[HN Gopher] Worldwide power grid with glass insulated HVDC cables
___________________________________________________________________
Worldwide power grid with glass insulated HVDC cables
Author : londons_explore
Score : 133 points
Date : 2025-06-12 20:04 UTC (1 days ago)
(HTM) web link (omattos.com)
(TXT) w3m dump (omattos.com)
| msandford wrote:
| 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.
| bluerooibos wrote:
| > interesting take
|
| I think that's being generous.
| kashkhan wrote:
| 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.
| londons_explore wrote:
| > meters of foam around it to make it neutrally buoyant
|
| In the deep ocean (typically 4km deep), foam collapses and
| doesn't float...
| philipkglass wrote:
| 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).
| jrd79 wrote:
| I believe resistive losses are the primary limiting factor, not
| insulation.
| eru wrote:
| The higher your voltage, the lower your resistive losses.
| bob1029 wrote:
| Building a circuit breaker that can handle 14 megavolts of DC
| seems improbable to me.
| idiotsecant wrote:
| 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.
| jabl wrote:
| 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?
| idiotsecant wrote:
| GE has some replacement gas, I'm not sure of the
| composition, but it isn't as good as SF6 unfortunately.
| cyberax wrote:
| 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.
| ale42 wrote:
| 1.1MV?
| cyberax wrote:
| D'Oh. Of course.
| londons_explore wrote:
| 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.
| gwbas1c wrote:
| > _simply sacrifice the cable_
|
| How is that different from a fuse?
| londons_explore wrote:
| 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.
| gwbas1c wrote:
| But given how expensive the wire will be to lay, what
| about an actual fuse that's cheaper than laying a whole
| new wire?
| Dylan16807 wrote:
| 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.
| defrost wrote:
| 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...
| gsf_emergency wrote:
| Not to forget Pyrex (the original formulation, not the
| trademark)
| londons_explore wrote:
| > 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.
| amluto wrote:
| > 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?
| londons_explore wrote:
| 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.
| deepsun wrote:
| > 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 tsu)_/-
| femto wrote:
| I suspect the MV/m should have been MV/mm.
|
| edit: datameta is right. Both units should be MV/m.
| datameta wrote:
| I did some cursory snooping and it looks like it could be
| that both units should be MV/m
| femto wrote:
| I agree.
| femto wrote:
| > 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.
| D13Fd wrote:
| 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.
| hcknwscommenter wrote:
| fiber optic strands are glass tubes and they bend.
| shrx wrote:
| 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
| camtarn wrote:
| 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...
| hyperionplays wrote:
| 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.
| bell-cot wrote:
| 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.)
| dtgriscom wrote:
| 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.
| kleton wrote:
| Or you could build nuclear power plants and not depend on
| sun/weather
| ben_w wrote:
| 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.
| londons_explore wrote:
| Realistically, most cables last until some ship's anchor
| destroys them and they aren't economic to repair.
| kumarvvr wrote:
| 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?
| NooneAtAll3 wrote:
| 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
| elric wrote:
| This seems like the most feasible part of the whole operation
| to me. International cooperation in these weird times being the
| least believable part.
| mousethatroared wrote:
| 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?
| pstuart wrote:
| In Peace and Harmony Land(tm) 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.
| colechristensen wrote:
| Nukes and trade are the biggest bringers of peace.
| mikeyouse wrote:
| Tell that to Iran tonight..
| clort wrote:
| Iran doesn't have nukes..
|
| (yet, I guess)
| jahnu wrote:
| And the case for acquiring them as quickly as possible
| has been strengthened.
| rozab wrote:
| https://en.wikipedia.org/wiki/United_States_withdrawal_fr
| om_...
|
| The US abandoned trade as a means to peace
| ceejayoz wrote:
| Iran is well aware of it.
|
| They see the difference in how we treat Iraq/Libya and
| North Korea.
| jimmySixDOF wrote:
| >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.
| mousethatroared wrote:
| 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.
| K0balt wrote:
| 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?
| jmyeet wrote:
| 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.
| idiotsecant wrote:
| This is quite definitely _not_ just a problem China has. We
| desperately need more transmission in the US.
| Animats wrote:
| 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...
| roschdal wrote:
| Doesn't anyone know that Glass breaks Easily ?
| tejtm wrote:
| 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.
| hwillis wrote:
| Ever heard of fiberglass...?
| jillesvangurp wrote:
| 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.
| cyberax wrote:
| Why not just use a thicker plastic sheaf? It's a cable, it
| doesn't have to be thin.
| ZiiS wrote:
| 9 times the volumn adds up.
| cyberax wrote:
| Sure, but it's pretty cheap. And mechanically far easier to
| work with.
| ZiiS wrote:
| AFAIK, every one who has ever made a cable agrees with you.
| hwillis wrote:
| 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.
| hyperionplays wrote:
| Modern cable layers can carry thousands of kilometers of
| cable. they have massive tanks.
| ansgri wrote:
| 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.
| notepad0x90 wrote:
| Don't forget ships and their anchors.
| londons_explore wrote:
| 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.
| TheEnder8 wrote:
| 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
| testing22321 wrote:
| It seems like every landmass should at least have a huge
| east/west power line to lengthen the daylight hours as much as
| possible
| londons_explore wrote:
| 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.
| lightedman wrote:
| 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.
| Dylan16807 wrote:
| > 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.
| hwillis wrote:
| 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.
| ACCount36 wrote:
| 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.
| ben_w wrote:
| 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
| ACCount36 wrote:
| "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.
| ben_w wrote:
| 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?
| ACCount36 wrote:
| 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.
| londons_explore wrote:
| > 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...
| mschuster91 wrote:
| 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.
| ACCount36 wrote:
| 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.
| jauntywundrkind wrote:
| 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.
| aitchnyu wrote:
| 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).
| ben_w wrote:
| > 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.
| nick3443 wrote:
| Solar roadways might get the last laugh!
| ben_w wrote:
| Just so long as they don't try to be absolutely everything
| to everyone this time.
| dcanelhas wrote:
| Does molten glass solidified in contaminated salt water have good
| insulating properties?
| hwillis wrote:
| 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.
| perihelions wrote:
| 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"_)
| ben_w wrote:
| 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 1O, 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.
| KaiserPro wrote:
| 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.
| londons_explore wrote:
| 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.
| hwillis wrote:
| > 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.
| londons_explore wrote:
| 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.
| londons_explore wrote:
| > 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.
| hwillis wrote:
| > 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.
| tomthe wrote:
| 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+..._
| eru wrote:
| Exploiting the pricing difference would probably diminish it?
| tomthe wrote:
| To some degree, yes. I just looked it up and the EU produced
| ~2500GWh in 2023, which is around 280 GW on average.
| ben_w wrote:
| 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.
| drtgh wrote:
| 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.
| tomthe wrote:
| 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.
| londons_explore wrote:
| 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
| tlb wrote:
| 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.
| londons_explore wrote:
| 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.
| namibj wrote:
| 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.
| timerol wrote:
| > 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
| Workaccount2 wrote:
| 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.
| bilsbie wrote:
| 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?
| Workaccount2 wrote:
| >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
| quickthrowman wrote:
| > 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.
| anon_cow1111 wrote:
| 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.
| Workaccount2 wrote:
| 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.
| MrBuddyCasino wrote:
| Tokyo Electric Power has 1MV lines afaik.
| Workaccount2 wrote:
| Sorry, 800kV is the highest HVDC.
| philipkglass wrote:
| 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._
| londons_explore wrote:
| > 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.
| Workaccount2 wrote:
| 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.
| londons_explore wrote:
| > 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.
| Workaccount2 wrote:
| 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.
| londons_explore wrote:
| 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...
| namibj wrote:
| 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.
| hyperionplays wrote:
| 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.
| janalsncm wrote:
| 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.
| roomey wrote:
| It sounds like they need to lay the cable with a submarine not a
| boat, to avoid waves etc
| Out_of_Characte wrote:
| 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.
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