Modelling, Design and Experimental Study of Semi-Transparent Photovoltaic Windows for Commercial Building Applications

As the building sector is moving to net-zero energy building performance targets and beyond, the use of building integrated solar systems becomes essential. Semi-transparent photovoltaic (STPV) window technologies are expected to play a key role in on-site electricity generation of new and retrofitted high-performance commercial and institutional buildings. In most commercial and high-rise residential buildings where reducing the costs of cooling energy is important, STPV windows can be used as integrated strategy to reduce solar heat gains and generate solar electricity while still providing adequate daylight and view to the outdoors. The research presented on this thesis is based on the conviction that window technologies should be considered as an integral part of a broad strategy of energy-conserving, energy-efficient building design. The main objective of this work is to provide a systematic study of STPV windows through experimental work and simulations that will allow these technologies to become ubiquitous on buildings in the near future. The end goal is to transform buildings from energy consumers to energy producers without compromising on occupancy comfort. Hence, all performance characteristics (e.g., electrical, thermal and daylighting) should be studied and quantified individually and in combination in order to capture the impact such technologies have on the building energy performance and occupancy comfort. In this work, design concepts of windows integrating STPV technologies are developed, modelled and studied in typical perimeter zones. The thermal and electrical performance of four crystalline Si-based prototype STPV windows was studied experimentally. Specially designed prototypes were mounted in a calibrated hot-box calorimeter apparatus developed for this study. The apparatus is placed inside a two-storey high environmental chamber with a solar simulator (SSEC) and exposed to emulated sunlight produced by a continuous solar simulator. The SSEC facility allows tests to be performed under fully controlled and repeatable conditions (temperature and irradiance). Operating cell temperatures of up to 80.5°C were observed under 1000 W/sq.m irradiation, still air and ambient air temperature of 21°C. An experimental procedure for the determination of Solar Heat Gain Coefficient (SHGC) for STPV windows is also developed. It was found that the electricity generation from the STPV windows can result in up to 23% reduction of SHGC in comparison to a heat absorbing (e.g., tinted or fritted glass) window with the same optical and thermal properties. In addition, the performance data generated was used to verify thermal-electrical performance models for the prediction of cell operating temperatures and solar energy yield. Low-order thermal models for various STPV window assemblies were developed. Using typical meteorological weather data as inputs, the thermal models could predict the operating cell temperatures of an assembly (e.g., double glazed low-e argon window with integrated photovoltaics) within +/- 5°C, resulting in less than +/- 3% error in the annual solar energy yield. A general simulation methodology was developed integrating thermal, electrical and daylighting performance modelling. The methodology was applied to evaluate the potential benefits of various STPV façade designs in cooling-dominated commercial building applications under continental climate. The simulations revealed that the selection of the ideal STPV optical properties is sensitive on the daylight and lighting controls applied in the building, and photovoltaic cell technology utilized (crystalline Si-based spaced cells, a-Si “see-through” and fully transparent organic thin film technologies were examined). In regards to design of a building façade, it was shown that the three-section design concept integrating Si-based spaced PV cells on the upper section of the façade (daylight section) and “see-through” thin PV film on the middle section (view section) has the potential to maximize daylight utilization and view to the outdoors while minimizing the possibility for glare to occur and producing an optimal amount of solar electricity