The impact of solar spectra on PV module performance

Scientists from the University of Opole and the AGH University of Science and Technology in Poland have analyzed the impact of the diffuse component of global solar radiation on the efficiency of photovoltaic panels during bright and sunny as well as cloudy summer days and have found that these changes may affect their performance depending on the semiconductor materials used in the modules.

In the study Modelling and analysis of the influence of solar spectrum on the efficiency of photovoltaic modules, published in Energy Reports, the researchers proposed a method to obtain the characteristics for solar radiation spectra in variable weather conditions without the need for expensive and sophisticated measurement devices. This model, in their view, can represent a low-cost solution to estimate how changes in the solar radiation spectrum distribution can have an impact on the properties of various photovoltaic modules.

Their analysis was performed through the SolarSpectrum, which is a spectrum simulator used to measure the influence of changes in the solar radiation spectral distribution. The simulation took into consideration the geographic coordinates of the study location, the local atmospheric conditions, the solar time, season of the year, azimuth, and the PV module slope exposition.

These data were then compared with those resulting from the simulation made with other simulators such as the Smarts2, Spectal2, Modrtran, and Brite models. “The obtained measurement results are mean values, with variable measurement intervals, to provide the solar radiation spectrum covering all the elements crucial for the analysis of the photovoltaic conversion present in the PV modules, such as location and size of the absorption holes in the spectrum characteristic,” the academics specified, adding that the spectral simulation error was within 5%.

The analyses showed that PV modules relying on crystalline silicon and copper indium selenide (CIS) cell technologies may be better suitable to deal with the impact of solar spectra in projects with tracking systems, for which the conversion of direct radiation is of crucial importance, according to the Polish group.

Single and multijunction thin-film modules based on amorphous silicon, and eventually CIS products, are indicated as the best option for stationary projects without tracking systems or BIPV projects on facades, where the conversion of diffuse radiation play a particular role. “Theoretical analysis of the a-Si structures, both single as well multijunction, shows better performance of these devices at low irradiance conditions, during days characterized by spectral distribution common for cloudy days with large water vapor content in the air,” the authors of the papers stated. “These types of device should exhibit unchanged efficiency both at midday as well as during morning and late afternoon.”

The reported fluctuations in the module efficiency are the result of the change of the solar radiation stream falling on the exposition plane, the researchers noted. The choice of the optimum semiconductor material for operation in a PV system should depend on its capability to work in irradiance conditions characterized by various diffuse radiation contents, they added.