Solar thermal plants [1] effectively already use this system. They heat a model salt container, which drives a heat engine. The molten salt remains hot enough enough to keep producing energy through the night. However this scheme requires both solar collectors (in the form of mirrors) as well as the molten salt tank plus a heat engine. The resulting levelized cost is about the same as nuclear power [2].

If this startup does manage to produce energy storage at the efficiencies and costs as advertised that'd make intermittent sources more viable. Ultimately building solar and wind is betting that we'll be able to build efficient, cheap, and massively scalable energy storage.

1. https://en.wikipedia.org/wiki/Concentrated_solar_power

2. https://www.lazard.com/media/450784/lazards-levelized-cost-o...