Effect of clearness index on the optimum efficiency of an array of silicon solar cells

We have investigated the effect of clearness index on the optimum efficiency of an array of silicon solar cells. Analysis of data collected from two geographical locations in Nigeria (Port Harcourt, which is on lat 4.43°N and long 7.10°E; and Enugu, which is on lat 6.20°N and long 7.30°E), reveals that the optimum efficiency decreases as the clearness index increases; the rate of decrease being smaller for high values of clearness index than for lower values. This means that the array of cells perform more efficiently under dull weather conditions and less efficiently under clear weather conditions. Temperature fluctuations contribute minimally to the overall changes in efficiency.