EL CENTRO, Calif. » The sun is so strong here that people often talk about the temperature being "in the teens," meaning 113 or above. The wind is so powerful that, west of town, signs on an Interstate display the number of miles remaining in which drivers will face dangerous winds, like signs that give the distance to the next city.

And to the north, near the end of the San Andreas fault, water underground, hot enough to make steam, flows up through cracks nearly to the surface.

Together, those resources constitute "the most productive renewable energy fields in the world," as Michael R. Niggli, the chairman of San Diego Gas & Electric, the region’s biggest utility, bullishly puts it. "Where else in the world in the same area do you have wind, spectacular solar and geothermal?" he said.

This cluster of resources, a little more than 100 miles east of San Diego, would seem to be a boon, given that California requires utilities to meet quotas for shifting from fossil fuels to renewable energy sources. Niggli’s company, for example, is lagging, and it is avidly pursuing agreements with solar plants.

But the problem, sometimes insurmountable, is how to get the energy to consumers. In what may be a dress rehearsal for skirmishes across the country over renewable energy and transmission, San Diego Gas & Electric has spent seven years and $100 million trying to start work on a 117-mile high-voltage line to reach the resources of El Centro.

The $1.9 billion line would run from the depths of the Imperial Valley over a range of mountains and back down to the southern end of the urban sprawl that runs from Los Angeles through San Diego to the Mexican border. It would double the capacity for transmitting electricity from the valley to the coast, to 2,000 megawatts.

Although the line won approval from the U.S. Forest Service, the federal Bureau of Land Management and the state of California after the utility submitted an 11,000-page environmental impact statement, neighbors and wilderness advocates have filed lawsuits challenging those decisions.

Opponents argue that the transmission line is not mainly about renewable energy. It could also carry electricity from a plant in northern Mexico that burns natural gas brought in by tanker to a port in Baja California, they say, with attendant fossil fuel emissions. Both the tanker terminal and the power plant were built by San Diego Gas & Electric’s parent, Sempra Energy.

"They’re using wind as a cover," said Donna Tisdale, an environmental advocate in Boulevard, Calif., in the mountains between the Imperial Valley and San Diego, who filed a suit to block the transmission line.

Tisdale and other opponents also argue that a combination of power lines and wind farms set amid the area’s live oaks, buckwheat sage and sahara mustard would ruin a fragile wilderness. Test towers that measure wind speed have been sprouting in her area in advance of wholesale wind farm construction.

"Our whole area will be transformed into an industrial energy park," she said.

She and others say the utility has given insufficient consideration to simpler ideas like covering rooftops in San Diego with solar cells. A federal judge in San Diego recently dismissed her legal challenge, ruling that she did not have standing; her lawyer says he will refile.

The idea of giving expedited treatment to transmission lines for renewable energy even though some will carry electricity powered by fossil fuels has surfaced in many places around the country. But experts point out that in a power grid, hardly any lines carry only "green" electrons.

"Electrons don’t have colors," said Yakout Mansour, the president and chief executive of the California Independent System Operator, which runs the grid in most of the state.

"If you don’t have it, it can’t accommodate renewables," he said of the proposed transmission line. "If you have it, it will carry everything."

San Diego Gas & Electric has tried a variety of means to gain public support, like buying a $38 million helicopter to place transmission towers in roadless areas rather than carve out truck routes and allowing San Diego County firefighters to use it to drop water on wildfires.

While power lines are named for the obscure substations they run between, this transmission line bears the more market-friendly moniker Sunrise Powerlink.

One factor working in favor of the transmission line is that it promotes California’s renewable energy goals, among the most ambitious in the nation, and lies entirely within state lines.

By contrast, some proposed lines elsewhere would move renewable energy across multiple state lines and do not serve the goals of every state they would cross.

San Diego Gas & Electric has already begun upgrading a substation and assembling some materials but has not yet started building the transmission line. Meanwhile, the federal government recently approved the lease of 6,360 acres here for a 709-megawatt solar farm to be constructed by Stirling Energy Systems that would feed power into the system.

(All told, the Imperial Valley has an estimated 16,000 megawatts of renewable energy potential, many more times than the amount that could be carried by any contemplated power lines.)

Beyond supplying renewable energy, Mansour said, the Sunrise Powerlink line would improve reliability in the San Diego region and would allow cheaper power from east of the city to displace more expensive local generation, saving money for customers.

Yet others point out that the transmission project carries very little risk for the utility because the federal government commonly approves a rate of return of about 10 percent on transmission to encourage such construction.

"Once it’s built, it’s money in the bank; it doesn’t matter what happens to it," said Bill Powers, an engineer based in San Diego who works as a consultant for opponents of the line. "It’s the best return you can get for a dollar spent."