THERE is a lot of energy from ancient sunshine stored in the oil that sits below the deserts of Oman. There is also a lot of sunshine hitting those deserts today. A new wrinkle to an established technology should allow some of that current sunshine to be employed to get at more of the ancient stuff.

Using heat—in the form of steam—to liberate disobligingly thick and gunky oil which would otherwise stay in the ground is nothing new. Such enhanced-recovery techniques date back to the 1950s and 40% of California's oil production now depends on steaming subterranean rocks in this way. The steam, however, is made by burning other fossil fuels—normally natural gas—and because heating rock takes a lot of steam, making that steam takes a lot of money. It also adds to the oil's climate footprint. The amount of gas used means that a barrel of Californian heavy oil gives the stuff from Canada's tar sands a run for its money in terms of associated greenhouse-gas emissions.

GlassPoint, a small Californian company, thinks it can make steam for oil recovery more cleanly and cheaply by using sunshine to do the heating. This sounds surprising. Solar-thermal power stations, which employ mirrors to concentrate sunlight on boilers and thus raise steam to generate electricity by turning turbines, are far from cheap compared with gas-fired stations. But solar-thermal electricity faces exacting challenges. To feed a turbine you need particularly pure steam, which can be a problem if you are in a desert. And to get the most out of the system you need the steam to be both very hot indeed and available in copious amounts.

Oil wells, GlassPoint's founders noticed, are far less demanding consumers in these respects. The steam used can be comparatively dirty. Nor does it have to be infernally hot. And even a small amount of it, added to an existing gas-based recovery process, can make a useful contribution.

There are, though, disadvantages to having to work in an oilfield. People building solar-thermal power stations prefer sites low in dust. Those serving the oil industry must go where the rigs are, however dusty and mucky the air. GlassPoint seems to have found a neat solution to this: it puts its mirrors indoors. Greenhouses are easy to buy, quick to erect and, thanks to off-the-shelf kit designed for the purpose, simple to keep clean, too. Moreover, sheltering the mirrors from the wind allows those mirrors to be a lot lighter, making them both cheap to build and ship, and easier to turn in order to follow the sun.

GlassPoint's boss, Rod MacGregor, thinks that taking capital costs and the lifetime of the plant into account his firm can produce steam at $3.78 per million British thermal units (btu), which is $3.58 a gigajoule. Steam from gas comes in at $5.79 per million btu. A pilot project in California, he says, has been producing steam as intended since the beginning of the year. And the company has now signed a deal with Petroleum Development Oman for 7 megawatts of plant—a 16,000-square-metre greenhouse providing some 57 billion btu of steam a year.

If it pans out, the technology could spread fast. Mr MacGregor expects Oman to be using 200 trillion btu of steam a year for oil recovery by 2015. Not all of that steam could be solar, but a system which used high-pressure solar steam during the day and low-pressure gas-generated steam by night, to keep the pipes hot, might get 80% of its power from the sun. That would free up a lot of gas for export—or for turning into petrochemicals.

Enhanced oil recovery currently uses a quite remarkable amount of energy: 1.7 quadrillion btu of gas around the world every year, according to GlassPoint. Not all of that is in sunny places, but there are many deserts besides Oman's that have oil beneath them. The paradoxical possibility, then, is that solar-thermal technology might end up producing a lot more oil than electricity in the years to come.