California just ran on 100% renewables

 From  OPB

On a mild Sunday afternoon, California set a historic milestone in the quest for clean energy. The sun was shining, the wind was blowing and on May 8, the state produced enough renewable electricity to meet 103% of consumer demand. That broke a record set a week earlier of 99.9%.

Energy experts say the falling records are a sign of the remarkable progress that renewable energy has made. But that doesn't mean fossil fuels were out of the picture.

Even as the record was broken, natural gas power plants were still running in California.

Because despite the dramatic growth of renewable energy, turning off natural gas power still isn't possible in California. The reason is due to a tricky time of day: when the sun sets and solar farms stop producing. California needs to replace that power quickly and seamlessly with other sources, like hydropower and natural gas.

The state is rapidly building huge battery projects for that purpose, so power generated during the day can be stored for use at sunset. But so far, it's still a small fraction of what's needed.

It's a sign that, even as California and more than a dozen other states work towards long-term goals of getting 100% clean energy year-round, weaning off fossil fuels is no simple task.

"Their role is not going to go away until we have a substitute for the service that natural gas generation provides," says Arne Olsen, senior partner at Energy + Environmental Economics, an energy think tank. "The good news is that you can get an awful long way just by adding wind and solar and batteries to our current grid."

Springtime is an ideal time of year for renewable energy in California. The days are getting longer, so solar energy is on the rise. Wind power and hydropower from dams is humming along and mild temperatures mean air conditioners aren't turned up, so electricity demand is still relatively low.

For about an hour on April 30th, grid operators at the California Independent System Operator (ISO), which serves about 80% of the state, had enough electricity from solar, wind, geothermal and small hydropower dams to meet all of the demand in their area More power was being generated than was needed at that moment, so some was exported to other Western states.

"That's quite an accomplishment because it demonstrates if you can do it for one instantaneous hour, you can do it for longer periods of time," says Mark Rothleder, senior vice president at the California ISO.

Records have fallen consistently in the spring over the last few years, due to the dramatic expansion of solar farms. Renewable energy, including solar panels on building rooftops, has more than tripled in the state since 2005. In 2019, 63% of the state's power came from carbon-free sources, including renewables, hydropower and nuclear.

Still, at the time the record fell, natural gas power plants were generating about 10% of the electricity on the California ISO's grid, including the power being exported out of state. That's because those power plants are still vital to keeping the lights on later in the day.

When the sun sets, solar power disappears from the grid rapidly, which means grid operators must turn up other sources of electricity. Supply and demand must stay delicately balanced, so the entire system doesn't fail.

To replace solar at sunset, California generally uses hydropower, imports from other states and natural gas power plants. But most large natural gas plants are massive industrial facilities that aren't designed to turn on quickly. Many take 4 to 8 hours to switch on, so in order to use them at sunset, they must already be running during the day.

"We back them down as far as they can go," Rothleder says. "Anything below that, we'd have to shut them off. But the decision is that if you shut them off, you may not have them when you need them a couple hours later."

That means even when there's plenty of solar power during the day, natural gas power is still part of the energy mix. In fact, on some days, solar farms are told to turn off because there's simply too much power on the grid.

California is working to store extra renewable energy generated during the day so it's available later in the evening. Large battery projects are popping up around the state and in the past two and half years alone, energy storage has grown 20-fold in California.

"The more storage that we can get online that can be charged by solar, the better our chances are of making sure that when the state needs power the most, it's the cleanest it can be," says Shannon Eddy, executive director of the Large-Scale Solar Association.