SUMMARY 



PROBLEM 



The U. S. Navy utilizes bottom-mounted, tethered, and floating self-contained elec- 

 tronic devices for detection, measurement, and recording of oceanographic, ocean surveillance, 

 and antisubmarine warfare data. The operational life of these devices is in most cases limited 

 by the storage capacity of electrochemical batteries which supply power for operation of 

 electronic components. Any economical means to extend the operational life of these devices 

 would make their operation significantly more cost effective. 



APPROACH 



Photovoltaic cells were selected as a possible source of power for trickle charging of 

 batteries aboard submerged devices containing electronic instruments. Although it is known 

 that sunlight intensity rapidly decreases with depth, it was hoped that there would be adequate 

 illumination on photovoltaic cells below the water surface to generate sufficient power for 

 trickle charging of batteries. 



The evaluation of solar (photovoltaic power) cells for undersea power applications 

 was conducted by submerging two solar cell panels to different depths and measuring the 

 power output caused by downwelling and upwelling solar irradiance. To establish the lower 

 and upper limits of solar cell performance, tests were conducted in waters whose visibility 

 varied from excellent to poor. 



RESULTS 



The power output of solar cells decreased rapidly with depth and water transparency. 

 Experimental data indicate, however, that sufficient power density is generated by solar cells 

 from the air-sea interface to the visual contrast limit depth (Secchi depth) to be of practical 

 value to the designer of power supplies for submerged electronic devices. The power density 

 of silicon solar cell panels was found to vary in this depth range from 1 2 W/ft^ at the surface 

 to 1 W/ft^ at the visual contrast limit depth under standard 100-mW/cm^ sun insolation intensity. 



RECOMMENDATION 



Solar cells should be seriously considered as power supplies for electronic devices 

 operating in the ocean between the air-sea interface and the visual contrast limit depth. In 

 the open ocean, the lower limit of this depth range varies from 20 to 100 ft, depending on 

 location and time of the year. 



