According to Engadget, the Finnish company claims to be the first one that developed a fully functional system of this kind.

Polar's solution stores energy generated by renewable sources, such as wind and solar, that is not needed at that very moment and keeps it for later use.

Polar keeps the energy as heat in sand, since this solution is inexpensive and very good at storing heat at temperatures of 500-600 degrees Celsius.

When needed, the heat is distributed via Vatajankoski's services.

The resistive heating process is used in order to warm up water that is then send through homes, offices and even pools and the solution currently serves only one city.

There is a caveat, though, as the energy storage solution is very ineffective when it comes to returning the electricity back to the grid, so it's most useful when it comes to heating.

With time, the storage system could become more advanced and work better when it comes to distributing electricity as well.