A Texas company, Quidnet Energy, is developing what it claims could be a breakthrough, low cost means of storing energy.
Quidnet is pumping water under pressure deep into the earth to fill up the cracks and cavities in rocks that previously held oil or gas in now depleted wells. When the pressurised water is released, it acts like a spring as it flows back through a turbine-generator above ground, producing electricity.
The equipment needed is similar to that used for pumped hydro energy storage.
The company believes that this will be a much cheaper way of storing renewable energy from wind and solar farms than using lithium-ion batteries, although it still needs to overcome some technical challenges to make it feasible for large scale energy storage.
One of the biggest concerns is locating well-sealed underground reservoirs to prevent the pressurised water from leaking. However, a pilot project has recorded just 1% of the water lost per week, which is far lower than anticipated.