Understanding the Behaviour of Building Integrated Photovoltaic Facades. Numerical and Experimental Analysis

Climate research has shown that anthropogenic CO2 emissions are the primary cause of global warming. The higher global temperatures associated with global warming are disrupting local climates and ecosystems in a catastrophic manner. In order to limit global warming, a deep transformation of all human systems is imperative. Among others, an unprecedented increase in the use of renewable energy sources is necessary to achieve a climate-neutral society. Photovoltaic systems have been proven a suitable renewable energy source at both utility and distributed scales. A promising decentralised photovoltaic application is the concept of building-integrated photovoltaic (BIPV) facades. The assessment of BIPV facades is challenging due to their multi-physics and multi-scale nature. BIPV facades require the integration of both photovoltaic and building physics at different spatial scales: multiple photovoltaic cells compose a BIPV module; multiple BIPV modules compose a BIPV facade; a BIPV facade is part of a building, which in turn is part of a larger built environment. From this multi-physics and multi-scale perspective, one particular aspect in the assessment of BIPV facades that deserves further attention is the representation of thermal and airflow phenomena, including cavity ventilation and wind effects. Moreover, the current BIPV research is scattered across photovoltaic and building physics literature. Photovoltaic research tends to focus on energy conversion aspects, while building physics research tends to focus on thermal, airflow and building-related aspects. As a result, simulation tools and specific guidelines for the assessment of BIPV facades are still scarce. This doctoral research has the following four main objectives: (1) understand and describe the multi-physics and multi-scale behaviour of BIPV facades, integrating both photovoltaic and building physics perspectives; (2) quantify the influence of wind effects on the BIPV performance and improve the prediction of wind effects in the assessment of BIPV facades; (3) better understand natural cavity ventilation in BIPV facades; (4) provide recommendations for the assessment and design of building integrated photovoltaic facades. In order to achieve these goals, this work makes extensive use of numerical and experimental methods, including field data analysis. This dissertation provides a set of tools and frameworks for the assessment of BIPV facades. The dissertation starts with the development of multi-physics BIPV models with varying degrees of complexity. The models are compared against each other and against experimental data. Next, a probabilistic sensitivity analysis is performed to identify key parameters influencing the BIPV performance. Two key parameters are identified and investigated in depth: exterior convective heat transfer and cavity ventilation. Then, insights into the real performance of BIPV facades are obtained from an extensive analysis of field data. In addition, simplified empirical temperature correlations are derived from the field data, which are useful for the fast assessment of BIPV facades. Additional simulations provide information about the performance of BIPV facades for different locations around the world with diverse climatic conditions. Finally, the findings of this work are distilled into general recommendations for the assessment and design of BIPV facades. The experience with experimental BIPV setups and field data analysis is also translated into practical recommendations for the design of experimental BIPV setups.

Publication year:2021

Accessibility:Open