A first-of-its-kind energy-storage system has been added to the grid in the UK. The 5MW/15MWh system stores energy in an unusual way: it uses excess electricity to cool ambient air down to -196°C (-320°F), where the gases in the air become liquid. That liquid is stored in an insulated, low-pressure container.
When there's a need for more electricity on the grid, the liquid is pumped back to high pressure where it becomes gaseous again and warmed up via a heat exchanger. The hot gas can then be used to drive a turbine and produce electricity.
The system is called Liquid Air Energy Storage (LAES, for short), and if you're thinking it sounds remarkably like Compressed Air Energy Storage (CAES), you're right. LAES takes filtered ambient air and stores it so it can be used to create electricity later, just like CAES. But LAES liquifies the air rather than compressing it, which creates an advantage in storage. Compressed-air storage usually requires a massive underground cavern, but LAES just needs some low-pressure storage tanks, so it's more adaptable to areas that don't have the right geology.