| Summary: | This study was performed in outdoor conditions to quantify the level of influence on the electrical performance of the Multi-junction (MJ) solar cells. It was discovered that non-uniform illumination on the solar cell could reduce the MJ electrical output by more than 40%. Also, the irradiation uniformity was improved by applying several methods; increasing the distance between the concentrator and the receiver (l) and introducing a secondary optical element (SOE) on the receiver. The outdoor measurement also revealed that the electrical efficiency of the solar cell increased from around 22% to 37% with an increment of 68%, due to improvement of irradiation uniformity. However, the optical efficiency substantially fell when increasing the distance (l). To address this issue, a 0.06 m high SOE having a surface reflectivity of 90% above the PV assembly was implemented to enhance the irradiation uniformity and to minimise the dramatic decline in optical efficiency. The hot spot initiated by non-uniform illumination was also examined in outdoor conditions by measuring the temperature at the centre and both sides of the PV cell. Accordingly, a variance of about 13 K was observed between the centre and both sides (0.005 m distance) of the PV cell’s surface area, which was further reduced to 1 K after improving the illumination uniformity.
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