Study On The Overall Energy Performance And Structure Optimization Of Amorphous Silicon Photovoltaic Windows With Various Transmittances

Semi-transparent amorphous silicon photovoltaic(a-Si PV)windows can block and absorb a part of solar radiation,which can not only reduce the cooling load caused by solar heat gain passively,but also avoid the indoor daylighting glare effectively.In addition,a-Si PV windows can convert solar energy into electricity through the photovoltaic effect so as to reduce solar heat gain actively.The electricity generated by PV panels can be consumed to compensate the indoor air-conditioning and lighting energy use as well.However,there are many problems regarding the design and utilization of a-Si PV windows need to be solved.The transmittances of semi-transparent a-Si PV windows would affect its photoelectric conversion efficiency,indoor daylight performance and solar heat gain,which can affect the lighting and air-conditioning energy consumptions.Moreover,for the common ventilated a-Si PV window,its energy conservation is related to the structural parameters and ventilation modes of itself.Therefore,in order to determine the optimal visible light transmittance,structure parameters and ventilation strategy of a-Si PV windows,a ventilated a-Si PV window and a hollow a-Si PV window were employed to investigate the overall energy performance in this study.A method for determining the power generation characteristics of a-Si PV modules with different transmittances was proposed firstly for the Sandia Array Performance Model(SAPM).An integrated model of heat transfer,daylighting and power generation of a-Si PV windows was developed in EnergyPlus and then validated by experiment data.Furthermore,the validated model was used to study the overall energy performance and energy saving potential of a-Si PV window under different climatic zones.The indoor static and annual dynamic daylight performance of a hollow a-Si PV window were simulated utilizing the building light environmental simulation tool — DIVA-for-Rhino.The daylight performance of an a-Si PV window and an ordinary double-glazed window were compared afterwards.Further,the overall energy performance of a-Si PV windows with various air gap depths was calculated based on Airflow Network Model in EnergyPlus.Then the optimal air gap depth and ventilation strategy for ventilated a-Si PV windows were studied.Finally,From the perspectives of overall energy performance and visual comfort,the comprehensive optimum design and energy-saving potential analysis of the a-Si PV window with different transmittances were investigated.The significant conclusions from this study are summarized as follows:(1)Considering the minimum energy consumption of buildings,the optimal transmittances of a-Si PV windows for Guangzhou,Kunming,Changsha,Beijing and Harbin are 0.22~0.25,0.25,0.25~0.3,0.25~0.3 and 0.35,respectively.For severe cold regions such as Harbin,we hope more solar radiation enters in the room through the window to reduce the heating energy consumption,thus the a-Si PV modules with higher transmittance should be adopted.For hot-summer and warm-winter regions such as Guangzhou,we hope less solar radiation enters in the room through the window,so the a-Si PV modules with lower transmittance would be a good choice.For the others regions of China,the optimal range of transmittances for a-Si PV modules are 20%~30% for the purpose of energy conservation.(2)Considering the daylighting performance and visual confort,the optimal transmittances of a-Si PV windows in Guangzhou,Kunming,Changsha,Beijing and Harbin are 0.4~0.5,0.3,0.4~0.6,0.22 and 0.22,respectively.For regions with higher latitudes such as Harbin and Beijing,due to their lower solar altitude,it is hoped to utilize the a-Si PV thin film modules with lower transmittance to reduce glare.For regions with lower latitudes such as Guangzhou,due to its higher solar altitude angle,the a-Si PV modules with higher transmittance would be a good choice to achieve the optimum illuminance.(3)The cooling energy consumption of the natural ventilation mode in Changsha is the least compared with other ventilation modes,while the heating energy consumption of the non-ventilation mode with the all louvers closed is the least.The mode that minimizes the total energy consumption of air-conditioning is still the natural ventilation mode.Taking into account the seasonal factors,the natural ventilation mode in summer for the purpose of heat dissipation and the no-ventilation mode for the purpose of thermal insulation could be adopted.In transition season,the buoyancy-driven ventilation mode would be a good choice for the ventilated double-skin PV window.The results of this study can be used as a guidance for the design and utilization of semi-transparent a-Si PV windows in different climatic regions in China.