Solar cell efficiency decreases as its temperature increases. Therefore, it is necessary to design a thermally optimal solar
cell carrier that will maintain a minimal solar cell temperature. To achieve this optimal solar cell carrier design, a finite-element
analysis model of the solar cell on carrier was developed. This numerical model was experimentally calibrated
against a known design, in which the average solar cell temperature was determined by examining the shift in the open
circuit voltage. This allowed us to explore the relationship between the carrier geometry and the average solar cell
temperature. That is, the solar cell carrier is characterized by two independent thermal resistances: the uniform flow
thermal resistance, and the thermal spreading resistance. As the copper thickness was increased, the uniform flow
resistance acted to raise the cell temperature while the spreading thermal resistance decreased the cell temperature.
Therefore, when the carrier geometry minimized the thermal resistances, it was found that the minimum solar cell
temperature was achieved at a copper thickness between 1.5 and 3 mm depending on the surface area of the carrier. This
optimized carrier design reduced the average solar cell temperature by 16 °C, which corresponds to an increase of 0.8%
in cell efficiency at 1666 suns as compared to the original design used to experimentally calibrate the numerical model.
KEYWORDS: Solar cells, Receivers, Sun, Solar concentrators, Multijunction solar cells, Calibration, Temperature metrology, Computer simulations, Copper, Device simulation
The thermal performances of multi-junction solar cells, mounted on receivers, are studied to determine the change in
device efficiency with respect to sunlight concentration under continuous illumination. Experimental characterization of
the device was performed by measuring the solar cell current-voltage curve using both flash and continuous-illumination
solar simulators. We are able to extract the change in efficiency and open circuit voltage with respect to the change in
concentration from experiments with respect to the application of thermal paste between the receiver and the heat
exchange. We show the efficiency linearly decrease at a rate of -0.0094%/°C (no paste) and -0.0043%/°C (paste). We
used the calibrated numerical model to determine the solar cell temperature and incorporate the corresponding efficiency
when scaled up to 2000 sun concentrations under continuous illumination.
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