Pumped storage hydroelectricity has been around for more than 100 years. An alternative to battery storage, pumped storage stores and generates energy by moving water between two reservoirs at different elevations. Water is pumped from the lower reservoir to the upper reservoir at night when electricity demand is low and rates are less expensive. During periods of high electricity demand, water from the upper reservoir is released into the lower reservoir. Water flows through turbines at the base of the lower reservoir, generating electricity.
Pumped storage can be used to store solar or wind power, it can balance sudden changes in demand, and it offers far greater storage capacity than batteries. While there are some disadvantages to pumped storage — it demands a large upfront capital investment, finding an appropriate site is difficult, and such systems may use more energy to pump the water uphill than they produce — it is considered one of the most economical options for large-scale energy storage, accounting for more than 99 percent of bulk storage capacity worldwide.
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