Energy from Sand
THE Vatajankoski power plant in Kankaanpää, a small town
located northwest of Helsinki, Finland’s capital, is unique. It has the world’s
first commercial scale battery powered by sand.
The battery acts as a reservoir for excess electricity
produced by the town’s solar and wind farms and stores it in the form of heat
energy. The sand, 110 tonnes of it, is fully enclosed in a 7-m-tall steel
container. The air inside the sand is heated up to 600 degrees Celsius using a
resistance heater that runs on solar and wind energy. The hot air is then
circulated by a fan through heat exchange pipes. The thick insulation
surrounding the sand keeps the temperature inside the battery at 600 degrees
Celsius, even in freezing weather conditions. The battery stores 8 MWh
(megawatt hours) of thermal energy when it is full. In use, the battery
discharges 200 kilowatts of power through the heat exchange pipes—enough to
provide heating and hot water to 100 homes and a public swimming pool in
Kankaanpää. It supplements the power supplied from the city grid. The sand is
charged at night when clean electricity is more cheaply available. The
electrical energy is transferred to the battery using a closed loop air-pipe. The
battery is low maintenance. The sand is the cheap, low quality one rejected by
builders, and not the high quality river sand utilised for construction. The
fan is the only moving part and it’s easy to replace if necessary. Sand retains
heat for a long time and can store power for months. The sand can be heated and
cooled any number of times. It becomes denser after a while, at which point
more sand has to be added. Four young Finnish engineers, Tommi Eronen, Markku
Ylönen, Liisa Naskali and Ville Kivioja, who were childhood friends, invented
the battery.
How does a sand battery score over a lithium-ion battery?
Lithium ion batteries that power laptops, smart phones and
electric vehicles degrade continually even when not in use. A sand battery
doesn’t age because there is no chemical reaction. Lithium batteries are not
completely safe as they are flammable. Lithium extraction and refining has a
much greater impact on the environment because of the carbon dioxide emissions.
The sand battery is also eight to ten times cheaper than a lithium battery for
the same amount of energy.
