Recharging the Power Grid
Enormous flow batteries make large-scale electricity storage on the grid possible for the first time. Expect fewer blackouts and a thoroughly revamped electric power industry.
Fighter jets scream over Columbus Air Force Base, a sprawling military facility in eastern Mississippi that is especially busy these days training aviators for the war on terror. But for all the high tech aeronautics on display overhead, the bustling Air Force base often relies on an old-fashioned diesel generator to keep radar and communications humming and the jets from colliding. That’s because the region’s antiquated, overloaded power grid dishes out 25 blackouts a year, as well as another hundred or so voltage fluctuations that crash sophisticated flight simulators.
The solution-the world’s largest battery-is under construction nearby. Two cavernous steel tanks, each one 10 meters tall and 20 meters in diameter, will soon hold nearly four million liters of concentrated salt solutions, electrolytes that will be charged and discharged by 24,000 fuel cells in an adjacent building. At night this installation, known as a flow cell battery, will suck electricity from the grid and store the energy, which it will discharge during the day when power lines are strained. When blackouts strike-common in this tornado-prone region-the huge battery will keep the base humming for up to 24 hours.
This massive battery represents more than a backup power supply for an isolated military facility. It’s a bold experiment in large-scale electricity storage on the power grid-the aging maze of interconnected power plants and transmission lines that cover the country. Today’s grid operates with minimal storage, so at all times, electricity flows must exactly balance the power that’s being consumed. Partial solutions are available in a new class of digital switches that more efficiently deliver electricity during crunch periods (see “A Smarter Power Grid ,” TR, July/August 2001). But devices such as the Columbus flow cell, which is being built by the federally operated Tennessee Valley Authority and Swindon, England-based Regenesys Technologies, go one step further. By storing hours of electricity, flow cells offer, for the first time, the possibility of freeing the grid from the need to continuously balance production and consumption.
The implications of a newly flexible grid are immense. Sufficient storage capacity would relieve pressure to build new power plants and transmission lines, prevent regional blackouts, even speed the adoption of wind farms and solar panels by transforming intermittently produced power into steady reserves. Also, by dampening glitches and power spikes, the more flexible grid would provide the high-quality power needed for today’s sensitive electronic equipment. Problems ranging from blackouts to the voltage fluctuations that cause chaos in high tech manufacturing sap an estimated $119 billion from the U.S. economy every year, says Kurt Yeager, CEO of the Electric Power Research Institute, a utility-funded R&D consortium in Palo Alto, CA. This hemorrhage is just one indicator that power grid fundamentals need rethinking, he adds. “The world as we know it can’t continue. Prudent people would not wait for the lights to go out to do something about it. We’ve got to change the architecture of the grid,” he says.
The storage solution is coming, albeit slowly. About a dozen companies worldwide are developing and testing technologies capable of storing large amounts of electricity on the grid (see “Battery Power for the Grid,” table on last page). Over the past decade, for example, advanced battery systems have been demonstrated by Tokyo-based NGK Insulators at more than 30 sites in Japan. A smaller version of flow cell technology developed at the University of New South Wales in Australia and distributed by VRB Power Systems of Vancouver, Canada, will soon support power flows to a remote but growing community in southern Utah. And electricity distributors in California, Hawaii, and Denmark are eyeing Regenesys’s flow cell technology as a way to ease congestion and prepare their transmission networks for rapidly expanding flows of renewable energy. “Storage distributed around the grid would make the whole system more robust and more efficient,” says Ali Nourai, a technology consultant at American Electric Power in Columbus, OH, one of the largest electric utilities in the United States. “The need is there, the market is there, and the price is coming down,” he says. “In two to five years, storage will be all over the place.”
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.
Making these giant batteries a widespread reality on the grid, however, requires presenting a compelling economic case to electric utilities. “The technology not only has to work. It has to work economically,” says Hoagland. He estimates it will cost $25 million, or $2,000 per kilowatt, to build the Columbus battery. That’s double the price of a new power line and diesel generators to back up the base. “They’ve got to be below $1,000 per kilowatt in capital costs before they’re going to be something the utility industry is really going to take notice of,” Hoagland says.
One thing sure to get the attention of power system operators is the potential of flow cells to save and even earn money by optimizing the use of existing power plants and lines. The Tennessee Valley Authority’s studies show, for instance, that flow cells can pay back $250 per kilowatt per year if the cells enable power companies to buy electricity at a low price, store it, and later sell it at a higher price, while simultaneously providing power reserves and some stability control to local power lines. And in such congested electricity markets as Pennsylvania, New Jersey, and Maryland, deferring construction of a new power line by installing a flow cell instead could save more than $1,000 per kilowatt per year, says Joseph Iannucci, principal with Distributed Utility Associates, an energy consulting firm in Livermore, CA. By unclogging transmission bottlenecks while simultaneously playing the power markets, flow cell operators could not only make the technology practical, but also earn $4 billion in revenue annually in the United States alone, Iannucci maintains.
It sounds great, but the current regulatory climate is still murky for flow cells. Deregulation is separating the business of power generation from the business of shipping and distributing electricity, but the business of energy storage falls in a gray area somewhere between those two. Giant batteries affect distribution by unclogging bottlenecks on the lines, but they also act like power generators, supplying markets with cheap electricity from their stash of stored power. “Under the present uncertain semi-deregulated situation, it is very difficult to ask a utility to spend $25 million or $100 million on a storage system which tomorrow it may not be allowed to own,” says American Electric’s Nourai.
Nor is there much incentive for new entrepreneurial players to build flow cells. That’s because deregulation has not yet introduced true competition in the transmission and distribution business. Upstarts who challenge the power industry with flow cells could easily be thwarted by the monopolies that control the power lines. “Even if my numbers show that the markets would be worth billions, who is going to take that risk?” Iannucci asks.
Much as they initiated competition in the power generation business in the early 1990s, federal energy regulators are now writing new ground rules that would unleash competition in the transmission markets. The regulators might, for instance, raise the cost of sending power through the most congested regions of the grid. Such so-called congestion pricing would stimulate investment in flow cells to relieve those costly bottlenecks.
Despite these uncertainties, there’s little doubt giant batteries are coming. Favorable federal regulation could get them here sooner, but they’ll get here in any case, says Imre Gyuk, who manages the U.S. Department of Energy’s energy storage research programs. “As we get more and more congestion and it becomes more and more difficult to build new transmission lines, and as environmental constraints become greaterthere will be a price crunch,” says Gyuk. And then even the most costly grid battery will look attractive to transmission operators, he adds. “What is the price of air when you’re being hanged? Or when you’re drowning?”
Such morbid analogies don’t sound too extreme to the engineers at Columbus Air Force Base. Last November two tornadoes tore through Columbus, shredding power lines and houses and plunging the city into 48 hours of darkness. The base lost power for three hours. That’s not too long for most homeowners, but when it’s a question of keeping jets aloft, three hours is an eternity. The base commander, Colonel Stephen Schmidt, says it seemed longer with the lights out, warning sirens inoperable, and no way to know when the next tornado might hit. “It would have been awesome if we’d been able to keep the power on,” he says. In Columbus, at least, that ability is coming soon.
Battery Power for the GridCOMPANYPROJECTTECHNOLOGYSaft (Bagnolet, France)Supplementary power source for Fairbanks, AKArray of nickel-cadmium batteries to help provide steady voltage and supply energyVRB Power Systems (Vancouver, Canada)Backup power supply
for Castle Valley, UTVanadium flow battery in lieu of upgrades to a 190-kilometer transmission lineZBB Energy (Menomonee Falls, WI)Solar-power delivery in White Cliffs, Australia
Zinc-bromine battery to store and deliver power from remote solar-power stationActive Power (Austin, TX)Protection from faulty
power in Rousset,
FranceFlywheel batteries to protect semiconductor factory against voltage fluctuationsRegenesys Technologies (Swindon, England)Steady, reliable power source for Columbus, MS, and Little Barford, EnglandFlow battery using sodium bromide and sodium polysulfide to provide backup electricity