Mechanical energy storage involves storing energy in physical systems, typically using kinetic or potential energy. Common methods include pumped hydro storage, where water is moved to a higher elevation, and flywheels, which store energy by spinning a rotor at high speeds. These systems can release energy quickly when needed, making them useful for balancing supply and demand in power grids. Another method is compressed air energy storage, where air is compressed in underground caverns and released to generate electricity. Mechanical energy storage is advantageous because it can provide large-scale energy solutions and has a long lifespan compared to chemical batteries.