British research club reports the results of their analysis of a liquid air storage system (LAES). The idea is to use renewable electricity to liquefy air for energy storage purposes. Result: storage cost 11 euro cent/kWh for a 20MW/800 MWh storage installation at a round-trip efficiency of ca. 50%. Storage pressure ambient. Recuperation by boiling the liquid and drive a turbine in a Rankine cycle. Efficiency could be increased by combining solar of waste heat, thus increasing the temperature at the expansion phase. Storage of liquid air in large volumes is fairly easy with an energy density of 83 kWh/m3.
To really solve the renewable energy storage problem, as a rule-of-thumb, a country needs to be able to store ca. 41% of its annual energy consumption, in order to reasonably guarantee energy supply security. Let’s apply this to a country like the Netherlands, with an average power need of 13 GW. Given the energy density of 83 kWh/m3, a storage volume of 562 km3 would be required, which is unrealistic. Liguid air storage is a short term storage possibility (think in a range of hours, not months).
The real solution of the long term storage problem doesn’t lie in gravity batteries or even phase change solutions, like the one presented her, but in combustible material, reduced with renewable means: hydrogen, iron powder, borohydride, ammonia, methanol, formic acid and a wide range of other possibilities.
[brighton.ac.uk] – An analysis of a large-scale liquid air energy storage system
[wikipedia.org] – Rankine Cycle