Coupling ventilated semi-transparent photovoltaic windows with air-conditioning systems: electrical, thermal, and daylight performance across diverse cooling-season climates in China for varying window-to-wall ratios

Building-integrated photovoltaic (BIPV) technology offers a promising solution for combining electricity generation with architectural functionality. Building on a previous study that introduced an innovative semi-transparent photovoltaic window (STPV-W) system integrated with an air-conditioning system, this research quantitatively evaluates its energy and daylighting performance under varying window-to-wall ratios (WWRs) across five representative cooling-season climates in China: Beijing, Hefei, Guangzhou, Haikou, and Urumqi. Electrical and thermal performance was simulated using energy balance equations in a Matlab environment, while daylighting performance was analyzed through DesignBuilder software to assess natural light distribution and artificial lighting demand. Results show that increasing the WWR significantly boosts summer electricity generation, with Beijing achieving the highest output (676.18 kWh at 100 % WWR). Heat recovery performance improves sharply up to 60 % WWR but shows diminishing returns beyond 80 %. Cooling energy consumption decreases with WWR increases up to 80 % but rises slightly at higher WWRs. Daylighting analysis reveals glare-free performance at WWR ≤40 %, while higher WWRs lead to perceivable glare in most cities. Overall, increasing the WWR reduces net energy consumption by 62.22 %–68.11 % across the cities, with greater savings in higher-latitude regions. These findings offer valuable insights for optimizing coupled STPV window and air-conditioning system designs to achieve energy-efficient buildings across diverse climates.