Wind farms and solar-energy plants produce free energy, but the availability can change from minute to minute. In order to be able to compete with more traditional forms of energy production it is important to store surpluses on a large-scale for times of scarcity. Pumped storage, as it is called, was until recently, dependant on convenient geography to be built and done so on a two-reservoir-model. Two individual projects are investigating how to adapt the principle of pumped storage to cheap and reliable systems in order to smooth the output of energy and to become large-scale contributors to power generation.

The first project has been running for a year in Toronto, Canada and is situated at the bottom of Lake Ontorio. Compressed air is pumped to a storage vessel 55 metres below the surface of the water where it is stored in spherical bags made by proprietary material. When energy is needed, the air is released to the onshore plant, its expansion there back to normal pressure drives a turbine.

In Germany the StEnSea system (Storing Energy at Sea) has been launced at a depth of 100 metres in Lake Constance. Rather than storing compressed air, this system uses water to pump energy to and from a series of concrete pressure vessels, turning turbines as it travels.

In The Economist an interesting article about both projects and their expected storage capacity.

Image source: © HOCHTIEF Solutions – Storing Energy at Sea