Pumping Water a Path to a Cleaner Grid

Next100 An iPhone or Blackberry without a battery is just a dead lump of metal and silicon. In much the same way, many experts believe that an electrical grid without energy storage will forever be just a bunch of dumb wires.

That’s why PG&E on Friday filed a request with state regulators for funding to study the feasibility of building a major new “pumped hydro storage” facility in the Mokelumne River watershed in Amador County. The facility, if built, would provide critical backup energy to even out the fluctuations of wind and solar energy, thus supporting California’s ambitious goal of providing a third of the state’s electricity from renewable power by 2020.

The wind can blow strongly for hours, only to die out for days at a time. Solar modules can gush electrons in full sun, then go dormant when clouds pass overhead. Since customers don’t want their lights to flicker on and off as the weather changes, today’s utilities—lacking much of any stored energy to call upon—must ramp generators powered by fossil fuels up and down as needed to keep supply in balance with demand.

…Energy storage has won many converts, including the California Independent System Operator, key technology advisers to the California Air Resources Board, a new report by KEMA for the California Energy Commission, and the U.S. Department of Energy, which has doled out millions of dollars in grants to support storage R&D.

Major technology options include batteries, flywheels, ultracapacitors, compressed air storage and pumped hydro. PG&E is actively investigating battery and compressed air storage and has operated a pumped storage facility in Fresno County since the 1980s.

Pumped hydro, which dates back to 1929 in the United States, is particularly suited to large-scale applications. It uses two water reservoirs at different elevations. When customers need more energy, the utility releases water from the higher reservoir, running it through a turbine to generate clean hydroelectric power. When demand slackens, the utility can use cheap, surplus power to pump water back from the lower reservoir to the higher one for future use.

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