Although pumped hydroelectric storage makes up most of the total electricity storage capacity in the United States, nonhydro storage has doubled in electric power sector capacity from 160 megawatts (MW) to nearly 350 MW over the past five years. About 98% of the U.S. electricity storage is pumped hydroelectric storage, where water is pumped to a higher-elevation reservoir during off-peak demand and then run back down through a turbine during peak demand. However, pumped storage facilities are expensive to build and have specific siting requirements , making additional capacity builds in pumped storage infrequent. Nonhydro storage systems, which include compressed air, batteries, and flywheels, can provide several ancillary services to the grid , including regulating the grid’s frequency on a second-to-second or minute-to-minute basis and fast-ramping capacity to cover sudden and unexpected gaps between electric demand and supply. The economic value of these services is beginning to be captured […]