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Water will be limited to 100C, and tanks are going to be way more expensive to maintain.

You don’t get much long-term storage with your black paint as it’s just going to heat the surface. The point here is to heat up a big enough pile of dirt that you can draw out power months later.

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Liquid doesn’t need to mean water? Traditional solar thermal systems use special liquids that can get way more hot than 100C.

You can get to around 200C with oil-based media. But oil goes bad pretty quickly, and it leaches tons of crap out of everything.

Above that temperature, you need molten salts or liquid metals that are extremely corrosive. Your other option is to use gaseous media instead.

And those have the problem of not having enough density so they'll be pretty inefficient.

Yeah good point. I think the point about cost is the real crux here, regardless of working temp. (CSP has used molten salt but it is quite expensive to store and maintain.)

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