# Grid energy storage **Grid energy storage** is the set of methods used to store electrical [[Energy|energy]] on a large scale so that it can be supplied when needed. It lets a grid with a lot of solar and wind power move surplus energy from sunny or windy hours to hours of shortfall. The largest form by far is [[Pumped-storage_hydroelectricity|pumped-storage hydroelectricity]], which held 189 GW of capacity worldwide at the end of 2024;[^iha2025] batteries return 60 to 90% of the energy put in, while storing it as hydrogen returns only about half.[^murphy-16] A hydroelectric reservoir is itself a store: holding water back is the same as holding energy back. <div class="microsim-player"> <iframe src="https://wikitube-3d-microsims.netlify.app/Grid_energy_storage.html" width="100%" height="620" frameborder="0" loading="lazy" sandbox="allow-scripts allow-same-origin" allow="accelerometer; gyroscope" title="Grid energy storage — p5.js microsim"></iframe> </div> *Microsim (THY-107): add storage to a sunny, windy grid and watch unmet demand and curtailed power fall; change the round-trip efficiency. ILLUSTRATIVE: two synthetic days, storage power unlimited.* Videos: [16:9](https://wikitube-3d-microsims.netlify.app/media/Grid_energy_storage_16x9.mp4) · [9:16](https://wikitube-3d-microsims.netlify.app/media/Grid_energy_storage_9x16.mp4) ## Roles in the power grid Storage shifts energy in time (charging at surplus, discharging at shortfall), supplies fast reserves that hold frequency when a plant trips, and firms variable output. Hydroelectric reservoirs can do the same job without storage losses by holding water back while other sources generate: since June 2020, Manitoba Hydro's stations have backed up Minnesota Power's wind generation across a 500 kV line carrying 250 MW of firm power.[^mb-hydro] ## Forms Storage technologies differ in how much energy they hold, how fast they deliver it and how much they lose on each cycle. ### Batteries Electrochemical batteries respond in milliseconds and return 60 to 90% of the energy used to charge them.[^murphy-16] They dominate new short-duration grid storage. ### Electrical Capacitors and superconducting magnetic stores hold energy directly in electric or magnetic fields; they are fast but hold little. ### Hydrogen and chemical storage Electrolysis can store surplus electricity as hydrogen with 65 to 80% efficiency, but converting it back — at about 65% in a fuel cell — brings the round trip to about 50%, well below batteries.[^murphy-16] See [[Electrolysis]] and [[Fuel_cell]]. ### Mechanical Pumped hydro, compressed air and flywheels store energy mechanically. Pumped storage uses pumps powered by otherwise idle plants to lift water to an elevated reservoir and releases it through turbines when demand is high.[^kerlin-9] It is limited by the small number of suitable sites.[^murphy-16] ### Thermal Thermal storage holds heat or cold — in molten salt, water or rock — for later use, either as heat or to generate electricity. ## Economics Storage earns its keep from the difference in the value of energy between charging and discharging, and from services such as reserves; its losses and capital cost set how large a difference it needs. ### Costs Capital cost scales with power (the converters) and with energy (the reservoirs or cells); technologies with cheap energy capacity, like pumped hydro, suit long durations, while batteries suit hours. ### Market and system value As solar and wind grow, storage reduces both the demand left unmet at night and the surplus that would otherwise be curtailed, which is the trade the microsim shows. ## See also - [[Pumped-storage_hydroelectricity]] - [[Electrical_grid]] - [[Capacity_factor]] - [[Hydrogen_production]] ## References [^iha2025]: International Hydropower Association (June 25, 2025). "Global hydropower generation rebounds in 2024 and pumped storage development surges — flagship 2025 World Hydropower Outlook out now." https://www.hydropower.org/news/flagship-2025-world-hydropower-outlook-out-now [^murphy-16]: Murphy, Tom W., Jr. (2021). *Energy and Human Ambitions on a Finite Planet*, ch. 16 (hydrogen and battery round-trip efficiency; pumped storage limited by suitable sites). eScholarship, University of California. https://escholarship.org/uc/item/9js5291m [^mb-hydro]: Manitoba Hydro (July 2020). "New transmission line makes grid more reliable and benefits Manitobans." Company release. https://www.hydro.mb.ca/articles/2020/07/new_transmission_line_makes_grid_more_reliable_and_benefits_manitobans/ [^kerlin-9]: Kerlin, Thomas W. (2013). *Future Energy: Opportunities & Challenges*, ch. 9 "Hydroenergy," pp. 203–216 (§9.4 dams and small systems; §9.5 pumped storage; §9.6 river-flow converters). ISA; CC BY 4.0. https://open.umn.edu/opentextbooks/textbooks/future-energy-opportunities-challenges ### Cited sources - Murphy, Tom W., Jr. (2021). *Energy and Human Ambitions on a Finite Planet* — [eScholarship](https://escholarship.org/uc/item/9js5291m); on the [[PORTAL_Energy]] shelf. - Kerlin, Thomas W. (2013). *Future Energy: Opportunities & Challenges* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/future-energy-opportunities-challenges); on the [[PORTAL_Thury_Hydrodynamics_Apex_Spine]] and [[PORTAL_Energy]] shelves. ## External links - [Water Power Technologies Office](https://www.energy.gov/eere/water/water-power-technologies-office), U.S. Department of Energy ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Grid_energy_storage) : [Wikitube](https://en.wikitube.io/wiki/Grid_energy_storage) · pinned revision [1368842312](https://en.wikipedia.org/w/index.php?oldid=1368842312) · 2026-09-10 ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_Energy]]. --- *Thury station wave · 2026-09-10 · drafted · microsim THY-107 (p5.js) · parent [[Hydroelectricity]].*