Pumped-storage hydroelectricity, or pumped hydroelectric energy storage, is a type of hydroelectric energy storage used by electric power systems for load balancing. A PSH system stores energy in the
The upper reservoir, Llyn Stwlan, and dam of the Ffestiniog Pumped Storage Scheme in North Wales. The lower power station has four water turbines which generate 360 MW of electricity within 60 seconds of the need arising.