Stanford University engineers have figured out how to simultaneously use the light and heat of the sun to generate electricity in a way that could make solar power production more than twice as efficient as existing methods and potentially cheap enough to compete with oil.

Called “photon enhanced thermionic emission,” or PETE, the process promises to surpass the efficiency of existing photovoltaic and thermal conversion technologies.

Most photovoltaic cells, such as those used in rooftop solar panels, use the semiconducting material silicon to convert the energy from photons of light to electricity. But the cells can only use a portion of the light spectrum, with the rest just generating heat.

This heat from unused sunlight and inefficiencies in the cells themselves account for a loss of more than 50 percent of the initial solar energy reaching the cell.

If this wasted heat energy could somehow be harvested, solar cells could be much more efficient. The problem has been that high temperatures are necessary to power heat-based conversion systems, yet solar cell efficiency rapidly decreases at higher temperatures.

Combining light and heat could almost triple efficiency

A group headed by Nick Melosh, assistant professor of materials science and engineering, figured out that by coating a piece of semiconducting material with a thin layer of the metal cesium, it made the material able to use both light and heat to generate electricity.

Melosh is senior author of a paper describing the tests the researchers conducted. It was published online Aug. 1 in Nature Materials.

“What we’ve demonstrated is a new physical process that is not based on standard photovoltaic mechanisms, but can give you a photovoltaic-like response at very high temperatures,” Melosh said. “In fact, it works better at higher temperatures. The higher the better.”

Melosh calculates the PETE process can get to 50 percent efficiency or more under solar concentration, but if combined with a thermal conversion cycle, could reach 55 or even 60 percent – almost triple the efficiency of existing systems.

“The PETE process could really give the feasibility of solar power a big boost,” Melosh said. “Even if we don’t achieve perfect efficiency, let’s say we give a 10 percent boost to the efficiency of solar conversion, going from 20 percent efficiency to 30 percent, that is still a 50 percent increase overall.”

And that is still a big enough increase that it could make solar energy competitive with oil.

The research was largely funded by the Global Climate and Energy Project at Stanford and the Stanford Institute for Materials and Energy Science, which is a joint venture of Stanford and SLAC National Accelerator Laboratory, with additional support from the Department of Energy and the Defense Advanced Research Projects Agency.

More info: Stanford University news