In Coalinga, California, an odd marriage of green and brown technologies likely has environmentalists chewing their nails.

The technologies are concentrating solar power and oil extraction, and the 29-megawatt BrightSource solar steam plant – which covers 100 acres with 7,000 mirrors that will focus sunlight on a water-filled tank that sits 323 feet off the ground – is, in essence just another CSP. But this one uses steam not to run a turbine/generator setup to produce electricity, but to thin very thick petroleum deposits so that they flow more freely.

The technology is aimed at a Chevron oil field in Coalinga, and the CSP system is being put together by Oakland-based Bright Source Energy, a design-build solar engineering firm whose flagship solar test facility, the Solar Energy Development Center (SEDC, located in Israel’s Negev Desert) demonstrates its proprietary Luz Power Tower (LPT) Technology.

Fortunately, the use of steam to thin petroleum deposits is not the same as “fracking” technology, which uses immense pressure to open vents in subterranean rock to allow oil and gas to flow to the surface. In that respect, at least, Chevron will escape the eagle eye of environmentalists and regulators, who are beginning to tag fracking as the likely cause of ground water contamination.

Chevron, one of BrightSource’s major investors, says it will use CSP technology to reduce its carbon footprint. Normally, natural gas is used to make steam to thin petroleum, but the wild swings in the price of natural gas impact oil operations, and oil profits, so the use of CSP is a double win for firms like Chevron, who get to improve their green image while saving money.

BrightSource, for its part, will use the deal to ramp up technology. Other than the Negev Desert demo plant, the company has not built a CSP plant, though it has signed contracts for up to 2,610 megawatts of solar electricity to California utilities.

Although the Chevron contract seems like a back-door entrance to the solar energy field, BrightSource’s Senior Director of Corporate Communications, Keely Wachs, says the use of solar-generated steam in oil fields is potentially lucrative market. Other BrightSource investors include oil giants BP and StatoilHydro.

The Coalinga project will be owned and operated by Chevron, and is scheduled for completion by the end of next year. The exact financial terms have not been revealed, but BrightSource competitors Ausra, based in Mountain View, and Pasadena-based eSolar are also investigating the oil industry as a potential market for solar, with Ausra CEO Robert Fishman revealing that he has been in talks with oil firms about deploying Ausra’s technology.

Because the steam-based version of CSP technology only works when the sun is shining, oil producers will still have to rely on natural gas-fired steam at night and on cloudy days. However, molted salt CSP has already shown the way to storing power for times when the sun is absent, so future advances in these areas might replace natural gas altogether.