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Loughborough Researchers Reduce PV Glare
One of concerns about the introduction of large scale solar projects has been the issue of glare from the modules.This is especially true for drivers passing PV installations whether they are ground or building mounted. UK researchers have developed a coating that can reduce the glare without impacting the energy output.
Researchers from CREST at Loughborough University in the UK have developed a multi-layer anti-reflection (AR) coating for glass surfaces to improve the efficiency of PV modules and also reduce the annoying glare often seen from the sun's reflection from PV panels.
Each glass surface reflects about 4% of the incident light representing a significant loss of light into the module. Piotr Kaminski, Fabiana Lisco and Michael Walls, members of CREST at Loughborough University, have come up with a multi-layer AR design which cuts the reflection down by more than 70% across the wavelength range accepted by PV devices. The effectiveness of the coating is demonstrated in Figure 1 where a glass cover sheet has been placed above a crystalline silicon PV cell. The area covered by the AR coated glass is clearly visible whereas the part of the cell covered with non-coated glass is obscured by reflections.
Figure 1. A comparison of the refection from a cover glass on a crystalline Silicon cell with and without the multilayer AR coating
The design used by Loughborough consists of only 4 alternate layers of zirconium oxide and silicon dioxide and the whole stack is less than 300nm thick. These materials were chosen because they are abundant and low cost. Commenting on the design Dr Kaminski said "The AR coating has to be cost effective and so the design is a compromise. We want the best quality AR coating but with inexpensive materials and as few layers as possible. Also the whole stack should be very thin to save time in manufacturing".
The coatings have been deposited using magnetron sputtering using a machine developed by Power Vision Ltd to deposit AR coatings on spectacle lenses. Although the IEEE report is specifically aimed at the improvement in efficiency of thin film CdTe devices, the coatings can be applied to other thin film technologies such as CIGS and amorphous silicon.
Figure 2. The AR coatings were deposited using a Power Vision Ltd machine designed to coat spectacle lenses.The magnetron sputtering process is easily scaleable and already used by glass manufacturers.
They can also be applied to cover glass on crystalline silicon modules and even third generation devices such as organic or perovskite devices. Dr Kaminski goes on to say "Each PV technology operates in a different wavelength range and it is relatively simple to accommodate this in the multi-layer design for each case".
Magnetron sputtering is an easily scaleable technology already used by glass manufacturers for other types of coatings. The materials are scratch resistant and very durable and would be effective for the full 25 year warranty offered by PV module manufacturers. Professor Mike Walls commented "This work was funded by the EPSRC SuperSolar Hub. We really want to see these AR coatings implemented by manufacturers. They improve the module power output by about 4% and will be low cost if manufactured in high volume. It's a great added value proposition for float glass manufacturers".
The results have been published in a IEEE Journal of Photovoltaics report.
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