KRAWCZYNSKI, M. ... et al, 2010. Influence of spectral irradiance measurements on accuracy of performance ratio estimation in large scale PV systems. IN Proceedings of the 25th European Photovoltaic Solar Energy Conference and Exhibition (EUPVSEC) and 5th World Conference on Photovoltaic Energy Conversion (WCPEC 5), Valencia, pp. 4710 - 4714.
Understanding the quality of irradiance measurements is an essential part of PV monitoring. For
precise estimation of solar radiation all of its properties must be considered. There are two different ways to describe
irradiance – broadband and spectral. Broadband irradiance measurements are by far the most commonly applied
technique and can be undertaken by the use of pyranometers or calibrated reference cells. Broadband measurements
give integrated power over a specified bandwidth. Spectral irradiance describes not only the integrated energy of the
sunlight, but also its distribution by wavelength. PV modules are strictly wavelength selective devices. Their spectral
sensitivity depends mostly on the cell material technology. Spectral effects can be observed at their most extreme for
thin-film a-Si modules. Knowing the accurate intensity and spectral distribution of the sunlight may have a
significant influence on accurate prediction of the available energy for different types of PV device.