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| ▲ | bryanlarsen 13 hours ago | parent | next [-] | | Sure, thermal is great where it's possible. But there aren't that many places where district heating is viable. | | |
| ▲ | pfdietz 13 hours ago | parent [-] | | 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 13 hours ago | parent [-] | | 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? | | |
| ▲ | pfdietz 11 hours ago | parent [-] | | That's what they're focusing on to start with, but the temperature is high enough to drive heat engines to make power. There's more on the concept at the seed company's (Orca Sciences) web site and at Austin Vernon's blog. https://www.orcasciences.com/articles/standard-thermal https://austinvernon.substack.com/p/building-ultra-cheap-ene... They talk about temperature up to ~600 C, which I believe is limited by the desire to use cheap steal (much hotter and creep becomes a problem). This is also perhaps not coincidentally about the temperature of steam from a coal fired boiler, so one of the eventual goals is to repower retired coal fired power plants with this storage providing the heat instead of coal combustion. You're right this is not good for something needed "a few times a year" for relatively short periods, for example to cover Dunkelflauten. Combustion of an e-fuel is better for that. But it's well suited to seasonal storage of solar energy, as that would be extracted over months, more or less continuously. The resistive heaters should also be much cheaper per W than electrolyzers. | | |
| ▲ | bryanlarsen 10 hours ago | parent | next [-] | | > But it's well suited to seasonal storage of solar energy, as that would be extracted over months, more or less continuously. But what is that useful for? During almost all of those months it would be a lot cheaper to use renewables & short term storage. And it's not fast enough for the few days it's not beaten by something cheaper. | | |
| ▲ | pfdietz 10 hours ago | parent [-] | | It's useful for storing cheap solar energy for use in winter. Sizing the solar collectors for winter would require them to be much larger. Basically, this lets 2.5 W of solar in summer deliver 1 W of solar in winter. For a high latitude where the change in insolation is higher than that, this is superior. In Hamburg, for example, insolation varies by more than a factor of 10 from July to December. Put another way: if you oversize the solar to be adequate in winter, you have enormous amounts of surplus solar in summer. So why not store it? | | |
| ▲ | bryanlarsen 10 hours ago | parent [-] | | > So why not store it? Because 0.10 $/kWh(th) / 0.4 kWh(e)/kWh(th) is expensive. | | |
| ▲ | pfdietz 8 hours ago | parent [-] | | That's the capex for storage capacity. It's amortized over the number of charge/discharge cycles. Divide by 20 or more. It's amazingly cheap, actually. |
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| ▲ | skybrian 5 hours ago | parent | prev [-] | | I thought that post was interesting when I read it over a year ago, but the startup seems to have gone dark since then. | | |
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| ▲ | cyberax 7 hours ago | parent | prev [-] | | 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 6 hours ago | parent | next [-] | | 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 5 hours ago | parent [-] | | > 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. | | |
| ▲ | adgjlsfhk1 4 hours ago | parent | next [-] | | Realistic designs for this can achieve 450C delta t. Your energy store can store at ~1000C (slightly below rock melting point), and run steam turbines with a hot side of 600C and a cool side of 150C. Over the season, your sand drops from ~1000 to ~600 (which is fine since your power needs drop in the spring) | | |
| ▲ | cyberax 33 minutes ago | parent [-] | | Sorry, but 1000C is wildly unrealistic. There are no bulk materials that can be used to construct heat exchangers for this kind of environment. 600C is already a stretch. At 1000C steel will react with _water_. To be clear, I'm not talking about cooling a small crucible but a structure that is at least 20 meters in size. |
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| ▲ | pfdietz 4 hours ago | parent | prev [-] | | That is wrong, and I already explained why. |
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| ▲ | Panzer04 6 hours ago | parent | prev [-] | | 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 4 hours ago | parent | next [-] | | 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. | |
| ▲ | pfdietz 6 hours ago | parent | prev [-] | | The cost of putting dirt in a pile is $1-2/ton. | | |
| ▲ | PaulDavisThe1st 5 hours ago | parent | next [-] | | so $36-72k for days of 1GW of power? Sounds pretty cheap to me ... | | |
| ▲ | pfdietz 5 hours ago | parent [-] | | They also state the cost per kWh(th) of storage capacity is about $0.10, or $100,000/GWh(th). This is thermal energy, which is converted to work at maybe 40% efficiency, mind you. There are costs over and above the dirt (for example, pipes laid through the dirt to carry heat in/out). |
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| ▲ | cyberax 5 hours ago | parent | prev [-] | | The biggest expense will be the pipework inside that pile. That you won't be able to service easily. And you'll also need a LOT of insulation around it to prevent heat from leaking out too quickly. | | |
| ▲ | adrianN 3 hours ago | parent | next [-] | | Thermal storage benefits from the square/cube scaling, so the amount of insulation goes down as you scale up the storage. | |
| ▲ | pfdietz 4 hours ago | parent | prev [-] | | The insulation is just more dirt. | | |
| ▲ | cyberax 3 hours ago | parent [-] | | Homework: compute the heat flux from a 40 meter radius sphere, given the surface temperature 600C and the ambient temperature 0C. Now compute the amount of insulation needed to keep its temperature above 500C for 3 months, given that dry sand has an R value of 0.25 W/mK. |
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