Reduction of Data. Prior to plotting of VI data and calculation of power output, the 

 current readings were standardized at a 80-mW/cm insolation level. In this manner, variations 

 between plotted VI and W curves reflected only differences in optical quality of water and 

 not small variations in insolation of the water surface. Two types of graphs were generated: 

 potential as a function of current (VI) and power output as a function of potential (WV) 

 measured at the end of 200-ft-long pigtails. On the basis of these families of plots, a designer 

 can estimate the size of a submerged solar cell array* needed to power electronic instrumen- 

 tation with known power and potential requirements. 



Test Findings. The electrical performance of upward-facing, horizontally positioned 

 solar cells decreases rapidly with depth after the first 0.25 in (6 mm) of submersion. Under 

 ideal underwater visibility conditions, represented by water with visibility in the 95-ft range 

 (29 m), approximately 40 percent of potential power output is lost in the first 1 ft (0.3 m) 

 of submersion (figures 15 and 16). With greater submersion the rate of performance deterio- 

 ration decreases, but even under ideal water clarity conditions the loss amounts to approximately 

 95 percent at 95 ft (29 m) and 98 percent at 200 ft (61 m). In water with visibilities of 16.5, 

 8, and 2.5 ft, 95 percent of potential power output loss occurs at approximately 16.5-, 8- and 

 2.5-ft depths (5, 2.4, and 0.75 m), respectively (figures 17 through 22). 



The electrical power output of submerged, downward-facing, horizontally positioned 

 solar cells equals approximately 1- to 3-percent power output of upward-facing cells at the 

 same depth (figure 23). The power output of submerged vertically positioned cells depends 

 markedly on their orientation with respect to the sun. Cells facing the sun generate power 

 which approaches the 30-percent level of upward-facing cells with horizontal position at noon 

 and the 70-percent level during early and late hours of the day (figures 24 and 25). Cells 

 facing away from the sun produce power which approaches 5 percent of upward-facing cells 

 with horizontal position. The output of vertically positioned cells that do not face the sun 

 directly falls between the two above mentioned limits. 



The performance characteristics of the selected solar cells must match those used in Solarex high-density 

 test panels 100177 and 100178. 



22 



