ARI SHAPIRO, HOST:
Renewable energy like solar and wind is finally coming of age. Costs are way down. Of course, the sun doesn't always shine, and the wind doesn't always blow when we need it to. It's All Tech Considered.
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SHAPIRO: Today the race to store energy - as our three stories point out, it is going far beyond the typical battery. Lauren Sommer from member station KQED in California starts us off.
LAUREN SOMMER, BYLINE: Like a lot of solar companies in California, things have been have extremely busy for Recurrent Energy and its vice president, Michael Wheeler. In his San Francisco office, he points to a screen showing how all their solar farms are doing.
MICHAEL WHEELER: Pretty much every day, we hit peak output.
SOMMER: But earlier this spring, something happened that at first doesn't seem to make any sense. It was the middle of the day when one of their solar farms was cranking out electricity, and they got a message.
WHEELER: The grid operator is telling us they don't need all of it.
SOMMER: There was too much electricity on the grid. The folks managing the grid were telling solar farms to shut down.
WHEELER: Project went from almost peak output to zero for about two hours.
SOMMER: This often happens in the spring when Californians aren't using a lot of air-conditioning yet, and it's only expected to get worse as solar keeps growing. The state plans to get fully half of its electricity from renewable sources in just 15 years.
WHEELER: We built these solar projects, and to the extent that we have to turn them off more and more often doesn't make a lot of sense. It would be a lot better to figure out uses for that electricity.
SOMMER: And there's a really obvious way to use it. California needs lots of power in the evening right after the sun goes down, so a solar farm could store the extra electricity it generates during the daytime.
WHEELER: And then use it later in the evening.
SOMMER: Storing energy isn't a new idea, but building massive banks of batteries - that's expensive. California regulators donât want to see solar go to waste, so now they're requiring utilities to build energy storage. And that's launched startup companies looking for a different way to do it.
STEVE CRANE: So what youâre looking at really is best described as a giant scuba tank.
SOMMER: Steve Crane is pointing to a huge, 25-foot tank in the warehouse of his company, LightSail Energy, in Berkeley, Calif. A scuba tank really is the inspiration for his technology. It compresses air.
CRANE: The electrical energy is hard to hold onto. Compressed air is relatively easy to store for hours or even days.
SOMMER: Here's how it works. When there's extra electricity, Crane turns on a giant air pump. It fills the tank, compressing the air by 200 times. Then when electricity is needed, the air is released to drive an electric generator. The hard part has been dealing with all the heat this makes.
CRANE: Any air compressor that's used, even a bicycle pump, creates heat. You know, a bicycle pump will feel warm after you've used it for a while.
SOMMER: Crane's technology uses water to capture some of the heat so the energy isn't lost. The technology is still in the early stages, but Crane says it could have an edge over batteries. It's cheaper, and it lasts longer.
CRANE: If you have a laptop or cell phone, you know that after two to three years, you start to see significant deterioration.
SOMMER: But Crane's company isn't the only one trying to beat batteries.
JEFF BRADY, BYLINE: Another company is one state over in Nevada. I'm Jeff Brady, and on the Las Vegas strip, a lot of electricity is needed at night to power all those casinos and lights.
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BRADY: To use solar energy after the sun goes down, you have to store it. That's being done at a new power plant in the desert more than 200 miles north.
We're at the gate of facility, and we're just outside a little town called Tonapah, Nev.
Kevin Smith is CEO of SolarReserve, the company behind the very unique Crescent Dunes Solar Energy Plant. Instead of neat rows of solar panels, it has more than 10,000 billboard-sized mirrors arranged in concentric circles. The whole thing stretches a mile and three quarters across. The mirrors reflect heat from the sun to a tower that's twice as tall as the Statue of Liberty. High up, it's glowing white-hot.
KEVIN SMITH: At the top of that tower is a heat exchanger which is where kind of all of the energy collection happens, and through that heat exchanger flows molten salt.
BRADY: Molten salt - that's the key to this project. The salt is liquid. Smith says it looks like water. It's heated to 1,050 degrees in that white-hot section of the tower. Then the molten salt travels down pipes to an insulated tank.
SMITH: And then when we want to generate electricity, we utilize that heat in molten salt to generate steam through a conventional steam turbine on the back end.
BRADY: Smith says this plant can generate electricity for 75,000 Nevada homes, and it can do that for up to 10 hours after the sun goes down. Probably the biggest barrier to building more plants like this is money. This facility cost nearly a billion dollars. The electricity has to be sold well above market rate, but Smith says future plants like this will get cheaper.
So that's an example of storing energy with heat. My colleague Leigh Paterson says you can also store energy with ice.
LEIGH PATERSON, BYLINE: I'm here to meet Greg Miller.
GREG MILLER: We're in downtown Fort Collins, Colo. It's a beautiful downtown area.
PATERSON: He works for company called Ice Energy.
MILLER: Let's go this way. We'll go the alleyway.
PATERSON: We walk behind buildings, passing dumpsters and air-conditioners. Then we come across a large box covered in a brightly painted mural.
MILLER: How do you like the Bears (laughter)? We've got the polar bear. We've got the honey bear and the panda bear.
PATERSON: The panda is munching on bamboo. The honey bear is licking up honey. It's all very snuggly and cute, but the art is meant to disguise an industrial, practical piece of equipment called the Ice Bear.
MILLER: This is a thermal energy storage battery.
PATERSON: Regular battery stores energy in chemical form. A thermal battery uses temperature.
MILLER: This unit stores energy at night. It freezes 450 gallons in the tank.
PATERSON: Four-hundred-fifty gallons of water - that gigantic block of frozen ice is then used to cool down the building next door during the hottest time of the day and into early evening.
MILLER: So essentially what we're doing is we're shutting air conditioners off during the day, consuming energy at night and displacing that peak load for the utility company.
PATERSON: Peak load - that's the time of day or year when we're using the most electricity. In Fort Collins, that's in the summer between the hours of 2 p.m. and 7 p.m. The Ice Bear brings down the total amount of electricity needed during those busy peaks. But there's an important limitation to all of this. In Colorado, it's still practically winter. The city building that this Ice Bear services doesn't need AC right now.
MILLER: It's really just - it's sitting idle, waiting for that cooling demand to hit.
PATERSON: The Ice Bear, unlike compressed air or molten salt storage, saves up energy for temperature control but can't feed electricity back onto the grid. But when temperatures soar in the summer and it's 80 degrees instead of 8, the Ice Bear goes to work. For NPR News, I'm Leigh Paterson in Fort Collins, Colo. Transcript provided by NPR, Copyright NPR.