Comparing energy performance of different semi-transparent, building-integrated photovoltaic cells applied to “reference” buildings

Semi-transparent, building-integrated photovoltaics (BIPVs) are receiving significant attention by several research groups, given their increasing efficiencies combined to improved visual performance (being cell transparency and color rendering index, two key features to ensure their widespread use). Several technologies have been developed in the last years, based on the use of amorphous silicon cells, Cu(In,Ga)Se2 (CIGS) cells, organic PV cells, photoelectrochemical (DSC) cells, and perovskite-based cells. Each technology has pros and cons, but among them the two most reliable and promising seem to be the first one (ηSTC= 3-6% and Tvis= 7-40%) and the last one (ηSTC= 6.6% and Tvis= 42.4%). The second, in particular, may be processed so to appear neutrally colored, resulting in a substantially gray glass, while the first one, absorbing nearly all the blue-green radiation, presents an orange-brown coloration. The paper investigates how the use of both technologies affects the energy balance of buildings. For this purpose the EnergyPlus platform was employed and two validated reference buildings were used for comparison (one residential and one office building). Energy yield due to BIPV technologies, variation in heating and cooling loads due to cell transparency, and implications on visual comfort and on artificial lighting usage are finally discussed.