EFFECTS OF SOLAR IRRADIATION CONDITIONS ON THE OUTDOOR PERFORMANCE OFPHOTOVOLTAIC MODULES

Energetic losses, relative to the standard conditions of testing, in p hotovoltaic modules in outdoor operation, were analyzed and the role o f the optical effects is discussed. The following four loss effects we re estimated: (a) reflection of unpolarized light, (b) spectrum, (c) i ntensity of the light and (d) temperature of the module. Four independ ent models were used to describe these four losses. The models were va lidated by the experimental data of an outdoor measurement campaign pe rformed on 0 degrees tilted modules at 41 degrees N latitude in South Italy. Disagreement reaching 5% under clear sky conditions was found b etween theoretical predictions and experimental data for the instantan eous total loss. As a result of a critical analysis of the literature data on this subject, it could be explained by invoking the presence o f a fifth loss mechanism: the polarization of the incident light. Fina l relative losses, due to the particular state of the incident sunligh t, amount to about 7-8% of a total of 14-15%. Of these, 3% is due to t he low irradiation level, 1-2% to the polarization of the skylight and 3% to the reflection of the incident light on the front cover of the module. The spectral effects are negligible (less than 1%). The remain ing 7% loss is due to temperature effects on the module. All the loss data are reported as a function of the air mass (AM). The maximum oper ating efficiency is reached at AM approximate to 1.5. (C) 1998 Elsevie r Science B.V. All rights reserved.