> For solar, seasonality would be best addressed by thermal storage
Still, adds a lot of cost and complexity onto cheap solar + 12h of chemical battery storage.
> This is being pursued most interestingly by Standard Thermal's "hot dirt" approach.
Pity they want to do only 400°C. Because once you go towards firebricks and >700°C, you can run practically all thermal chemical processes in a refinery or a polymer plant off the heat, and you can make electricity with a supercritical CO2 turbine at >50% efficiency (in a comparatively tiny package). At the cost of much harder engineering problems, of course.
But its probably worth solving those, because you can do interesting stuff with ultra low cost hot gas. Preheat the charge for a steel mill, design a Hall–Héroult aluminium smelter that keeps the electrolyte bath molten via a gas heat exchanger instead of electricity, ect.
And once you have several GW of guaranteed heat consumers, adding a couple of CO2 peaker turbines isn't such a big leap anymore.
Solar + 12 H batteries are just fine in places without much seasonality. India, for example.
But at high latitudes, this would require either unaffordable amounts of batteries, or so much solar that enormous amounts of it is being wasted during the summer. So why not store instead of waste that excess?
The alternative for those high latitude areas would be wind, which is available in winter. But then you have to deal with how you cover the rare dark-calm extended periods in winter, so you still need a backup supply (like e-fuels in turbines), or else batteries cheap enough to cover those (maybe a couple of weeks). Iron-air batteries might be good for that.
I'm guessing the 400 C is just because they have customers who only need that. They should be able to get to 600 C pretty easily; that's the temperature limit for cheap steel before creep becomes important. They don't want to use firebricks since the scheme depends on the storage medium being extremely cheap, which means dirt (maybe $1-2/ton if sourced locally). Seasonal storage requires extremely low cost storage media.
Still, adds a lot of cost and complexity onto cheap solar + 12h of chemical battery storage.
> This is being pursued most interestingly by Standard Thermal's "hot dirt" approach.
Pity they want to do only 400°C. Because once you go towards firebricks and >700°C, you can run practically all thermal chemical processes in a refinery or a polymer plant off the heat, and you can make electricity with a supercritical CO2 turbine at >50% efficiency (in a comparatively tiny package). At the cost of much harder engineering problems, of course.
But its probably worth solving those, because you can do interesting stuff with ultra low cost hot gas. Preheat the charge for a steel mill, design a Hall–Héroult aluminium smelter that keeps the electrolyte bath molten via a gas heat exchanger instead of electricity, ect.
And once you have several GW of guaranteed heat consumers, adding a couple of CO2 peaker turbines isn't such a big leap anymore.