BAPV modules: Installed-NOCT and temperature coefficients after 1-year exposure

Building applied photovoltaics (BAPV) is one of the major applications for photovoltaic (PV) modules. The performance of PV modules is heavily influenced by their operating temperature; for example, the power of crystalline silicon drops at a rate of about 0.5%/°C. The operating temperature is primarily dictated by three major parameters: ambient temperature, irradiance and wind speed. The magnitude of the influence of these parameters depends on the type of installation: open-rack or building-applied. Recognizing these issues, the design qualification standard of PV modules, IEC 61215, requires reporting NOCT (nominal operating cell temperature) values for the open-rack but not for the BAPV modules. This paper deals with the NOCT determination of BAPV modules, herein called installed-NOCT (INOCT). The effect of air gap (between module and rooftop) on INOCT values is also quantitatively determined in this work. The INOCT values determined for different air gaps (0, 1, 2, 3 and 4-inch) using the conventional thermal model of IEC 61215 are also compared with the values determined using the BAPV thermal model previously developed by Arizona State University. Furthermore, it is commonly assumed that the temperature coefficients of PV modules do not change over time in the field and all the energy yield calculations are performed based on the temperature coefficients of fresh modules. This work investigates if this assumption is accurate or not, through the determination of temperature coefficients of 14 modules before and after 1-year of rooftop exposure.