The commission that regulates California's utilities voted unanimously to cut a key incentive for rooftop solar that helped make the state the largest solar market in the nation.

California is considered the bellwether for the nation's renewable energy policy. Solar advocates worry that getting rid of the incentive will slow the state's solar market, and will embolden opponents of rooftop solar incentives in other states to adopt similar policies.

The vote by the California Public Utilities Commission (CPUC) centered on a scheme established decades ago to win Californians over to installing solar panels on their roofs. If California solar customers end up making more solar power than they use, they can sell that excess power back to the grid.

Under the incentive, utilities compensate solar customers for that power at basically the same amount that they pay for electricity. This payment plan is called net metering, and it helped California reach around 1.5 million homes with solar.

The utilities commission voted to reduce the daytime compensation for excess solar power by around 75% for new solar customers starting in April 2023.

Before the vote, the commission had a time for public comment, where Californians could call in. The overwhelming majority of the dozens of callers said they wanted to keep the old incentive structure in place.

The callers argued cutting the compensation payment would stifle the growth of rooftop solar because homeowners and businesses would decide that solar panels are no longer worth the investment.

"I'm strongly opposed to the CPUC's proposed changes that would make it more expensive for everyday people to put solar panels on their roof," said caller Carol Weiss from Sunnyvale, "My husband and I are both retired and we would never have invested in rooftop solar under these proposed rules."

After about three hours of public comment, the commission voted unanimously to approve the proposal changing the incentive system. The commission argued that the old payment structure served its purpose, and that now the pricing plan needs to evolve.

"It's not designed to last forever," says Matt Baker, director of the Public Advocates Office, which supported the change in solar payments, "This incentive is no longer fit for purpose, so we need a new incentive to fit the next problem."

The new pricing plan offers higher prices for solar in the evening when the sun isn't shining but the state needs more power — especially power from greener sources, said Commissioner John Reynolds. Supporters of the proposal argue the new pricing structure will incentivize customers to buy energy storage batteries along with their solar. That way, customers can store their daytime sunshine to sell power back to the grid at night for higher compensation.

"In short, we are making this change because of our commitment to addressing climate change," Reynolds said, "not because we don't share yours."

But this plan only works if the state can encourage people to buy batteries, says energy economist Ahmad Faruqui. Batteries are expensive, and it will be hard to incentivize customers to make the investment in both storage and solar panels, he says.

The commission "is saying we want to promote storage, but who's going to put storage if they don't have solar? The two go together," Faruqui says.

Reynolds also says that this proposal is addressing the so-called cost-shift. That's the idea that affluent people are more likely to buy solar panels, and that utilities finance solar incentives from the power bills of lower income customers who don't have solar.

But 2021 data from Lawrence Berkeley National Laboratory shows low and moderate income homeowners are growing adopters of solar in California, and critics fear that by decreasing daytime rates, this proposal will prevent more of them from getting panels.