The Coalinga oil field in California has been pumping out crude since 1887, and the remaining oil has gotten heavier and heavier and harder and harder to extract—but it will soon get a boost from the sun. Specifically, the old field will use steam generated by concentrated sunlight to help melt the remaining heavy oils and make them liquid enough to be pumped to the surface.

"It's operating and providing the bulk of the steam generated to support enhanced oil recovery," explains Jerry Lomax, vice president of emerging energy at Chevron, the energy company that funded the project. The idea is to "turn photons into solar steam and then… get that into an oil field injector."

Chevron partnered with BrightSource Energy, a company that designs and builds concentrating solar power plants, to build a version of that technology in the Coalinga oil field. They have built more than 7,000 mirrors on mechanized devices—known as heliostats—to track the sun on 65 acres and concentrate sunlight from this broad area to a point atop a 327-foot-tall tower. Inside that tower, water turns to steam at a pressure of 700 pounds per square inch and an average temperature of 500 degrees Fahrenheit. That steam flows to a heat exchanger, where it turns water from the oil field to steam so that it can be pumped back underground to loosen the remaining oil. All told, the power tower system pumps out 350 barrels of steam an hour, which will be used to supplement water boiled to steam by burning natural gas if testing goes well.

"It's an extra 5 percent for them," Lomax says, "and they save that much natural gas." As it stands, Chevron pumps nearly 8,000 barrels of "oil equivalent" per day out of the Coalinga field.

Over the course of 2012, Chevron will determine how reliable the solar steam is, as well as what kind of steam volumes it can expect under various conditions. By next year, once hookups are in place, the solar steam will start supplementing that from burning natural gas. "Solar steam will always be an augmentation of an alternate traditional fuel source, such as natural gas, so we have 24-hour coverage," Lomax says. On the sunniest days, the system can produce steam almost 12 hours of the day, but Chevron will investigate whether it is feasible to run an oil field exclusively on solar steam as part of this demonstration project.

Heavy oils are a big part of new oil being produced around the world, whether oil from the tar sands of Canada or thicker crude from Indonesia. Chevron has brought up 150,000 barrels of heavy oil in California alone and roughly 500,000 barrels per day around the world. Solar steam—should it prove successful in California's San Joaquin Valleymight make sense to get more oil out of the ground in places like the partition zone between Saudi Arabia and Kuwait or Indonesia. "All three locations have sites with ample sunlight and ample amounts of flat acreage near oil fields where you could include a solar field of this scale," Lomax says, and the company is also studying whether solar steam might make sense for complexes that refine oil or produce petrochemicals, both of which employ a lot of heat.

Of course, oil fields are not the friendliest or cleanest places for mirrors that must remain highly polished to be effective. Thus far, the oil company has only broken one of the heliostats by running into it with machinery and has been pitting human crews against automated cleaning machines. "The machine uses slightly less water than a manual crew," Lomax says.

Chevron and BrightSource are not the only companies pursuing the technology. GlassPoint aims to create even cheaper solar steam by placing the mirrors inside a greenhouse. They can then be lighter because they are protected from the wind and need to be cleaned less often. The company has its own demonstration project with Berry Petroleum Company near McKittrick, Calif.

But it will be "challenging" for any solar steam to compete with falling natural gas prices, Lomax says, which suggests the technology may only find a future in places where natural gas is either unavailable or expensive. Regardless, Chevron sees the solar steam technology as another tool to cope with rising energy demand globally. In the end, petroleum prices killed the first and second solar revolutions, but now solar may help extend the reign of oil.