I calculated about 40%, mostly due to the turbines.

I read about some liquid batteries being developed at MIT by a guy named Sadoway, but as far as I know, there’s still no demonstrated application of the technology.

I do know of an installed Ni-Cd array they built in Fairbanks, and the energy density of the thing is appalling. It’ll only give you 26 megawatts for 15 minutes, and it’s a huge monster.

Molten salts are being used in power towers already in Spain and elsewhere. It seems to me it would be fairly simple to scale it up by digging a giant insulated pit and filling it with salt and heating elements… totally earthquake-proof and inexpensive too.

It would only be 40% efficient when buffering, which would not necessarily be all the time. If you had a long-distance, high-voltage smart grid (something I remember president Obama proposing a few years back), you’d minimise the amount of buffering you’d need with wind… but you’d still need some buffering, or else renewables will always be auxiliary and it will never be possible to get rid of dirty baseload power like coal.

Pump-up hydro is definitely more efficient, but I’m not so sanguine about the number of places you could do it … plus, it doesn’t have the added benefit of using the waste heat in a molten salt system to pyrolyse our waste stream. If you were to do that, you could go carbon negative in addition to turning the tables on baseload coal.

My issue with batteries is the toxic waste problem, plus the speed with which they wear out. I think they’ll be indispensable for transportation, but not so useful for buffering… We’ll see though. Once we get a global carbon tax, it may turn out to be cheaper because of the efficiencies even with the added cost of replacement and recycling.

Connecting the Montana wind is definitely a big step, but I’d love to know why population centers like Chicago and New York aren’t connected with HVDC. Offshore wind in both of these places is fairly decent, and they are huge power draws. Out west, it seems like they should connect the Norcal coast with the pacific intertie. Wind is supposed to be pretty good out there too.

I would assume sodium-ion batteries have even lower energy densities than Ni-Cds, or else they’d already be in use all over the place… plus, once again: you can heat and cool molten salt indefinitely. It doesn’t wear out.

You’re running into a power issue with the dams too. According to the paper, the most they can give you nationwide is 6GW, which doesn’t come close to matching the 400GW of electrical energy you’d need to buffer the whole country. With thermal storage, there’s no limit to the amount of power you could generate.

lol! Hot salt just seems like a much better storage option for places that don’t have readily available water reservoirs, and (in lieu of better batteries) required to meet the majority of our buffering needs… plus, there’s the carbon sequestration benefit.

All thermal plants operate at 40% efficiency: coal, nuclear, natural gas, etc. It’s a theoretical thermodynamic limitation of the turbines. One thing heat gets you though is readily dispatchable power, to a much greater degree than hydro can provide.

As far as batteries go, the energy density isn’t a technical problem, it’s a cost problem. We could cover huge areas with sodium-ion units to buffer renewable energy, but you have that stuff spread out everywhere and going bad every few years, and it’s a maintenance nightmare. You’d need a small army to keep the thing going. You might be doubling the efficiency, but you’re multiplying your cost by a factor of 10 or more.

If you have a single thermal storage plant, however, you have one point that needs to be repaired if pumps fail or turbines go down. You’d need just a few specialists to take care of entire cities, and you could cut corners wherever you wanted! There’s absolutely no danger of nuclear or toxic waste entering the environment.

The idea with connecting population centers is to minimise times when you require buffering. If the wind is blowing offshore in NYC, but not in Chicago, you pipe whatever you don’t need in NYC west and you meet your needs without having to store any of it. It’s the same with Norcal/Socal. Both sites have decent offshore wind and population centers. If you connect them, you minimise storage requirements. Then, if you connect the coasts with inland wind and population centers, you’ve picked all the low-hanging fruit in terms of eliminating buffering requirements… you’d still need some buffering though.

It looks like solar thermal plants cost about $0.30/kWh, where the biggest cost is the heliostat arrays. If you want to be generous and say the storage portion accounts for half of that, you’re left with $0.15/kWh, which is already in the hydro neighbourhood of around $0.08 to $0.16. The 40% figure is round-trip and included in this cost. Heating something is pretty much 100% efficient.

It is a bit like comparing apples and oranges, because it’s storage not generation, but my guess is that you’d get better economies of scale the larger you built the thermal storage unit, and if you had to BUILD your own hydro system, you’d knock yourself out of the park with expenses. You don’t merely need water to do hydro inexpensively, you need mountains or some kind of terrain with a bottleneck.

It’s not the dispatchability of hydro that’s a problem, it’s the power. With a temperature differential of thousands of degrees, you can get almost whatever power you want out of a thermal plant, but you can only drain a lake so quickly… that’s why the 6 GW maximum is important.

Distributed storage is fine with cold-storage techniques, but when you’re talking about heat, the larger the storage unit, the lower your energy leakage. Considering the crazy-efficiency of transmitting power over HVDC (something like 98% per 1000km), it makes sense to have a centralised unit.

There are about 16,000,000 Angelenos who might disagree with you about no one living in the desert, BTW…

Lol! From what I read, thermal solar costs on average $0.30/kWh, with the storage cost being only part of the total. From what I read, hydro costs $0.08/kWh to $0.16/kWh, with a reverse-pumped system and fluid containment system not being included in this cost.

If you think these numbers are wrong, feel free to provide your own.

We WILL see if anyone builds thermal storage systems, or any kind of storage systems, but I rather think this is more a question of whether or not humans get our act together before we go extinct.