Energy storage is the capture of energy produced at one time for use at a later time. A device that stores energy is generally called an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic. Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms.
Nature has stored energy for billions of years (e.g., fossil fuels, biomass). Human-made energy storage dates back to pumped hydro storage in the early 20th century. The Voltaic pile (1800) was the first electrical battery. The development of the Lithium-ion battery in the 1980s and 90s revolutionized personal electronics and electric vehicles.
Grid-scale energy storage is crucial for the transition to renewable energy, as it smooths out the intermittency of wind and solar power. Technologies range from pumped hydro (currently the largest capacity) to advanced batteries (Li-ion, solid-state, flow batteries), compressed air, and thermal storage. The market is growing exponentially as costs plummet and demand for electric vehicles and clean grid stability rises.