The definition of a large energy storage system is

Grid energy storage, also known as large-scale energy storage, is a set of technologies connected to the electrical power grid that store energy for later use. . Energy from fossil or nuclear power plants and renewable sources is stored for use by customers. Energy storage solutions for electricity generation include pumped-hydro storage, batteries, flywheels, compressed-air energy storage, hydrogen storage and thermal energy storage components. The ability to store energy. . Energy storage systems are tools or collections of tools that save energy for use. 1 Batteries are one of the most common forms of electrical energy storage. The first battery, Volta's cell, was developed in 1800. [pdf]