The effect that fossil fuels are having on the climate emergency is driving an international push to use low-carbon sources of energy. At the moment, the best options for producing low-carbon energy on a large scale are wind and solar power.
But despite improvements over the last few years to both their performance and cost, a significant problem remains: the wind doesn’t always blow, and the sun doesn’t always shine.
A power grid that relies on these fluctuating sources struggles to constantly match supply and demand, and so renewable energy sometimes goes to waste because it’s not produced when needed.
One of the main solutions to this problem is large-scale electricity storage technologies. These work by accumulating electricity when supply exceeds demand, then releasing it when the opposite happens. However, one issue with this method is that it involves enormous quantities of electricity.
Existing storage technologies like batteries wouldn’t be good for this kind of process, due to their high cost per unit energy. Currently, over 99 percent of large-scale electricity storage is handled by pumped hydro dams, which move water between two reservoirs through a pump or turbine to store or produce power.
However, there are limits to how much more pumped hydro can be built due to its geographical requirements.
One promising storage option is pumped thermal electricity storage. This relatively new technology has been around for about ten years, and is currently being tested in pilot plants.
Pumped thermal electricity storage works by turning electricity into heat using a large-scale heat pump. This heat is then stored in a hot material, such as water or gravel, inside an insulated tank.
When needed, the heat is then turned back into electricity using a heat engine. These energy conversions are done with thermodynamic cycles, the same physical principles used to run refrigerators, car engines or thermal power plants.