Performance estimate of semi transparent photovoltaics through modeling and characterization

Abstract

As building sector consumes a large portion of electricity worldwide, several tech- nologies are under research to reduce the energy demand and carbon footprint. To convert buildings into net-zero energy building, Semi-transparent photovoltaics (STPV) can play a major role. STPV a variant of conventional thin-film photovoltaics transmits visible light and produces on-site electricity simultaneously. The purpose of this thesis is to find whether STPV can achieve net-zero energy building. In this thesis silicon based STPV is considered. The relevant material parameters (e.g., electrical, thermal and optical) are studied and quantified individually in order to assess STPV performance on the building energy for different climatic conditions. Based on the model, thermodynamic limit of efficiency (around 10% at 50% visible transparency), visible transparency and solar heat gain are derived and estimate of yearly net energy footprint of an office building for various climatic conditions are presented. Building energy simulation is performed using EnergyPlus, combined with power generation calculation from a solar irradiance model. STPV with different glazing configurations are studied and the U-value are quantified for each case. The building energy simulations suggest that for 50% visible transmittance, STPV on clear glass saves about 50% and 30% of the energy demand in tropical and hot desert regions respectively and around 20-25% in Scandinavian and cold continental regions. When combined with a low-emissivity glass, the net saving reaches as high as 90% in tropical regions, 60% in hot desert regions and 45-70% in the rest of the regions. In this study, device and system level figures of merit taking into account usage of natural light as well as overall energy saving. The figures of merit capture the trade-offs between efficiency, solar heat gain and transparency and predict a much lower optimum transparency for places with abundant sunlight. The re- search show that the low net saving for these hot regions can be improved to nearly 100% if such optimization strategies are adopted. This makes STPV, combined with low-emissivity glass, a promising technology across the globe.