- 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).
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?
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.
How is that different from a 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.
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...
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 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 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.
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)_/¯
edit: datameta is right. Both units should be MV/m.
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.
[1] https://physics.stackexchange.com/questions/12913/hollow-tub...
[2] https://www.mtbiker.sk/forum/download/file.php?id=207637
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...
(From vague memory, stiffness is proportional to the cube of the thickness.)
Or at least, could be. No reference to how long the cable would last (only the ship), which is kinda important.
as I understand it, nobody is doing cable laying this way - and this dream of 14MV cable is kinda hinges on that
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?
(yet, I guess)
The US abandoned trade as a means to peace
They see the difference in how we treat Iraq/Libya and North Korea.
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.
Solar Sahara powering Europe makes sense.
Solar Sahara powering the North East does not.
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.
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...
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.
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.
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.
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.
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.
Glass insulated cable sounds like a tech that should be prototyped on smaller scales - and could be somewhat useful on those smaller scales.
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
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.
You make a good point about the other uses of insulation, and ISRU, on the moon.
Would ceramics work for transformers?
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.
Take a close look at an incandescent light bulb... There is an inch of glass insulated cable there...
Turns out it's rather tricky to make glass bond to metal well enough.
> 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.
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.
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")
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.
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.
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.
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.
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.
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.
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+...
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.
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
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.
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.
I admire that the author wrote this sentence and continued with the thought experiment anyway
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.
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?
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:
Hell, even the difference between 600V (low voltage) THHN (thermoplastic) or XHHW (XLPE) insulation and a 2.4kV/5kV (medium voltage) cable is enormous.
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.
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.
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.
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.
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.
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...
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.
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.
msandford•1d ago
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.
bluerooibos•1d ago
I think that's being generous.
kashkhan•1d ago
londons_explore•14h ago
In the deep ocean (typically 4km deep), foam collapses and doesn't float...