In Finland in summer you can have around 20 hours of sunlight per day, so there's a lot of energy free for the taking. But could this tech work affordably at the level of individual properties (homes, apartment blocks) ? Could it be scaled down ?

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.

Once I asked the cold-battery question as well and I got a very smart answer: there is no "colder", there is just less warmer.