[Hamuko]

Well, bad idea for now. If we can start storing up solar energy for the winter, then it might start making a lot of sense. The sand battery that can store thermal energy for months seems pretty interesting in this aspect.

https://www.bbc.com/news/science-environment-61996520

[Retric]

Getting one discharge per year and being less than 30% efficient is a major limitation for any kind of construed thermal battery.

A more viable though still impractical approach is to store energy in rocks underground. Essentially trading the need for a multi km deep borehole for geothermal with the need to provide your own heat.