Spain has the same culture and architecture as Poland or Lithuania.
It is a somewhat fair generalisation of urban europe to have more innside parking or tall ish buildings that give shade.
To my thinking, the best use of a solar panel on a car is running a low power AC unit all the time whenever the car is in the sun. Parking in the shade often isn't possible.
I don’t think you’d have to run the AC any more aggressively with the solar panels than with a traditional steel roof?
If you’re suggesting it wouldn’t work in a garage, that’s obviously true (and another factor in whether car solar makes sense) but many (most?) people park their cars outside during the day anyway. I for one can’t remember the last time I parked under cover
That's still 3-6 fewer miles worth of charging to do from more expensive sources. Even if it can't come close to covering your full use it's still covering something
Not if it won't recover it's own costs.
It may still lose on this, but you would also want to include the externality costs that the consumer doesn't themselves bear for whether it is worth it overall.
Cost is convenience.
Manufacturing cost is like $40 cells, $20 electronics and $200 in glass fusion, mounting, etc.
My car eats 200W just being online so it would be useless to charge from solar.
There is going to be a parasitic drag loss to figure into it as well. I think the only way to accurately calculate that would be in a wind tunnel or maybe an amp meter with a before and after installation under identical conditions.
The Prius Prime solar roof is a $610 option available only on the top XSE trim level, so a hypothetical buyer is paying ~$7500 to access this effectively negligible amount of energy.
ETA: and the fact that this option is tied to the significantly less efficient 19" wheel package, instead of the standard 17" wheels, means that this will never, ever be a net benefit.
Not if they were getting that trim level anyway.
I just started doing this with my car, mostly to add a camera/temp monitoring for when I leave my dog in the kennel in the car (she's well watched over, please don't fret over it).
I'm hooking it up via starlink specifically so it works in remote areas with no cell coverage too.
Monitoring and proxying everything via an RPI as well. Victron DC-DC inverter to keep the bluetti battery pack charged with bluetooth relay boards so we can turn loads (camera/starlink/others) on/off programmatically (it only turns the starlink on when there's no good/known wifi for example).
Fun project, combines software dev (which I'm fairly good at) with hardware work (which I'm less) and my dogs (which I'm a big fan of).
It’s interesting to see how many people in this thread have the same idea. I’m doing something similar and learning that hardware is just plain hard
The maths says that the *mean* number of miles driven by a vehicle is surprisingly low, and that tiling the surface of a car can get to about 80% of that *mean* in places where the car is just left out on the street and not shaded parking.
But!
That's a practical consideration at the level of "should a government require EV makers to design the roof, bonnet, doors etc. to be tiled in PV in order to reduce, but not eliminate, the induced extra demand on the grid" and definitely not "should I personally bolt a small, fixed, PV panel and inverter into my EV as an aftermarket DIY job?"
The former gets wind-tunnel tests for efficiency, QA, designed around all the other safety concerns cars have e.g. crash safety.
The latter, doesn't.
Very nice. How long does that tend to stay alive for? And what kind of cold weather conditions do you have to contend with?
If only we didnt start off with having 3000+ lbs of metal to move a 100-200lb person as a design limitation
> You add a lot of complexity for marginal gains. Peak time you get maybe 500W which doesn't go very far.
The complexity should not be overlooked. The PV panels add a lot of things that can fail: An additional layer that must be adhered or fastened the roof. Transparent panel covers that can become damaged in ways that aren’t as easy to repair as a rock chip in paint. Extra wiring that runs into the vehicle. A charging regulator. Systems to monitor that it’s all working and give the appropriate diagnostic codes if it fails.
Having worked on a lot of older and newer cars when I was younger, I’ve come to appreciate a degree of simplicity in vehicles. Modern electronics and vehicle systems are more reliable, but when the number of motors, sensors, and functions in a car goes up by 10X with all of the new features, a lot of little things start to fail in annoying ways as cars age out.
With solar I imagine old car owners would just ignore the system when it stopped working, but you’re still hauling all of that extra weight around for the lifetime of the car. That extra weight subtracts from your efficiency.
The simplicity of EVs is one of their big strengths! Compare all the cooling, transmission, lubrication and fuel systems of an ICE car to the simple Electric Motor of an EV. Vastly simpler. As an end user, I see it to, my EV has no scheduled maintenance, whereas the ICE wants me to take it to the dealer every 20k miles.
Mechanically simple, yes. Electronically simple, no.
But most of that electronic complexity is just as present in ICEs as in EVs, no? It’s not like most of it is in the drivetrain. All those auxiliary systems.
> All those auxiliary systems.
That's the problem. I don't need or want any of that extra nonsense. You can't replace the radio in these contraptions. The only thing a car needs is: drive-line control, braking/ABS/ESP, steering, HVAC. Electronics wise dump the lame glued on tablet look and just give me a single up front dash display and a double DIN cutout in the dash. HVAC only needs knobs. I hope a Chinese auto maker comes out with an EV that dumps all of this stupidity and just gives us cars again.
Backup cameras (and the associated display in the dash) are a significant safety improvement. I wouldn't want to buy a car without one at this point, despite the increase in tech that it necessitates.
Take a look at https://www.slate.auto
Right, I agree. But the context was about the differences between ICE BEV. And they, afaik, have comparable bells and whistles.
To be fair, modern PV cells are purely solid state (no moving parts, no lubricants or coolants), so a solar system shouldn't add a scheduled maintenance burden, just add to potential unscheduled maintenance costs in worst case scenarios.
There was some car which used a small solar panel to pass fresh, cooler air into the cabin during sunny days. This both made the car more pleasant to enter and lowered the initial AC surge. I don't know if it also trickle charged the starter battery so it never could get completely depleted from just standing for longer periods. Both these things seemed worthwile.
The 2010 Prius IV had this as an option - one of my favorite cars due to low maintenance (the lowest maintenance visits per year for its era). The solar panel air vent circulation is a nice feature (even if slightly gimmicky) and I suspect extends the hybrid battery life as well by preventing some marginal battery heat death while parked.
The newest (2023+) Prius brought back the solar roof as an option - and this time it charges the battery (albeit marginally / but not bad for those that drive minimally).
A more practical solution is to leave the windows slightly open so the hot air escapes.
There are places where a marginally open window will invite vandalism, or rain, or bugs, or smoke and bad smells.
ok, so in those places, you don't leave a window gap. in all the other places, you do.
Not practical if rain is forecast.
The car already has a rain sensor so it can close the windows automatically. I do believe some VWs already do/did that.
My car has that to activate the wipers. To say it works reliably is to lie.
This is a perfect nerd snipe. I can't imagine any car owning (esp ev owning) engineer hasn't or wouldn't eventually think about "why can't I charge my car from my car".
You might like the series by youtuber 'Power of Light' where he packs solar panels in his car to charge his car to do a solar cannonball run from New York to California on those solar panels alone: https://m.youtube.com/playlist?list=PL9nfj0jfPXYBF8FO7sckzvV...
Can't remember how long it took, think a couple weeks at least?
he planned for 30 days and it wound up taking 60. he didn't strategize to minmax it, though? there was a lot of up and down and he stopped mostly at places where there were fun public camping parks. also he went solar -> battery -> ac -> tesla with an alternator to a standard tesla house plug iirc? whoo.
i think there was an interview later where he said, "yeah never doing that again" or something to that effect.
Agreed. Using solar to power vehicles is great, but there's little benefit in the panels being on the vehicle. Put panels on your house, charge your EV, and you've got a solar powered vehicle (and house).
Say the car gets 4 miles per kWh. So a 500 W charging rate (neglecting losses) can be expressed as 2 mph.
Compare to a fast charger which will be several hundred mph.
Not sure if I've slipped a 0 here but 500w taken over the year, at say a 10% capacity factor, is still over 3500 miles of range per year. A fair bit short of the average mileage (in the UK somewhere around 10k) but still more significant than I expected. Of course 500w is a lot of solar for a car and 4 miles / kWh is also quite efficient.
I think this is a flawed comparison. You only care about speed when driving, but charging we care about whenever the car gets sunlight. I would argue for most people car in sunlight time is a multiple of car driving time. Still pretty abysmal, but less bad than 2 mph.
This is a good way to look at it, but perhaps a new unit, like range per hour? Since mph is alreday a unit of velocity.
Range isn't a unit though, so it isn't actually telling you anything technical. Since range is a distance unit, it would still be "miles per hour" or "kilometers per hour" or "meters per second" or anything to let you know how long it will take to top up to full range.
Could be "%/minute" maybe, but that is less useful if you know you need to go 45 miles, you would want to know how many hours (or fraction there of) that would take.
It expresses how many miles you can get in a given number of hours. It is a velocity.
Same dimensions, same units. Sure it can be expressed more specifically e.g. "miles of nominal range per hour". But it's still miles per hour to facilitate mental calculation.
Miles (of range) per hour (of charge) is somewhat widely (and accurately) used as a metric for charging speed
People don't seem to talk about Watt hours per mile much but when you're generating the power yourself it really matters. Tesla's model 3 is AFAIK one of the more efficient EVs and gets ~260 Watt hours per mile. With solar a good rule of thumb is to take the nominal rating for the panels you can point south and multiply it by 4 to get the approximate daily energy you'll generate in watt hours. If you could optimally park a car and let's assume you could cover it in a couple 100 Watt panels that would give you about four extra miles of daily range.
Maybe it's interesting if you live in a city and drive once a week.
I wonder if it would be OK-ish to build a very lightweight, very long, low powered solar "bus" (or a tram like chain). Just enough to roam around a city at 15-20mph for free.
You'd get enough surface to get ~4kW
There have been solar car competitions that colleges have been doing for decades. Here's a YouTube compilation of one that ran last week: https://www.youtube.com/watch?v=ZBin-oXBJzM
I think it can help calibrate people's intuitions about what you can expect out a pure-solar car.
You also need to remember that inside those shells is basically nothing but a driver. No AC, no seats for people beyond the bare minimum. And that's broad daylight. So you need to look at them doing 20-30mph and bear in mind that it's still not comparable to a street-legal sedan of a similar size doing 20-30mph... those cars are essentially as close to "a mobile cardboard box" as the competitors can make them.
You might be able to build something that people would agree is "a bus" that moves with a couple of people on board, but it probably will stop moving once it enters shadow. Anything that we'd call "a bus" is going to need a lot more physical material per unit solar input than those cars have. I'm not sure that even "moves with a couple of people on board" will necessarily end up being faster than those couple of people walking, either. It's effectively impossible to power a vehicle with its own solar footprint in real time. It also ends up difficult to use them to power batteries because having to move the additional mass of the batteries eats up the advantages of being able to gather power for larger periods of time. It's possible, because of course you can hook a car up to solar panels and eventually charge it, but you don't get very many miles-per-day out of it for what fits on the car itself alone if you work the math.
Yup, was just going to link something like that— here's the University of Waterloo's solar car team's vehicles: https://www.uwmidsun.com/our-cars
And even those IIRC don't drive continuously. They drive for part of the day, then park them angled into the sun for the other part of the day to top up the batteries.
It's pretty hard to beat fixed panels + fast charging + parking your vehicle in a garage where it doesn't see the sun anyway (or get super hot).
Thx that was a really awesome video!
Commenting here to encourage other HNers to go watch it. Right now it has under 400 views and no comments.
It's an interesting idea. I did some napkin math based on the Solaris Urbino 18 bus. The buses have about 45 square meters of ceiling area (18m by 2.5m). Assuming efficient solar panels you could get 250w/sqm. That works out to 11.25 kwh/hour. The bus advertises with 600km of range with 800kwh of batteries so that is 1.33 kwh/km. Hence it could do ~8km/h on average when it is sunny.
The math does not really work out to a viable product with this bus, but it is not too far off. A city bus that has been purpose-built for low speed in urban areas without other traffic may work as it can make some sacrifices. For instance, since it runs much slower on average it would need smaller engines. It could also use more light-weight material since it won't need to handle high speed collisions. If it is just used for short distances within a city center it could also do away with seats. Lower speed should also lead to lower consumption.
The Solaris Urbino 18 weighs 17.5 tons curb weight. Assuming fuel consumption is pretty linearly related with weight and you could get it down to less than half, you could get a bus with a range of 10 miles per hour of charging. If it drove for 6 hours a day, but got charged for 12, 20 miles on average per hour is possible.
Yeah I wasn't clear enough but I was really thinking about the most limited form of "transportation", low speed, low weight, so minimal frame and no protections really. Basically a string of bus stops on wheels. Maybe an average speed of 13mph would be enough. That's 3 three times the average walking speed.
Why bother? Put the charge station in the bus stop instead. They have a longer runtime to charge and the bus does not have to be slow. Potentially easier to maintain too.
Or even do light rail and electrify the tracks with a solar network wherever you want.
Would that be more interesting with tram because of the low-friction wheels?
I imagine that could be viable in, say, Dubai or some other extremely sunny place ?
Why bother ? Have the solar panels on top of the tram warehouse, use the tram batteries for storage, swap empty ones for full ones when needed. If the solar array is down use the grid. That way you divid points of failure instead of multiplying them
Or... power the tram lines from the grid and feed solar power into the grid somewhere else.
Trams use fixed infrastructure, including overhead power lines. I'm sure they must exist somewhere, but battery-powered trams are not popular.
> I'm sure they must exist somewhere, but battery-powered trams are not popular.
Yes, they do exist. The Alstom Citadis at Rio de Janeiro, which I take often, uses a supercapacitor for small pieces of its route (mostly crossings where the third rail would be damaged too often by vehicle traffic, or be impractical); according to the Wikipedia article (https://en.wikipedia.org/wiki/Alstom_Citadis), the Alstom Citadis at Nice uses batteries for parts of its route (https://www.railway-technology.com/projects/nice-trams/). I'm sure there are others.
4kW on a bright sunny day, for a few hours around noon. Even my small EV outputs 100kW when floored, and 4kW doesn't get it very fast.
In direct, unshaded sunlight. Which is the opposite of any significant sized city I’m aware of.
We have trams. We don't need to make worse trams
One horsepower is roughly equivalent 754 watts. 4000/754 = 5.305 horsepower. Even tripling it only gets you to 15 HP.
I am not an automotive engineer but I doubt that is enough power for a bus that people can ride.
I suspect the lightweight, and hence low power requirements, are the correct part of the hypothesis. But making the vehicle as big as a bus implicates a lot of weight. Maybe a solar charging cargo bike fairing would have some benefit, but that's an expensive bike and it will tend to get stored indoors.
Maybe an electric assisted pedal bus with a solar roof would make sense.
Very location specific, might do wonders in Cancun or San Francisco or Vegas, not so much in Gatlinburg or Seattle or anywhere where there is not a lot of tourism or where there is a lot of rain or that has a long snowy season.
Well, if you have a fixed route you are not limited by space on the vehicle to put solar on, but can provide electricity via a rail or wire or something and then gather energy on some larger Solarstation or from wind turbines or what else comes to mind.
Then you can reduce rolling resistance by using steel tracks and steel wheels ...
... and oh, you have invented the tram/light rail ;)
(But even with solar you need to finance the construction and maintenance, even the slow vehicle need some ... thus either tax finance or charge fares or mix income)
Only advantage is if you use car rarely, park outdoors and don't want onboard battery to drain, tho way smaller panel needed to cover that
Yep. A solar car ceiling seems great to make EVs more reliable on the hands of people that only charge them rarely or may travel to the middle of nowhere and can get surprised by battery faults.
Those are a very small share of car owners, and EVs are nowhere close to the market penetration to care abut them. But it will eventually make sense.
I agree on this. Using the pvwatts calculator for a very rough estimate of cumulative kWh produced per *month*, a theoretical 380W panel on top of a car that is in perfect sunshine from sunrise to sunset, never shaded or obstructed, on a car in the sunny climate of San Diego CA will produce the following:
61 kWh per month in the best month of the year (August)
39 kWh per month in the worst month of the year (December)
As you can see from this, the kWh per day is quite minuscule, not enough to charge a car to go any appreciable distance.
I believe that solar panels were an option on the Maybach 62S, and they would run the ventilation fan while you were parked so you wouldn't return to a hot car after going to the store.
Like everyone else has said - there just isn't enough area on the top surfaces of a car to do any noticeable charging.
If you were to theoretically have a perfect 400W PV panel on top of a car, and left in direct sunlight, it might be enough to run a medium sized peltier/TEC cooling unit to somewhat cool down the car while you leave it parked. Or a very small heat pump. Would definitely add a lot of extra cost in manufacturing and complexity.
Or just keep the car fan running and use the existing AC system (in ventilation mode, no compressor) to keep the car just as hot as outside (instead of much hotter). If you have some spare power maybe even run the AC when the key gets back in range.
Using "270Wh/mile" from another comment,
(61kWh/month) / (270Wh/mile) / (31day/month) = 7.3mile/day =~ 11.7km/day
(39kWh/month) / (270Wh/mile) / (31day/month) = 4.7mile/day =~ 7.5km/day
My conmute is like 3 or 7 miles (4 or 11 km), depending on where I have to go.
Anyway, I expect that a rooftop installation is much more efficient.
The rough estimate calculation for the theoretical 39 to 61 kWh per month are for a perfectly mounted, south facing, 15 degree tilted PV panel such as might be on the roof of a warehouse, or in a field somewhere. With no buildings or trees or shade obstructions around it. And perfectly exposed to sunlight from the moment of sunrise all the way to sunset. That's the 'default' assumptions built into pvwatts for calculating a fixed installation PV site.
On an actual car that parks under trees, in parking garages, beside buildings in the shade, etc, the actual production would be much less. Not to mention the panel would be 'flat' on the roof and rarely if ever angled facing south, unless you happened to park on a hill with the roof of the car angled south...
It's also not possible to say that a theoretical 39kWh can be turned into so many miles at 270Wh/mile because it's not a perfectly efficient system, I'd guess at least 15-20% would be lost to heat in charging the battery and DC-DC conversion.
60kWh may be enough for occasional short trips.
The math is biased towards when you are using the vehicle. The solar panels also work when you aren't using the vehicle. They work from when the sun comes up until it goes down. And actually most people don't actually use their cars most of the time. It's just sitting there parked doing nothing well over 90 percent of the time. And especially hybrids have tiny batteries to begin with. Instead of charging those burning petrol, you could be partially charging those with solar.
If you get 400W watt performance for a few hours per day, that's maybe a couple of kwh per day. 2 would be alright. 4 would be amazing. 6 probably not that likely unless you live in a very sunny place. Most decent EVs do at least 3 miles per kwh. So, you get maybe 6-12 "free" miles per day. Maybe more with an efficient one. Up to 20 miles even.
Most commute round trips aren't that long. You are might need more power than that. But not a lot. You could be cutting how often you charge by some meaningful percentage. It's not going to be that useful on a long journey. But most people don't do those all the time but they drive small distances on a daily basis. Imagine you drive to work, and back maybe covering 20 miles. You go to sleep, and the car is back at 100% charge. Because you only used a few kwh driving there and back and the car had plenty of time parked to collect those back because the weather is nice. Or maybe it got to 95%. The difference is meaningless because you only use a few percent on a given day. Basically you'd be charging a bit less often and stretch existing charges a bit longer.
If you have a 60kwh battery and you get 2kwh per day from the sun, that's 1 full charge per month. Most people would charge maybe 2-4 times per month. So that's a meaningful amount. Cutting them amount of power that you have to pay for by 25 or more percent can be interesting. I think for most the savings aren't going to be dramatic. But it's nice that the car just sits there slowly topping its battery up without you having to worry about it. That's convenient.
When I'm not using my vehicle, it's in my garage.
Can you comment more on the complexity? Like, is it running wire harnesses everywhere, is it the power electronics, cooling, mechanical mounting, something else, all of the above?
Of course. It is an intriguing idea, but a local maximum.
- The panel sits at open-circuit voltage of 48V
- That then needs to be converted/boosted to 400V (conversion loss)
- The converter needs to talk to the BMS to make sure batteries can be charged at this moment (component that is live all the time and is a current draw)
- Need to think about it, but you want another set of contactors between panel and HV-Bus where the battery sits (current draw)
1km of driving is 150Wh so 1kWh gets you 6.6km or 4.1 mi
Let's be generous and say you have a 500W panel(punchy) for 8 hours at full blast (doesn't happen), you get 500W x 8 hrs = 4kWh. Lets say isolated converter loses you 10% so you are at 3.6kWh Thats 24km or 15mi of driving in perfect conditions.
2x Gigavac contactors, keep them closed costs you 24W, so that lowers the input further to 476W * 8hrs = 3.8kWh, less 10% = 3.42kWh ...
Someone who studied EE might be able to make this more accurate. Back of the napkin math, not totally impossible, but not worth adding it for a trickle charge. Adding components that can break, adding weight etc.
There are interesting solar cars out there where you reduce the weight heavily and fold out big solar sails. Then you are getting somewhere, for a city car you don't have enough surface. For an SUV or American Style Flatbed truck you have so much weight it's not worth it either.
> not totally impossible, but not worth adding it
I don't drive 24km per day, and don't have a good way to get to the train station other than by car. The bus is too tight, they miss each other often. Cycling isn't safe between towns, you have to basically go on a highway without any separation (yes that's legal in Germany to cycle on, as there is no other way than perhaps a farmer's grass path to go between towns, so they don't call them highways but cars drive highway speeds - or more, if they don't stick to the limit). I also don't have charging infrastructure or a driveway. A vehicle that does those couple km a few times per week without needing to drive elsewhere to charge gets me a long way. Charge me up, Scotty
I've looked into this and the moment the Aptera ships (probably never but here's for hoping) I'm buying my first car. I've looked critically at the range they assume you get at my latitude and it would keep topped up for enough months of the year that it's totally worth it (maybe it was even year-round because they're so efficient, I don't remember now, but I'm also okay charging it thrice a year)
But 24 km per day is under ideal conditions (perfectly sunny day, mid-latitude, panels angled southward) and 500W requires 2 square meters of panels[1].
Unless you own a big American pickup truck, it's hard to see where those panels fit on the car. And if you do own a big American pickup truck, you will not achieve the 150 Wh/km assumed by the GP (it will be more like double that). GP also used quite optimistic loss figures for conversion.
It begs the question: Why not a Nissan Leaf and solar panels on your (home) roof?
[1] Only 1000 W of solar energy falls on each square meter of the earth's surface at noon. The best commercially available solar panels have about 25% efficiency converting light to low voltage DC. This means you need a flat surface of about 2 square meters directly facing the sun to collect 2000 W of light, which will achieve 500 W of electrical power.
Why not on your home roof: because I don't have a home roof or a place to run the cable to the car. I could ask the landlord if they'll allow me to pay for solar panels on their building but I still don't have a driveway as mentioned
Why doesn't the Leaf have it: afaik the leaf is a normal car, not like the Aptera that I'd be looking to buy. Even the Lightyear One was claiming to be more efficient than normal but pretty disappointing in how much range you get from the solar roof. Still more than zero though, so yeah ask them why they don't sell that variant ¯\_:|_/¯ While we're at it, let's find out why there isn't a smartphone that fits my niche (modern chipset with dual frequency GNSS for less than twice the price that competitors charge for it, operable with one average-sized hand, sdcard slot, and ideally a headphone jack but at this point I'd settle just for a bit of storage and really don't feel like it should be a hard-to-find device) or a laptop that makes sense (arrow keys and no annoying tapered edges that don't fit a network port, for example, already limits your options to a tiny percentage of the available systems)
Thanks! That helps clarify the engineering challenges. There’s never a free lunch!
Maybe an RV could be covered with solar? The top is much bigger, and if it isn’t charging fast enough you can always pull over and have lunch while the battery catches up.
But an RV is also way bigger and heavier.
RV panels make sense for the boondocking use case, where you want to charge computers or power a satellite internet terminal or something, but I can't imagine actually trying to drive on that trickle of juice.
Agreed. There’s an EV camper van with rooftop solar. IIRC it gets about 1000W peak, which isn’t bad for the home batteries but is basically nothing for the high voltage drive system
How about charging your house batteries, which power fans and lights and perhaps cooking and A/C? This kind of solar setup can be rather cheap and quite effective.
Yes, that's what I'm meaning. AIUI off-grid camping tends to be more limited by the drinking water supply more than electricity, but if collecting solar power lets you avoid running the generator quite as often, that sounds like a win.
This and you could also charge an ebike
Boats have been doing this for ages.
https://www.youtube.com/watch?v=BmbH-TAM2Wk&list=PLQp8FoQ4t-...
It’s always going to be anecdotal. I reckon a mid size RV (say upper class B) will have 1500-2000W of solar capacity, if it’s really boxy. It’s going to have the aerodynamics of a brick. Meaning you’ll be lucky to get 1mi/kwh at highway speed, maybe 2~2.5 if you keep under 30.
So you’ll be charging at 2~5mi/h, if the sun is shining straight overhead.
It’ll count for something if you park the RV in the sun for a week as you camp somewhere, but on the road it gives you some limping ability and that’s about it. The main benefit is not running the AC off of the engine.
It doesn't make sense to power any vehicle with onboard solar. There are no electric RVs yet because the batteries required to have any amount of range are cost prohibitive and heavy.
I put 1800W on my RV and that's covering the roof end to end. I'd guess it'd be enough for something like 1-2 miles a day on an electric drive train, assuming you don't use power for anything else.
> I'd guess it'd be enough for something like 1-2 miles a day on an electric drive train
It's probably more 10~20, possibly as much as 30, if it's a long and sunny summer day FWIW.
For references:
- the F150 lightning gets close to 2 miles / kWh on average, ~1.5 at highway speeds but as much as 3~4 at consistent low speeds
- on the other side of an RV, Volvo markets their FH Electric (cabover semi) for 1.1kWh/km — 0.7 mi/kWh — at 80km/h (50mph), DAF/Innovate UK's Battery Electric Truck Trial yielded similar results (1.08kWh/km over 287000 km), it's also close to the numbers of the electric trucker in their very recent MAN eGTX video (0.83 kWh/km = 0.75 mi/kWh)
It averages something like 12mpg diesel. This is a 25' long, 16k lb vehicle. There's no way it would get 2mi/kWh. 0.7 mi/kWh sounds closer to what it'd be.
But that's assuming you use no power. When I was living in it I was using 50% to 100% of the solar output a day.
Even better to get a fixed structure such as a garage or carport, that keeps the vehicle safe and out of the sun, and cover that in Solar.
It has larger surface area, doesn't weight the vehicle down at all even if it's built in a less weight-efficient way, and the vehicle doesn't need to be exposed to the elements.
Who lunches for several days/weeks? logically you would charge high speed through a plug with energy generated by panels that are much more efficiëntly (money+yield) placed and not have to carry around.
People are absolutely starting to populate their RVs with solar. What I've seen so far is just a few panels - around 600 watts. Usually connected to a battery separated from the RV wiring.
One can now get (flexible-ish) multi-junction PV (say 29% efficiency) from the factory for under $1/W. Still a higher price than the $0.2/W, lower efficiency panels, but when I messed with panels I felt like we were living in the future.
Anyway, one could also set up the panel to output a much higher voltage by having the factory wire cells in series (though how well that trades off with partial shading for a car roof I have no idea, and I have no idea the minimum quantity required to get that).
... but I agree, even with all that, it seems like a stretch to make it work.
They're not wrong but if you stick a solar panel on a car that's almost constantly going to be in less than perfect conditions to gather power the EROEI for the panel is going to struggle to be above 1.
Stick a panel on the bloody roof of a house or building and use that to charge the car. It'll do orders of magnitude more good.
Or above the parking lot. Shadow and energy for the car :)
Yes! Exactly this.
My last EV used 22 MWh over 6.5 years. That works out to 390W.
My solar array is located at high latitudes (northern Minnesota), the mounting angle isn't great, it's occasionally covered in snow, etc. In these conditions, I need 6.3 solar panels to produce 22 MWh over 6.5 years.
The area used by 6.3 solar panels -- enough PV to cover _all_ my EV's energy needs -- works out to be a parking spot large enough to fit the vehicle but not large enough to fully open any of the doors.
Exactly.
Only thing holding off my EV purchase is that I want proper V2G support. If I'm paying for 100kWh of lithium battery capacity I damn well want to use it as a backup for my house.
My understanding is that V2G (vehicle to grid) requires transfer switches etc to be installed to your home electrical setup so you don't accidentally backfeed electricity into the grid. So it's never going to be a simply a matter of getting a better EV.
Why exactly do you want a backup? If you're looking to maintain a few key appliances or internet during a grid outage a vehicle with V2L like an MG4 or BYD might be sufficient.
You probably already know this, but for the sake of providing context to other readers: V2G - vehicle to grid, providing power to the grid from your car battery like is common for home solar batteries; V2L - vehicle to load, a power outlet using energy from your car battery.
Transfer switches are trivial to have installed. I already have a manual, interlocked one for a portable generator.
I have a 13kW array on the roof and live in a place where ice storms make power outages a thing most years. My solar inverter is grid following. Even if I can't get grid forming from a car I'd only have to pay for a small battery and grid forming inverter to cold start the whole operation rather than $10K of extra batteries for them to do the grid forming. Then I can let the solar and vehicle do their thing and follow the islanded grid during the outage.
> Only thing holding off my EV purchase is that I want proper V2G support.
I always find this argument strange and it just feels like an excuse people use to sound informed while also dumping on EVs.
Do you have frequent enough power outages that you need a backup power solution? Why don't you have that solution already? Did the lack of ability to use an ICE vehicle as a generator for your home stop you from purchasing ICE vehicles? What's your definition of "proper V2G support" and why don't current EVs with V2G suffice?
V2G has a number of downsides. The most glaring is that you're stranded at home during a power outage or your house is without power while you go out. It requires to your EV to be plugged in, and won't automatically kick in when the power fails.
The power needs of a home are minimal compared to an EV, if having power during power outages is important then you're far better off investing in a whole home battery backup system. They're significantly cheaper than an EV because they aren't optimized for density and portability.
My understanding is that the only vehicle for which both the vehicle and the necessary house-side equipment are _currently_ available on the market is the Ford Lightning. Several other manufacturers have promised that their vehicles will support it, but there isn't yet any available source of the house side yet.
I assume this means that no one is using open standards or else you could conceivably just use the Ford Lightning equipment with any other vehicle.
The Quasar 2 bi-directional charger has been on the verge of coming out for years now but still isn't ready to just go out and buy it.
I agree with you though. I work from home and so my EV sits in front of my house for the vast majority of the time, and the battery is more than 2x my total usage during high cost hours. I don't have solar, but I do have time of use rating, so if I could use the giant battery to demand shift, that would save me a ton of money every year.
I suspect the main issue is the north american 2 split phases+neutral design.
Specifically, without the neutral, the car can already generate that with the onboard charger. A bidirectional charger costs no more than a unidirectional one if you are designing it.
But generating that neutral is expensive. You either need a hundred lbs of transformer, or some expensive power electronics.
That's actually mandatory in France for large parking lots
Honestly we should consider giving generous tax benefits so that every open air parking lot in any city in America that has more than 50,000 residents would be stupid to not have solar installed that covers the front of the cars in the parking lot and the walkways between the lot and the stores.
That's so much real estate available that would lower electricity costs, decrease the amount of AC used to cool cars down, and make going to malls and similar places a little nicer for everyone.
Sorry, that would actually be rational and we can't have that.
You’ve made an assumption - that the owner of the car has a roof, and can charge the car from there. People who don’t live in a place with off street parking to install a cable need a slightly different solution.
Exactly. Maybe just because I live in a city and almost everyone I know with a car will just find street parking somewhere within walking distance of their apartment.
So .. it would make sense to make a law that requires new parking spaces to have a solar roof which can charge the cars which park there for a few. This would spread rather quickly, I think.
I have solar panels at home and can charge a car .. but I'm mostly parked elsewhere when the sun is shining the most.
There's no reason to assume the charger and the panel have to be colocated if the panel isn't on the car. We have an electricity grid.
So do we, but you can't produce the electricity at one location and consume it in another. In the non-practical sense where our government decided that this is not possible.
Sure, probably true!
If solar parking lots are such a great idea, why do you need the threat? It seems like businesses or environmental groups would already be clamoring to install them.
PV parking is a highly visible status symbol and good PR signal for your community or company (hence the few installations), but actually it isn't a great RoI either financially or for the environment.
Sorry - I wasn’t explicit enough. The vast majority of existing and new developments where I live have on street parking - it’s not allocated, there’s no bays.
Still doesn’t solve the problem for people who use street parking.
The panels themselves would be more efficient, but in terms of getting that power into the car you might be better off having inefficient panels that work everywhere you go rather than optimized panels that only work when you go to a charging station
The study literally proves you wrong.
Having only read the abstract, no?
In high sun areas there’s a positive ROI
One big benefit:
Electrical engineers in 2025 have so many little power drains that any car left undriven for a few months has a dead battery.
A small book sized solar panel is enough to counteract that.
> Electrical engineers in 2025 have so many little power drains that any car left undriven for a few months has a dead battery.
Interestingly enough, the quiescent current drain of my 2020s era vehicle is lower than either of my past 2000s era vehicles when I measured it.
The phenomenon of batteries being drained after a few months of being left unattended is not new.
The big issue tends to be complex logic for going to sleep often getting stuck. Ie. "oh, I was trying to use the LTE connection to poll for updates, but the connection got reset so I kept the CPU awake forever whilst retrying every 5 minutes rather than going to sleep mode".
Older cars had this too - I had a bunch of cars which would kill their own batteries if not locked - the engineers assumed that all owners lock the car when walking away, which often isn't the case in your own garage.
It's not, but older cars tried to keep their batteries fully charged. Newer cars with the so-called "smart" alternators never keep the battery full, they always leave some empty capacity to recover energy while moving.
I had this same problem in my 2005-ish Lexus! I got a cheap switch[1] on Amazon and put it in-line with my battery. If I’m going to leave the car undriven for more than a week, I just disconnect the battery with the switch. It’s been great, no complaints so far.
[1] this is the switch I got https://a.co/d/90K0QiH
Doesn't anti-theft precautions kick in when you do this? On my Honda, if the battery goes completely dead or when I replace it, I have to enter a code in after, and IIRC all my radio stations reset, so it would be really inconvenient to do this often.
My way around this, which is also somewhat inconvenient- is that I pop the hood and connect a trickle charger if I have a feeling I won't be driving for a few weeks. I have a garage so this is the lesser evil.
Hmm I do have to put the key in the door when I’m reconnecting the battery, or else the car alarm will go off. That’s the only thing I’ve noticed though — maybe it’s just too old to have more complex features? I never listen to radio, so the stations may be reset and I just don’t notice.
My accord is a 2007 so not much newer than yours. We can Uber around for most trips but find it very convenient to have a car at times. If it works for you great, I thought that was a fairly common thing- particularly in cars of that era, because radio theft used to be so common.
I use a PV trickle charger, the panel is barely 1 square foot or so. Would be nice if it was integrated instead of having to connect/disconnect it constantly. Although, and I'm just guessing, many vehicles that are so seldomly driven are being kept indoors/garaged? (Mine is)
I haven't found any appreciable drain on my EV's primary battery over the longest period I've left it sitting so far (a little over a week, so not that long, admittedly), but the car _does_ do a very bad job of keeping the 12V battery charged and I've already had to replace it once in <2 years of ownership, plus I bought one of those small jump start packs in case it ever dies not at home (luckily, for an EV, it barely requires any power at all to turn everything on and get it started, so the very smallest, cheapest, jump packs are way more than sufficient). A built in trickle charger to combat that would indeed be nice, if the car companies are incapable of figuring out the logic necessary to do it off of the massive primary battery.
EV's are the worst at keeping their 12V batteries charged. Many EV's don't even charge the battery if they're plugged into an AC charger!!!
You can literally leave it plugged in charging for a month and come home to find it dead.
Alternator delete is a very common hack in the ecomodder community (usually coupled with LiFePo or Lithium battery instead of the regular lead-acid). It reduces the complexity and load on the engine, and does give a few percentage better fuel efficiency. But if you mostly ride at night, yeah ...
Everyone except you has approached this discussion with the intent of using the solar power to drive the car, but they should actually be thinking of using it to power the cars electrical system, and thus negating the need for the alternator.
A current gen 2.5L petrol Camry has a 12v 80A alternator. That 80amps likely covers driving at night in the rain (ie headlights on, window wipers going, HVAC fan blowing, etc). Normal daytime driving would be much less demanding, say 50A load, thus 600W power. Then you have to factor in the alternators inefficiencies, which could raise that demand to 1kW.
Next consider what the engine is having to generate whilst cruising, which could be 20kW for the Camry. In this scenario, that 1kW of alternator load is responsible for 5% of the engines load. So ditching the alternator would give 5% fuel efficiency increase on this Camry. A smaller car that only needs 12kW to cruise would see an 8% improvement (8% of a low consumption value though), whilst a much bigger car that needs 50kW to cruise would only see a 2% gain (but that's 2% of a high consumption value).
So if "solar body panels" could generate 500W like people have already guessed in this thread, then that would be close to offsetting the normal day-time electrical load. In this scenario it's probably a good idea to power the vehicles electrical system from a lithium battery, which wouldn't mind the gradual draw-down, because that could then be offset by parking the car in the sun (and possibly even by regenerative braking). Then there could still be an isolated lead-acid battery that is purely for starting the engine (because that needs high cranking amps), and that could be DC to DC charged from the vehicle circuit.
That 12v 80A alternator can generate almost 1kW at max effort. So even if you drive all night in the rain, that's still less than 1/5th of the energy in a Tesla or BYD vehicle battery. So this alternator-less car could get away with a much smaller battery, and it might even be smaller in area than the cars boot!
ICE Vehicle is hiding a major category division here, hybrid vs. traditional ICE. I think in the case of the latter this would only make sense as a bandaid to deal with parasitic battery drainage on a vehicle that is usually parked outside.
The cyclic nature of the sun actually makes for way better maintenance of lead acid batteries in practice than float chargers. Basically everyone with a boat, RV or rarely used heavy equipment has switched over at this point.
Can you elaborate here?
Float chargers do fairly frequently kill batteries by evaporating the fluid over time. It's like the difference between a battery being dead in a month or two of non-use vs 3-6 on a conventional float. It's hard to get the charge current just right. By contrast a charger that's voltage naturally decreases in proportion with what the battery is willing to suck up and tapers its charging and turns off overnight has the effect of more or less just "topping off" the battery without boiling much/any of the fluid. If you don't have a parasitic draw in excess of what the solar charger can make up for a battery is likely to be good for 6+mo without being touched. I can go 6mo on cars and other stuff that has digital electronics that draw a little bit and I can go 12+ for heavy equipment that has a hard cutoff switch.
And yet I know quite some people who report to be very happy with their plugin hybrid, doing max 40 km they hardly have to use fuel anymore and some can charge off their own PV setups (in summer).
I guess it’s a testament to the Netherlands being very compact.
I went the plugin hybrid route. The added complexity caused a lot of maintenance and reliability issues. I ended up having to dump the vehicle at a loss.
Something to keep in mind: A full EV doesn't require oil changes, which you still need to do with a plugin hybrid.
If you're able to do all your daily driving on battery only, then why bother with a gas engine that you aren't using? High speed charging works very well for the occasional road trip; it's at the point where if you take your bathroom breaks at high-speed chargers, you don't even need to "think" about charging.
I'm sure; it's certainly intuitive that a hybrid could do quite a lot with a PV setup. I just don't see PV doing much for a non-hybrid ICE vehicle outside of acting as a battery tender.
I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon. Even though the sun doesn't really shine all that much there, he still got enough power out of it, to never have to charge his car for his 20kmish daily commute.
No he didn't. Sweden gets ~2.6kWh/day per kW of solar panels. Malmö is at 55N latitude. If he put the panels on the car I hope he had a decent anti reflection coating because at that latitude he could be looking at 25% reduction in performance from the incident angle.
A purpose built EV gets something like 270Wh/mile in near perfect conditions little alone in a colder climate like Sweden.
12.5 * 270 = 3,375
So we've made absolutely every assumption greatly in his favor and we're already 750Wh short.
The math ain't mathing.
Let's not forget to do the math on how much less efficient the vehicle is over all with panels strapped to the top messing with the aerodynamics.
Even then, he said hybrid.
If he only drives Mo-fr the math works out though
Are we sure his car wasn’t a Twike or something? There’s ultralight EVs for which this could work.
Edit: Never mind, “hybrid station wagon”.
Regardless, it's not going to generate the claimed 1kW.
I don't remember the exact details, it's possible that he charged it over the weeked (or just didn't use it, thus getting 2 extra day of charge).
You can play around with assumptions, like what if it was driven in stop-and-go traffic at very low speeds? Then your quoted 270Wh figure might be lower.
But anyways, with these general conditions, with the numbers you quoted, and with a 10 kwh battery (aspull), you'd be looking at a net loss of 775Wh/day, which means you could go 13 days between charges.
The point I tried to make, is that solar panels on hybrids/EVs add a lot of practical value to people who can't charge at home/work, and it's not just meaningless greenwashing.
Also that 2.6kWh figure is a yearly average probably, sunlight varies greatly over the year.
> I remember reading about this Swedish dude who added 2 solar panels totaling about 1 kW to his hybrid station wagon.
I want to see a picture of that.
Apparently 1 kw fits on an extended box van [1]. But I don't now how you'd do it on a wagon without making it look like some sort of Burning Man art car.
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1. https://www.reddit.com/r/vandwellers/comments/1dpcxu4/if_any...
My exact numbers might be off (which is kind of a problem it seems on HN), but the point still stands - you can add practical amounts of range by having the car just sitting there, even in places where there's not that much sunlight.
Besides, I just checked out panels, and there's a lot of 500w ones that are appx 1mx2m, these station wagons are huge, easily 2m wide and 5m long, half of it a flat roof, so its not outrageous.
Won't work for most cars in cities, as they will be parked in indoor/underground garages, so no solar to speak of for their parking time, and the bit of solar you get while driving will maybe power the lights/electronics/audio system at most.
(Driving a full EV, but needing to charge 30+kwh/week, and my small (but larger than a car could fit) home-solar only provides max 20kwh/week in spring/summer.
A lot of car parks have chargers. Wiring up low wattage chargers is no big deal, considering AC chargers are just wiring+breakers. Considering cars will spend a long time here, large wattages are not needed, you could wire up a multi-story parking lot for chump change, and the entire wattage would be still less than a DC fast charger serving half a dozen cars.
Even the Aptera, which is designed to be super lightweight, can only regen about 10% of the battery (40 mi vs. 400 mi total capacity) with rooftop solar (https://aptera.us/)
Good reminder with respect to the CAFE standards (rip) that sometimes engineering doesn't trend towards what is "good" with respect to SWaP-C but rather what games the current regulatory environment best.
But the average American drives less than 40 miles per day (33 is the current estimate). The relative charge doesn't matter, because what this suggests is that most Americans would be able to go most days without spending any effort or money at all on charging.
You're forgetting america loves its covered parking
America also loves reserving vast swathes of the road for on-street parking, as well as endless fields of parking lots, not to mention that an enormous number of homeowners would rather park in their driveway and use their garage for storage.
I'm not trying to say solar roofs on cars make sense as a default option, but focusing on "percentage of battery charged" is the wrong metric. Most Americans would get by just fine on a relatively modest amount of charge per day, especially if we got over our range anxiety of insisting on massively oversized batteries for the average EV, which drastically increases weight and decreases efficiency.
Double an ioniq 5's miles per kw/h to 8m/kWh, use the maximum possible insolation (1kw/m^2) and theoretical PV efficiency (70%, reality is 30% btw) and you get... 8kw/h@12hrs a day generated and 3.75kwh needed. about double what this impossibly optimistic calculation gives. Half all the inputs and double the consumption and you get a quarter of the power needed.
It's interesting how much people expect an EV battery to be at 100% charged at all times but have you met the sort of person that tries to keep an ICE vehicle 100% fueled at all times? (It's costly and wasteful and a logistics nightmare, before also getting into questions of how dangerous it can be.)
10% of the battery per day, which would cover all of my driving other than the rare long road trip. I have plenty of weekends where I drive 200 miles, but then the battery would recharge over the week when I drive less than 40 miles a day
Maybe I am missing something but this feels like a study for the sake of a study? Has this not been solved for a long time. The complexity cost and the potential losses from drag make this fairly pointless. You would be better off with a fixed solar installation.
It might shut up some of the people who think solar panels are magic.
Those people dont read papers or believe science
But solar has been getting cheaper and more efficient by leaps and bounds.
What would have been a poor investment 10 years ago, or even 5, might well be net-positive today, potentially even in suboptimal weather conditions.
I don’t believe the primary cost is so much the physical panel but the cost to engineer and design it into a roof, also the additional systems needing to hook it into the wiring harness. It’s a fun toy for some but has no real benefit for the many.
But even stipulating this, with the way solar is improving, it may very well not be the case for much longer.
If you can guarantee that, in moderately sunny weather, the solar panel on your car's roof can provide enough power to keep the car going at, say, 30mph indefinitely, that's no longer just a fun toy.
Now, that level of utility may still be a long way off—or may even never be possible!—but I'm not willing to write it off for good, given solar's curve.
ETA: sorry, realized I should unpack a bit why I think this is worth mentioning: Your GP post was expressing confusion over why people would study this; I think it's very valuable to continue studying it as solar continues to improve, so that we can understand just where we are in relation to that utility curve.
Drag can be resolved by installing a flush panel conformal to the roof. If the vehicle is a van or truck, the flatness of the top makes it far easier.
Needless manufacturing complexity. Far better having static panels with current tech.
They are nice gimmicks like that newer model of Prius but far from being economic reality.
For larger utility vehicles you can cover 80% or more of the top, almost doubling the numbers of the study. Depending on the region, this seems to be an obvious way to extend range without adding larger batteries.
For most of my own commutes, this would mean I’d almost never have to plug the vehicle in. While abundant stationary chargers without stupid mobile app requirements would be preferable, this sounds like a perfectly fine plan B.
I’d miss the sun roof though.
Again, needless manufacturing complexity. You would be paying for a gimmick and not a real economic benefit.
Almost everything humans do is a gimmick. Eating anything other than nutrient slop is a gimmick. Gimmicks make life interesting.
Huh? This paper is about the economics or gain from adding solar powers to vehicles hence my statement that it’s a gimmick and it adds complexity (cost) for a gain that is not beneficial. Now if we were talking about marketing the vehicle, sure it perhaps drives a fun idea for buyers.
From an economic standpoint solar panels on vehicles are a gimmick.
One thing the paper does is introduce a mathematical model that allows us to decide when it's a gimmick and when it actually becomes useful. As PV panels get more efficient and lighter, there is a point it'll start to make sense despite conversion losses. It's very unlikely to make much sense in Sweden (or even in Ireland, where I live), but different locations, with different infrastructure and, most important, solar exposure, will drive different economics.
It's also not something that needs research IMO: Toyota has a Prius with solar panel option.
That option is a gimmick though.
This couple drove their EV the length of West Africa (and more) powered by solar panels they brought with them. Very cool.
https://www.instagram.com/4x4electric
It was a cool trip but everyone needs to understand how much downtime they had waiting for their batteries to charge. They had to deploy their solar while stopped, not while driving.
They drove the route faster than I did in my gas powered 4x4.
I am happy to go that slow when I’m such a fascinating part of the world.
It appears they didn't cover cargo transportation in the analysis. Curious if it may be worth for large trucks, over 20m long, as there is a large area available to install panels, and cargo transport is a hard to decarbonize sector. In long routes that extend east-west, I also imagine one coud try to adjust timing so the truck travels along the sun while it's day, and against it while it's night, so days in the local frame are slightly lenghtened, and nights are slightly shorter, improving light availability.
20m by 3m is 60m^2, with 300W/m^2 solar panels, it's less than 20kW.
A truck departs NY at the crack of dawn on the longest day of the year and cannonball-runs west at 100mph without hitting a single red light. The sun covers 15 degrees per hr. Denver is 30 degrees west of NY. The truck doesn't quite make it to Denver though, the sun sets on it somewhere in the middle of Nebraska. By chasing the sun, instead of 1700 miles, it gained a whole 1hr40mins of extra sunlight. That 20kW array turns that into 36kWh of extra power. By doing this chasing the sun instead of west-to-east, our truck turned a 1700 mile trip into something like 1718 miles.
On any 'typical' daily long-haul of 600 miles, we're looking at something more like an extra 3000-4000 feet. On something not as perfectly east-to-west like 900 miles NY to Atlanta, we're in the extra 100-200 feet, as long as it's not overcast.
If someone just put a battery-powered and solar-charged AC system in a car, I think it'd do a lot to reduce idling, if nothing else.
Good idea! The AC in my Nissan Leaf uses about 3kw so I assume it'd be about the same in my Corsa. However the Corsa disables auto-start stop and keeps the engine idling whenever the AC is on, negating any fuel savings!
Solar sun roofs for ICEs were a thing 20 years ago. Solar was able to ventilate your car on sunny days.
Yes, the Priuses circa 2010 had them.
I've wondered if there could be a way to make it so that internal combustion cars don't need lead acid batteries w/ a few solar panels and a setup like a scaled version of a solar watch. But that wouldn't be about big efficiency gains, just dropping a little space and the annoyance of them going dead every three years.
even EVs still have the 12V battery
When I looked at the title, I immediately thought that even if this makes sense from an engineering standpoint, psychology is going to be the bigger problem. For some reason many people are hell-bent on burning fossil fuels, almost in a sect-like belief kind of way. I do not understand it, but the backlash against anything electric for example is real.
Burning fossil fuels is relatively simple and well understood by general public. Modern business strategies to squeeze every cent out of a customer that involves subscriptions, planned obsolescence, adding bizarre complexity for marginal gains are not helping. Buying a very expensive black box with questionable reliability, possible dependency on a manufacturer provided internet services (APIs for updating etc), questionable availability of parts and probably not really fixable by yourself or your local shop with rednecks with wrenches is not very appealing when you are living paycheck to paycheck.
This is the real answer.
A friend of my family is a carpenter who came from a very bad family situation, and is just climbing out of poverty. He has an old Chevy K1500 that gets him to and from work, with all his tools.
His transmission went, but he was able to find one at a local junkyard and swap it in over the course of a day and be back on the road for a few hundred dollars.
If you proposed this guy get a F-150 Lightning (or god forbid, a Cybertruck) to reduce his carbon emissions, he'd keel over laughing.
People make noise about a lot of subjects, but money is what really talks. Whatever is cheaper will end up gaining market share until it wins.
Top Gear, one of the most popular car shows of all time, was responsible for a lot of this. They spent years spreading myths about electric cars being worse for the environment and doing things like filming fake segments where they were pushing an EV claiming the battery had died.
They did come around in later years, changing their tune to be more pro-EV. A lot of the damage was done, though.
Or maybe you are just blind to the realities of normal people. Most people are not hell-bent on burning fossil fuels. There are numerous valid reasons for people to continue to choose ICE. I want an EV. I want to dump every piece of outdoor equipment with an ICE for something with an electric motor. I very much prefer the pieces I have switched to electric. I've been wanting to make the switch for years. It just does not make sense for me at this time.
Solar Freakin' Roadways:[0] Mobile Edition
0. https://www.youtube.com/watch?v=HOZBrHqTJk4&list=PLvOlSehNtu...
If you have a small battery and use it to add ventilation in the vehicle on hot days when parked would be cool.
A similar question:
How large does a solar panel array have to be on a solar laser crop weeder, and how much acreage can it cover on a sunny day?
Is there potential to optimize solar beyond the perceived limits?
mirror https://sci-hub.se/https://www.jstor.org/stable/26169128
And that’s exactly why we added 1000 watts of solar to any vehicles’ roof rack here at DartSolar. We created and aftermarket roof rack so any car can add solar. More details at https://dartsolar.com
I'd like to see PV added to a Ford Maverick hybrid.
"significant increase in the range of 10.7-42.2% for lightweight and aerodynamic efficient vehicles" shout out to aptera motors https://aptera.us/vehicle/ that's currently vapor ware "Designed with ~700 watts of integrated solar cells, drive up to 40 miles per day completely off the grid and enjoy 400 miles of range per full charge"
(2016)
Moot point since Trump just killed CAFE. No more mileage standards will be enforced in the US.
> [ ... ] by adding on-board PVs to cover less than 50% of the projected horizontal surface area of a typical mid-size vehicle (e.g., Toyota Camry or Nissan Leaf), up to 50% of total daily miles traveled by an average U.S. person could be driven by solar energy.
This is nonsense and would easily be proven false except that the article's technical content is paywalled. But common sense says that, if the claim were true, simple economics would make it a reality.
The publishing journal, the "SAE International Journal of Alternative Powertrains", appears to be one of thousands of online-only journals meant to provide a fee-based publication opportunity for authors who have no chance to publish in a reputable journal. In short, the authors pay, then the readers pay -- quite a system.
For a moment I thought this was somehow about putting solar PV panels inside an engine and getting energy from the light from the detonation.... I need a cup of coffee
[flagged]
Since the title said "internal combustion" my first thought, too, was could they make an engine a bit more efficient with some electrical process that increases the efficiency. The actual article was much more nonsensical than this take.