In recent years, a substantial progress in improving the efficiency and reducing the cost of photovoltaic (PV) modules has been made. A new generation of thin-film CIGS (copper indium gallium selenide) PV cells reaches up to 20% efficiency and can be mass-produced cost effectively. Due to the low weight, its thinness and the possibility to adapt to non-standard shapes, thin-film CIGS PV modules offer new opportunities for building integrated photovoltaics (BiPV). A key challenge for the successful application of PV modules in a building context is the occurrence of partial shading of PV cells that strongly influences efficiency and may cause overheating, and thus highly constrains design options. The electrical performance of individual CIGS modules and array configurations in partial shading were investigated in collaboration with Flisom AG. A high-resolution electrical model of CIGS modules and arrays, which captures the effects of non-uniform irradiance in partial shading of CIGS modules and array was developed and successfully calibrated using empirical data. Coupling the electrical model of thin-film CIGS modules with precise information of the expected shading pattern and solar irradiance allows calculation of electrical energy yield of complex BiPV systems, such as dynamic PV shading modules.
The Adaptive Solar Facade (ASF) is a modular facade system of dynamic shading elements for daylight control and PV electricity production. A prototype consisting of 50 modules has been installed at the ETH House of Natural Resources (HoNR) in 2015; the actuation is based on novel soft pneumatic actuators. Another experimental prototype of the ASF consisting of approximately 20 photovoltaic shading modules produced by Flisom AG is continuously tested on the rooftop of the HPZ building at ETH Hönggerberg. The pneumatic actuators achieve high-range, reproducibility and can be used for adaptive shading and two-axis solar tracking. A similar ASF design will be implemented at the NEST HiLo building at EMPA and is currently in construction.
The early ASF prototype at the ETH HoNR allowed for continuous outdoor stability testing and gathering user feedback. Outdoor wind tests show that the ASF can withstand very strong wind conditions. A questionnaire with office occupants revealed that the ASF is appreciated as an active shading element in summer. The interaction with occupants also helped to improve the design, e.g. a less constrained view by full integration of all PV cables and electronics within structural parts. In addition, the default position of the PV panels is more open and improves daylighting. In solar tracking experiments, precise control of the PV modules in solar altitude and azimuth was achieved and the electricity yield in solar tracking against a reference position was measured.
For more details, please contact Prof. Arno Schlüter, ETH Zurich.