(The author is a Reuters Breakingviews columnist. The opinions expressed are her own.)

DALLAS, May 11 (Reuters Breakingviews) - California is sending a message on renewable energy - one that supports the global Paris accord, but also one that challenges both Washington and places like Irving, Texas to think differently. The most populous U.S. state is making solar panels mandatory on most homes built after 2020. It should push other states along, and fossil-fuel producers like Irving-based Exxon Mobil will have fewer excuses to ignore the renewable writing on the wall.

The rooftop panels will cut greenhouse-gas emissions only a little - an estimated 1.4 million metric tons over the next three years, the California Energy Commission said. That's the equivalent of taking 115,000 fossil-fuel cars off the road, but it's a mere 0.3 percent of estimated total emissions of carbon dioxide equivalents in the Golden State. The commission added an extra carrot by saying the installations should save residential homeowners some $40 a month.

Grumblings started immediately. Home prices could rise if builders are able to pass along the costs, some critics say. Severin Borenstein, an economist from the University of California at Berkeley, sent a letter to the commission before the ruling noting that large solar installations would be a more efficient way of reducing carbon emissions.

Still, it's one more step in many taken globally and across the United States, despite President Donald Trump's rejection of the Paris agreement to reduce climate warming and of other environment-friendly initiatives. In January, California Governor Jerry Brown signed an executive order aiming to more than double the number of zero-emission vehicles in the state by 2030. Last month Minneapolis officials announced the goal of running completely on clean energy by then. New York Governor Andrew Cuomo last month delivered new targets to reduce emissions by 40 percent.

Boosting solar panels - which are increasingly viable economically, even at smaller scale - is just one path to cutting down on dirty power. A few weeks ago, the UK ran without coal-fired power for three days - the longest spell since the 1880s, according to the BBC - by pulling from a mix of natural gas, nuclear energy, wind and other renewable sources.

Large fossil-fuel producers, including Exxon, have been slow to embrace the gradual replacement of coal, oil and even gas. California is speaking to them, too.


- The California Energy Commission passed new standards on May 9 that will require most new homes built after Jan. 1, 2020 to fit solar panels.

- The commission said the move should reduce greenhouse-gas emissions by 1.4 million metric tons over the next three years. A recent assessment by the California Environmental Protection Agency put the state’s total emissions at around 440 million metric tons.

(Editing by Richard Beales and Amanda Gomez)

© Reuters News 2018