supplied by a horizontally submerged array, it is postulated that in latitudes of 30 to 40 deg 

 the total energy input is represented by normal insolation of 80-mW/cm intensity falling 

 upon an agitated water surface for an average of 4 hr each day. In the tropics (between the 

 Tropics of Cancer and Capricorn) the same intensity of insolation can be considered to act 

 normally to the water surface for an average of about 5 hr per day. At latitudes above 40 

 deg the average daily length is about 3 hr and in the polar region less than 1 hr. 



In practical terms this means that for a horizontal, upward-facing, high-density silicon 

 solar cell array positioned at the visual contrast limit depth, the average daily energy output 

 varies from approximately 0.5 to 2.5 W-hr/ft (0.5 W/ft^ X hours of insolation at 80-mW/cm^ 

 intensity at right angle to the water surface). Thus the square area of solar arrays for a given 

 energy requirement will vary approximately by a factor of 5 between devices designed for 

 tropical and polar regions. 



Downward-facing, horizontal solar cell arrays have a power density of less than 0.02 

 W/ft at the visual contrast limit depth when the ocean surface is normally insolated with 

 solar radiation at 100-mW/cm intensity level. For this reason they have very little practical 

 value as a potential power supply for submerged electronic devices unless the devices are 

 submerged to less than the visual contrast limit depth at locations where a white sandy bottom 

 is clearly visible from above the ocean surface. In such cases the reflected light from the ocean 

 bottom can increase the power output of a downward-facing solar cell by as much as an order 

 of magnitude and thus make the power density high enough to be of practical value to the 

 designer. 



Vertically positioned solar cell arrays submerged under water deliver more power than 

 the downward-facing horizontal arrays located at an identical depth. The output of the verti- 

 cally positioned array oriented to face the sun is approximately an order of magnitude larger 

 than that of a vertically positioned array facing away from the sun. The vertically positioned 

 array, facing the sun, produces at noon power equal to about 30 percent of the upward-facing 

 horizontally positioned array, while the array facing away from the sun produces power only 

 equal to about 5 percent of the upward-facing array. Vertically positioned arrays with inter- 

 mediate orientations between facing the sun and facing away from the sun produce power 

 which falls between the two above mentioned power output limits. 



Since vertically positioned solar cell arrays, regardless of their orientation with respect 

 to the sun, have a higher power output density than downward-facing horizontally positioned 

 arrays, they should be preferred over the latter ones by the designer. One further reason for 

 their desirability is that their power output decreases only moderately in the early morning 

 and late afternoon because of slanting sun rays, while the power output of upward-facing 

 horizontally positioned arrays decreases significantly. Thus vertically positioned solar cell 

 arrays are considered to complement the power output of upward-facing, horizontally 

 positioned arrays. An additional reason for using the vertical orientation is that this orientation 

 is easy to achieve by bonding narrow solar panels on the exterior surface of cylindrical buoys 

 along their axis of revolution. 



It thus appears that if both the top and exterior surfaces of a cylindrical- or polygon- 

 shaped buoy are completely covered with solar cells, an adequate electric energy supply 

 exists to power even the most sophisticated oceanographic or navigational equipment on a 

 year-round basis. Using conservative power density factors, the energy output on a year-round 



35 



