Alphabet spinoff Malta raises $26M for technology to store power in molten salt
The rather extreme losses associated with electricity > heat > heat engine > electricity seem like an absolute deal killer. Assuming they are at an extreme 50% round trip efficiency you need to be extremely cheap to have a hope of breaking even.  Worse heat has fairly low energy density and cools over time so they can’t really scale the up or down that much.It might be possible if they where starting with heat, but feeding this from wind and solar just seems unlikely.