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This is ALL THINGS CONSIDERED from NPR News. I'm Melissa Block.
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California is required to get a third of its electricity from renewable sources like wind and solar by 2020. Now that could be tricky since the wind doesn't always blow and the sun doesn't always shine. But the utilities have just a few years to figure out how they're going to cope with variable power supplies.
Giant batteries might help and NPR's Richard Harris got a glimpse of what these batteries can do and what they can't, near the Northern California town of Vacaville.
RICHARD HARRIS, BYLINE: If you stroll down a certain dirt road outside of Vacaville and pay attention to sights that your brain normally filters out, it's remarkable what you can see.
TODD STRAUSS: This is like nirvana or the epicenter for California electricity in the 21st century.
HARRIS: Todd Strauss, from Pacific Gas & Electric, starts with the obvious, a small solar farm that the company owns that's just off to our right.
STRAUSS: These flat panels laid out for a few acres. And right across the ravine we can see the transmission towers in the distance.
HARRIS: Visual clutter to the folks speeding by on Interstate 80, but actually a critical link to bring power from dams in the Pacific Northwest all the way down the state. There's also a wind turbine on the horizon. It's not spinning on this calm day.
What's new and different in this landscape is almost hidden among the transformers at PG&E's Vaca-Dixon substation: There are two boxes the size of moving vans.
UNIDENTIFIED MAN #1: Good morning. Thank you.
UNIDENTIFIED MAN #2: All right. All right.
HARRIS: Strauss' colleague Dave Fribush tells us these are enormous batteries.
DAVE FRIBUSH: You know, unfortunately there's no dancing bears, there's no mice running on wheels, so it's not that exciting.
HARRIS: Not exciting but potentially quite important. California's Public Utilities Commission recently directed companies to install about $5 billion worth of batteries to support the grid. The idea is to help smooth out the quixotic power that comes from windmills and solar panels. But here's the catch: Strauss says nobody really knows how the batteries will fit in.
STRAUSS: There are many possible different uses for a battery on an electric grid. And the question becomes: How does it actually get used in practice in those different ways? What are the relative costs of actually using a battery in those different ways? And so this is, you know, one attempt to try to get a sense some of that.
HARRIS: You can think of a fully charged battery as a source of energy ready to sell its product to the electric grid, just the way a power plant does. For that to work, they'd need to buy electricity to charge the battery when the price is low and then sell that electricity back to the grid when the price is high.
But Fribush says that turns out to be a bust.
FRIBUSH: I think in the hour we did it the battery made nine dollars. So we have a long way to go before, you know - we're not even making minimum wage with the system yet.
HARRIS: At least not San Francisco minimum. Considering this battery setup cost $10 million, they need to find a more valuable use of its time. Strauss expects batteries could be useful keeping the overall grid reliable and the grid operators will pay for that service, too. Electricity supply needs to match electricity demand second-by-second, and batteries can provide some of that essential fine-tuning.
STRAUSS: So there's no doubt that as we get more renewables, particularly more wind and especially more solar photovoltaics on the system, there needs to be a lot more flexibility in the system than we have today for the - within the day to move up and down, and within moment-by-moment to respond to cloud cover and so forth.
HARRIS: What if you have a period of time in California - which I know has happened in the past - where you basically get no wind for a week? What do you do then?
STRAUSS: Right, and this battery is not designed to make up for a week's worth of energy.
HARRIS: In fact, there's no energy storage system that can do that right now.
STRAUSS: And so, we'd be using either more gas-fired generation, with the entailed variable cost for gas, and the carbon emissions; possibly more imports of other energy from outside of California; and also we'd look to the customer side.
HARRIS: Industrial customers can sometimes scale back their power demands. And maybe someday home appliances will be able to reduce their power consumption automatically when supply is lean.
Batteries aren't the only options for smoothing out short-term power fluctuations. PG&E pumps water uphill to a reservoir and then lets it back down through a turbine, when they need extra electricity. They're also thinking about a system that stores energy as compressed air underground, and spins a turbine to generate power.
STRAUSS: Lots of choices, it all seems technologically possible. The end of the day, the question is: What will it cost.
HARRIS: Batteries will likely find some role but they are still very expensive. Strauss says for batteries to succeed, the technology needs the kind of revolution that brought solar-panel prices down by about 75 percent over the past decade.
STRAUSS: If we get that for batteries, terrific. If battery costs remain what they are today, not so good and likely to look for different kinds of technology.
HARRIS: And there's not much time to figure this out. Utilities like PG&E are preparing for a huge surge of on-and-off power supplies in the next six years as California's wind and solar industries ramp up to meet the state's 2020 renewable energy goal.
Richard Harris, NPR News.