GlassPoint has built a greenhouse with lightweight mirrors that it says could also be used to make steam for electricity production.

A California company has begun using solar power to squeeze oil out of an old oil field, flooding the underground rock with steam that comes from the sun’s heat instead of from burning natural gas.

The technique was tried in the 1980s by the Atlantic Richfield Company, but GlassPoint Solar, of Fremont, Calif., which cut the ribbon on a pilot project Thursday, says its plant is the only one of its kind now operating. Other companies have discussed such projects.

The process is cheaper than using natural gas, even at today’s depressed prices for that fuel, and trims the carbon footprint of the gasoline, according to GlassPoint. The pilot plant, completed in January in Kern County, is very modest, occupying less than an acre and producing only about a million B.T.U.’s per hour. But the company says it could quickly be replicated on a larger scale and could eventually displace 80 percent of the natural gas used to produce a barrel of oil.

GlassPoint said that at a full-size plant, its technology could produce steam at a cost of $3 per million B.T.U., compared with a market price of gas today of around $4 per million B.T.U.

Whether GlassPoint can get that far remains unclear. The company has no track record in the oil industry and has had three different business strategies in less than two years. Formerly known as CleanBoard, GlassPoint changed its name in October 2009 when it abandoned plans to use a solar-powered factory to make gypsum-based wallboard and said it would work with other wallboard manufacturers. Last year, it refocused its business yet again on using solar power to extract oil.

Rod MacGregor, GlassPoint’s chairman, said that burning natural gas to make steam for oil recovery was the largest single use of natural gas in California. About 40 percent of California’s oil is produced through such “enhanced oil recovery,” and the steam can account for as much as two-thirds of the production cost of such oil, according to GlassPoint.

The amount of steam needed to produce a barrel of oil varies according to the age of the field, but two million B.T.U. per barrel is typical. Several companies use curved mirrors to focus the sun’s light to make steam, but on Thursday, GlassPoint unveiled a radically different design, one it says could also be used to make steam for electricity production.

In existing steam-electric solar plants with curved mirrors, the mirrors sit on heavy, rigid frames so that they will not be deformed by wind and can survive storms.

GlassPoint has built a greenhouse and suspended extremely lightweight mirrors from the skeleton of the building. The greenhouse is kept at higher air pressure than the outside environment, so no dust can come in, reducing the problem of cleaning the mirrors. A robot crawls across the glass roof to wash it. The wash water is collected for reuse, an important point since many old oil fields are in deserts.

A different solar energy company, BrightSource Energy, is building a solar steam system at a Chevron oil field project in Coalinga, Calif. It is supposed to go into service in the second half of this year.

Using solar power for oil recovery makes moot one of solar’s most difficult characteristics, its intermittency, according to John O’Donnell, vice president of GlassPoint. “You’re heating a cubic mile of rock,’’ he said. “It doesn’t matter if you heat it up a little higher in the day.’’

In the pilot project, the greenhouse is too far from the wellhead to send the steam by pipeline, so it is preheating the water, which will then be boiled by natural gas, reducing natural gas use but not as much as in a mature production facility.

Another advantage, according to Mr. MacGregor, is that the well is not fussy about steam quality, in contrast to a steam turbine that makes electricity, which demands constant temperature and pressure. “If there are hot water droplets in the steam stream, the rock won’t care, but a turbine certainly would,’’ he said.