Grid energy storage (also called large-scale energy storage) refers to the methods used to store electricity on a large scale within an electrical power grid. Electrical energy is stored during times when production (from power plants) exceeds consumption and the stores are used at times when consumption exceeds production. In this way, electricity production need not be drastically scaled up and down to meet momentary consumption – instead, production is maintained at a more constant level. This has the advantage that fuel-based power plants (i.e. coal, oil, gas) can be more efficiently and easily operated at constant production levels.

As of March 2012, pumped-storage hydroelectricity (PSH) is the largest-capacity form of grid energy storage available; the Electric Power Research Institute (EPRI) reports that PSH accounts for more than 99% of bulk storage capacity worldwide, around 127,000 MW. PSH energy efficiency varies in practice between 70% to 75%.

In particular, the use of grid-connected intermittent energy sources such as photovoltaics and wind turbines can benefit from grid energy storage. Intermittent energy sources are by nature unpredictable – the amount of electrical energy they produce varies over time and depends heavily on random factors such as the weather. In an electrical power grid without energy storage, energy sources that rely on energy stored within fuels (coal, oil, gas) must be scaled up and down to match the rise and fall of energy production from intermittent energy sources (see load following power plant).

Energy storage is accomplished by devices or physical media that store energy to perform useful operation at a later time. A device that stores energy is sometimes called an accumulator.

All forms of energy are either potential energy (e.g. Chemical, gravitational, electrical energy, etc.) or kinetic energy (e.g. thermal energy). A wind-up clock stores potential energy (in this case mechanical, in the spring tension), a battery stores readily convertible chemical energy to operate a mobile phone, and a hydroelectric dam stores energy in a reservoir as gravitational potential energy. Ice storage tanks store ice (thermal energy) at night to meet peak demand for cooling. Fossil fuels such as coal and gasoline store ancient energy derived from sunlight by organisms that later died, became buried and over time were then converted into these fuels. Even food (which is made by the same process as fossil fuels) is a form of energy stored in chemical form.

Energy storage as a natural process is as old as the universe itself - the energy present at the initial formation of the universe has been stored in stars such as the Sun, and is now being used by humans directly (e.g. through solar heating), or indirectly (e.g. by growing crops or conversion into electricity in solar cells).

The Grid are an English electronic dance group, consisting of Richard Norris and David Ball (formerly of Soft Cell), with guest contributions from other musicians. They are best known for the hits "Swamp Thing", "Crystal Clear", "Rollercoaster", "Floatation", and "Cybernetic" (with Robert Fripp and Phil Manzanera).

The Grid formed in 1988 and had their first success with debut single, "Floatation", released on East West Records in 1990. They went on to release a string of ten UK hit singles and four albums, and toured the UK, Europe, Asia and Australia. The group's 1994 album Evolver reached #14 in the UK Albums Chart. The lead single from this album, "Swamp Thing", featuring elaborate banjo lines played by Roger Dinsdale. "Swamp Thing" proved to be a commercial success in the UK, Europe and Australia, reaching #3 in the UK and Australia and selling a total of one million copies.^{[citation needed]}

In 1996, Norris and Ball agreed to a hiatus period in order pursue individual music interests. Norris formed the Droyds, which went on to remix tracks by musicians including Armand Van Helden and Siobhan Fahey, and wrote the official biography of Paul Oakenfold (published in 2007): Ball reformed Soft Cell with Marc Almond, and also wrote music scores for films.^{[citation needed]} Norris has since formed the psychedelic duo, Beyond The Wizard's Sleeve, with DJ Erol Alkan, and has released a number of solo records and remixes under the name The Time and Space Machine.