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23 Jul 2008
An anti-reflection coating from a Silicon Valley start-up boosts a module's efficiency without having to modify the manufacturing process.
An effective anti-reflection coating can improve the conversion efficiency of a photovoltaic (PV) module, by reducing the amount of incident light that is reflected away by the module's protective cover and lost. However, combining reflectivity with acceptable cost and durability has proven difficult. California start-up XeroCoat has developed a coating that could change this situation.
"To date, the ideal anti-reflective coating has not existed, and less than 5% of PV solar systems currently employ anti-reflection coatings for the module's cover glass," Beth McAllister of XeroCoat told optics.org. "The best coating for a cover glass needs high optical performance and durability over the lifetime of the module. Plus the cost of the anti-reflective coating must be less than the value of the additional output power generated by the module. We believe that our anti-reflective coating uniquely meets these requirements."
XeroCoat has developed a porous single-layer silica coating with a low refractive index. "The process starts with a liquid coating step, followed by a low temperature, atmospheric pressure curing step," said McAllister. "This creates the mesoporous silica structure that gives the coating its anti-reflective properties."
The result is an increase of as much as 3% in the solar energy reaching the solar cells at noon, and up to 6% at early morning and evening periods when the incident angle of the light is shallower. This means that the solar module makers can expect a 3% increase in power output on a peak watt basis, and a 4% rise in energy produced on a kilowatt-hour basis. The efficiency of the cell is increased by approximately 0.5–0.75%, according to McAllister.
The XeroCoat technology can be applied across all solar energy technologies, including crystalline, thin-film and concentrating PVs as well as solar thermal collectors. No changes to existing poly- or mono-crystalline module manufacturing processes are said to be necessary to implement the coating.
"Current commercial PV technologies convert 10–20% of the incoming light to electricity," said McAllister. "The same module with a suitable anti-reflection coating can deliver an additional 0.3–0.6% power conversion. Increased energy output translates to higher revenue. In addition, because the peak watt per module is higher, fewer modules are needed to achieve the same total watt rating."
XeroCoat originated in research at the University of Queensland by Michael Harvey and Paul Meredith. The company is now headquartered in Silicon Valley.
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