Amonix's III-V move brings solar system record
By electing to use compound semiconductor rather than silicon solar cells, Amonix has produced the first photovoltaic systems to reach 25 percent efficiency.
The newly-released Amonix 7700 concentrated photovoltaic (CPV) system is being demonstrated at the Renewable Energy World Conference and Exposition in Las Vegas from 10-12 March.
The leap in efficiency comes largely from replacing the 27.6 percent efficient back-junction silicon cells that Amonix had manufactured itself with 37 percent efficient GaInP/GaAs/Ge triple-junction cells.
Twenty years of industry experience has seen Amonix install 13 MW of silicon-based CPV systems and claim the efficiency record for silicon cells under concentration. It is now using the lenses and tracking systems developed in that time with III-V cells to deliver its latest record.
“The company is now transitioning to multi-junction [cells] because of efficiency advantages,” Clark Crawford, Amonix s senior director of marketing, told compoundsemiconductor.net.
“We ve changed the focal point to optimize it for the multi-junction solar cell,” he said. “Given our heritage of solar cell manufacturing, we do some processing of the solar cell that s proprietary to us that really optimizes it for concentrating.”
The 53 kW Amonix 7700 panel operating at the University of Nevada, Las Vegas, boasts a 77 foot wide and 50 foot high receiving surface. That assembly is the company's largest to date, featuring seven semi-truck sized “megamodules”, each containing 36 solar modules.
Amonix has also converted its five-megamodule systems to use compound semiconductor cells and is currently deploying that format in a 250 kW installation for the Southern Nevada Water Authority. Construction on that site is set for completion before the end of April.
The Torrance, California, company moved to compound semiconductors after winning US Department of Energy funding to produce low-cost concentrators in collaboration with cell producer Spectrolab in 2007.
Since then it has signed a long-term supply contract for 200 MW of high-efficiency cells from an unnamed supplier.
The ability of the system to convert a quarter of the sunlight falling onto it into electricity is not a "best-case" scenario, it is claimed. The Amonix 7700 might provide this level of performance from around 10 am to 4 pm, Crawford says.
“You have to track the sun, keep the focal point on the solar cell,” he explained. “Once you do that you run at that high efficiency for the majority of the day.”