Energy saving potential of photovoltaic windows: Impact of shading, geography and climate

Abstract

Engineering the thermal and optical properties of windows is a key to reducing building energy demand, which constitutes a major portion of worldwide electricity consumption. Depositing thin-film photovoltaic coating that simultaneously generates power and allows visible light can be a viable route towards nearly zero energy building (nZEB). Such windows with Semi-Transparent Photovoltaics (STPV) have unique physical properties that require comprehensive modeling to properly estimate the performance. In this paper, we adopt an integrated approach to unify device simulation – yielding electrical, optical and thermal parameters – with building energy simulation using EnergyPlus and a Matlab based power generation platform. The power generation code contains models for shadow from nearby buildings, geography and climate dependent solar insolation and ambient temperature variation to predict efficiency accurately. We also develop a thermal model to find the U-value of a glass coated with STPV. We find that such coating dramatically improves insulation by reflecting infra-red radiation. Our results show that – contrary to roof-top solar panels – STPV modules, when put on all four vertical surfaces, produces significant output in the presence of both shadow and cloud. The net energy footprint of a building with a perovskite based STPV is found to be in the range of 45–80 KWh/m2-yr, well below the source energy use intensity goals set by different countries.