Just outside Vacaville sits a battery pack big enough to power more than 1,500 homes.
The system, installed last year at a Pacific Gas and Electric Co. substation, uses a combination of sodium and sulfur to store energy. It can back up the electricity generated by a small solar power plant nearby, whose output changes with the rising and falling sun. Or PG&E can use the 2-megawatt battery pack to smooth out other fluctuations in the amount of electricity traveling over local power lines.
Little noticed by the public, large-scale energy storage may soon get its moment in the spotlight.
This month, California energy regulators proposed requiring the state’s utility companies to buy more than 1.3 gigawatts of electricity storage by 2020 – enough electricity to supply 993,750 typical homes at any given instant.
The storage would help ensure that the lights stay on as California adds large amounts of solar and wind power – both highly variable – to its grid. Big energy storage projects would also cut the number of new fossil-fuel power plants built in the state. And they would make the aging grid more reliable.
The proposal from the California Public Utilities Commission could also transform the storage industry.
Companies have been exploring different ways to bottle energy for years, using batteries, water – even compressed air. But the business has never taken off. California’s proposed rules could do for storage companies what the state’s fight against global warming has done for renewable power in the last decade, triggering a burst of economic activity and innovation. That’s the hope, at least.
“This really gives an opportunity for the storage community to step up and put forward some projects,” said utilities Commissioner Carla Peterman. “The cost reductions we’ve seen in renewables, the technology advances, have been spurred by deployment – just putting more of it out there. This proposed decision is designed to really get some new technologies and new competition.”
The storage industry couldn’t be more pleased.
“This mandate will give us the framework and the focus we need,” said Janice Lin, executive director of the California Energy Storage Alliance. “Storage has been at the bottom of the priority list, so nothing got done in a systematic way.”
The utilities’ worries
Not everyone is convinced the industry is ready.
Utilities fear there won’t be enough solid, well-designed projects from financially stable companies to meet the state’s proposed requirements. They also worry about price. Under the state’s proposal, the utilities could only sign contracts with storage companies if the commission deems those contracts to be cost-effective. But right now, the costs are hard to predict. And money spent on those contracts would ultimately come from the utilities’ customers.
“Clearly, there are some proven technologies, and there are a lot of technologies that are still in the early stages of deployment,” said Todd Strauss, PG&E’s senior director of energy policy and planning. “We really don’t have a good idea of the cost. We’ll see when the rubber meets the road and we see what projects are proposed.”
PG&E, California’s largest utility, already has long experience with one form of large-scale energy storage, known as pumped hydro.
In the mountains 50 miles east of Fresno sit two reservoirs, one at 6,500 feet, the other at 8,200. PG&E carved a tunnel between them and installed pumps and turbines. When electricity prices are low, typically in the middle of the night, the company runs pumps that move water into the higher reservoir. Then, during times of high electricity demand, the water is allowed to flow back to the lower reservoir. The rushing water turns turbines and generates electricity. In use since 1984, the Helms Pumped Storage Plant can churn out 1.2 gigawatts of electricity, enough for 909,000 homes.
Pumped hydro isn’t the only form of energy storage to rely on geology.
$50 million project
PG&E is also working with the state and federal governments on a $50 million project to demonstrate compressed air energy storage. Electricity from wind turbines will compress air and pump it into depleted natural gas reservoirs underground. When electricity demand peaks, the air can be released through a turbine to produce electricity. The company has not yet picked a site for the project.
Other types of storage lack the grand scale of pumped hydro or compressed air. Some companies, such as Vycon and Beacon Power, have developed large spinning flywheels that store energy in the form of motion. The heavy flywheels, typically housed in a vacuum to reduce friction, use some of that energy to power a generator when electricity is needed. (Beacon, which received a $43 million loan guarantee from the federal government in 2010, gained notoriety when it filed for bankruptcy in 2011. But private investment firm Rockland Capital bought Beacon’s assets in 2012 and relaunched the company.)
Industrial-size battery packs, like the one in Vacaville, can be deployed inside utility substations, factories or corporate campuses, giving them a flexibility some other forms of storage lack. Many use the same lithium-ion technology as the batteries that power cell phones, laptops and electric cars.
A massive solar power plant under construction in Nevada, meanwhile, has its own form of storage built into the plant’s design. The Crescent Dunes Solar Energy Project, developed by SolarReserve of Santa Monica, will store heat in molten salt. That heat can then be used to generate steam and turn turbines even after sunset.
Pumped hydro left out
California’s proposed storage requirements, which could be approved by the commission as early as Oct. 3, are largely agnostic on technology. But they exclude pumped hydro. If they didn’t, the utilities would be able to comply with the requirements simply by building one new pumped hydro project.
Storage advocates say having multiple types of storage scattered across the state will make for a stronger, more resilient and efficient grid.
“Our electric power system is not a model of efficiency,” Lin said. “It’s an amazing thing, and it works pretty darn reliably, don’t get me wrong. But there’s room for improvement.”
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