Solar ♦ news digest
continuum system. “The fibre heavily attenuates wavelengths below 450 nanometres,” Dennis says, “so you’re not getting photons in the 300 nm to 450 nm range you see from the sun. We’re thinking of using some sort of arc-based source to fill those short wavelengths in. With that addition and a little more spectral shaping, we can get a perfect solar match,” Dennis points out.
did. Then we measured the efficiency, and the difference went down to 5 percent. Some materials showed even better agreement with the NREL results.”
If the super-continuum system eventually joins xenon as an accepted standard solar simulator, Dennis says, it could alleviate a number of difficulties that arise in studying the newest high- tech PV materials. For one thing, its collimated beam can be tightly focused to selectively probe and excite very small features such as nanowires and carbon nanotubes.
Graph comparing the output of the solar simulator with the standard solar reference spectrum AM 1.5
But even without a UV component, the team wanted to determine how well their simulator performs compared to results with xenon-source measurements taken on exactly the same materials by colleagues at the Department of Energy’s National Renewable Energy Laboratory (NREL) in nearby Golden, Colorado, which is the federal agency responsible for certifying the efficiencies of different PV materials.
So earlier this year, Dennis and Schlager took measurements on the performance and efficiency of four different PV materials (p-type crystalline silicon, GaAs heterojunction, a thin film of CIGS, and amorphous silicon) illuminated by the super- continuum light.
“We did it two different ways,” Dennis says. “First we adjusted our light to 100 mW per square centimetre, which is the average for solar radiation reaching the Earth’s surface. The match to NREL’s data was pretty good, but still off by around 10 percent, illustrating the challenge of an absolute calibration measurement. The discrepancies are likely caused by beam non-uniformity and spectral mismatch.
“In the second method, we just did whatever it took to tune the intensity until we got exactly the same current density for each sample that NREL
Another advantage of the novel solar simulator may be in the testing of multi-junction solar cells. According to NREL researcher Daniel Friedman, who develops III-V multi-junction concentrator cells, “The highest-efficiency solar cells use multiple junctions, with each junction tuned to a different slice of the solar spectrum. To test these multi- junction cells, the spectrum of light from the solar simulator must be rapidly and accurately adjusted, which PML’s supercontinuum simulator provides.”
Testing will continue on additional PV materials, along with ongoing research into using a focused beam to produce spatial maps of materials.
STMicroelectronics unveils SiC modules for solar applications
The firm’s expanding portfolio of silicon carbide power devices increases energy yield for the solar generation
STMicroelectronics is revealing innovations in SiC devices at Solar Power International (SPI) 2012.
The firm’s latest products enable systems producers to build ultra-efficient electronics for converting raw solar energy into grid-quality power.
The firm is showcasing its 1200V SiC diodes, which replace ordinary silicon diodes, in the DC-DC boost converter and DC-AC inverter. They convert the photovoltaic module’s low-voltage output into high- quality AC power at the correct line voltage.
October 2012
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