How do you make mirror-concentrated sunlight cheaper than burning natural gas? Put it in a greenhouse, argues new solar start-up GlassPoint, which unveiled its first such solar hot water greenhouse on February 24—in a dusty, old oil field in California's Central Valley. Why? Because cheap steam means more oil.

Ensconced amidst the derricks of Berry Petroleum Company's oil field in McKittrick, Calif., the 650-square-meter demonstration of a greenhouse-based solar thermal steam plant will help pre-heat water to 88 degrees Celsius. That hot water will then be boiled to steam with natural gas and used to heat the rock in old oil fields to pump out more petroleum.

"Steam is the largest cost associated with producing oil in these thermal projects," says GlassPoint vice president John O'Donnell. "Now you can run them longer because the steam is cheaper. You can get 10 to 20 percent more oil production out of the same well."

View a slide show of the new greenhouse-based solar thermal plant

The goal is to provide a cleaner and cheaper way to heat up the steam used to melt the field's thicker oils and scour out more of the black gold. Essentially, the technology heats cubic volumes of rock to roughly 175 degrees Celsius to melt heavy oils and get them flowing. Roughly 40 percent of the oil produced from California's century-old fields relies on the steam technique—and it is the largest industrial use of natural gas in that state.

As it stands, the two rows of mirrors in this initial solar thermal greenhouse can generate some 1 million British thermal units of heat an hour. The company claims its technology can produce steam at a cost of $3 per million BTUs, based on U.S. National Renewable Laboratory calculations; natural gas currently costs some $4 per million BTUs, though that price may continue to fall as natural gas freed up by fracking floods the market.

Here's how the technology works: GlassPoint builds a fairly conventional greenhouse with a crenellated roof to maximize the amount of sunshine inside year-round. Below, the seven-meters-across mirrors to concentrate the sun's rays—along with the tube carrying the water to be heated—are suspended from the greenhouse itself. Since the greenhouse blocks the wind, the mirrors and tubing in this plant are roughly 10 percent of the weight of a traditional solar thermal mirror installation, which requires steel supports. As O'Donnell notes, what makes solar thermal power plant technology expensive "is the cost of the hydraulics and steel and concrete associated with maintaining a half-degree of pointing accuracy in a 20 mile-per-hour breeze."

Another advantage is speed: the glass house and solar thermal mirrors took six weeks to build, compared to a solar thermal power tower project under construction since 2009 by BrightSource Energy for Chevron in California's Coalinga oil field near Fresno. "The project is still under construction," says Chevron spokesman Morgan Crinklaw, adding "we expect to have it completed this year…. This is a demonstration project to determine the viability of the technology."

That viability will come down to cost, as projects in previous decades foundered in the face of cheap natural gas. There is only one other solar thermal project delivering heat to an industrial process—a SunChips plant in Modesto, Calif., produces snack chips with the sun's heat—and this marks the only one in the world currently working in an oil field. The company estimates that a full-scale field could deliver as much as 80 percent of the heat energy required for such projects, displacing natural gas in the process.

It is also one that is not confined to California. "There is reasonably good solar radiation in places where steam floods are going," O'Donnell says, such as Kuwait, Oman and other Persian Gulf oil-producing states. "There are resources both over your head and under your feet."

But the greenhouse also offers another key advantage: keeping the mirrors clean of the dust, dirt, sand and humidity that plague oil fields (and deserts generally) around the world. And automated washing equipment borrowed from the agricultural greenhouse industry—essentially automated water sprayers with brushes like those in a car wash—scan clean the glass house that shields the solar thermal equipment from the wind and dust.

"With 100 years of optimization the greenhouse industry has gotten really good at lower shading and lower cost. After all, 1 percent more light is 1 percent more tomatoes," O'Donnell notes. "These reflectors are in a dry, dust-free, non-condensing environment, which means we can use materials that couldn't survive outdoors."