Will solar power ever be as cheap as coal?

“Solar power is the energy of the future – and always will be.”

That tired joke, which has dogged solar-generated electricity for decades due to its high cost, could be retired far sooner than many think.

While solar contributes less than 1 percent of the energy generated in the United States today, its costs are turning sharply downward.

Whether using mirrors that focus desert sunlight to harvest heat and spin turbines or rooftop photovoltaic panels that turn sunshine directly into current, solar is on track to deliver electricity to residential users at a cost on par with natural gas and perhaps even coal within the next four to seven years, industry experts say.

“We’re confident that we’re not that far away from a tipping point where energy from solar will be competitive with fossil fuels,” said Ray Kurzweil, a National Academy of Engineers panel member after the panel reported on the future of solar power in February. “I personally believe that we’re within five years of that tipping point.”

To do that, however, the cost of electricity produced by rooftop solar panels, for instance, will need to fall by half – from about 32 cents per kilowatt hour (kwh) today, including subsidies, to about 15 cents per kwh by 2012, according to a new report by FBR Capital Markets, an investment bank, and market researcher Solarbuzz.

Evidence of a shift appears to be taking shape around the country. Google, the Internet search company, has invested in several young solar-power start-ups with an explicit cheaper-than-coal goal. San Jose, Calif.-based Nanosolar already claims to be shipping “thin-film” solar panels that generate electricity on par with the cost of coal-fired power. And in Lexington, Mass., Frank van Mierlo and Emanuel Sachs are leading a team of engineers with one audacious mission: Make a silicon photovoltaic cell that turns sunshine into electricity as cheap as electricity from a coal-burning power plant.

“There’s no doubt that we’re going to see solar as cheap as coal power a lot sooner than many people realize,” says Mr. van Mierlo, president of 1366 Technologies, standing beside an industrial furnace inside the company’s pilot manufacturing facility.

Proof of what he says lies a few footsteps down a hallway where Sara Olibet, an applied physicist, is painstakingly measuring the efficiency of dozens of solar-cell prototypes, each with a different combination of chemical coatings designed to maximize power output.

In her lab, she uses tweezers to select one-inch-square cells and put them into a refrigerator-size machine that shines light with sun-like intensity. In addition to efficiency ratings, readings are taken along the light spectrum to evaluate the cells’ coatings and other aspects being tweaked toward a single optimum formula.

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