AUDIE CORNISH, HOST:
California just approved one of the most ambitious renewable energy goals in the country, 100 percent clean energy. This happened as world leaders are gathering in San Francisco this week to discuss efforts to fight climate change. California's taken the lead on the global stage as the Trump administration rolls back climate efforts. But as Lauren Sommer from member station KQED tells us, reaching the state's energy goal is going to be difficult.
LAUREN SOMMER, BYLINE: It really wasn't long ago that solar energy was just a niche idea, kind of quirky. But in the early 2000s, California got serious, passing laws that mandated renewable energy. After that, there were a lot of ribbon cuttings for new solar farms...
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UNIDENTIFIED PERSON: Three, two, one - flip that switch. It's live.
SOMMER: ...In San Francisco, Sacramento, even...
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SOMMER: ...On turkey farms, which led to California's latest goal just signed into law by Governor Jerry Brown - 100 percent clean energy by 2045.
LAURA WISLAND: The easy part is bringing renewables onto the grid.
SOMMER: Laura Wisland works on energy policy for the Union of Concerned Scientists. She says electricity from solar and wind - these days, it's just as cheap as fossil fuels. But now comes the hard part.
WISLAND: How do we actually turn down the fossil at the same time?
SOMMER: That fossil fuel in California is natural gas. And getting rid of it - not so simple. Just ask the people trying to keep California's lights on.
NANCY TRAWEEK: This is kind of a heads-up display. So if something happens, alarms will go off.
SOMMER: Nancy Traweek works at the California Independent System Operator, which runs most of the state's electric grid. When I visited two years ago on a sunny day, she pointed to a huge wall of screens that showed lots of solar power on the grid. But what happens when the sun goes down or...
TRAWEEK: All of a sudden, you have a major cloud that comes over a big solar field.
SOMMER: The power supply drops.
TRAWEEK: That needs to come from somewhere else immediately.
SOMMER: So Traweek has to keep natural gas plants running in the background. She can't turn them off because they take hours to start up. But here's the problem. Running solar and natural gas together - some days, that's more power than California needs, and you can't flood the grid with too much power. It overloads it and causes blackouts. So she has to tell solar farms to shut off. And so far this year, California has foregone enough solar electricity to power San Francisco for 20 days. All of this has created a strange marriage between solar and natural gas.
MATT BARMACK: The bulk of, you know, sort of the modern gas fleet is going to stick around and is going to be needed for a while.
SOMMER: Matt Barmack works at Calpine, a company that owns 20 natural gas power plants in California. He says renewable energy has made natural gas more important, not less. But Calpine's power plants aren't making as much money as they used to because they're competing with solar.
BARMACK: We've retired several plants already probably before the end of their, you know, economically useful lives.
SOMMER: Barmack says there's a real risk that many natural gas power plants will go out of business while California still needs them. Laura Wisland of the Union of Concerned Scientists agrees, actually. But she's confident technology will develop to replace fossil fuels - maybe giant batteries to store power.
WISLAND: California never ceases to surpass and exceed people's expectations when we set our minds to it.
SOMMER: Governor Jerry Brown will be counting on that if California's power system is going to go completely clean. For NPR News, I'm Lauren Sommer in San Francisco. Transcript provided by NPR, Copyright NPR.
