Investigation of decoupling of thermal and electrical performance of semi-transparent photovoltaic windows based on the external quantum efficiency

•Thermoelectric decoupling method using EQE was proposed for PV window in MPP state.•The absorptance of PV laminate is split into thermal and electrical components.•The difference of energy use of air-conditioning exceeds 19% between the OC and MPP states.•The difference of SHGC at different operating states increases with coverage ratio increasing.•The decoupling calculation is essential for PV windows with a high coverage ratio. Semi-transparent photovoltaic (STPV) windows have great potential in buildings energy saving due to their power generation and reduction of buildings energy consumption. STPV windows have a complex optical-thermal-electrical coupling mechanism. However, previous studies have rarely considered the coupling mechanism when simulating the thermal and electrical performance of STPV windows, which has resulted in the power generation being incorrectly treated as waste heat. As has been mentioned in EN 50583:2016 and IEC 63092:2020, the calculation of thermal performance of STPV windows should consider the mechanism that part of absorbed solar energy is transformed into electricity rather than heat. With considering the mechanism, based on the external quantum efficiency (EQE) of solar cells, a decoupled optical, thermal, and electrical performance simulation method for STPV windows was proposed in this study. Firstly, the optical characteristics of STPV windows and the EQE of the integrated solar cells were measured by a spectrophotometer and a monochromatic incident photon-to-electron conversion efficiency (IPCE) testing device, respectively. The EQE was used to calculate the spectral photoelectric conversion efficiency (SPCE) of STPV windows. Then, the SPCE was subtracted from the original absorptance and added to the front reflectance at corresponding wavelength, thereby decoupling the thermal and electrical performance. To verify the importance of the decoupling, the thermal and electrical performance of STPV windows with and without decoupling were investigated using EnergyPlus and WINDOW programs. An outdoor experimental rig was used to validate the simulation results of EnergyPlus, it was found that the decoupled results match well with experimental results. The simulation results show that in the coupled case, the window temperature and cooling load were overestimated, while the heating load was underestimated. However, the impact on power generation was negligible due to the low temperature coefficient of efficiency. Besides,