Vincent Signorotti's power plant sits on the edge of the Salton Sea, surrounded by irrigated cropland in the middle of a scorched desert.

Beyond the lake, beyond the patch of green fields, the desert seems empty. But it holds all the energy Signorotti's plant will ever need -energy that could play a key role in California's fight against global warming.

The plant runs on hot water, pumped from deep underground and flashed into steam to turn turbines. With 10 generators near the lakeshore, the facility produces enough electricity for 255,000 homes, and the company that owns it wants to expand. Other companies are drilling nearby, hoping to build their own geothermal plants.

"We're very lucky," said Signorotti, a vice president with CalEnergy Operating Corp., as he considered all the energy beneath his feet. "This is really the crown jewel of undeveloped renewable resources."

A renewable-energy boom is under way in the Southern California desert. The region's open, empty spaces have room for big projects - such as vast solar energy farms - that can generate energy on a grand scale while producing few, if any, greenhouse gases. Dozens of new solar and geothermal generating stations have been proposed, from Lancaster to the Arizona and Mexico borders. They won't be cheap to build, possibly raising the costs Californians pay for power. But with the state's utilities scrambling to find more renewable energy, the projects are moving forward.

Few places in the country have better potential. Low-level volcanic activity near the Salton Sea - a large, salty lake in Imperial County - can feed geothermal plants running 24 hours a day, seven days a week. And with its cloudless skies and bone-dry air, the desert has ideal conditions for solar plants.

"You're creating all this power without harming the environment," said Avi Brenmiller with Solel Solar Systems, which plans to build a giant solar facility in the Mojave with backing from Pacific Gas and Electric Co. "This can be like the next oil supply for California."

The desert energy boom won't end California's reliance on fossil fuel power plants. But the amount of electricity involved is substantial.

The U.S. Bureau of Land Management, which controls immense swaths of the desert, has received land-use requests for 34 solar plants, each of them capable of generating as much electricity as a traditional power plant burning natural gas. It's unlikely that all will get built, but if they were, they would generate enough power to light 18 million homes.

California utilities have already announced their financial support for a few of the projects. State law now forces the utilities to increase the amount of renewable power they use. The utilities must ensure that 20 percent of the power they sell by the end of 2010 comes from renewable resources. As a result, they are willing to fund big, expensive projects that investors in many states probably wouldn't touch.

The power does come at a price.

Electricity from renewable resources often costs more than power generated by fossil fuels. When considered over the lifespan of the facilities, the cost of generating electricity with a big solar installation is nearly three times the cost of using a natural gas plant, according to the California Energy Commission. Geothermal energy, in contrast, costs a little less than power from natural gas plants, over time.

Californians could see their electricity bills increase as utilities back large renewable projects.

"Some of them are quite expensive," said Peter Darbee, PG&E's chief executive officer.

He added, however, that as more renewable facilities are built, the cost of the solar reflectors or wind turbines they use should come down. That could keep the price consumers pay from soaring.

"Manufacturers are gearing up to meet this worldwide demand, and their volumes are increasing," Darbee said. "So that (increase) will be, in part, offset."

The big facilities planned for the desert also pose environmental issues.

Solar installations, for example, can blanket hundreds of acres, rendering the land useless for native plants and animals. And pitched battles have been fought over proposed transmission lines that would bring electricity from the desert to energy-hungry cities on the coast.

But some environmentalists see little choice. If California hopes to meet its goal of reducing the greenhouse gas emissions that come from fossil fuel power plants, it will need more than rooftop solar panels.

"We need renewables at this scale, urgently," said Ralph Cavanagh, director of the Natural Resources Defense Council's energy program.

By his calculation, the same area occupied by Edwards Air Force Base near Lancaster (Los Angeles County) could generate roughly 17 percent of the state's electricity supply if used for solar farms. "They're a very good idea for California," Cavanagh said. "They're also a really good idea for the world. This is one of the scalable solutions that can make a big difference."

The Southern California desert already has a history in renewable energy.

Giant windmills fill the San Gorgonio Pass just west of Palm Springs, immense white blades wheeling slowly over the moonscape along Interstate 10. To the north and west, on the other side of the San Bernardino and San Gabriel mountains, large solar farms first appeared in the 1980s.

Not all the area's renewable-energy efforts have been successful. Several solar projects were abandoned in 1992 when the company behind them went bankrupt. Years of low energy prices dried up funding.

But some early efforts worked, and still do.

Row upon row of curved glass mirrors fill a flat, treeless plain in northern San Bernardino County. As the sun arcs overhead, the mirrors follow, keeping the light focused on long tubes running down each row. A synthetic fluid flowing through the tubes absorbs heat from the concentrated sunlight, the liquid's temperature rising to 730 degrees. That heat is then used to turn water to steam, which powers a turbine and generates electricity.

The facility has been here since 1986. Along with a companion solar farm several miles to the east, it produces about 310 megawatts of power, with each megawatt capable of lighting about 750 homes. A high-voltage transmission line marches south from the plant, carrying the power to the booming San Bernardino Valley.

"The whole reason we're here is the sunshine," said Harvey Stephens, the plant's production manager for FPL Energy. "We farm the sky as the sun goes by every day."

The plant - called Solar Energy Generating System or "Segs" - sits nearly 2,500 feet above sea level, with mountains shielding it from coastal fog and urban smog. Cloudy days are rare and rain is scarce. Even in winter months, the sunlight stays steady and strong.

That's a magnet for solar developers. America's southwestern desert, stretching from California to Texas, receives more solar radiation per square foot on average than any other part of the country, according to federal estimates. And while the population in California's Mojave Desert is growing, the area still has the vast stretches of empty land that developers need.

"At the end of the day, if you want clean power, you have to put those plants someplace," said Solel's Brenmiller. "And this is an ideal place."

The California government, eager to boost renewable energy, has so far been receptive to the idea, solar developers say.

"The state government wants all the solar it can get," said Ryan O'Keefe, FPL Energy's executive director of development. The company is upgrading its equipment at Segs with new fluid-filled tubes and wants to build more solar thermal projects in California, possibly two or three generating "several hundred" megawatts.

"Nobody wants to be seen as the guy holding this stuff up," he said.

While solar developers scout locations in the high desert, geothermal companies study the low desert near the Salton Sea.

They are drawn by the region's geology. The San Andreas Fault fractures into a jigsaw of subterranean cracks beneath the sea's southern end, allowing the earth's heat to seep up and push underground water temperatures past 550 degrees. Small mud volcanoes east of the sea spit gray ooze onto the parched land and hiss with the sound of escaping gas.

Geothermal plants have been selling electricity here since the 1980s, producing a total of more than 500 megawatts. But just as with solar energy, interest in the technology ebbed when energy was cheap.

Now, companies are scouring the barren landscape for places where they can drill wells and build plants. It's a pursuit much like prospecting for oil, just with a different underground resource in mind.

About 5 miles from the sea's western shore, a towering drill rig bores into the dry, powdery earth. Three flags wave from the rigging - California's, the United States' and Iceland's.

Iceland America Energy plans to build a 49-megawatt power plant here in the next three years. Water temperatures beneath this site aren't as high as they are on the other side of the sea - around 350 degrees. But that's still hot enough to generate electricity. The company has already signed an agreement to sell the energy to PG&E. A Santa Rosa firm, ThermaSource, handles the drilling.

It's no accident that a company with its roots in Iceland would try to develop geothermal power. The volcanic island generates roughly 19 percent of its electricity from geothermal plants and uses the earth's energy to heat 90 percent of its homes, according to the Icelandic National Energy Authority.

"We're very much aware of the benefits of geothermal, and the possibilities," said Magnus Johannesson, Iceland America's chief executive officer. "That is not yet the case in America, and we need to change that."

The company, based in Los Angeles, formed in 2004, and its shareholders include several Icelandic energy companies. Although the company looked elsewhere, it decided to start its first project here in the Imperial Valley.

"California has a lot of potential, high-temperature potential," Johannesson said.

ThermaSource, meanwhile, has seen demand for its services jump. The company, which has worked for years in the Geysers geothermal field north of Calistoga, has six drill rigs operating in California and Nevada. Two years ago, the company had three employees. Now it has 160, said founder Louis Capuano Jr.

"The business community is into geothermal big-time right now," he said. "We've got foreigners coming into the U.S. to develop this resource, because it's here. There's a lot of people taking a look."

The new interest in mining power from the desert does face obstacles.

They include transmission. Many people in the energy business, and in government, say the high-power transmission lines currently strung across the landscape can't carry much more energy. Yet several proposals for new power lines have run into determined resistance.

Sempra Energy, which owns the San Diego Gas & Electric utility, wants a new high-voltage line to ship power from the Imperial Valley. But the company's preferred route for the Sunrise Powerlink runs right through Anza Borrego Desert State Park, a wild expanse of dry mountains separating the desert from the coast.

Opponents say the line is unnecessary. They want to add solar panels to new homes and commercial buildings in the San Diego area and improve energy efficiency, lessening the need for energy generated elsewhere.

In addition, they say the existing transmission network should be able to handle more electricity in the future, after some of the power-purchase contracts signed by the state during the 2000-2001 energy crisis expire in 2011. Upgrading the existing high-voltage line between San Diego and the Imperial Valley, as well as other parts of the network, makes more sense than building from scratch.

"At this moment, there's a lot of capacity tied up on that line, but that evaporates in 2011," said Bill Powers, an energy industry engineer who issued a report proposing alternatives to Sunrise Powerlink.

Signorotti said that while he doesn't prefer any particular route, the area will need new transmission lines if the state hopes to wring as much energy as possible from the Imperial Valley geothermal fields. And the state will need that energy to meet its renewable-power goals. His company estimates that its small corner of the Salton Sea shore could generate at least an additional 900 megawatts, perhaps as much as 2,330.

"To meet the renewable ... standard, it's going to be absolutely critical that the Salton Sea resource be developed," Signorotti said. "I don't see any way around it."