Process optimization and performance evaluation of back contact integrated cooling devices for CPV cells

Abstract

Despite their high efficiency, concentrator solar cells have one major issue: they produce a significant amount of waste heat. This leads to excessive temperatures inside the cell, which reduces the efficiency of the electrical conversion and shortens the life of the cell. Therefore, efficient cooling solutions are needed. In this paper, a novel approach for the cooling of concentrator solar cells is proposed. Compared to the solutions found in the literature, the proposed solution incorporates microchannels into the backside metal contact layer of the solar cell. This way, there are no restrictions regarding the semiconductor material, no decrease in mechanical stability, and no thermal interface material is required. First, the appropriate channel geometry and theoretical performance were determined for a 2 × 2 cm² solar cell using Siemens FloTherm computational fluid dynamics and an in-house analytical modelling tool written in ANSI C. The paper describes the step-by-step iterations of the design and the manufacturing process that were necessary to reach the theoretically calculated ideal performance. Hydrodynamic and thermal measurements were performed generation by generation, taking into account the results obtained from simulation results. For the latest generation, comparing the hydrodynamic properties at a flow rate of 80 cubic centimeters per minute, the difference between the simulated and the average difference of measured pressure drop values is 2.29 %. The measured data confirms that the partial thermal resistance of the microchannel-based cooling device is 0.32 K/W at a maximum applied pressure drop of 1 bar. This means that the temperature increment for a solar cell with a surface area of 4 cm² exposed to a concentration level of 100 suns is only 11.5 K.