The importance of total hemispherical emittance in evaluating performance of building-integrated silicon and perovskite solar cells in insulated glazings

Temperature control in solar cells is important as elevated temperature adversely affects performance and lifetime. In building-integrated photovoltaics (BIPV), the overall energy management of an installation must include not only the electrical output from the photovoltaic component but also the net light and heat flows as well as the temperature distributions. As the light reflectance and emittance of solar cells are strongly angle dependent, total thermal hemispherical emittance should be used instead of normal spectral emittance for accurate calculation of radiative heat transfers and hence solar cell operating temperature. Here we report the analysis of solar cell and internal glass temperature as a function of the measured total hemispherical emittance for the first time. We present a comprehensive model using total hemispherical emittance for determining solar cell and internal glass surface temperatures for insulating and laminated glazing units incorporating an operating photovoltaic cell. In warm weather (30 degrees C outdoors), solar cell and internal glass temperatures are 45-55 degrees C in laminated glass while in an insulated glazing the solar cell temperature is 60-75 degrees C and the internal glass temperature is maintained close to ambient temperature (20 degrees C indoors). We show that the solar cell front and rear emittance, location, and encapsulation method as well as the type of glazing system impact on the solar cell performance and internal glass temperatures. This study provides recommendations for designing BIPV glazing systems that minimize power loss from the solar cells while optimizing transmitted heat and shows the importance of engineering the correct front and rear solar cell emittances. [GRAPHICS] .