Engineers in Australia set record for solar efficiency

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Engineers from the University of New South Wales (UNSW) have set a new world record for solar efficiency, converting sunlight to electricity at a rate of about two-thirds the theoretical limit.

Dr Mark Keevers with one of the spectrum splitting, four-junction mini-modules (Credit: UNSW)
Dr Mark Keevers with one of the spectrum splitting, four-junction mini-modules (Credit: UNSW)

The new world record for unfocused sunlight saw the engineers achieve a conversion rate of 34.5 per cent. This marks nearly a 50 per cent leap on the previous record of 24 per cent efficiency, set by Alta Devices of the United States, although that was achieved over a larger surface area. The theoretical limit for the type of device used is believed to be 53 per cent.

For the new record, the UNSW researchers used a 28-cm2 four-junction mini-module embedded in a prism. This maximises energy extraction by splitting the incoming rays into four bands, using a hybrid four-junction receiver to squeeze electricity from each beam of sunlight.

“This encouraging result shows that there are still advances to come in photovoltaics research to make solar cells even more efficient,” said Dr Mark Keevers from UNSW’s Australian Centre for Advanced Photovoltaics.

“Extracting more energy from every beam of sunlight is critical to reducing the cost of electricity generated by solar cells as it lowers the investment needed, and delivering payback faster.”

solar_prism_diagram_1

The mini-module combines a silicon cell on one face of the glass prism, with a triple-junction solar cell on the other. The triple-junction cell targets discrete bands of the incoming sunlight using a combination of three layers: indium-gallium-phosphide; indium-gallium-arsenide; and germanium. As sunlight passes through each layer, energy is extracted by each junction at its most efficient wavelength, while the unused part of the light passes through to the next layer.

Keevers conducted the research alongside the centre’s director, Prof Martin Green, who has worked in photovoltaics for over 40 years. According to him, Australia’s solar research has already generated flow-on benefits of more than $8bn to the country, and further efficiency gains will continue to add to that total.

“What’s remarkable is that this level of efficiency had not been expected for many years,” said Green. “So things are moving faster in solar cell efficiency than many experts expected, and that’s good news for solar energy.”

Multi-junction solar cells are unlikely to be seen on domestic rooftops any time soon due to their cost. However, the researchers say their spectrum-splitting approach would be ideal for solar towers, where mirrors are used to concentrate sunlight.