SOLAR CELL PERFORMANCE 



The power output of silicon solar cells varies with their area and with the temperature, 

 intensity, and spectral composition of the light impinging on the light-sensitive surface. The 

 potential of a single cell is independent of its size and remains constant in the 0.45- to 0.5-V 

 range over a wide range of illumination intensities and ambient operating temperatures 

 (figures 2 and 3). However, the amount of current generated by a single cell is directly 

 proportional to the area of the cell and the solar light intensity. Changing the spectral com- 

 position of impinging light will also influence the current output as the quantum yield of 

 solar cells varies with the wavelength of light (figure 4). 



Since the power output (voltage X current) of a single cell is primarily a function of 

 light intensity, steps must be taken to maximize the intensity of light falling upon a solar cell. 

 This is accomplished by minimizing obstructions to sunlight and maximizing its intensity. 

 The first is done by keeping the thickness of the protective cover to a minimum (decreasing 

 transmission losses) and eliminating the air space between the protective cover and the light- 

 sensitive surface of the solar cell (decreasing reflection losses). The second is performed by 

 aligning the light-sensitive surface of the cell at right angles to the rays of the sun and by 

 concentrating sunlight upon the surface of the cell with mirrors or lenses. If sunlight is con- 

 centrated, steps must be taken to keep the solar cell cool to minimize power output loss 

 caused by the increased ambient temperature of the cell. 



- 







— 



T = 70°C 





- 



T = 50°C "~~ 





_ 



T = 25° C -^ 



^PFft 







T = 10°C "^ 



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Figure 2. Effect of ambient cell temperature on 

 the electrical performance of silicon solar cells. 



Figure 3. Effect of insolation intensity on the 

 electrical performance of silicon solar cells. 



