THAT WAS EASY:

Right now, most batteries are made with lithium and are expensive with a large, physical footprint, and can only cope with a limited amount of excess power.

But in the town of Kankaanpää, a team of young Finnish engineers have completed the first commercial installation of a battery made from sand that they believe can solve the storage problem in low-cost, low impact way.

"Whenever there's like this high surge of available green electricity, we want to be able to get it into the storage really quickly," said Markku Ylönen, one of the two founders of Polar Night Energy who have developed the product.

The device has been installed in the Vatajankoski power plant which runs the district heating system for the area.

Low-cost electricity warms the sand up to 500C by resistive heating (the same process that makes electric fires work).

This generates hot air which is circulated in the sand by means of a heat exchanger.

Sand is very effective medium for storing heat and loses little over time. The developers say that their device could keep sand at 500C for several months.

So when energy prices are higher, the battery discharges the hot air which warms water for the district heating system which is then pumped around homes, offices and even the local swimming pool.

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