Most commercially available solar panels only are able to convert between 15 and 22 per cent of the sunlight they're exposed to into electricity. As part of an ongoing effort to improve the efficiency of increasingly important solar technology, a team from UNSW has created a solar cell module that boasts a world record efficiency rate of 34.5%.
This result completely eclipses the previous world record for a scalable solar module, which was set at 24 per cent by Alta Devices in the US, making the new result almost 44 per cent better than its predecessor. The tiny module tested by the UNSW team used a surface area of only 28 square centimeters to achieve this result, though the technology is quite expensive to produce, meaning it may be a while before it sees proper commercial use. Still, it's another exciting step towards reaching the theoretical limits of this technology.
The record was set by Dr Mark Keevers and Professor Martin Green of the Australian Centre for Advanced Photovoltaics, and confirmed by the US National Renewable Energy Laboratory. The 28 square centimeter four-junction mini-module uses the light-catching properties of a prism to extract the most energy from each beam of sunlight. The module splits incoming light into four bands, with energy extracted from one of the four junctions at its most efficient wavelength.
"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," said Dr Keevers.
Australia has always been a leader in solar technology research, and the team at the Centre for Advanced Photovoltaics doesn't plan on slowing down. A different type of solar cell called a PERC cell was also invented at UNSW, and this efficient technology is gradually becoming the commercial standard around the world.
The new module is a bit different. It combines a silicone cell on one side of a glass prism and a triple-junction cell on the other. The triple junction cell uses a combination of three layers, each with a different chemical composition — indium-gallium-phosphide, indium-gallium-arsenide and germanium. Energy is extracted by each successive junction at its most efficient wavelength, with the unused light passing through the layer to the next level.
Some of the infrared band of the incoming light is filtered out and bounced onto the perpendicular silicon cell, and by this process of bouncing sunlight around the glass prism almost all of the energy from each beam of sunlight hitting the module can be extracted.
The next step for this piece of technology is for it to be scaled up for further trials. The theoretical limit of efficiency for a four-junction device is said to be 53 per cent, which means that the result announced today is already two-thirds of the way there. The technology will also have to be refined (and made more cost effective) before they find their way onto commercial buildings or residential rooftops, though the technology has a number of advantages over traditional single-junction cells. Efficiency aside, this kind of module can also absorb light that hits it from any angle, thanks to the light-bouncing properties of the prism.
"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. But we must maintain the pace of photovoltaic research in Australia to ensure that we not only build on such tremendous results, but continue to bring benefits back to Australia."