Influence of spectral irradiance measurements on accuracy of performance ratio estimation in large scale PV systems

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.