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Nowadays, the most recent optical configuration based on Cassegrain and Fresnel lens designs of concentrator photovoltaic(CPV) has shown a race to achieve the ultrahigh concentration ratio. Still, none of those has experimentally shown an optical concentration ratio (GC) beyond 2000 suns. This is because their energy concentration ratios are challenged by the excessive temperature raised throughout the optical stages, which diminishes the efficiency of the solar cell. In this context, this research work aims to numerically investigate a microscale pin-fins heat sink configuration to enhance the thermal performance and the cost-competitivity of ultrahigh CPV thermal receiver. The impacts of the solar cell area, cell efficiency, and heat sink's material have been analyzed and discussed. The results showed that a circular pin-fins heat sink could accomplish a drop of 23.28% in the maximum operating cell temperature at 10 000 suns for cell area of 1 × 1 mm 2 relatively compared to the conventional flat-plate heat sink. Furthermore, for a circular pin-fins heat sink with a cell area of 2 × 2 mm 2 , the cell temperature started exceeding the safe operating range of temperature (80 C) at 8000 suns with an average temperature of 96.1 C and reaching a maximum of 113.91 C at 10 000 suns. A gradient temperature on the planar direction of the aluminum circular pin-fins heat sink was about 1.187 C at 10 000 suns whereas 0.703 C was recorded in the case of a copper circular pin-fins heat sink. The circular pin-fins heat sink showed the highest thermal performance resulting in maintaining the solar cell temperature within its safe operating range even beyond 10 000 suns. From an economic point of view, aluminum circular pin-fins heat sink has been found to be less costly than the copper one. Finally, it was found that at 8000 suns, the flat-plate heat sink cost is more expensive than the traditional pin-fins heat sink by 14.7%, where the flat-plate heat sink becomes the worst economic configuration at 10 000 suns. At that concentration ratio, the cost has increased by 43.38%, 5.75%, and 10.61% compared to the traditional pin-fins heat sink, cylindrical pin-fins heat sink, and circular pin-fins heat sink, respectively.

The present work is carrying out the performance of an actively cooled Fresnel-based single-cell ultra-high concentration photovoltaic/thermal (UHCPV/T) system under concentration ratios (CR)s ranged between 500Â and 2500Â. Four cooling finned heat sink designs have been studied, that is, the in-line cylindrical pin fins (ICY), staggered cylindrical pin fins (SCY), inline conical pin fins (ICO), and staggered conical pin fins (SCO). The analysis was performed to study and optimize the maximum operating MJSC temperature, coolant flow outlet temperature, pressure drop across, and the thermal, electrical, and overall efficiency enhancement of the whole Fresnel-based UHCVP/T system. The numerical model has been first validated and then used to simulate the impact of the concentration ratio and Reynolds number on the limitations and records of each cooling finned design of the UHCPV/T. It was found that even though the aluminum-based-ICO pin fins heat sink can achieve the optimum overall efficiency of 80.20% under 2000Â and Re of 428; yet the aluminum-based ICY is the most appropriate pin-fins heat sink design for desalination purposes since it corresponds to the highest water outlet temperature of 66.16 C with a second-ranked overall efficiency of 72.5% under the same operating conditions.cooling microchannel, overall efficiency, pin-fins heat sinks, ultra-high concentration ratio | INTRODUCTIONConcentrating the incoming light on a small surface of high-efficiency multijunction solar cell (MJSC) can be seen as a bright energy source to generate more costeffective electricity. Recently, most of the efficiency records have been reached with the concentration photovoltaics (CPV) technology. 1 It is an advanced technology for increasing PV systems' utilization and deployment. To increase the efficiency of the MJSC with the growing intensity of the system's power at ultra-high

Summary The cogenerated energy from the densely packed ultrahigh concentration photovoltaic thermal systems (UHCPV/T) can not only promote higher exergetic efficiency but also enable the usability of the collected thermal energy for potential desalination purposes. In the present study, three finned heat sink designs of UHCPV/T have been proposed toward maximum collected thermal power and minimum required pumping power. A conjugate heat transfer model has been developed and validated to simulate the different designs under various operating conditions. The cooling setups are based on copper millimeter‐scale finned heat sinks immersed in fully developed laminar flow in a rectangular microchannel. It was found that the configuration from the more efficient heat sink design to the poorest thermal one is the rectangular fins (RFs), elliptical fins (EFs), diamond pin‐fins (DPFs), and then traditional round pin‐fins (TRPFs) heat sink. The RF heat sink has demonstrated the best thermal performance with a maximum multi‐junction solar cell (MJSC) temperature of 81.4°C and water temperature increase of 14.21°C under ×1200 and water inlet velocity of 0.02 m/s. Despite the RF heat sink has recorded the highest values of pressure drop and required pumping power equal to 78.74 Pa and 570.7 mW, respectively, it was selected as the optimal heat sink design, ensuring the highest net electrical output power and thermal collected power.