The Quest for a Big Battery
THE PROBLEM WITH intermittent sources of power is just that; they're intermittent.
One of the challenges facing utilities that want to take advantage of wind and meet increasingly demanding standards for renewable energy is to find a way to store the power when it's plentiful and make it available when it's not. There are a number of techniques for doing that - compressed air, pumped hydro and batteries, for instance - but cost and reliability have remained significant stumbling blocks. Still, the issue is of enormous potential value, and Duke Energy recently announced a major project to store energy at its Notrees Windpower Project in west Texas.
Duke chose Xtreme Power, based in Kyle, Texas, to design and produce the system. XP, which makes integrated energy storage and power management systems, already has a contract to provide storage and energy management for a wind farm in Hawaii, but the Notrees project, at 36 megawatts, will be the largest such undertaking to date. "Figuring out how to change the variable nature of wind and match it to our customers' needs is the long-term ideal game-changer for this business," says Greg Wolf, president of Duke Energy Renewables.
One reason Duke finds XP's approach attractive is that it uses proven technology - their battery is essentially an array of lead-acid batteries - but at a hitherto untried scale. Lead-acid technology is employed in other applications, including large commercial and industrial UPS devices, but no one has yet employed it on this scale. Wolf says Duke's goal is to make it an economically viable option, but he acknowledges that this particular project depends on a matching grant from the DOE of roughly $22 million.
Cost has been the chief factor limiting deployment of battery storage. Both of the main alternatives to lead-acid batteries, lithium ion and sodium sulfur, are expensive.
Donald Sadoway, professor of materials chemistry at MIT, is focusing his research on finding a cost-competitive battery technology. "The world needs a cheap battery, especially for use with intermittent energy sources, where the price point is so low. It's low because it's not a case of battery versus battery, it's a case of battery versus internal combustion, and when you're competing against internal combustion of a hydrocarbon fuel, hydrocarbon wins. The challenge then, from a green perspective, is enabling renewables by addressing their intermittency and doing so with storage that's robust and cheap."
Sadoway believes that some large power companies are beginning to deploy battery technology, despite the fact that on a cost basis it is not competitive with peaking plants, in the hope that costs will come down as manufacturers scale up production.
AEP deploys two different battery technologies. It's testing the use of sodium sulfur batteries at five locations for capital deferral, providing some relief for substations during peak times. These are rated at either 2 megawatts and 14.4 megawatt-hours or 4 megawatts and 25 megawatt-hours. AEP also plans to deploy 80 lithium ion battery systems to provide backup power to retail customers as part of its AEP Ohio gridSMART demonstration project in northeast Columbus. The price for these batteries is still high, according to Emeka Okafor at AEP, but the company hopes the automobile industry will drive the cost down.
The batteries AEP is deploying are 25 kilowatts each. They will be placed in boxes underneath transformers at the residential level, and each will provide backup power anywhere from several minutes to two or three hours for two to five homes. Deployment is scheduled for August. Like Duke, AEP considers this a demonstration because the cost remains too high for widespread use. "Our vendors tell us that within three to five years they can get to price points that would make it reasonable for us to deploy batteries to solve grid challenges," says Okafor. He sees load leveling to defer capital expenditures as the most immediate benefit of energy storage systems. And as the pressure mounts to expand the renewable portfolio, the need to address the issues of intermittent power sources will make battery storage systems ever more attractive.