Assessing the energy efficiency and grid friendliness of smart photovoltaic windows incorporating crystalline silicon cells and electrochromic film

Building integrated photovoltaic (BIPV) technology plays an important role in achieving zero-energy buildings. However, their large-scale application poses challenges to the steady operation of the utility grid due to the uncertainty and discontinuity of solar radiation. To address this issue, this study proposed a smart photovoltaic (SPV) window as well as its operation control strategies to simultaneously improve building energy efficiency and grid friendliness. The SPV window combines an electrochromic film and uniformly arranged thin-strip solar cells, which has the dual advantages of active utilization and regulation of solar radiation. To clarify the performance of the SPV window, the model was established in WINDOW based on the measured data, and the corresponding optical and thermal characteristics were calculated. Then, the SPV window model was exported to EnergyPlus software and integrated with a south-facing perimeter zone of a typical medium-sized office building. Two control strategies of the SPV window, viz. the incident solar radiation control strategy and the heat flow density control strategy, were proposed. Finally, the annual dynamic energy consumption simulation, including air conditioning energy consumption, lighting energy usage and photovoltaic power generation, was carried out and compared in four cooling-dominated cities. The results revealed that the SPV window with the solar radiation control strategy performed better in terms of daylight utilization. Nevertheless, when considering comprehensive improvement in useful daylight utilization, peak loads, daily peak-valley difference, and net energy consumption, the SPV window with the heat flow control strategy outperformed the others. Compared to the conventional Low-E window, the SPV window with the heat flow control strategy was able to achieve significant reductions in excessive daylight illuminance ratio, peak loads, average daily peak-valley difference, and net annual energy consumption, ranging from 81.6 % to 93.1 %, 49.3 % to 54.5 %, 54.7 % to 65.8 %, and 49.1 % to 69.2 %, respectively. This study provides a new idea for the application of building integrated photovoltaic technologies, which can simultaneously improve energy efficiency and grid friendliness.