Visual impact assessment of BIPV in building retrofits using saliency models

Limited fossil energy resources and the potential danger of nuclear power plants led to growing popularity of solar energy. In Switzerland, Building Integrated Photovoltaic (BIPV) is expected to be responsible for up to quarter of the energy production from renewable resources by the time of 2035. In order to protect the existing natural landscape, BIPV must be concentrated in urban spaces, which means that certain amount of existing building envelopes have to be turned into energy generators. There is a growing concern about BIPV retrofits because they may change the visual appearance of the existing city images to a large extend and/or in a negative way. In order to manage the potential visual impact resulting from BIPV expansion in urban spaces, evaluation methods should be able to measure it appropriately. Existing evaluation methods show insufficiencies for this purpose: either they cannot guarantee objectivity and continuity of evaluation standards throughout assessments of different BIPV projects, because their qualitative criteria are vulnerable to subjective preferences; or they only use formal design parameters to evaluate the visual integration quality of BIPV and therefore lack neuroscientific base. In order to tackle these insufficiencies, an objective evaluation method is proposed that is capable of measuring the BIPV visual impact in building retrofits in a quantified approach based on neuroscience knowledge. The assessment should be made in concept phase of the project, so as to identify the BIPV designs that have the least negative visual impact. The proposed evaluation method integrates saliency model, which imitates the mechanism of human visual attention, into assessment procedures. First, the probability of a BIPV installation attracting human visual attention in the respective visual scene is calculated quantitatively with the saliency model. Then the modifications of saliency values in this very visual scene before and after the BIPV retrofit are assessed. In the end, the modifications of saliency values are transformed into BIPV visual impact and objectively expressed as single values. The analyses are based on renderings generated from RADIANCE and programming in MATLAB. This method is demonstrated with a small case study that simultaneously serves as proof-of-concept. The proposed evaluation method is applied on a realistic case study: BIPV designs for a church roof. In total, 5 designs were developed with variations in BIPV installation location, roof coverage percentage, module size, PV material und design approach. The lowest visual impact value was induced by the BIPV design with the most careful and considerate integration approach, the design with the boldest integration approach obtained the highest visual impact value. The evaluation method proved to be feasible to a large extend. It is believed that the synergy between architecture and neuroscience can contribute to a growing understanding of human responses to the built environment. Hopefully the findings from this thesis can help in minimizing the negative visual impact induced by BIPV expansion in urban spaces, and also aid architects in gaining new understandings for visual aspects in architecture design.