Investigation on the energy performance of a novel semi-transparent BIPV system integrated with vacuum glazing

The development of vacuum glazed windows in recent decades has provided a foreseeable energy saving opportunity in the design of low-energy consumption buildings and the application of building integrated photovoltaic (BIPV) has experienced rapid development for application in buildings. This paper reports our investigations on the combinations of the vacuum glazing and BIPV integration. Semi-transparent photovoltaic windows can convert solar energy into electricity, but most of absorbed solar heat is transferred into indoor environment which becomes additional cooling load. The proposed vacuum photovoltaic insulated glass unit (VPV IGU) in this paper combines vacuum glazing and solar photovoltaic technologies, which can utilize solar energy and reduce cooling load of buildings at the same time. Various experiments were conducted to evaluate the thermal performance and determine the key characteristics of the VPV IGU in this study. It was found that the VPV IGU can achieve very low total heat gain coefficient (U-value) of around 1.5 W/(m(2) K) and block most of undesired solar radiation from penetrating through the window. Compared with a common double-pane glass sheet, the vacuum PV glazing can maintain the indoor environment at a relatively low temperature due to its excellent thermal insulation performance in summer. A detailed simulation study has been conducted by EnergyPlus and Berkeley Lab WINDOW. The simulation work has indicated that the cooling load can be reduced by 14.2% by a south-oriented VPV IGU compared with common glazing products while power generation is not compromised compared with normal BIPV systems. The results show that the application of the VPV IGU has a huge energy saving potential and can minimize the drawback of common PV insulating glass units.