A, nn 



Figure 4. Typical spectral response of low-light-level, terrestrial, silicon solar 

 cells fabricated by Solarex Corporation. 



SOLAR CELL ARRAYS 



Because the power output of a single solar cell is generally not adequate for its 

 intended application, an array of cells must be employed. The leads from the cells may be 

 connected in series or in parallel, depending on the total voltage required. The desired 

 voltage may be also attained by incorporating one of the following: ( 1 ) an oscillator circuit 

 for converting the low-voltage, direct-current (DC) output of the cells into a low-voltage, 

 alternating current (AC), (2) a transformer which raises available AC voltage to any desired 

 value, and (3) a rectifier which converts the AC output of the transformer into DC at the 

 same voltage as the AC output of the transformer. 



The major shortcoming of connecting cells in series is that for optimization of the 

 power output all cells must have identical electrical performance characteristics and be illu- 

 minated with light of the same intensity. In outer space or in fixed terrestrial applications, 

 this poses no problem as the sunlight illuminating an array at any given instant is generally 

 the same intensity for all cells. However, this is not valid in nonfixed terrestrial applications, 

 for example, cells mounted on the top and sides of a portable radio housing. Here the intensity 

 of illumination may vary substantially from one cell to another, depending on its location 

 and the orientation of the radio housing to the sun. 



When the illumination of cells connected in series is nonuniform, the power output 

 of the series-connected solar cell array decreases out of proportion to the loss of illumination 



