Solar radiation measurement on thin-film cylindrical photovoltaic surfaces

Abstract

The measurement of the intensity of solar radiation is one of the environ- mental measurements required to test performance (efficiency) in a photovoltaic (PV) system. The procedure is part of the administrative protocol for eligibility for Italian state incentives, granted by GSE (Gestore Servizi Elettrici); it is also recommended to the system designer as an addition to the declaration of compliance. In PV systems with flat-plate PV modules this measurement is automatically calculated. Once the system rated power is manually entered and the environmental measurements are acquired by probes and sensors, the unit processing station calculates if the conversion of solar ra- diation power into electrical power (DC side) and that of direct current into alternating current (AC side) are greater than the minimum performance values defined by CEI (Comitato Elettrotecnico Italiano). Conversely, radiation intensity on PV cylinders can- not be measured following the guidelines of IEC 61646 (transposed into Italian legisla- tion as CEI 82-25) which are specifically written for flat modules, although datasheets by Solyndra, manufacturer of cylindrical modules, certify their rated power with refer- ence to this standard. The present study outlines the method used to measure the com- ponents of direct, reflected and diffuse light radiation on the surface of a cylindrical PV module and justifies the hypothesis, experimentally tested, that IEC standards are met when reducing global radiation intensity by a certain percentage. These tests have been carried out in cooperation with Hessiana srl, who have installed a cylindrical PV system on the roof of an industrial building in central Friuli.