Accommodating high levels of variable generation
Pumped hydro storage, the technique of pumping large volumes of water to an elevated storage reservoir so that it can descend through power generating turbines at a later time, has a large installed capacity of about 20GW, with most of it installed over 30 years ago.
This capacity will undoubtedly increase in the future, but siting and environmental concerns make this a lengthy and involved process. CAES is potentially capable of very high capacities but currently there is only one US installation, a 110 MW plant operating in Alabama, with a few others now proposed and in development (over 700MW total in California, Iowa and New York).
Sodium sulfur batteries are currently being applied in wind farm pilot projects and transitioning to commercial application.Perhaps the most successful currently is the high temperature sodium-sulfur battery that exhibits high power levels and high total energy capacity.Flow batteries that employ liquid electrolytes, such as the vanadium redox or zinc-bromine, provide excellent scalability because the liquid electrolytes can be stored independently of the power producing cell.Some utilities offer rebates but generally, the time-of-day dependent charges (demand and energy) incorporated into virtually all commercial electrical rate structures provide the energy cost savings that justify thermal storage for cooling applications.These are installations that building owners request and pay for now – at costs far below typical battery or utility side technologies.