[bb123]

But this would stop you getting the sand hotter than 100c - which is one of the main advantages of using sand over water for heat storage.

[kgabis]

You can make it work under pressure and/or add salt.

[omegabravo]

You would need a pressure vessel and corrosion resistance, and potentially a pump driving up the cost.

solar panel with sand is mechanically and electrically much simpler