Most hydroelectric power comes from the [[potential energy]] of dammed water driving a [[water turbine]] and [[electrical generator|generator]]; to boost the power generation capabilities of a dam, the water may be run through a large pipe called a [[penstock]] before the [[turbine]]. A variant on this simple model uses [[pumped storage hydroelectricity]] to produce electricity to match periods of high and low demand, by moving water between [[reservoir (water)|reservoirs]] at different elevations. At times of low electrical demand, excess generation capacity is used to pump water into the higher reservoir. When there is higher demand, water is released back into the lower reservoir through a turbine. (For example see [[Dinorwic Power Station]].)
