Water as a battery

Water’s a substance of many uses. We use it to irrigate gardens, boil potatoes, bathe the dog, wash the car, put out fires, swim in, fish in and generate power. Add to the list: act as a battery.

We store energy with compressed air, flywheels, electrochemical capacitors and lead or lithium batteries, but none of these technologies does the job in such volume in the United States as pumped storage.

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It works this way: water’s sucked out of a river or a lake and pumped up to a reservoir, where the water sits until a certain moment when this same water is sent rushing back down the same pipes through which it came where it turns turbines.

The energy storage part of this equation is the lake at the top, to be drained only when the marketplace needs more electricity.

There are about 40 pumped storage plants in the nation today, and more coming. The industry behind them is facing two big changes – one involving the electricity that pumps water up to the elevated reservoir and the other involving environmental sensitivities about where the water comes from.

More than a few pumped storage plants were built decades ago when nuclear power plants first went into service. Nuclear power plants, like coal-fired power plants, run steadily day and night, leaving the question what to do with all their output when market demand for power is slack, say at 2 o’clock in the morning?

Answer: use the excess electricity at that hour to pump water from down below to up above. Later, when factories are running and people are up and demand for power is peaking, release the water in the elevated reservoir to generate electricity for the marketplace.

It’s a supply-and-demand economic equation: electricity is way cheaper at 2 a.m. when it’s purchased to run the pumps than it is at 2 p.m. when demand for electricity is high and pumped-storage operators can charge high prices.

What happens, then, when the source of electricity to power the pumps changes, as it has been happening when nuclear power plants with their steady production shut down and electricity increasingly comes from intermittent producers such as solar and wind? How might that change affect the daily operations of these plants?

The second big change has to do with where the water for pumped storage comes from. All 40 plants in the United States today suck water out of rivers or lakes that are fed by rivers. That means that the water level in those sources can rise and fall by many feet over the course of a day.

Who cares about that? Answer: Most people who care about fish life and riverbank erosion. They say that pumped storage operators are harming the environment by constantly sucking water out of rivers and later shooting it back in.

In response, the industry is increasingly looking at what are called “closed loop” systems in which water simply recycles between a contained lower reservoir and a contained upper reservoir, meaning no intrusion on the flow of rivers or river-fed lakes. In some parts of the country pumped storage promoters are looking at filling up abandoned coal mines with water to use as reservoirs.

That would be an interesting and pleasing turn of events – using the remnants of a polluting fossil-fuel operation to sustain the operations of a renewable-energy generation.

More on the topic:

Energy Storage Association

Energy Storage News

Subsurface pumped storage projects

Federal Energy Regulatory Commission licensing

A study of environmental impacts of pumped storage