Comment by pfdietz

18 hours ago

> Agreed, e-fuels seem to be far and ahead the front-runner.

For covering Dunkelflauten? Yes.

For seasonal storage with a prolonged discharge (so, low power/storage capacity ratio)? I think thermal storage wins there.

27 comments

pfdietz

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bryanlarsen  18 hours ago

Sure, thermal is great where it's possible. But there aren't that many places where district heating is viable.

  • pfdietz  18 hours ago

    I'm not talking about district heating. I'm talking about high temperature storage for conversion back to electricity. Round trip efficiency could be around 40%, better than green hydrogen burned in combined cycle plants.

    • bryanlarsen  17 hours ago

      Standard Thermal's website's front page only covers heat delivery; did you mean to link to somewhere else?

      Those are 2 very different use cases.

      Thermal is low rate extraction. It's 1 cycle per year, but the extraction is performed over months so is low rate.

      Electricity long term storage is high rate extraction. It's only used a few times a year, but when it is used it needs to cover roughly 100% of the entire grid's needs. I doubt thermal storage is suitable for high rate extraction, but I'd love to be wrong.

      Edit: rereading your parent comment you seem to think thermal is suitable for a different use case? Could you elaborate further? When is "prolonged discharge" useful?

      7 replies →

cyberax  11 hours ago

I just don't see it with thermal. You have to pay the Carnot tax, and you also need humongous amounts of material.

E.g. 100 GWh (4 days of 1GW thermal power) with a 100C temperature swing (you can't go down all the way to room temperature) will need around 3.6*10^4 tons of sand. That's a lot.

Honestly, power-to-gas sounds like the only reasonable way for now. In theory, with SOFC (Solid Oxide Fuel Cells) for power generation, it can beat the steam cycle.

  • pfdietz  10 hours ago

    The temperature swing can be much greater than 100 C. Heat can be extracted as a wave passing through the store, then heat added back by reversing the flow. It would operate like a counterflow heat exchanger.

    View another way: if we hook several piles in series, then lukewarm air from a first mostly discharged pile can be directed into later piles for more heating. In the continuous limit this is the concept I described above.

    • cyberax  10 hours ago

      > The temperature swing can be much greater than 100 C.

      No, because your steam will be at a lower temperature as you draw down the heat, bringing down efficiency.

      4 replies →

  • Panzer04  11 hours ago

    36000 tons... doesn't actually sound like that much? That's a ~30x30m cube of dirt.

    But I have no reference for the cost of setting up such a storage and how it compares to battery or hydro.

    • adgjlsfhk1  8 hours ago

      The ~grid scale design of this for reference is somewhere around 200mx200mx50m for above ground, or ~100m cube (or bigger) for quarry infill. Such a design is going to get crushed by battery/hydro over the hours/days, but wins on cost for seasonal usage.