One principle tenant to avoid the worst of climate change is to electrify everything and move away from fossil fuel sources towards renewable sources. Unfortunately renewable sources are intermittent and so we need to find solutions for when the sun doesn’t shine or the wind doesn’t blow.

One way around this is to physically place these renewable sources spatially apart so that cloud coverage or doldrums over one generation point doesn’t affect the other. Local spatial distribution is great for solar in case of localized cloud coverage, but this distribution doesn’t help at night.

What would help out at night though is to place these generation stations on different sides of the planet. So lets think that out: What if we combined our grids with a cable under the Atlantic? What would it look like? And how could it be done?

Lets start with some assumptions and goals.

1. How much power should we transfer?
   • For a quick snapshot I took a look at the trough (aka nightime) of the US energy demand per hour: https://www.eia.gov/electricity/gridmonitor/dashboard/electric_overview/US48/US48
     • EIA is seriously my favorite data website. So pretty.
   • Its approximately 450,000 MWhr – which over a one hour interval means we need 450 GW of power. ~372 DeLorean’s worth.
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2. Which route should we take?
   • Lets follow some historical precedence and follow the routing studies for TAT-1. Lets also cheat and find the shortest distance that still counts -> Newfoundland to Ireland = ~1770NM = 3278km.
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As a first attempt at tying things together lets consider some practical problems. First off an AC system is almost immediately ruled out given that European power systems operate at 50hz while North American power systems operate at 60hz. What this means is that there must always be some kind of converting station on either end of the transmission line. If you must have a station you might as well use that capital to make it a AC-DC conversion station too. Given a 450GW power load it’ll be quite the facility, but that’s not the problem we’re solving for right now.

Making our transmission line on DC vs AC has a lot of benefits:

1. Better mass efficiency
   • Without the skin effect we can fully utilize the cable’s cross-sectional area.
   • Having 2 poles rather than 3 phase means less conductors in general.
2. No reactive power – AC transmission lines have a reactive component that is compounded by length (longer cables means more capacitive loading means more loss). Being an undersea cable drastically increases the capacitive loading as well.

There’s naturally a tradeoff between AC vs DC systems. Typically AC systems win out when the distances are short (100s km) vs long (1000s km). In our case we’re pushing everything to the extreme so we easily fall within DC territory.

So given that we’ve got a DC system lets run some numbers. Lets assume we can use the latest and greatest HVDC cable – 600kVDC with a conductor cross section of 3000mm2 (60mm diameter). https://www.entsoe.eu/Technopedia/techsheets/hvdc-xlpe-cross-linked-polyethylene#:~:text=The%20basics%20for%20HVDC%20submarine,other%20insulated%20DC%20cable%20types.

So how do things stackup. Lets go through some scenarios:

1. Immediately evident is that the power cable selected above has a rated power rating of only 1GW. That automatically puts us at 900 strands (2 each way)!
   • We could technically do better and just do a single strand and utilize the ocean’s conductivity as the return path. But not sure how environmentally friendly it would be to dump 450GWs let alone the corrosion problems.
   • We’re fudging the numbers a bit with this 1GW mark – the specification didn’t define a length, which I’m sure is muuch less.
2. We could force 450GW into 2 strands- whats the power loss like?
   • With the cross-sectional area, length, and a resistivity of 1.68e-8 we get the resistance of 2 strands as 36.7ohms.
   • 450GW @ 600 kVDC –> 750kA
   • which yields an absurd power loss of 20,651GW. Clearly not worth it!
   • The issue is the 750kAs. Given that power loss is proportional to the square of the current we really want to reduce this number. Easiest way is to up the voltage, but eventually we hit a ceiling on the best dielectric strengths.
3. Lets re-run try 2 with a higher voltage.
   • 1MV -> 7435GW loss
   • 4MV -> 465GW loss (on parity with power delivered)
   • 8MV -> 116GW loss (25% of power delivered)
   • 16MV -> 29GW loss (6.4% of power delivered).
   • Cool things trend in the right direction. But good luck finding a material reliable enough to block 16MV!

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Clearly copper has its physical limits, if only we could have a cable that had no resistance… lets try using high temperature superconducting tapes (HTSTs)!

Lets start with our assumptions:

1. We’re going to use 15MA/cm2 for our maximum current density. https://www.nature.com/articles/s41598-018-25499-1
2. Assuming a 12mm width tape with 4.8um thick (Gd,Y)BaCuO layer.
3. 1 & 2 yields a 8.64kA tape capacity.

With the above assumptions lets run some numbers. If we assume a 600kV system (same as current state of the art HVDC) we’ll need 174 strands of HTSTs. If we bump ourselves to 1MV we can get away with 104 strands. Lets go with 1MV which would result in a total length of 341458km of tape. That’s quite a lot, is it at all reasonable?

The SPARC reactor by CFS uses 270km of REBCO tapes per coil (https://indico.cern.ch/event/975584/contributions/4430919/attachments/2352866/4014284/TFMC_FinalPresentation_MT27_Hartwig.pdf ). Considering a single reactor utilizes 22 of these coils each reactor would consume 5950 km of high temperature tape. Meaning you could create 57.5 reactors for the quantity needed to span the Atlantic.

Is that a reasonable number? I would argue maybe. Its doable if we consider the engineering just exceptionally difficult. It far exceeds the worlds current HTS production, but that’s scaling regardless given the needs driven by fusion and other green energy development.

We haven’t even considered the cooling energy required to bring this cable down to the 4.2-20K requirement. Overall it seems like the solution could be technically feasible, but not economically or geo-politically.