Record 29% Concentrating Solar Cell Aims At Low-Cost Manufacturing

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A novel combination of high-grade spacecraft solar cell material and advanced light-concentrating lenses has yielded solar panels with a record 29% efficiency that may become available for general rooftop use by 2022. The crux in the commercialization of the planar optical micro-tracking technology will be cost-controlling manufacturing process, which is the current stage of study for Insolight, the cell developer.

The Insolight cells first set a record in lab tests two years ago, when it achieved a yield of 36%. The system has since been standardized for mass production with the 29% yield – far ahead of competitors’ 17% to 19% yield for standard silicon cells – as confirmed in tests by the Institute of Solar Energy at the Technical University of Madrid (IES-UPM), Insolight says.

This higher lab result suggests that if the 29% efficient version can be manufactured at a low enough cost for commercial use, then the efficiency might be tweaked thereafter for much higher efficiency levels.

The Insolight panels start with high-priced gallium arsenide-based solar cells, which degrade more slowly than silicon in the radiation present in space, Wikipedia instructs. The most efficient solar cells currently in production are multi-junction photovoltaic cells that use a combination of several layers of gallium arsenide, indium gallium phosphide, and germanium to capture more energy from the solar spectrum.

Spacecraft solar panels use close-packed solar cell rectangles that cover nearly 100% of the sun-visible area of the solar panels. Standard commercial roof solar panels use cell circles that cover about 90% of the panel. The Insolight panel uses far less than either, but employs concentrating lens that focus a wide circle of light onto a small cell.

Thanks to the optical concentration, less than 0.5% of the total surface has to be covered with cells to reach optimal performance. This enables the use of high efficiency space-grade solar cells for the mainstream market. The panel’s protective glass embeds a grid of lenses which concentrate light by several hundred times, Insolight explains.

Such a combination might seem promising without further elaboration. But Insolight has also developed a cell array that shifts horizontally by a few millimeters each day to track the sun. The whole system is encased in a slim module, similar to standard solar panels, which keeps mechanical parts protected. Insolight’s product has the same form factor and appearance as standard panels and can be easily mounted in the industry-standard configurations, on rooftops or on the ground, the company says.

The Insolight modules were also tested in real-life conditions for a whole year on a pilot installation at the Swiss Institute of Technology in Lausanne (EPFL) and successfully endured heat-waves, winter conditions, and storms. The Insolight concept was first tested on a lab prototype by Fraunhofer ISE in 2016, setting a record for a rooftop technology. Insolight was formed in 2015.

“Over the last two years, our team has brought the product from a lab prototype to a full-size solar panel, connected to the grid and monitored 24/7. Our system has been extensively tested and we are now preparing an industrialization strategy for large-scale production,” says Mathieu Ackermann, CTO of Insolight.

In order to speed up its market entry, Insolight is now discussing with several solar manufacturers to license its technology. “Our technology involves a few extra assembly steps, which can be added at the end of existing production lines, taking leverage of production capabilities already in place,” says Laurent Coulot, CEO of Insolight.

Last year, Insolight announced a successful seed funding with investment from, Zürcher Kantonal Bank, and a group of private business angels. In years past, Insolight received funding from FIT (Fondation pour l’Innovation Technologique) and the the ESA Business Incubation Centre Switzerland (ESA BIC Switzerland). ESA is a nationwide initiative that opened in 2016, sponsored by the European Space Agency (ESA) and ETH Zurich, a leading university.

Planar optical micro-tracking technology involves sunlight collected by each of two lens in a two-dimensional lens array, coupled into a shared, planar waveguide using localized features placed at each lens focus, according to a 2010 paper published by Jason H. Karp and associates from the Department of Electrical and Computer Engineering, University of California, San Diego. This geometry yields a thin, flat profile for moderate concentration systems which may be fabricated by low-cost roll manufacture, suggested Karp.

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