Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms. Some technologies provide short-term energy storage, while others can endure for much longer. Bulk energy storage is currently dominated by hydroelectric dams, both conventional as well as pumped. Energy storage is the capture of produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an. In the 20th century grid, electrical power was largely generated by burning fossil fuel. When less power was required, less fuel was burned. , a mechanical energy storage method, is the most widely adopted mechani.