Complete Performance Model of Optic Filters for PV Applications

Abstract

Building energy consumption is one of the highest of any sector. Building integrated Photovoltaics (BIPV) have the potential to eventually contribute to 50%-70% of the total energy demand. However, one of the main barriers that hinder the acceptance of solar energy systems as an integrated part in the buildings’ envelope is the limited aesthetics. The common black and blue panels with visible cells usually cause incompatibility with the outer appearance of architectural structures. Consequently, the combination of BIPV technology with colored PV modules will provide solutions to architects and stakeholders who are often skeptical on embed PV systems in buildings attributable to their appearance. To overcome this barrier, different techniques have been developed to provide color to photovoltaic modules. One of the most promising technologies are optical filters. These devices selectively reflect light via interference effects, thus providing the possibility of changing the color appearance of a module. Light reflection, however, reduces the current generated by the solar cells, but also, reduces thermalization losses that negatively impact the cell performance by increasing its operational temperature. In this thesis, a spectrally resolved thermal model in MATLAB has been developed to fully assess what is the real impact of different optic filters under real operational conditions in terms of temperature, efficiency and energy yield. The model considers the angular dependence of optic filter’s on PV modules on both appearance and performance for installations on a façade, roof and free mounted PV (BAPV). In addition, the optimum optic filter thicknesses for ten main colors has been determined based on maximum energy yield.
The model has been validated for three consecutive days and the simulated results for colored modules and module without optic filter were proved to be very close to the corresponding measured values; deviation of 1.5 degrees of simulation models have been obtained during the temperature peak of the modules. The simulation results show that the performance of the optic filters changes depending on the location, installation layout and the incident irradiance. More specifically, temperature drop of 9 degrees has been observed on roof installations from colored modules compared to the corresponding standard module. In addition, the implementation of air gap between the module and the roof has been verified to decrease up to 20 degrees the working temperature and significantly increase the overall energy yield for both colored and standard modules. Nevertheless, in terms of yearly energy yield (kWh/m2), from the tested colors the relative decrease with respect to the standard module was found approximately 16% observed from the most lossy colors.