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The importance of optical characterization of PV backsheets in improving solar module power

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By Salvador Ponce-Alcántara, Head of the PV Module Section, Valencia Nanophotonics Technology Center, UPV; Alberto A. Vivas Arangú, Valencia Nanophotonics Technology Center, UPV; Guillermo Sánchez Plaza, Director of Technology, Valencia Nanophotonics Technology Center, UPV

With the objectives of reducing cell-to-module losses, improving module efficiency and reducing the price per watt, increasing importance is being placed on the optical properties of backsheets. It is assumed that a higher reflectance backsheet allows a better reuse of incident sunlight. However, this statement is not always true: another factor must be taken in account, namely the angular dependence of the reflected light. In this regard, backsheets with a high specular component deviate from the ideal Lambertian reflectance, resulting in a minor increase in module current. As a result, differences can be found in module power because of the use of backsheets with similar global reflectance but different angular components of reflected light. A total of 33 industrial backsheets with Tedlar, Kynar, EVA and PET layers from different suppliers were analysed. A comparison of backsheets with low and high global reflectances revealed that the power variation in a standard PV module reaches 0.54% abs. In the same vein, and for backsheets with similar global reflectances, it was experimentally found that the angular response of the reflected light was responsible for a power difference of 0.22% abs. in a standard module.

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Looking back, 2014 was a year of convalescence for a PV industry still battered and bruised from a period of ferocious competition. End-market demand continued apace, with analysts towards the end of 2014 predicting the year would see between around 45 and 50GW of deployment. That has begun to feed through to the supplier end of the market, with all the main manufacturers announcing capacity expansions in 2015 and further ahead.

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