Now less than 19 percent of the 80,000 or so new homes built each year in the state incorporate solar power systems.
Builders in California will be required to fit solar panels on most new homes from 2020 under new building standards adopted on Wednesday, a move that is the first in the United States and could provide a big boost to the solar industry. How much this hurts other users is disputed, and varies by location, but California's energy commission says it could conceivably cost other ratepayers money.
"This is an undeniably historic decision for the state and the U.S. California has always been our nation's biggest solar champion, and its mass adoption of solar has generated huge economic and environmental benefits, including bringing tens of billions of dollars of investment into the state". "But on the other hand, increasing the energy efficiency of homes has always been a state priority, so there's no free lunch".
Making California homes more energy-efficient is part of a broader initiative to shrink the state's greenhouse gas emissions 40 percent below 1990 levels by 2030.
"This is huge", said Rachel Golden, senior campaign representative for the Sierra Club. One back-of-the-envelope calculation estimates an increased cost of $65 per customer per year. And in California overall, half as many people can afford median priced housing as in the rest of the country.
Critics have been quick to note that the solar panel mandate will add between $8,000 (£5,900) and $12,000 to a home's cost. Utility savings will balance out that cost over the long term, but the higher sales point will still hurt developers, real estate agents and some homebuyers.
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California's economy added 2.3 million jobs over the past five years. Since 2012, median home prices in the state have almost doubled.
The California Energy Commission, the agency that approved the plan, estimates that new home prices will increase by about $10,538. The measures will protect residents from air pollution originating from outdoor and indoor sources, according to the California Energy Commission.
"This is a very large market expansion for solar", said Lynn Jurich, co-founder and co-chief executive of Sunrun, a leading solar installation company.
Just 9 percent of single-family detached homes in the state of 39.5 million people now have solar panels, according to a 2017 U.S. Department of Energy report the Energy Commission cited.
The state is already the nation's leader for solar capacity.
The approved requirement is expected to give a strong lift to California's already hot solar market. They typically target existing homeowners rather than companies building new homes. "If you're working with homebuilders, it's a completely different thing".