Building form optimization for renewable energy-economic utility of flexible solar cells as building integrated photovoltaics

Buildings are responsible for considerable amounts of global energy consumption, and promoting renewable energy in buildings is conducive to sustainable development of modern society. In this paper, flexible solar cells (FSCs) were proposed to be used as building integrated photovoltaics (BIPVs) on free-form building surfaces, and the building form was optimized so that the renewable energy utility (REU) and economic utility (ECU) of FSCs could be enhanced. Both the REU and ECU were characterized by solar radiation calculated from a previously proposed analytical model, and the building geometry was controlled through control node method. A penalty strategy-based constrained differential evolution (PS-CDE) algorithm was developed for building form optimization, which was conducted in four cities at different latitude and climate zones. Results demonstrate that PS-CDE is effective. Both the building forms with maximum REU and minimum ECU show a frustum-of-cone geometry, while those with minimum REU and maximum ECU can be well described with a hyperbolic model. For a given height-radius ratio, the optimal building forms under the same objective are parallel, with the ECU remaining constant and REU proportional to the square of the height ratio. As the height-radius ratio increases, the maximum REU increases linearly, while the maximum ECU decreases in a hyperbolic mode. The optimal building form for REU-ECU trade-off is roughly consistent with that of the dominant objective, suggesting amplitude-variation of REU and ECU across the design domain. Based on the findings, an empirical framework was established for efficient FSC-oriented building form design, which exhibits good robustness (0.2 % ∼ 0.6 % for discretization-related error) and reliability (around 10 % difference in simulation validation). The study is expected to offer a systematic approach for building form design with enhanced performance of the next-generation FSC-based BIPVs.