Keeping heat within the winter is not straightforward in Finland, one in all Europe’s coldest nations. But in a single Finnish city, residents are saved toasty heat due to low cost, environment friendly and renewable warmth saved in a so-called “sand battery”. Our France 2 colleagues report.
https://www.france24.com/en/freezing-cold-this-town-in-finland-is-keeping-warm-with-sand