OK, my day job is doing HV engineering, not transmission, but high energy stuff.
The author did something kind of equivalent to:
"If we scale a GPU clock to 75 Petahertz, we can make datacenters that fit in bed rooms! Here are the FLOPS calculations to prove it!"
This whole thing is so crazy I don't know where to begin. I applaud the author for jumping into a new subject, but there is _way_ more complexity here than laid out. HV is very difficult to penetrate too because there really isn't much info available online about it.
Those initial dielectric strength numbers are definitely off (maybe they used Wikipedia, which references a value from a 1920 physics book). As from what I can find fused silica has a dielectric strength around 50-100MV/m, which is taken from the AC figure and doubled to get the DC figure (which is fairly typical). Also these numbers are extrapolated, and dielectrics often have non-linear properties. The testers used to get these figures can be a little fickle, and HV is always fickle.
On top of that, in actual HV system design, you really need to be using 25% of the actual dielectric strength for any kind of reliability. So the practical strength of fused silica would ultimately be around ~20MV/m. Which pretty much kills the whole idea right there. Never mind that a single fracture or dielectric breakdown anywhere in the whole glass sheath would require the entire thing to be replaced. Spoiler: You cannot patch HV dielectrics. Trust me, I and many others have tried.
Some other hurdles would be dealing with the insane parasitics, which the author didn't even mention, but are one of if not the most limiting factor in transmission. HVDC lines can have up to 10% ripple, which for the author would be 1.4MV of high frequency ripple. And sea water is conductive! You are basically building a massive capacitor with sea water! The losses would be enormous.
And I don't even want to think about the electronics...14MV is so insane I cannot fathom anything that would be able to reliably handle it. 1MV is already nuts. 800kV is the highest in the world, and that is kinda just a flex.
Jumping on this bandwagon - these days I'm working in the submarine telco cable industry.
Considering a cable from singapore <> LA direct can run up $1.4bn USD. I think author needs a lot more research.
1. route planning takes a long time, the ocean floor moves (see: Fault Lines, Underwater Volcanos, pesky fisherman)
2. The ships do move _ a lot_ even with fancy station keeping and stabilisation.
3. cables get broken - a lot. Even now there's 10-15 faults globally on submarine cables. There are companies (See: Optic Marine) who operate fleets of vessels to lay and maintain cables. I'm sure the HVDC industry has the same.
Cool idea, I have been pondering it a lot myself, I figured maybe a ground return HVDC cable might be better for inter-country power grid links.
I know Sun Cable out of Australia want to build a subsea powercable to sell energy into ASEAN.
That's exactly why one uses a high switching frequency, MOSFETs and has a tiny ripple (perhaps 0.1%). This can be obtained cheaply with multiphase convertors.
Mosfets are now cheaper than IGBT's where you are paying for power losses and plan to run at full load for more than a few days to months. That's why nearly all EV's use MOSFETs - (and will use GAN MOSFETs at MHz switching rates when the patents run out)
Remember that the cable acts like a capacitor/inductor pair to ground. Ripple currents that are lost through it are not wasted money - merely wasted capacity and resistive losses in the cable. At these currents, you can assume earth is a perfect conductor, so no losses there either.
400V electric vehicles and 400,000V transmission lines play by different rules.
There are no MOSFETS anywhere in HV applications. IGBTs, but no MOSFETS. Most converters use thyristors and newer ones use IGBTs. No matter what, PN-junctions are king for HV silicon applications.
Also ripple is a function of filtering not switching. The reason higher switching frequencies generally have better ripple characteristics is because smaller capacitors can filter them and/or larger capacitors filter them better. So in a cost constrained/size constrained product you get more filtering for the same buck same size.
I also can't figure out what you are saying in your last line, apologies.
Well, SiC MOSFET do get used, but yeah.
SiC JFETs are indeed better, lower lower with the same wafer technology, avalanche proof, high heat proof (the polyimide passivation hurts beyond ~220 C).
Much easier to drive when you stack them for HV.
That said, GaN is there for capacitive converters due to being able to run very efficient at >10 MHz switching frequency.
These converters in principle fit in very compact phase change coolant/insulator vessels, for example with propane. The capacitors at those frequencies get to be tiny, like, smaller than the transistor package by volume.
> 400V electric vehicles and 400,000V transmission lines play by different rules.
When stacked, they don't. Plenty of research on stacking both MOSFETs and entire power converters.
With stacking, the figure of merit (ie. Kilowatts per dollar, loss percentage) isn't a function of voltage (although the fact that you have to have an integer number in series and parallel could influence the design if you want to use off the shelf components)
Today's HV converter stations use IGBT's mostly because they used to be the best thing to use back in the 2010's when the design process for them started.
The reasons for using IGBTs is not only because BJTs withstand higher voltages, but also because their Vce(sat) can provide much lower loss than Rds(on) at high currents. I x V vs I^2/R.
Vce never really goes below 2 volts... Which for a 1000 amps means the running costs of the converter are 2000 watts * number of stages (~2800). 5.6MW of heat. That quickly dwarfs the purchase cost of those IGBTs.
Whereas the same calculation for MOSFETs [1] gives 4242 stages and an Rdson of 1.9 milliohms... = 8 Megawatts! Which sounds worse... But you can parallel the MOSFETs by spending double the money on them, reducing the loss to 4 megawatts... Or you can double it again to reduce the loss to 2 megawatts, etc.
When you run something 24*7, energy losses cost way more than capital costs - and MOSFETs let you make that tradeoff, whereas IGBTs do not.
>I’m curious if there are any exotic materials that would be way better dielectrics?
There are, but like glass they tend to be rigid crystalline structures, and not necessarily formable into what you need. There also is the problem that the dielectric needs to be perfect, as any imperfection becomes a pressure point and once you get even a microscopic breakdown, the whole thing is junk. Any practical repair is going to be very imperfect on the molecular level, so see what I said earlier. Also gaps are imperfections, so usually layering layers of dielectric is a non-starter too (but can be done, it's just very engineering intensive). The HV will "leap" from imperfection to imperfection until it finds it's ground. Insulating HV is a totally different world than your typical 240V, 480V, even 1kV insulation.
>Also are there ways to step down really high voltages? I can’t picture how the electronics would work without shorting
Yes, they basically use stacks of thyristors or IGBTs to actively switch the DC "phases" which get fed into a transformer to step down. Wikipedia has a surprisingly good article on it:
> Insulating HV is a totally different world than your typical 240V, 480V, even 1kV insulation.
Hell, even the difference between 600V (low voltage) THHN (thermoplastic) or XHHW (XLPE) insulation and a 2.4kV/5kV (medium voltage) cable is enormous.
It's also the picture I had in mind when thinking about 14MV. The size of everything to space out the stages would need to be so vast I don't even know if it would be structurally possible.
The Changji-Guquan ultra-high-voltage direct current (UHVDC) transmission line in China is the world’s first transmission line operating at 1,100kV voltage.
I swoop in on something like this looking for the first obvious error in units/arithmetic/materials that renders the whole thing ludicrous, but the author has a spreadsheet and it looks like the units are about right. It's an absurdly cheap cable in terms of materials to transmit 10 GW across an ocean. The main things that render it dubious as a practical matter:
- I don't know if operating at 14 million volts is achievable in terms of converter stations. Today's highest voltage HVDC projects operate at 1.1 megavolts and it took years of development to get there from 0.6 megavolts.
- The mechanical practicality of thousands of kilometers of silica clad aluminum. There's a big mismatch in coefficients of thermal expansion and silica is brittle.
Still, this appears to be facially valid in scientific terms if not in engineering terms. That's impressive! It's a really thin intercontinental cable carrying a lot of power.
The whole thing reminded me of this discussion here from 3 years ago:
It has rough numbers for a globe-spanning HVDC cable on the order of a meter in diameter (assumes voltages more like present day commercial HVDC, much thicker conductor to compensate).
> There's a big mismatch in coefficients of thermal expansion and silica is brittle.
The way these are manufactured together means the silica with the lower CTE solidifies first - giving a tube filled with molten aluminium. Next the aluminium solidifies. Then the whole thing cools down and the aluminium probably delaminated from the walls of the tube, leaving a gap of a few hundred micrometers. The aluminium also ends up stretching slightly (one time).
During use, the inner core will heat up and cool down, fairly substantially (perhaps by 100C), using that gap that formed as the cable was manufactured.
I considered that. Considering the cheap cost of the cable, the best solution appears to simply be 'dont have a breaker'. In either over current or over voltage conditions, simply sacrifice the cable.
Obviously you engineer the convertor stations to minimize the chances of that happening - stopping the convertors automatically if anything looks abnormal. The cable has sufficient capacitance that you have multiple milliseconds to respond, so automated systems should have no difficulty.
14MV would be capable of sustaining an arc 1400 feet long in normal atmosphere. I struggle to imagine how you'd build such a thing. You could maybe have a high volume sf6 pump system that would cool and quench the arc on breaker trip with a constantly replenished sf6 supply.
Isn't sf6 on the way out due to it being an extremely potent GHG?
Not sure what the alternative would be for really high voltages? Vacuum insulated switchgear seems to be a hot topic at the moment, but not sure how it'd work with such extreme voltages?
Even 1.1GV systems use semiconductor breakers. Basically, stacks and stacks of transistors. The actual physical breakers are only operated when the voltage is safely off.
Not quite true. Glass optical fibre is reasonably flexible. More so than many coaxial cables. Just don't go below its minimum bend radius, as it is brittle and will snap.
Glass insulated power cables might work, provided the glass layer is thin enough and its band radius isn't exceeded. One can imagine a cable insulated with many thin layers/strips of glass, which have some movement relative to each other. Multiple layers of insulation is normal practise with plastic insulation, as the failure mode is typically pinholes in the insulation and multiple layers reduced the probability of pin holes going all the way through.
Biggest problem might be a conductor with decent diameter will put a lot of stress on the interior and exterior of a bend. Some ides:
* A multi-standed conductor with each individual conductor insulated. Maybe have high voltage in the interior stands and have a radial voltage gradient (to zero) across the outer strands so no one thin layer of glass is taking the full electric field?
* Could a conductor be insulated with a woven/stranded insulating layer? One can imagine many layers of extremely fine glass fibre finished off with an enclosing layer of something else to keep everything in place. Sort of like a glass insulated coaxial cable.
An insulator made of multiple materials will have the breakdown voltage of the weakest material. So, glass fibers in some sort of resin will break down at the resin's voltage, not the glass's.
Fiber optic strands are glass rods (solid interior) instead of tubes (hollow cylinder). The two shapes have different strength properties per unit mass [1, 2].
Current implementations break from simple vibrations such as a bus driving down the road and shaking the ducts the fibre is in. Lots of work required still. Crazy expensive and crazy fragile.
> The cable, if snagged by a ship anchor, would catastrophically fail. Not only would it snap, but the internal stresses would propagate the crack along the entire length.
I admire that the author wrote this sentence and continued with the thought experiment anyway
A stack of optically powered 15kV mosfets, to get to 14MV, sounds absurdly awesome. 933+ mosfets that you're trying to drive in series, egads. But neat weird idea.
> A 15 kV SiC MOSFET gate drive with power over fiber based isolated power supply and comprehensive protection functions
I distantly remember reading about someone stress testing a submarine drone tether at higher than rated voltages, seeing what practical voltage they could get out of it. I distantly recall there being a lot of concern about like corona arching or something with the sea water? That was a fun paper. I don't ever if it was only because they exceeded the insulation value, but I feel like there were some notable challenges to running high voltages in salt water that I'm not quite remembering.
The importance of repairability is underestimated here. All new infrastructure must be built under assumption that there will be multiple attempts at sabotaging it by actors of various level, and multi-megavolt unrepairable cables that can be fully disabled by one smallish unmanned sub don’t win here at all.
The original version of this post did have a repair plan.
Basically, every few kilometres you turn off the surface hardening of the cable for a yard or two. That spot won't propagate cracks - which means that if someone destroys part of the cable, the rest will be fine.
Those spots of cable have no tensile strength, so you wrap just those spots in a post tensioned steel sheath.
Then, you also make a few spare kilometers of cable that you lay in the ocean floor. When an incident happens, tow a new cable into position and connect it up. Underwater glass forming is a silly idea - but you can simply crack away the glass at the ends, reconnect the aluminium, then encase the whole thing in a couple of yards of epoxy.
The above plan I considered probably was of similar cost to simply laying a new cable across the entire ocean ahead of time in preparation though.
HVDC cables are kind of an often overlooked solution to net zero. Moving power over long distances, across timezones is kind of a super power. The main obstacle to scaling this from a few GW to tens/hundreds of GW is cost. Just by laying more cables can you increase capacity between regions and their ability to share excess power to each other. But each cable is a multi billion dollar project. Which means that there is only a little bit of capacity to move power around but not a lot. For example Europe can import a few GW of African solar in the middle of the winter. But it could probably need hundreds when it is dark and not windy there.
Likewise cross Atlantic cables have been talked about but so far don't exist. Same with getting power from the East coast US to the West coast and vice versa. The east coast goes dark while the west coast is still producing lots of solar. And in the morning on the west coast, it's afternoon on the east coast. There is a bit of import/export between California (solar) and Canada (wind / hydro). But it could be much more.
Cables have another important function: they can be used to charge batteries. Batteries allow you to timeshift demand: e.g. charge when the sun is out, discharge when people get home in the evening. And off peak, the cables aren't at full capacity anyway meaning that any excess power can easily be moved around to charge batteries locally or remotely. Renewables, cables and batteries largely remove the need for things like nuclear plants.
Yes it gets dark and cloudy sometimes but those are local effects and they are somewhat predictable. And if the wind is not blowing that just means it is blowing elsewhere. Wind flows from high pressure to low pressure areas. Globally, there always are high and low pressure areas. If anything, global warming is causing there to be more wind, not less. So, global wind energy production will always maintain a high average even if it drops to next to nothing locally. Likewise, global solar production moves around with the sun rise and sun set and seasons but never drops to zero everywhere. If it's night where you are, it isn't on the other side of the planet. If it's winter where you are, it isn't at -1 * your latitude.
If long distance cables get cheap and plentiful, that's a really big deal because this allows for moving around hundreds of gwh of power. HVDC allows doing that over thousands of kilometers across oceans, timezones, and continents. Cheaper HVDC lowers the cost of that power.
It's an interesting take to be sure. I suspect that the lack of flexibility is going to be the real killer.
You'd probably have to build offshore platforms on either side to bring the cables up and terminate them and now that's a nightmare, saltwater/salty air and electronics don't mix well.
Or you're going to have to trench very deeply for the first few miles.
Either way you're stuck with something that really doesn't want to be bent.
I think the "glass is great insulation" is a good insight and perhaps a composite glass fiber/polymer sheath would really increase the V/m without the brittleness.
a material that stretches 1% to failure (like steel/aluminum) can ballpark bend to a radius 100 times the thickness. so a 1 meter cable could bend 100m radius before cracking. assuming 10x margin that would be 1 km radius. large but not crazy. A tube that size can easily span 1 km trenches in water. you could also add a few meters of foam around it to make it neutrally buoyant and just barely press on the ocean floor.
The blog is suggesting 10 GW, which is well short of "the entire thing", and they also suggest a lot of redundancy.
If you were to use a single cable for everything, that would be silly because no redundancy, e.g. "A volcano? On the mid-Atlantic ridge? Who could have foreseen this?"
But at the same time, a cable big enough to carry the world's power is pretty big. I've done similar ballpark calculations, and to get the electrical resistance all the way around the planet and back down to 1Ω, you'd need almost exactly one square meter cross section of aluminium (so any anchor cable breaks first), and that would have so much current flowing through it that spinning metal cutting tools can't operate nearby thanks to eddy currents from the magnetic field.
This is the kind of transmission line design I've seen proposed for use on the Moon - where hydrocarbons are basically nonexistent, but aluminium and silicon are abundant.
Glass insulated cable sounds like a tech that should be prototyped on smaller scales - and could be somewhat useful on those smaller scales.
Yes, but it's just an inch - and we need a continuous extruded wire at least a dozen meters long. Even on the scale of an inch, thermal expansion coefficient mismatch problems exist - this was a notorious issue with manufacturability of early vacuum tubes.
Turns out it's rather tricky to make glass bond to metal well enough.
The glass in a lamp is not for electrical isolation, it's intended to prevent the cable from literally burning up by keeping oxygen out and protective gas in.
When you're on the moon, why bother with glass? You're surrounded by vacuum and dry rock.
I mean, sure, you can't go over 1022 kV or you get positron-electron pair production from free electrons, but that's still true on your outer surface even with insulation.
Would coaxial HVDC let you go further, because there's no external voltage gradient? I assume so, but mega-scale high-voltage engineering in space combines three hard engineering challenges, so I wouldn't want to speak with confidence.
That said, vacuum is also a fantastic thermal insulator, so perhaps you could do superconducting cables more easily.
I've heard of ballistic conductors*, I wonder if that would scale up… basically the same as the current flowing around a magnetosphere at that scale? https://en.wikipedia.org/wiki/Ring_current
On the other hand, you'd have to make the magnetosphere on the moon first, and "let's use the sky as a wire" sounds like the kind of nonsense you get in the "[Nicola] Tesla: The Lost Inventions" booklet that my mum liked, and therefore I want to discount it preemptively even if I can't say why exactly.
"Just burying your wires in lunar regolith" is another proposed option for long range transmission lines, yes!
We don't know how well that would work in practice though, because there's still a few unknowns about how properties of lunar regolith change across distance.
Some wire applications do require isolation though. For example, motor wiring and other coils.
It would be extremely challenging to make usable coils out of glass coated magnet wire - but it's not like there's oil on the Moon waiting to be made into polymer coatings.
PCB-based transformers exist, and so do ceramic substrate PCBs. If you combine the two, and find a process to weld the ceramic/glass substrate plates together instead of gluing them together, it could work as a transformer.
> The cable, if snagged by a ship anchor, would catastrophically fail. Not only would it snap, but the internal stresses would propagate the crack along the entire length.
I can’t this writeup seriously with comments like this. There is no mention of any attempt to calculate the allowable bend radius. Also, quenching a glass tube in a continuous process? Does that work?
The bend radius doesn't actually matter - one can fairly trivially adjust the factory ship to make bends at specific places if desired. Including, if necessary, to fit the contour of the seafloor.
The critical thing is the length of the longest unsupported span - and that's 64 meters, but surface hardening could possibly dramatically extend this, but it seems beyond available literature.
The Moore-like fall of solar+battery costs took away solar satellites, solar convection plants, submarine power cables and (widely deployed though) sun tracking hardware. Labour costs are becoming a bigger proportion so some installations plop panels on the ground than slant them to south (in northern hemisphere).
> Labour costs are becoming a bigger proportion so some installations plop panels on the ground than slant them to south (in northern hemisphere).
Even more than that: I was recently at GITEX Europe, and one of the startups* was pitching "they're so cheap, we should lay them flat for cheaper installation and maintenance".
* Their name was something like "slant solar" or "tilt solar", as they had initially thought of doing exactly what you say, but I can't exactly recall the name.
I like the article for brainstorming possible technological solutions. Though whats missed is the cost of maintaining and repairing seafloor cables. This is what makes or breaks your idea after its already built and broken in a couple days rather than its rated lifespan of decades.
Stepping back from the technical question of how to lay HVDC undersea, a globally connected power grid seems like a major win for renewable energy. There are a lot of places you’d like to put power plants, and having the infrastructure in place to be able to sell that energy makes it immediately more feasible. We could put nuclear plants anywhere. Solar plants across the Sahara. It would increase the energy available to developing countries without tempting them with dirty fossil fuel plants.
It's true that you can switch very high voltages with MOSFETs in series. But the next step after switching is a transformer that needs to handle 14 MV between the primary and lower-voltage secondary winding. I don't think anyone has built something like that before. Given the dielectric strength of transformer oil, the primary windings need to be 500mm away from both the secondary windings and the core, which seems like it'd be hard to do while getting good inductive coupling.
Nah, just do a few divide-by-2 capacitive converter stages to tame it.
Basically just a FC-3L buck running at exactly half to not need meaningful amounts of inductance.
Feed the radiation to adjacent phases of a radially symmetric setup, and it shouldn't be an issue anymore.
These classic HVDC transformers only exist because those lines plug directly into the AC grid; it's easier to just tame the HVDC and keep it DC for a bit, though, at these extreme facility sizes.
Since the ferrite core isn't a good insulator, the glass would need to fully encase either the primary or secondary winding.
At the sort of scales this transformer would likely be built, an extra 35mm would make the whole thing a little bigger and more expensive, but not massively so.
The glass tank could also double up as an oil bath for cooling the coil - the first 500 millimeters or so of the piping needs to be glass, but after that you can use a typical cooling radiator with no extra concerns.
The quenching is done on the boat with presumably purified water. That's a pretty small amount of heat to manage, so its not like you will run out of water.
It’s interesting. I think the real way to do this is gradually scale up. Crossing the ocean is hard mode. Instead start by something much shorter and land based. Then you at least have a stable platform to work on and can focus on the other hard problems
In 1st world countries, land based cables often cost more because you have thousands of people along the route who all don't want a power line through their small village.
1. The technical solution relies heavily on fantasy.
2. It is not needed. We have no significant power transmission across the low lying fruit of continental America or Eurasia, and those lines are built! Why bother crossing an ocean?
3. Why not cross Greenland and the North Sea and its islands? Under sea cables are expensive.
There was a big solar project proposed in Australia's outback to supply Singapore but never got off the ground perhaps advances in glass / dc infrastructure could change the calculations. Same story for Sahara solar supply to Eu.
In Peace and Harmony Land™ I could see the value of shipping excess power from sunny/windy locations to those that are without, but I don't think the present world is ready to collaborate at that level.
If I (and only I) owned such a cable from Europe to the US, how much money could I make by buying cheap solar energy from the bright side and selling it to the dark side of the Atlantic?
First thought:
10 GW * $0.03/kWh 4 hours/day = $1.2Mio per day [0]
I suspect you might earn a lot more than $0.03/kWh on average.
The difference between typical market daytime and evening wholesale electricity prices is around $0.06/kWh in the UK right now:
https://bmrs.elexon.co.uk/system-prices
You are ignoring many variables, ranging from cable resistance losses and maintenance costs to signal re-synchronisation systems. Not to mention environmental factors such as seabed warming and subsequent changes in ocean currents, over time.
Yes, of course I do ignore a lot in that calculation. I just wanted to calculate the biggest possible usefulness of this cable. Especially the resistance losses could be quite disastrous.
Probably more like 8 hours: you can sell in both directions, to US before sunrise in US, to EU after sunset in EU.
How much you can charge probably also depends on storage, but it seems plausible (same magnitude as current transmission/distribution costs?) to my amateur understanding.
Continuous melted silica coating is fine, but how does one account for all the movement, bends and vagaries of the high seas, especially for something that is so brittle?
I wonder if the glass sheath could be replaced with bundled glass fibers in a dielectric gel? Would that cross section allow for a much greater distance for current to trace through the gel? Seems like maybe it would give a 2x advantage, or maybe glass ribbons could be made instead for a micro braided insulation?
For the glass to be the insulator we need, I'm assuming the author envisions a solid tube, with no airgaps (can't do fibre braid as that would allow gaps which means loss of insulation, or you'd need oil to fill the gaps.)
This means huge bend radius in the order of hundreds of meters. Not only that but laying it on the ocean bed would require trenching and full support to stop localised bending.
Now to the manufacture:
> The cable is then quenched in water to surface harden it, before it moves out of the back of the ship and falls to the ocean floor over a length of many kilometers (due to very low curve radius).
So that'll cause the tube to break. Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop) so needs an annealing step. ( https://en.wikipedia.org/wiki/Annealing_(glass) )
Moreover changes in temperature mean that using aluminum is probably going to cause the glass to shatter when the temperature changes. which means that you either need https://en.wikipedia.org/wiki/Kovar or somehow make expansion joints every n meters.
Finally that cable is going to be heavy, so unless you make it around the same densisty as salt water, it'll have so much weight it'll snap as soon as you try and dump it into the sea.
apart from that, looks good. well apart from the units are wrong to start with.
TLDR:
you'd need 5x the width of Polyethylene to achieve the same level of insulation at high voltages. but as silica tube doesn't bend and shatters really easily, cant be transported and has a slow extrusion rate, it seems logical to just use PE.
PE doesn't work as well as you imagine. As well as needing waaaay more of it, due to the power of 2 in the volume of a cylinder formula, and it being much more expensive, it also can't withstand high temperatures, which means the current carrying capacity of the core is lowered.
Have you done an accounting of how many kilometers you can fit on a 200,000+ tonne boat? Seems to me you could cost-effectively carry nearly 20x as much cable weight as current cable layers. You need 25x the volume of polyethylene, but that's only 10x the weight and it isn't even counting the weight of the conductor.
> Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop)
That internal stress is deliberate. It counterintuitively makes the cable have more tensile strength since glass tends to only fail when a crack propagates from the outside.
But it can span ~64 meter gaps without support, so the need for trenching should be minimal.
During the laying process in deep water, one can use buoys along the length to gradually lay the heavy cable on the seafloor so the tension isn't in the cable.
> So that'll cause the tube to break. Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop) so needs an annealing step.
Did you miss that the prestress is the point? There also could still be an annealing step- a continuous oven just like glass fiber manufacturing. Annealing time for prestressed fibers is very short, although I am very skeptical you could actually get something like this to work in practice.
> Moreover changes in temperature mean that using aluminum is probably going to cause the glass to shatter when the temperature changes.
Does temperature change at the bottom of the ocean? I suspect the heat per meter from resistive losses will be very, very low, but it is a missing point.
> Finally that cable is going to be heavy, so unless you make it around the same densisty as salt water, it'll have so much weight it'll snap as soon as you try and dump it into the sea.
That is addressed in the post- balloons to keep the bend angle low as it descends.
> it seems logical to just use PE.
MSC Irina has a deadweight tonnage (cargo+fuel etc) of 240,000 tonnes. PE would be ~15 cm thickness and weigh ~66 tonnes per km, so you'd get somewhere in the region of 3600 km of cable per trip. Atlantic submarine cables are <7200 km, so yeah- it seems very hard to make the case that glass is worth it.
NB: I do not believe that 14 MV cables could be 30 cm in width, but it doesn't matter much. If you make 8 trips instead of 2, it's still hard to justify. Current cable-laying ships are pretty small, despite cables still being decently big- cargo ships are way bigger. Not scaling up the ships would be very silly when they already exist.
It does have to be thin. You need to fit as much as possible on a boat and volume increases quadratically with thickness- so if glass is 500 MV/m and XLPE is 150 MV/m you would need to carry 11x more of it. Refilling means hundreds of miles back to shore.
Everything looks nice but something very important was not considered in all of this.
High voltage and high current means Z-pinch - the conductor itself is going to compress itself, thus resulting in basically delaminating from the glass sheathing. This is why we have rubber/petroleum-based flexible sticky insulators on cabling like that, it can somewhat flex/shrink with the conductor and is more likely to stay attached and less likely to get damaged.
Just transmit laser power down fiber optics at that point. Either way you're going to need semiconductor switching (it's IGBTs all the way down baby!) nothing electromechanical is going to handle that kind of load.
High voltage does not induce pinch, only current. High voltage is used to create bursts of high current in can-crushing demonstrations. The cable is solid and the current is not concentrated in a thin cylindrical shell. The pinch is negligible, certainly in comparison to eg thermal expansion from changing load conditions.
> Just transmit laser power down fiber optics at that point.
How does that work? You can only get the glass so clear, so you're going to lose all the energy. There's no equivalent to cranking the voltage to increase range.
I watched a video recently that talked about how China is really the only country to have developed and built UHVDC power transmission. Some look at this and say how it's a failure of everyone else. My immediate thought was: "this solves aproblem only China has" and that turned out to be correct.
China produces most of its power in the west of the country between solar farms, the Three Gorges Dam and so on. Most of the population is 2000 miles away in the east of the country. For over a billion people, the cost of more efficient long-distance transmission make economic sense.
Someone asked "could Australia do this to transmit solar power from the West coast to the east coast in peak hours?". Technically? Yes. Practically? No. Why? It's obviously expensive with far fewer people but also all that space in between is uninhabited. So if you ever need to maintain it (which you will) you have to send people out into the wilderness to do it. China doesn't have that problem because it's not really unpopulated anywhere, at least not to the scale Australia is.
My point here is that you should always ask for something like this "what problem does it solve?" And the answer for more efficient long-distance power transmission is "almost nobody".
I think power grids are going to go in the other direction and become increasingly localized rather than nationalized.
Yes. The US wind belt is from the Texas panhandle north to Canada.[1] But there's no good connectivity to anywhere with a load. Some east-west EHV lines from that area would be a big win. There's opposition from oil interests. Just trying to connect East Texas to Mississippi has been stalled for over a decade.[2]
Don't need anything as exotic as the 14MV the original poster proposes. 1MV at 1000 amps, which is a gigawatt, has been done many times in China. One right of way can have several such lines. It would be best to have at least two distant rights of way, for redundancy. California's total load is around 13GW, so the number of 1GW lines needed is not large.
Undergrounding high powered lines is a huge headache, but possible. Here's an overview.[3]
OK, my day job is doing HV engineering, not transmission, but high energy stuff.
The author did something kind of equivalent to:
"If we scale a GPU clock to 75 Petahertz, we can make datacenters that fit in bed rooms! Here are the FLOPS calculations to prove it!"
This whole thing is so crazy I don't know where to begin. I applaud the author for jumping into a new subject, but there is _way_ more complexity here than laid out. HV is very difficult to penetrate too because there really isn't much info available online about it.
Those initial dielectric strength numbers are definitely off (maybe they used Wikipedia, which references a value from a 1920 physics book). As from what I can find fused silica has a dielectric strength around 50-100MV/m, which is taken from the AC figure and doubled to get the DC figure (which is fairly typical). Also these numbers are extrapolated, and dielectrics often have non-linear properties. The testers used to get these figures can be a little fickle, and HV is always fickle.
On top of that, in actual HV system design, you really need to be using 25% of the actual dielectric strength for any kind of reliability. So the practical strength of fused silica would ultimately be around ~20MV/m. Which pretty much kills the whole idea right there. Never mind that a single fracture or dielectric breakdown anywhere in the whole glass sheath would require the entire thing to be replaced. Spoiler: You cannot patch HV dielectrics. Trust me, I and many others have tried.
Some other hurdles would be dealing with the insane parasitics, which the author didn't even mention, but are one of if not the most limiting factor in transmission. HVDC lines can have up to 10% ripple, which for the author would be 1.4MV of high frequency ripple. And sea water is conductive! You are basically building a massive capacitor with sea water! The losses would be enormous.
And I don't even want to think about the electronics...14MV is so insane I cannot fathom anything that would be able to reliably handle it. 1MV is already nuts. 800kV is the highest in the world, and that is kinda just a flex.
Jumping on this bandwagon - these days I'm working in the submarine telco cable industry.
Considering a cable from singapore <> LA direct can run up $1.4bn USD. I think author needs a lot more research.
1. route planning takes a long time, the ocean floor moves (see: Fault Lines, Underwater Volcanos, pesky fisherman) 2. The ships do move _ a lot_ even with fancy station keeping and stabilisation. 3. cables get broken - a lot. Even now there's 10-15 faults globally on submarine cables. There are companies (See: Optic Marine) who operate fleets of vessels to lay and maintain cables. I'm sure the HVDC industry has the same.
Cool idea, I have been pondering it a lot myself, I figured maybe a ground return HVDC cable might be better for inter-country power grid links.
I know Sun Cable out of Australia want to build a subsea powercable to sell energy into ASEAN.
> HVDC lines can have up to 10% ripple
That's exactly why one uses a high switching frequency, MOSFETs and has a tiny ripple (perhaps 0.1%). This can be obtained cheaply with multiphase convertors.
Mosfets are now cheaper than IGBT's where you are paying for power losses and plan to run at full load for more than a few days to months. That's why nearly all EV's use MOSFETs - (and will use GAN MOSFETs at MHz switching rates when the patents run out)
Remember that the cable acts like a capacitor/inductor pair to ground. Ripple currents that are lost through it are not wasted money - merely wasted capacity and resistive losses in the cable. At these currents, you can assume earth is a perfect conductor, so no losses there either.
400V electric vehicles and 400,000V transmission lines play by different rules.
There are no MOSFETS anywhere in HV applications. IGBTs, but no MOSFETS. Most converters use thyristors and newer ones use IGBTs. No matter what, PN-junctions are king for HV silicon applications.
Also ripple is a function of filtering not switching. The reason higher switching frequencies generally have better ripple characteristics is because smaller capacitors can filter them and/or larger capacitors filter them better. So in a cost constrained/size constrained product you get more filtering for the same buck same size.
I also can't figure out what you are saying in your last line, apologies.
Well, SiC MOSFET do get used, but yeah. SiC JFETs are indeed better, lower lower with the same wafer technology, avalanche proof, high heat proof (the polyimide passivation hurts beyond ~220 C).
Much easier to drive when you stack them for HV.
That said, GaN is there for capacitive converters due to being able to run very efficient at >10 MHz switching frequency.
These converters in principle fit in very compact phase change coolant/insulator vessels, for example with propane. The capacitors at those frequencies get to be tiny, like, smaller than the transistor package by volume.
> 400V electric vehicles and 400,000V transmission lines play by different rules.
When stacked, they don't. Plenty of research on stacking both MOSFETs and entire power converters.
With stacking, the figure of merit (ie. Kilowatts per dollar, loss percentage) isn't a function of voltage (although the fact that you have to have an integer number in series and parallel could influence the design if you want to use off the shelf components)
Today's HV converter stations use IGBT's mostly because they used to be the best thing to use back in the 2010's when the design process for them started.
The reasons for using IGBTs is not only because BJTs withstand higher voltages, but also because their Vce(sat) can provide much lower loss than Rds(on) at high currents. I x V vs I^2/R.
Vce never really goes below 2 volts... Which for a 1000 amps means the running costs of the converter are 2000 watts * number of stages (~2800). 5.6MW of heat. That quickly dwarfs the purchase cost of those IGBTs.
Whereas the same calculation for MOSFETs [1] gives 4242 stages and an Rdson of 1.9 milliohms... = 8 Megawatts! Which sounds worse... But you can parallel the MOSFETs by spending double the money on them, reducing the loss to 4 megawatts... Or you can double it again to reduce the loss to 2 megawatts, etc.
When you run something 24*7, energy losses cost way more than capital costs - and MOSFETs let you make that tradeoff, whereas IGBTs do not.
[1]: https://www.infineon.com/cms/en/product/power/mosfet/silicon...
Thanks for the analysis!
I’m curious if there are any exotic materials that would be way better dielectrics?
Also are there ways to step down really high voltages? I can’t picture how the electronics would work without shorting?
>I’m curious if there are any exotic materials that would be way better dielectrics?
There are, but like glass they tend to be rigid crystalline structures, and not necessarily formable into what you need. There also is the problem that the dielectric needs to be perfect, as any imperfection becomes a pressure point and once you get even a microscopic breakdown, the whole thing is junk. Any practical repair is going to be very imperfect on the molecular level, so see what I said earlier. Also gaps are imperfections, so usually layering layers of dielectric is a non-starter too (but can be done, it's just very engineering intensive). The HV will "leap" from imperfection to imperfection until it finds it's ground. Insulating HV is a totally different world than your typical 240V, 480V, even 1kV insulation.
>Also are there ways to step down really high voltages? I can’t picture how the electronics would work without shorting
Yes, they basically use stacks of thyristors or IGBTs to actively switch the DC "phases" which get fed into a transformer to step down. Wikipedia has a surprisingly good article on it:
https://en.wikipedia.org/wiki/HVDC_converter
> Insulating HV is a totally different world than your typical 240V, 480V, even 1kV insulation.
Hell, even the difference between 600V (low voltage) THHN (thermoplastic) or XHHW (XLPE) insulation and a 2.4kV/5kV (medium voltage) cable is enormous.
Also note this image in the sibling reply's article
https://en.wikipedia.org/wiki/File:Pole_2_Thyristor_Valve.jp...
Which is part of a transmission station bridging islands in NZ and probably one of my favorite pictures on the internet.
That's the scale of the hardware you're looking at... for a voltage 40 times lower.
It's also the picture I had in mind when thinking about 14MV. The size of everything to space out the stages would need to be so vast I don't even know if it would be structurally possible.
Tokyo Electric Power has 1MV lines afaik.
Sorry, 800kV is the highest HVDC.
China has one 1100 kV HVDC line completed in 2018:
https://www.nsenergybusiness.com/projects/changji-guquan-uhv...
The Changji-Guquan ultra-high-voltage direct current (UHVDC) transmission line in China is the world’s first transmission line operating at 1,100kV voltage.
I swoop in on something like this looking for the first obvious error in units/arithmetic/materials that renders the whole thing ludicrous, but the author has a spreadsheet and it looks like the units are about right. It's an absurdly cheap cable in terms of materials to transmit 10 GW across an ocean. The main things that render it dubious as a practical matter:
- I don't know if operating at 14 million volts is achievable in terms of converter stations. Today's highest voltage HVDC projects operate at 1.1 megavolts and it took years of development to get there from 0.6 megavolts.
- The mechanical practicality of thousands of kilometers of silica clad aluminum. There's a big mismatch in coefficients of thermal expansion and silica is brittle.
Still, this appears to be facially valid in scientific terms if not in engineering terms. That's impressive! It's a really thin intercontinental cable carrying a lot of power.
The whole thing reminded me of this discussion here from 3 years ago:
https://news.ycombinator.com/item?id=31971039
It has rough numbers for a globe-spanning HVDC cable on the order of a meter in diameter (assumes voltages more like present day commercial HVDC, much thicker conductor to compensate).
> There's a big mismatch in coefficients of thermal expansion and silica is brittle.
The way these are manufactured together means the silica with the lower CTE solidifies first - giving a tube filled with molten aluminium. Next the aluminium solidifies. Then the whole thing cools down and the aluminium probably delaminated from the walls of the tube, leaving a gap of a few hundred micrometers. The aluminium also ends up stretching slightly (one time).
During use, the inner core will heat up and cool down, fairly substantially (perhaps by 100C), using that gap that formed as the cable was manufactured.
Building a circuit breaker that can handle 14 megavolts of DC seems improbable to me.
I considered that. Considering the cheap cost of the cable, the best solution appears to simply be 'dont have a breaker'. In either over current or over voltage conditions, simply sacrifice the cable.
Obviously you engineer the convertor stations to minimize the chances of that happening - stopping the convertors automatically if anything looks abnormal. The cable has sufficient capacitance that you have multiple milliseconds to respond, so automated systems should have no difficulty.
> simply sacrifice the cable
How is that different from a fuse?
If I said to build a 3000 kilometer fuse and quench it with the entire Atlantic ocean, people would tell me I was being silly.
But given how expensive the wire will be to lay, what about an actual fuse that's cheaper than laying a whole new wire?
How much cheaper, and what are the odds of needing the fuse?
If it's cost effective then go for it. But the specific thing they're skeptical about is whether a 14MV 750A fuse will be cheap enough.
14MV would be capable of sustaining an arc 1400 feet long in normal atmosphere. I struggle to imagine how you'd build such a thing. You could maybe have a high volume sf6 pump system that would cool and quench the arc on breaker trip with a constantly replenished sf6 supply.
Isn't sf6 on the way out due to it being an extremely potent GHG?
Not sure what the alternative would be for really high voltages? Vacuum insulated switchgear seems to be a hot topic at the moment, but not sure how it'd work with such extreme voltages?
GE has some replacement gas, I'm not sure of the composition, but it isn't as good as SF6 unfortunately.
Even 1.1GV systems use semiconductor breakers. Basically, stacks and stacks of transistors. The actual physical breakers are only operated when the voltage is safely off.
1.1MV?
D'Oh. Of course.
There's more to glass than simple silica soda lime formulations.
Glass chemistry is still a dark arcane art on the fringes with discoveries made all the time.
I'm not suggesting either of these are better suited or even equivalent insulaters but they are more flexible than what many think of as glass:
https://cen.acs.org/materials/inorganic-chemistry/glass-isnt...
https://www.corning.com/au/en/innovation/the-glass-age/desig...
Not to forget Pyrex (the original formulation, not the trademark)
I believe resistive losses are the primary limiting factor, not insulation.
The higher your voltage, the lower your resistive losses.
> glass isn’t known for its ability to bend
Not quite true. Glass optical fibre is reasonably flexible. More so than many coaxial cables. Just don't go below its minimum bend radius, as it is brittle and will snap.
Glass insulated power cables might work, provided the glass layer is thin enough and its band radius isn't exceeded. One can imagine a cable insulated with many thin layers/strips of glass, which have some movement relative to each other. Multiple layers of insulation is normal practise with plastic insulation, as the failure mode is typically pinholes in the insulation and multiple layers reduced the probability of pin holes going all the way through.
Biggest problem might be a conductor with decent diameter will put a lot of stress on the interior and exterior of a bend. Some ides:
* A multi-standed conductor with each individual conductor insulated. Maybe have high voltage in the interior stands and have a radial voltage gradient (to zero) across the outer strands so no one thin layer of glass is taking the full electric field?
* Could a conductor be insulated with a woven/stranded insulating layer? One can imagine many layers of extremely fine glass fibre finished off with an enclosing layer of something else to keep everything in place. Sort of like a glass insulated coaxial cable.
An insulator made of multiple materials will have the breakdown voltage of the weakest material. So, glass fibers in some sort of resin will break down at the resin's voltage, not the glass's.
I’m no engineer, but this is a glass tube, not a glass sheet. I thing the amount of bending it does without breaking will be very small.
fiber optic strands are glass tubes and they bend.
Fiber optic strands are glass rods (solid interior) instead of tubes (hollow cylinder). The two shapes have different strength properties per unit mass [1, 2].
[1] https://physics.stackexchange.com/questions/12913/hollow-tub...
[2] https://www.mtbiker.sk/forum/download/file.php?id=207637
Traditionally, yes.
Hollow air core fibre does exist and seems to be touted as the next big thing though.
https://www.optcore.net/hollow-core-fiber-introduction/#h-wh...
Current implementations break from simple vibrations such as a bus driving down the road and shaking the ducts the fibre is in. Lots of work required still. Crazy expensive and crazy fragile.
Pretty much every solid material gets vastly more bendable when it's very thin.
(From vague memory, stiffness is proportional to the cube of the thickness.)
> The cable, if snagged by a ship anchor, would catastrophically fail. Not only would it snap, but the internal stresses would propagate the crack along the entire length.
I admire that the author wrote this sentence and continued with the thought experiment anyway
A stack of optically powered 15kV mosfets, to get to 14MV, sounds absurdly awesome. 933+ mosfets that you're trying to drive in series, egads. But neat weird idea.
> A 15 kV SiC MOSFET gate drive with power over fiber based isolated power supply and comprehensive protection functions
https://ieeexplore.ieee.org/document/7468138
I distantly remember reading about someone stress testing a submarine drone tether at higher than rated voltages, seeing what practical voltage they could get out of it. I distantly recall there being a lot of concern about like corona arching or something with the sea water? That was a fun paper. I don't ever if it was only because they exceeded the insulation value, but I feel like there were some notable challenges to running high voltages in salt water that I'm not quite remembering.
The importance of repairability is underestimated here. All new infrastructure must be built under assumption that there will be multiple attempts at sabotaging it by actors of various level, and multi-megavolt unrepairable cables that can be fully disabled by one smallish unmanned sub don’t win here at all.
The original version of this post did have a repair plan.
Basically, every few kilometres you turn off the surface hardening of the cable for a yard or two. That spot won't propagate cracks - which means that if someone destroys part of the cable, the rest will be fine.
Those spots of cable have no tensile strength, so you wrap just those spots in a post tensioned steel sheath.
Then, you also make a few spare kilometers of cable that you lay in the ocean floor. When an incident happens, tow a new cable into position and connect it up. Underwater glass forming is a silly idea - but you can simply crack away the glass at the ends, reconnect the aluminium, then encase the whole thing in a couple of yards of epoxy.
The above plan I considered probably was of similar cost to simply laying a new cable across the entire ocean ahead of time in preparation though.
Don't forget ships and their anchors.
HVDC cables are kind of an often overlooked solution to net zero. Moving power over long distances, across timezones is kind of a super power. The main obstacle to scaling this from a few GW to tens/hundreds of GW is cost. Just by laying more cables can you increase capacity between regions and their ability to share excess power to each other. But each cable is a multi billion dollar project. Which means that there is only a little bit of capacity to move power around but not a lot. For example Europe can import a few GW of African solar in the middle of the winter. But it could probably need hundreds when it is dark and not windy there.
Likewise cross Atlantic cables have been talked about but so far don't exist. Same with getting power from the East coast US to the West coast and vice versa. The east coast goes dark while the west coast is still producing lots of solar. And in the morning on the west coast, it's afternoon on the east coast. There is a bit of import/export between California (solar) and Canada (wind / hydro). But it could be much more.
Cables have another important function: they can be used to charge batteries. Batteries allow you to timeshift demand: e.g. charge when the sun is out, discharge when people get home in the evening. And off peak, the cables aren't at full capacity anyway meaning that any excess power can easily be moved around to charge batteries locally or remotely. Renewables, cables and batteries largely remove the need for things like nuclear plants.
Yes it gets dark and cloudy sometimes but those are local effects and they are somewhat predictable. And if the wind is not blowing that just means it is blowing elsewhere. Wind flows from high pressure to low pressure areas. Globally, there always are high and low pressure areas. If anything, global warming is causing there to be more wind, not less. So, global wind energy production will always maintain a high average even if it drops to next to nothing locally. Likewise, global solar production moves around with the sun rise and sun set and seasons but never drops to zero everywhere. If it's night where you are, it isn't on the other side of the planet. If it's winter where you are, it isn't at -1 * your latitude.
If long distance cables get cheap and plentiful, that's a really big deal because this allows for moving around hundreds of gwh of power. HVDC allows doing that over thousands of kilometers across oceans, timezones, and continents. Cheaper HVDC lowers the cost of that power.
It's an interesting take to be sure. I suspect that the lack of flexibility is going to be the real killer.
You'd probably have to build offshore platforms on either side to bring the cables up and terminate them and now that's a nightmare, saltwater/salty air and electronics don't mix well.
Or you're going to have to trench very deeply for the first few miles.
Either way you're stuck with something that really doesn't want to be bent.
I think the "glass is great insulation" is a good insight and perhaps a composite glass fiber/polymer sheath would really increase the V/m without the brittleness.
a material that stretches 1% to failure (like steel/aluminum) can ballpark bend to a radius 100 times the thickness. so a 1 meter cable could bend 100m radius before cracking. assuming 10x margin that would be 1 km radius. large but not crazy. A tube that size can easily span 1 km trenches in water. you could also add a few meters of foam around it to make it neutrally buoyant and just barely press on the ocean floor.
> meters of foam around it to make it neutrally buoyant
In the deep ocean (typically 4km deep), foam collapses and doesn't float...
> interesting take
I think that's being generous.
Recent and related,
https://news.ycombinator.com/item?id=42513761 ("Undersea power cable linking Finland and Estonia suffers damage", 112 comments)
It's been half a year and it still[0] hasn't been fixed yet.
How does anyone, really, imagine building planetary infrastructure where a trivial amount of asymmetric warfare can take the whole thing down?
[0] https://yle.fi/a/74-20164957 ("Fingrid said that the EstLink 2 connection should be back online on June 25, earlier than expected")
The blog is suggesting 10 GW, which is well short of "the entire thing", and they also suggest a lot of redundancy.
If you were to use a single cable for everything, that would be silly because no redundancy, e.g. "A volcano? On the mid-Atlantic ridge? Who could have foreseen this?"
But at the same time, a cable big enough to carry the world's power is pretty big. I've done similar ballpark calculations, and to get the electrical resistance all the way around the planet and back down to 1Ω, you'd need almost exactly one square meter cross section of aluminium (so any anchor cable breaks first), and that would have so much current flowing through it that spinning metal cutting tools can't operate nearby thanks to eddy currents from the magnetic field.
This is the kind of transmission line design I've seen proposed for use on the Moon - where hydrocarbons are basically nonexistent, but aluminium and silicon are abundant.
Glass insulated cable sounds like a tech that should be prototyped on smaller scales - and could be somewhat useful on those smaller scales.
> Glass insulated cable sounds like a tech that should be prototyped on smaller scale
Take a close look at an incandescent light bulb... There is an inch of glass insulated cable there...
Yes, but it's just an inch - and we need a continuous extruded wire at least a dozen meters long. Even on the scale of an inch, thermal expansion coefficient mismatch problems exist - this was a notorious issue with manufacturability of early vacuum tubes.
Turns out it's rather tricky to make glass bond to metal well enough.
The glass in a lamp is not for electrical isolation, it's intended to prevent the cable from literally burning up by keeping oxygen out and protective gas in.
When you're on the moon, why bother with glass? You're surrounded by vacuum and dry rock.
I mean, sure, you can't go over 1022 kV or you get positron-electron pair production from free electrons, but that's still true on your outer surface even with insulation.
Would coaxial HVDC let you go further, because there's no external voltage gradient? I assume so, but mega-scale high-voltage engineering in space combines three hard engineering challenges, so I wouldn't want to speak with confidence.
That said, vacuum is also a fantastic thermal insulator, so perhaps you could do superconducting cables more easily.
I've heard of ballistic conductors*, I wonder if that would scale up… basically the same as the current flowing around a magnetosphere at that scale? https://en.wikipedia.org/wiki/Ring_current
On the other hand, you'd have to make the magnetosphere on the moon first, and "let's use the sky as a wire" sounds like the kind of nonsense you get in the "[Nicola] Tesla: The Lost Inventions" booklet that my mum liked, and therefore I want to discount it preemptively even if I can't say why exactly.
* Not superconducting in the quantum sense, but still no resistance because there's nothing to hit: https://en.wikipedia.org/wiki/Ballistic_conduction
"Just burying your wires in lunar regolith" is another proposed option for long range transmission lines, yes!
We don't know how well that would work in practice though, because there's still a few unknowns about how properties of lunar regolith change across distance.
Some wire applications do require isolation though. For example, motor wiring and other coils.
It would be extremely challenging to make usable coils out of glass coated magnet wire - but it's not like there's oil on the Moon waiting to be made into polymer coatings.
Bury? I was thinking just leave it exposed on the surface. Two chonky lines 2-3 meters apart, double use as a railway.
You make a good point about the other uses of insulation, and ISRU, on the moon.
Would ceramics work for transformers?
I see no reason why they wouldn't.
PCB-based transformers exist, and so do ceramic substrate PCBs. If you combine the two, and find a process to weld the ceramic/glass substrate plates together instead of gluing them together, it could work as a transformer.
> The cable, if snagged by a ship anchor, would catastrophically fail. Not only would it snap, but the internal stresses would propagate the crack along the entire length.
I can’t this writeup seriously with comments like this. There is no mention of any attempt to calculate the allowable bend radius. Also, quenching a glass tube in a continuous process? Does that work?
The bend radius doesn't actually matter - one can fairly trivially adjust the factory ship to make bends at specific places if desired. Including, if necessary, to fit the contour of the seafloor.
The critical thing is the length of the longest unsupported span - and that's 64 meters, but surface hardening could possibly dramatically extend this, but it seems beyond available literature.
The Moore-like fall of solar+battery costs took away solar satellites, solar convection plants, submarine power cables and (widely deployed though) sun tracking hardware. Labour costs are becoming a bigger proportion so some installations plop panels on the ground than slant them to south (in northern hemisphere).
> Labour costs are becoming a bigger proportion so some installations plop panels on the ground than slant them to south (in northern hemisphere).
Even more than that: I was recently at GITEX Europe, and one of the startups* was pitching "they're so cheap, we should lay them flat for cheaper installation and maintenance".
* Their name was something like "slant solar" or "tilt solar", as they had initially thought of doing exactly what you say, but I can't exactly recall the name.
Solar roadways might get the last laugh!
Just so long as they don't try to be absolutely everything to everyone this time.
I like the article for brainstorming possible technological solutions. Though whats missed is the cost of maintaining and repairing seafloor cables. This is what makes or breaks your idea after its already built and broken in a couple days rather than its rated lifespan of decades.
Stepping back from the technical question of how to lay HVDC undersea, a globally connected power grid seems like a major win for renewable energy. There are a lot of places you’d like to put power plants, and having the infrastructure in place to be able to sell that energy makes it immediately more feasible. We could put nuclear plants anywhere. Solar plants across the Sahara. It would increase the energy available to developing countries without tempting them with dirty fossil fuel plants.
Or you could build nuclear power plants and not depend on sun/weather
At the prices the blog post is estimating, PV + antipodal grid is cheaper than nuclear.
Or at least, could be. No reference to how long the cable would last (only the ship), which is kinda important.
Realistically, most cables last until some ship's anchor destroys them and they aren't economic to repair.
It's true that you can switch very high voltages with MOSFETs in series. But the next step after switching is a transformer that needs to handle 14 MV between the primary and lower-voltage secondary winding. I don't think anyone has built something like that before. Given the dielectric strength of transformer oil, the primary windings need to be 500mm away from both the secondary windings and the core, which seems like it'd be hard to do while getting good inductive coupling.
Nah, just do a few divide-by-2 capacitive converter stages to tame it. Basically just a FC-3L buck running at exactly half to not need meaningful amounts of inductance. Feed the radiation to adjacent phases of a radially symmetric setup, and it shouldn't be an issue anymore.
These classic HVDC transformers only exist because those lines plug directly into the AC grid; it's easier to just tame the HVDC and keep it DC for a bit, though, at these extreme facility sizes.
35mm of silica glass would do the trick.
Since the ferrite core isn't a good insulator, the glass would need to fully encase either the primary or secondary winding.
At the sort of scales this transformer would likely be built, an extra 35mm would make the whole thing a little bigger and more expensive, but not massively so.
The glass tank could also double up as an oil bath for cooling the coil - the first 500 millimeters or so of the piping needs to be glass, but after that you can use a typical cooling radiator with no extra concerns.
Does molten glass solidified in contaminated salt water have good insulating properties?
The quenching is done on the boat with presumably purified water. That's a pretty small amount of heat to manage, so its not like you will run out of water.
It’s interesting. I think the real way to do this is gradually scale up. Crossing the ocean is hard mode. Instead start by something much shorter and land based. Then you at least have a stable platform to work on and can focus on the other hard problems
It seems like every landmass should at least have a huge east/west power line to lengthen the daylight hours as much as possible
In 1st world countries, land based cables often cost more because you have thousands of people along the route who all don't want a power line through their small village.
I don't buy it
1. The technical solution relies heavily on fantasy.
2. It is not needed. We have no significant power transmission across the low lying fruit of continental America or Eurasia, and those lines are built! Why bother crossing an ocean?
3. Why not cross Greenland and the North Sea and its islands? Under sea cables are expensive.
4. Why not cross the Bearing Strait?
>not needed
There was a big solar project proposed in Australia's outback to supply Singapore but never got off the ground perhaps advances in glass / dc infrastructure could change the calculations. Same story for Sahara solar supply to Eu.
A lack of need is not the problem here.
In both those scenarios the sun and the consumer are relatively close, with the majority of the line being overland.
Solar Sahara powering Europe makes sense.
Solar Sahara powering the North East does not.
In Peace and Harmony Land™ I could see the value of shipping excess power from sunny/windy locations to those that are without, but I don't think the present world is ready to collaborate at that level.
Nukes and trade are the biggest bringers of peace.
Tell that to Iran tonight..
https://en.wikipedia.org/wiki/United_States_withdrawal_from_...
The US abandoned trade as a means to peace
Iran is well aware of it.
They see the difference in how we treat Iraq/Libya and North Korea.
Iran doesn't have nukes..
(yet, I guess)
And the case for acquiring them as quickly as possible has been strengthened.
If I (and only I) owned such a cable from Europe to the US, how much money could I make by buying cheap solar energy from the bright side and selling it to the dark side of the Atlantic?
First thought: 10 GW * $0.03/kWh 4 hours/day = $1.2Mio per day [0]
I am not sure about my assumptions...
[0]: https://www.wolframalpha.com/input?i=10+GW+*+%24+0.03%2FkWh+...
I suspect you might earn a lot more than $0.03/kWh on average.
The difference between typical market daytime and evening wholesale electricity prices is around $0.06/kWh in the UK right now: https://bmrs.elexon.co.uk/system-prices
You are ignoring many variables, ranging from cable resistance losses and maintenance costs to signal re-synchronisation systems. Not to mention environmental factors such as seabed warming and subsequent changes in ocean currents, over time.
Yes, of course I do ignore a lot in that calculation. I just wanted to calculate the biggest possible usefulness of this cable. Especially the resistance losses could be quite disastrous.
Probably more like 8 hours: you can sell in both directions, to US before sunrise in US, to EU after sunset in EU.
How much you can charge probably also depends on storage, but it seems plausible (same magnitude as current transmission/distribution costs?) to my amateur understanding.
Exploiting the pricing difference would probably diminish it?
To some degree, yes. I just looked it up and the EU produced ~2500GWh in 2023, which is around 280 GW on average.
It sounds like they need to lay the cable with a submarine not a boat, to avoid waves etc
Continuous melted silica coating is fine, but how does one account for all the movement, bends and vagaries of the high seas, especially for something that is so brittle?
I wonder if the glass sheath could be replaced with bundled glass fibers in a dielectric gel? Would that cross section allow for a much greater distance for current to trace through the gel? Seems like maybe it would give a 2x advantage, or maybe glass ribbons could be made instead for a micro braided insulation?
> Fused silica (glass) is a really good insulator (500 MV/m, vs 150 MV/mm for XLPE plastic)
500 MV/m is 0.5 MV/mm, so it's 300x worse insulator than XLPE plastic per article.
Would be a bummer if we build the worldwide insulated network, only to find out it's not insulated enough ツ)_/¯
I suspect the MV/m should have been MV/mm.
edit: datameta is right. Both units should be MV/m.
I did some cursory snooping and it looks like it could be that both units should be MV/m
I agree.
So the initial premise is the bit that gets me.
For the glass to be the insulator we need, I'm assuming the author envisions a solid tube, with no airgaps (can't do fibre braid as that would allow gaps which means loss of insulation, or you'd need oil to fill the gaps.)
This means huge bend radius in the order of hundreds of meters. Not only that but laying it on the ocean bed would require trenching and full support to stop localised bending.
Now to the manufacture:
> The cable is then quenched in water to surface harden it, before it moves out of the back of the ship and falls to the ocean floor over a length of many kilometers (due to very low curve radius).
So that'll cause the tube to break. Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop) so needs an annealing step. ( https://en.wikipedia.org/wiki/Annealing_(glass) )
Moreover changes in temperature mean that using aluminum is probably going to cause the glass to shatter when the temperature changes. which means that you either need https://en.wikipedia.org/wiki/Kovar or somehow make expansion joints every n meters.
Finally that cable is going to be heavy, so unless you make it around the same densisty as salt water, it'll have so much weight it'll snap as soon as you try and dump it into the sea.
apart from that, looks good. well apart from the units are wrong to start with.
TLDR:
you'd need 5x the width of Polyethylene to achieve the same level of insulation at high voltages. but as silica tube doesn't bend and shatters really easily, cant be transported and has a slow extrusion rate, it seems logical to just use PE.
PE doesn't work as well as you imagine. As well as needing waaaay more of it, due to the power of 2 in the volume of a cylinder formula, and it being much more expensive, it also can't withstand high temperatures, which means the current carrying capacity of the core is lowered.
> As well as needing waaaay more of it
Have you done an accounting of how many kilometers you can fit on a 200,000+ tonne boat? Seems to me you could cost-effectively carry nearly 20x as much cable weight as current cable layers. You need 25x the volume of polyethylene, but that's only 10x the weight and it isn't even counting the weight of the conductor.
> Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop)
That internal stress is deliberate. It counterintuitively makes the cable have more tensile strength since glass tends to only fail when a crack propagates from the outside.
The bend radius is huge yes.
But it can span ~64 meter gaps without support, so the need for trenching should be minimal.
During the laying process in deep water, one can use buoys along the length to gradually lay the heavy cable on the seafloor so the tension isn't in the cable.
> So that'll cause the tube to break. Glass builds up hige amounts of stresses when it cools down quickly (see prince ruperts drop) so needs an annealing step.
Did you miss that the prestress is the point? There also could still be an annealing step- a continuous oven just like glass fiber manufacturing. Annealing time for prestressed fibers is very short, although I am very skeptical you could actually get something like this to work in practice.
> Moreover changes in temperature mean that using aluminum is probably going to cause the glass to shatter when the temperature changes.
Does temperature change at the bottom of the ocean? I suspect the heat per meter from resistive losses will be very, very low, but it is a missing point.
> Finally that cable is going to be heavy, so unless you make it around the same densisty as salt water, it'll have so much weight it'll snap as soon as you try and dump it into the sea.
That is addressed in the post- balloons to keep the bend angle low as it descends.
> it seems logical to just use PE.
MSC Irina has a deadweight tonnage (cargo+fuel etc) of 240,000 tonnes. PE would be ~15 cm thickness and weigh ~66 tonnes per km, so you'd get somewhere in the region of 3600 km of cable per trip. Atlantic submarine cables are <7200 km, so yeah- it seems very hard to make the case that glass is worth it.
NB: I do not believe that 14 MV cables could be 30 cm in width, but it doesn't matter much. If you make 8 trips instead of 2, it's still hard to justify. Current cable-laying ships are pretty small, despite cables still being decently big- cargo ships are way bigger. Not scaling up the ships would be very silly when they already exist.
Why not just use a thicker plastic sheaf? It's a cable, it doesn't have to be thin.
It does have to be thin. You need to fit as much as possible on a boat and volume increases quadratically with thickness- so if glass is 500 MV/m and XLPE is 150 MV/m you would need to carry 11x more of it. Refilling means hundreds of miles back to shore.
Modern cable layers can carry thousands of kilometers of cable. they have massive tanks.
9 times the volumn adds up.
Sure, but it's pretty cheap. And mechanically far easier to work with.
AFAIK, every one who has ever made a cable agrees with you.
imo, least believable part for me is the "a custom ship with a glass factory onboard" part
as I understand it, nobody is doing cable laying this way - and this dream of 14MV cable is kinda hinges on that
This seems like the most feasible part of the whole operation to me. International cooperation in these weird times being the least believable part.
Everything looks nice but something very important was not considered in all of this.
High voltage and high current means Z-pinch - the conductor itself is going to compress itself, thus resulting in basically delaminating from the glass sheathing. This is why we have rubber/petroleum-based flexible sticky insulators on cabling like that, it can somewhat flex/shrink with the conductor and is more likely to stay attached and less likely to get damaged.
Just transmit laser power down fiber optics at that point. Either way you're going to need semiconductor switching (it's IGBTs all the way down baby!) nothing electromechanical is going to handle that kind of load.
High voltage does not induce pinch, only current. High voltage is used to create bursts of high current in can-crushing demonstrations. The cable is solid and the current is not concentrated in a thin cylindrical shell. The pinch is negligible, certainly in comparison to eg thermal expansion from changing load conditions.
> Just transmit laser power down fiber optics at that point.
How does that work? You can only get the glass so clear, so you're going to lose all the energy. There's no equivalent to cranking the voltage to increase range.
I watched a video recently that talked about how China is really the only country to have developed and built UHVDC power transmission. Some look at this and say how it's a failure of everyone else. My immediate thought was: "this solves aproblem only China has" and that turned out to be correct.
China produces most of its power in the west of the country between solar farms, the Three Gorges Dam and so on. Most of the population is 2000 miles away in the east of the country. For over a billion people, the cost of more efficient long-distance transmission make economic sense.
Someone asked "could Australia do this to transmit solar power from the West coast to the east coast in peak hours?". Technically? Yes. Practically? No. Why? It's obviously expensive with far fewer people but also all that space in between is uninhabited. So if you ever need to maintain it (which you will) you have to send people out into the wilderness to do it. China doesn't have that problem because it's not really unpopulated anywhere, at least not to the scale Australia is.
My point here is that you should always ask for something like this "what problem does it solve?" And the answer for more efficient long-distance power transmission is "almost nobody".
I think power grids are going to go in the other direction and become increasingly localized rather than nationalized.
This is quite definitely not just a problem China has. We desperately need more transmission in the US.
Yes. The US wind belt is from the Texas panhandle north to Canada.[1] But there's no good connectivity to anywhere with a load. Some east-west EHV lines from that area would be a big win. There's opposition from oil interests. Just trying to connect East Texas to Mississippi has been stalled for over a decade.[2]
Don't need anything as exotic as the 14MV the original poster proposes. 1MV at 1000 amps, which is a gigawatt, has been done many times in China. One right of way can have several such lines. It would be best to have at least two distant rights of way, for redundancy. California's total load is around 13GW, so the number of 1GW lines needed is not large.
Undergrounding high powered lines is a huge headache, but possible. Here's an overview.[3]
[1] https://unitedstatesmaps.org/us-wind-map/
[2] https://www.texaspolicy.com/proposed-transmission-line-in-ea...
[3] https://electrical-engineering-portal.com/res3/Undergroundin...
Doesn't anyone know that Glass breaks Easily ?
Prince Rupert's drops were mentioned in the article, plain window glass material, sufficiently stressed, is ridiculously tough.
try a web search for Prince Rupert drop vs bullet
https://duckduckgo.com/?q=prince+rupert+drops+vs+bullet&t=lm...
The article author did not say how a cable could be wrapped in pre-stressed glass but that plain glass can be pre-stressed is encouraging.
Ever heard of fiberglass...?