The Bad Creek facility two reservoirs (or lakes) to generate electricity: an upper reservoir and a lower reservoir. Water stored in an upper lake is released into underground power tunnels. The water rushes down the tunnels, driving huge turbines, which are underground at the base of a dam. The spinning turbines are connected to large generators, which produce the electricity. The water then flows through draft tubes into a lower lake.
A pumped-storage hydroelectric station uses the same water over and over again, making more efficient use of water resources. When demand for electricity is low, operators can refill the lake, as if they were “recharging” a battery. Using power from other generating stations, the generators act as electric motors spinning the huge turbines backward. This pumps water back up the power tunnels into the upper lake. Water is generally pumped back to the upper reservoir at night and on weekends.