California regulators approved a rule that would require the state’s utilities to get a third of their power from solar, wind or other renewable sources by 2020, the most ambitious standard in the U.S., Bloomberg News reports.

The California Air Resources Board voted yesterday at a meeting in Sacramento to require PG&E Corp.’s Pacific Gas & Electric, Edison International’s Southern California Edison and Sempra Energy’s San Diego Gas & Electric to meet the new standard. Thirty-three states and the District of Columbia have set renewable energy targets, all of which are lower than 33 percent, according to the U.S. Environmental Protection Agency.

“This standard is going to further diversify and secure our energy supply while also growing California’s leading green technology market, which will lead to cost savings for customers,” Mary Nichols, chairwoman of the board, said in a e-mail statement.

But the goal faces significant challenges. It will require more investment in infrastructure and transmission, and a shorter lead time for projects, says Christine Hersey, an analyst at Wedbush Securities in Los Angeles. The approval process in California now takes years, Reuters reports.

Unless that changes, “it will be hard to meet 33 percent… by 2020 with large scale projects,” Hersey said. She said there may be a trend toward projects in the 20-megawatt range that are “easier to site, permit, finance and connect to the grid.”

Governor Arnold Schwarzenegger ordered the board last year to adopt regulations for the one-third target under the authority of the state’s 2006 greenhouse-gas reduction law. That law could be suspended if voters in November approve a ballot proposition backed by the oil industry. It could also be suspended by the governor, including the new target, for up to a year. Republican candidate Meg Whitman has said she would do this if elected.

California law now requires utilities to get 20 percent of their electricity from renewable sources by the end of the year. The California Public Utilities Commission doesn’t expect that goal to be met and may push the deadline back as much as three years in cases where transmission lines are not available to connect new power plants.

The California legislature last month failed to vote on a bill that would have made the 33 percent target a state law after utilities, environmentalists and labor unions couldn’t agree on how much renewable power may come from out-of-state generators.

Laura Wisland, a clean energy analyst at the Union of Concerned Scientists, said her group wants a 33 percent standard, but not this one, she told the Associated Press.

She said the air board’s plan would actually slow clean technology investment because it allows utilities to meet the entire 33 percent by purchasing “renewable energy credits” rather than actually using renewable energy to supply their customers. The credits would represent renewable power that was generated at facilities outside California and never ends up in the state.

“California doesn’t get any power for that (energy credit) purchase, so we get no greenhouse gas reduction benefits, no air quality improvements and no clean jobs,” Wisland said. “But the utilities still have to provide electricity for customers, and that could still come from fossil fuels.”

Under current law, utilities are not authorized to use any renewable energy credits to satisfy the 20-percent targets. All the energy must be produced in California or in another state connected to its power grid.