Heat transfer modeling of concentrator multijunction solar cell assemblies using finite difference techniques

Information on the temperature of a packaged III-V multijunction solar cell mounted on a heat sink, operating under concentrated light is often not readily available. Availability of such information would facilitate the design of different receiver module configurations in a concentrating photovoltaic system (CPV). To this end, a heat transfer model is developed from finite difference techniques to predict the temperature from various parts of a concentrator cell assembly (CCA). The CCA consists of a solar cell mounted on a direct-bonded copper ceramic substrate with bypass diode. Temperatures of the solar cell with applied conformal coating are modeled as well as the temperature difference, ΔT, between the various layers within the CCA. Isotherm contour plots are generated for the cell under different conditions. It is found that the solar cell temperature in the CCA without conformal coating is 32°C when illuminated at 50 W/cm² with the CCA back surface temperature at 25°C. When the CCA is bonded to a surface with thin bondline of a silicone-based thermal adhesive of 2 W/m K under the same intensity and back surface temperature, the cell rises to 37.3°C. Further, the effects of the thermal adhesive thickness as well as the adhesive thermal conductivity on the solar cell temperature are examined. An effective thermal resistance of the CCA is determined to help in the design of a CPV system. The results from the model are validated against conservation of energy where the heat input from solar radiation on the solar cell is equal to the heat rate by conduction minus the converted electrical power of the cell.