By - Jim Vess

Researchers increase solar cell efficiency by more than 50 percent—cost is the big hurdle

Energize Weekly, September 6, 2017

Swiss and American researchers have developed a silicon-based solar cell with efficiencies as high as 36 percent—a 50 percent increase over the best performing cells on the market.

The cells were developed by researchers at the National Renewable Energy Laboratory (NREL) in Golden, Colo., and the Swiss Center for Electronics and Microtechnology (CSEM) and École Polytechnique Fédérale de Lausanne.

The existing photovoltaics market is dominated by modules made of single-junction silicon solar cells, with efficiencies between 17 percent and 24 percent.

The researchers created multijunction solar cells stacking a layer of gallium arsenide (GaAs), developed by NREL, on top of a film of crystalline silicon developed by CSEM. This tandem cell had an efficiency of 32.8 percent. A cell using gallium indium phosphide (GaInP) had an efficiency of 32.5 percent.

A third cell combining GaAs and GaInP atop the silicon layer, creating a triple-junction, reached an efficiency of 35.9 percent.

“This achievement is significant because it shows, for the first time, that silicon-based tandem cells can provide efficiencies competing with more expensive multijunction cells,” Adele Tamboli, one of the NREL researchers, said in a statement. “It opens the door to develop entirely new multijunction solar cell materials and architectures.”

Cost is the obstacle—at least for now—to the switch to multijunction silicon-based cells. Assuming a 30 percent efficiency, the researchers estimated GaInP-based cells would cost $4.85 per watt and GaAs-based cells would cost $7.15 per watt. The cost of commercial solar cells range from around 35 cents to just under a dollar per watt. As manufacturing ramps up and production reaches economies of scale and the efficiency of the cells rises to 35 percent, researchers predict, GaInP-based cells could drop to 66 cents a watt and GaAs-based cells to 85 cents.

The scientists noted, in a statement, that such a precipitous price drop is not unprecedented. For instance, the cost of Chinese-made photovoltaic modules fell from $4.50 per watt in 2006 to $1 per watt in 2011.

The cost of a solar modules in the United States accounts for 20 percent to 40 percent of the price of a photovoltaic system. Increasing cell efficiency to 35 percent, the researchers estimated, could reduce the system cost by as much as 45 cents per watt for commercial installations. 

The funding for the research came from the Energy Department’s SunShot Initiative—which aims to make solar energy a low-cost electricity source for all Americans through research and development efforts in collaboration with public and private partners—and from the Swiss Confederation and the initiative.

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