Determination of Solar Heat Gain Coefficients for Semitransparent Photovoltaic Windows: An Experimental Study

Semitransparent photovoltaic (STPV) windows integrate transparent photovoltaic film technologies or spaced opaque solar cells on the exterior glass layer. As these technologies are developed and eventually adopted in the building and window industry, the evaluation of key performance parameters such as the solar heat gain coefficient (SHGC), thermal conductance (U-factor), and electrical power output is required. These performance parameters are interdependent and they have a direct impact on the building cooling, heating, electric lighting loads, solar electricity generation, and occupancy comfort. Thus, STPV windows should be treated as integrated photovoltaic and fenestration technologies. This study focuses on the experimental determination of the SHGC of STPV windows under maximum power point operation, using an indoor solar simulator and calorimeter facility. The objective of this work is to provide input on the development of an experimental procedure suited to the determination of the SHGC of STPV windows. The results indicate that when the solar electricity generation of the STPV window is taken into account by operating the STPV windows at the maximum power point rather than open circuit conditions, the SHGC is reduced between 2% (for a STPV window with visible transmittance of 40% and nominal conversion efficiency of 7%) and 23% (for a STPV window with visible transmittance of 6% and nominal conversion efficiency of 15%). The reduction is expected to be even higher in a STPV window with no low-e coating due to significant increase of the inward-flowing absorbed solar energy.