And well, if you can have a heat battery then why not a cold battery too ? Winter cold spells in southern Finland can hang at around -20C (subzero F), so you could store that for summer use.
Years ago there was a meme that when Helsinki's snow removal created giant piles of the stuff ("lumikasat"), sometimes a pile lasted thru the summer - greatly diminished, but extant. It was a fun meme but then it disappeared from the mediascape: maybe the city thought it was bad PR for tourism.
https://northwiseproject.com/nbis-stock-mantsala-data-center...
molten salt works where there is very reliable sunshine in a hot climate, and is heated from huge assemblies of mirrors focusing on a single tower mounted heat exchanger, and is very high tech,runns very hot indeed,with many pumps and exotic materials, to run a conventional steam turbine.
heating sand for heat storage is much simpler, useing off the shelf electrical equipment, and materials to convert excess electricity to store heat at temperatures similar to what can be produced by domestic apliences, that is then used very localy for space and possibly water heating.
one is farm tech, the other is nasa grade.
It is a great solution for places where heating is the primary use of electricity and I hope it finds broader applications.
I personally like Rondo's pitch[0] which is stacking concrete bricks into "heat batteries".