Pumped storage, and how it works

Pumped storage saves power from electricity from any source for later use. Unlike an ordinary battery, which stores the power chemically, a pumped storage facility depends on gravity.

At low use hours, when supply exceeds demand, water is pumped to a reservoir at the top of a mountain. Then, when the demand is greater than the supply, water is run back down to the foot of the mountain to generate electricity. The relationship between supply and demand makes it possible to make money in the process. The graph above shows the effect. [Today in Energy, May 21, 2012]

Historically, the water was pumped up during the night after most people went to bed, and back down during the day when most people were working. Now, with the advent of renewable power that depends on natural sources, the process is a bit more complicated. Solar power is greatest at around noon, which also happens to be a peak demand time. Wind power is often greatest during the night. Pumped storage is one of several ways to use renewable energy to supply baseload power.

There is a nice example of such a plant at Northfield, Massachusetts. A person driving south from the middle of town on Route 63 is very likely to miss the fact there is an electric generating station, even after being told to watch for the sign. The facility has a small museum, so visitors can see how energy is stored. There are also nature trails for hiking, skiing, and snowshoeing, and a visitor’s sense of the place is more that it is a park than an industrial site. When it is making electricity, its output is 1040 MW, or about 160% of the Vermont Yankee plant, just a few miles upriver from it.

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