Potentials and Limitations of Concentrator Silicon Solar Cells Energy Utilization

Abstract

The maximum allowable concentration ratio of the silicon-based solar cells and their potential for thermal utilization applications are investigated. A three-dimensional thermal-fluid model is developed for silicon-based concentrator photovoltaics integrated with a generic heat sink. The generic heat sink is characterized by the heat transfer coefficient, resembling different scenarios of thermal management, and the heat sink temperature to reveal the potential of the CPV to provide high exergetic thermal energy. Under each combination, a wide range of concentration ratios are tested to obtain the performance characteristic maps of the solar cell, which assure the safe operation of the cell under 85°C (as recommended by manufacturers). The highest concentration ratio for the presented cell is ∼25 when the intensive cooling is applied at a heat transfer coefficient ranging from 104 – 105W/m2K under average heat sink temperature (i.e., 31°C) near the ambient one (i.e., 30°C). In addition, raising the heat sink temperature (e.g., 50°C) for thermal utilization reduces the maximum allowable concentration ratio (e.g., ∼17). Although the thermal utilization intuitively holds a higher potential at a high concentration ratio, the reverse is recommended for the solar cell when the safe operation is considered. This is attributed to the necessity of sufficiently reducing the temperature of the heat sink to draw the massive heat flux at a high concentration through the predefined solar cell thermal resistance. Consequently, low-quality thermal energy is extracted as indicated by thermal exergy efficiency. To conclude, if the objective of the CPV system is only power, working at a high concentration is recommended with a heat sink having a high heat transfer coefficient and working at a temperature nearly equal to the ambient temperature. On the other hand, if combined heat and power are intended, increasing the heat sink temperature to the target application is obtained at the cost of reducing the maximum allowable concentration ratio.