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Power Play

The idea of storing large amounts of electricity is, of course, not new. Indeed, the first large-scale storage systems were installed in Italy and Switzerland in the 1890s. These systems turned hydroelectric power stations into giant batteries. Pumps forced water uphill into reservoirs; later, gates opened, releasing the water to spin turbines and produce electricity. Today, hydroelectric storage facilities around the world provide about 90 gigawatts of electricity, a figure that translates into about 3 percent of global electricity capacity. But because not every location has mountain lakes-and few communities are eager to submerge thousands of acres to create a giant battery- it’s been nearly two decades since the United States has added a pumped hydro station.

Yet electricity storage is needed more than ever. Power companies are obliged to build supplemental electricity-generating plants, nearly all of which burn fossil fuels, to meet demand during the busiest hours of the day. Just turning those plants on and off emits blasts of pollution. It’s an expensive and wasteful way to generate power, says Nourai. “In your electricity bill, there’s a demand charge, which you have to pay whether you used the electricity or not. Why? Because a big generator has been purchased for the day that you need that power.” What’s more, the dearth of storage means more transmission lines are needed to respond to peak power demands, a job strategically placed giant batteries could perform with greater efficiency.

The reality is that those transmission lines aren’t being built. They’re about as popular as a hydroelectric storage lake, and they are uglier. As a result, the stressed-out transmission network is not always able to provide the steady supply of electricity required to run sophisticated electronic equipment. A single fallen tree limb can send shock waves down overloaded lines, causing nervous breakdowns in the communications servers, hospital equipment, home computers, and other digital devices that account for about 10 percent of U.S. power consumption.

Indeed, gridlocked power lines contributed to the crisis that nearly bankrupted California two summers ago, when energy traders were exploiting supply constraints and manipulating electricity flows to drive up prices. Only a deflated economy and dampened demand spared New York and other states with badly congested lines from similar woes. “A great deal of the market imperfections in terms of price spikes and the ability to game the market, the Enrons of the world, and so forth, are purely a result of the fact that we do not have large-scale storage capabilities distributed uniformly throughout the system,” Yeager says.

Flow batteries offer a mechanism for providing that large-scale storage. You can put them in the plains of North Dakota or next to a power plant in New York City. Unlike conventional batteries, they can charge and discharge power without deteriorating. And unlike other energy-storage devices such as ultracapacitors and flywheels, which pack only enough energy to snuff out brief voltage fluctuations, flow cell batteries have the ability to store enough power to unburden a transmission line for several hours or to store gusts of nighttime wind power.

Like the fuel cells being developed for cars, the critical component in Regenesys’s technology is a thin plastic film. By allowing only positively charged ions to pass through, this film choreographs an electrochemical dance in which electrons and positive ions jump between the battery’s electrolytes, storing and then discharging electrical energy. The flow cell is so named because instead of holding the electrolytes inside as does a conventional electrochemical battery, the technology pumps electrolytes from separate storage tanks, and they flow past either side of the film.

Anatomy of a Flow Cell Battery: A flow cell system (bottom image) can store power for a small city using 24,000 fuel cells (like the one shown in the top image).

Behind that seemingly simple operation is some advanced chemistry and plenty of plumbing. More than a decade ago, Regenesys’s parent, U.K. power giant Innogy, licensed the rights to a particularly energetic pair of electrolytes, and it has been quietly designing flow cells ever since. The battery at Columbus Air Force Base and a sister facility Innogy is building next to a gas-fired power plant in Little Barford, England, represent the first large-scale construction of the technology. For maximum efficiency, each requires fabrication of 24,000 cells with films and electrodes that perform identically, a difficult engineering feat. And the film at the heart of each cell-a 60- by 90-centimeter sheet just one-half millimeter thick-must be precisely secured to ensure no leakage or tearing for the cell’s anticipated life span, 15 years. Regenesys is making it all work on a large scale, says Joseph Hoagland, senior manager of clean and advanced energy at the Tennessee Valley Authority’s Public Power Institute, the research arm that directs the Columbus installation. “They are farther along in their development path in the sense that they have a much more sophisticated manufacturing capability on a large scale than the other companies,” Hoagland says.

Regenesys expects to begin installing the flow cells at Little Barford this spring, and the Columbus installation should follow this summer or fall. If all goes as planned, Regenesys estimates that the Columbus plant will discharge roughly 60 to 65 percent of the electricity it absorbs. (The rest is spent to operate the plant’s pumps or is lost as waste heat.) That power will serve the Air Force base and its neighbors after first passing through a circuit of high-voltage silicon switches that will transform the direct current that flows from the battery into a perfect wave of alternating current. The Regenesys plant may even be able to pump some power back into power lines that feed it, thereby dampening disturbances before they reach Columbus.

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