basis of a cylindrical buoy with 6 ft diameter and 6 ft length at the visual contrast limit depth 

 is estimated to vary from 80 W-hr/day in the tropics to 1 6 W-hr/day in the polar regions. The 

 energy output can be doubled by mooring the buoy at only one-half of the visual contrast 

 limit depth or it can be increased by an order of magnitude by allowing the buoy to float 

 awash at the surface of the water. 



In this case, selection of depth depends on how secure the deployed buoy is to be 

 from visual detection by surface craft, vandalism, or accidental damage by casual ship transit. 

 Since the average visual contrast limit depth in the open ocean is approximately 33 ft (10 m), 

 a buoy moored at that depth will be secure from all three dangers. A buoy moored at one-half 

 the visual contrast limit depth, 16.5 ft (5 m), will still be difficult to detect visually and hard 

 to vandalize, but it will be unprotected from damage by passing ships. Surface-moored or 

 floating buoys will lose all safety and visual protection provided by submersion, but will gain 

 immense increases in power output while still retaining some security from detection by radar. 



PROTECTION AGAINST MARINE ENVIRONMENT 



If solar cells are not protected from seawater, the generated electricity will be used to 

 generate hydrogen and oxygen with associated severe corrosion of all solar cell components 

 rather than to power the electronic device inside the buoy. The protection of solar cells from 

 seawater is accomplished by enclosing them in a transparent silicon-rubber potting compound. 

 Optical transmissivity and resistance to surface deterioration may also be enhanced by bond- 

 ing the light-sensitive surfaces of solar cells to glass or acrylic plastic panels with a transparent 

 adhesive and then potting the backs of the cells and the network of conductors with silicon- 

 rubber potting. Although all potting compounds are in some degree permeable to water vapor, 

 thick silicon rubber should provide adequate protection against seawater intrusion for several 

 years. 



In either case, unless steps are taken to prevent it, biofouling of the panel surface will 

 occur, dramatically decreasing the intensity of the light which reaches the light-sensitive sur- 

 face of the solar cells. Without any preventive measures, biofouling is estimated to decrease 

 the intensity of illumination on solar cells submerged in less than 30 ft of water by an order 

 of magnitude within 30 days. There are, however, passive and active techniques for prevent- 

 ing or, at worst, ameliorating the effect of biofouling. 



The passive approach consists of applying a transparent, poisonous, chemical coating 

 which slowly leaches a poisonous ingredient into the adjacent film of water. Because the 

 leaching of poisonous ingredients makes the coating ineffective after a period of time, the 

 buoy must be removed periodically from the water and a new coating applied. Transparent 

 coatings with TBTO (tri-butyl-tin oxide) applied to plastic surfaces have kept them free of 

 fouling for up to 60 days of submersion in depths of less than 30 ft. For applications, 

 however, where it is desirable to keep surfaces free of fouling for many months or years 

 without periodic recoating, the passive approach cannot provide the desired protection and 

 an active approach must be used. 



4. Stachiw, J.L., and Stachiw, J.D., "Effect of Weathering and Submersion in Seawater on the Mechanical 

 Properties of Acrylic Plastic," ASME Paper 77-WA/OcE-5, Winter Annual Meeting, 1977, New York. 



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