Storing energy using a "Sand Battery" - very clever!

 Here's an interesting idea that is working in Finland:

Use SAND to store energy from sources like solar and wind energy! Called a sand battery, excess energy not being used in real time from, say, solar cells, can be stored in the form of heat for future use (such as when the sun goes down). Sand batteries are being used in towns in Finland with great success, so it will be interesting to see if this catches on in other places. 

Clever ideas like this will only help with the transition from fossil fuels to 'clean' energies around the world.