That's the exact system behind molten salt storage [1]. It's just now getting to the point where it's really feasible, but is something that's being researched

That's the exact system behind molten salt storage [1]. It's just now getting to the point where it's really feasible, but is something that's being researched for the exact areas you described. [1] http://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_salt_technology http://en.wikipedia.org/wiki/Thermal_energy_storage#Molten_s...