Nah it's nuts to mobilise the sand as a working fluid. The more mature design option seems to be refractory brick for heat energy storage, with piping running

Nah it's nuts to mobilise the sand as a working fluid. The more mature design option seems to be refractory brick for heat energy storage, with piping running through it where you can raise steam. Running a steam turbine generator is generally seen as uneconomic due to the very low round-trip efficiency, and heat storage usually follows the principle of "if you store it as heat, use it as heat".