1985

Bath County Pumped Storage

If you are an engineer who is designing a power grid, there is one thing you would love to have: a big battery that can store power. The most obvious way to use the battery is to handle peak demand periods during the day. Another reason a big battery would be nice is to make use of idle time. At 3:00 a.m., when power demand is low, the power plant could be charging the battery.

Large chemical batteries are currently far too expensive. The technology that is used instead is called pumped storage. The basic idea is incredibly simple—connect two lakes at different elevations with pipes. At night, when power demand is low, pump water uphill to the higher lake. During the day when the power is needed, flip the pumps so they act like generators and let the water fall from upper lake to lower lake.

The actual implementation is more complex than that, mainly because of the scale. The Bath County Pumped Storage facility in Virginia, which opened in 1985, is a good example. Engineers built two dams to create two large lakes. The elevation difference between the lakes is about one quarter mile (0.4 km). The top lake holds about 12 billion gallons (45 billion liters). There are six pumps/turbines that are fed by pipes 18 feet (5 meters) in diameter. Each pump/turbine can produce 500 megawatts with a water flow rate of 37,500 gallons per second. That means that at the full flow rate, producing three gigawatts of power from all six turbines, it would take about 14 hours to drain the upper lake dry. Then that water can be pushed uphill that night to recharge the battery.

Pumped storage is one of the best “big battery” technologies available for power grids today. But it requires the ability to build two large lakes at two different elevations that are close together, so it does not work everywhere. In the places where the geography and water sources allow it, it is a great option.

SEE ALSO Power Grid (1878), Light Water Reactor (1946), Lithium Ion Battery (1991).

A panoramic view of the pump storage hydrostation Hohenwarte along the River Saale near Saalfeld, Germany, July 11, 2003.