Grid Energy Storage
Grid energy storage stores electricity for later use to balance supply and demand, mainly to absorb the variability of solar and wind. It spans electrochemical, mechanical, thermal, and chemical families. Pumped hydro is by far the largest installed form; lithium-ion suits short durations under about eight hours, and long-duration storage is the open frontier.
Grid energy storage is the collection of technologies that store electrical energy on a power network for later use, smoothing the gap between when electricity is generated and when it is needed. Its importance has grown with renewable energy, because solar power and wind power output varies unpredictably over timescales from seconds to weeks, and because inflexible sources such as nuclear power cannot easily follow demand. Storage is one of three main grid flexibility tools, alongside demand-side response and regional interconnection. Storage technologies fall into four families: electrochemical batteries (the Lithium-Ion Battery, the Flow Battery, the Iron-Air Battery, sodium-ion), mechanical systems (Pumped-Storage Hydroelectricity, Compressed-Air Energy Storage, gravity storage, flywheels, liquid air), thermal stores (see Thermal Energy Storage: Carnot batteries, concentrated solar thermal), and chemical fuels (hydrogen, ammonia, synthetic methane made by electrolysis). As of 2023, pumped hydro was the largest form globally at around 181 GW of installed capacity, exceeding all utility and behind-the-meter batteries combined at roughly 88 GW, at a round-trip efficiency of 75 to 85 percent. Lithium-ion is well suited to short-duration storage of under about eight hours but is limited by cost and degradation beyond that, which is why grids reaching very high renewable penetration need long-duration energy storage. Green hydrogen and thermal storage are leading seasonal candidates, though their economics remain challenging.