experienced by a single, or several, cell(s). The reason is that cells with less illumination act 

 like resistors through which the current generated by other solar cells in the circuit must pass. 

 Thus, for example, in a typical array consisting of 15 cells connected in series, the total 

 current output decreased by 66 percent from 450 mAwhen the insolation on a single cell 

 was decreased from 80 to 15 mW/cm . In this case, an 81-percent decrease in illumination 

 intensity on a single cell resulted in a 66-percent decrease in the total power output of the 

 solar array. If the same 1 5 solar cells in the array had been connected in parallel, the decrease 

 would have been only 5.5 percent of the total power output from the array. 



In most applications, solar cell arrays are used for charging batteries. As long as the 

 potential of the array exceeds that of the battery, current will flow to the battery and charge 

 it. If the light intensity decreases to such a degree that the array's voltage drops below that 

 of the battery, the current will reverse and the battery will discharge through the array with 

 all cells acting like resistors. To preclude discharge of batteries through the cells during 

 periods of darkness and avoid possible damage because of overheating, a blocking diode acts 

 like a one-way valve that allows the current to flow from the cells to the batteries with very 

 little resistance while effectively blocking the flow of current from the battery to the cells. 

 Blocking diodes are also employed to protect individual cells or groups of cells wired in parallel 

 from acting like resistors when some of them become shaded while others are still exposed to 

 bright sunlight. 



SOLAR CELLS IN MARINE SERVICE 



ABOVE-WATER APPLICATIONS 



When solar cells are utilized to supply electric power to marine devices located above 

 the ocean surface, few problems beyond those found in terrestrial applications are encountered. 

 Problems not commonly found in terrestrial applications are continuous or intermittent water 

 spray, defecation of birds, and dense fog. 



Water spray does not pose a major problem, as embedding solar cells in clear silicon 

 rubber, epoxy, polyester, or acrylic resins makes them waterproof without significantly 

 decreasing their power output. 



The defecation of birds is a more serious matter, as it can totally shade the surface of 

 the cell in a short period of time and thus reduce its electric output to zero. Since it is 

 virtually impossible to keep birds from alighting on any object protruding above the water 

 surface, the only solution is to deny the birds a foothold on the surface of the array. This is 

 easily accomplished by covering the individual solar cell panels with smooth acrylic or glass 

 sheets and arranging them on top of the buoy in the shape of a truncated pyramid capped 

 with a sharp plastic tip. As a result of this arrangement, there is at most a foothold for only 

 one bird. 



The performance of solar cells is also severely degraded by the presence of dense fog. 

 Since fog is a common occurrence in coastal areas, it must be considered when the power 

 output of a solar cell array is calculated. 



