Experimental Procedure. The typical field test consisted of measuring (1) the under- 

 water visibility (visual contrast limit depth) with a 1 2-in-diameter Secchi disc (figures 1 2 and 

 13), (2) solar insolation on an imaginary horizontal plane just above the water surface with a 

 portable insolation meter, and (3) current and voltage from the individual solar cell arrays. 

 The voltage and current readings from the upward- and downward-facing solar arrays were 

 recorded separately for each depth, as they represented the responses of the arrays to down- 

 welling and upwelling irradiance. To obtain the complete VI plot for each depth, a resistor 

 decade box was connected to the leads from the arrays and different resistors were switched 

 into the circuit while the magnitudes of current and voltage were read by a voltmeter and an 

 ammeter (figure 14). Typical values of resistors used for applying electrical loads to the solar 

 cell circuit were 1,5, 10, 30, 70, 100, 200, 1000, and 10,000 ohms. 



Since the optical properties of water are not only a function of geographical location 

 but also of time of year and weather conditions, it would have been presumptuous to take 

 many field readings until the performance of submerged solar cells could be definitely estab- 

 lished for all conceivable ambient water and weather conditions. Readings were instead taken 

 only to establish typical power performance curves for solar cells at several depth levels in 

 waters with widely ranging visibilities. This was accomplished by measuring the performance 

 of solar cells submerged in waters with visibilities of 95, 16.5, 8, and 2.5 ft (29, 5, 2.4 and 

 0.75 m). The readings obtained in water with a 95-ft visibility (29 m) serve as the upper 

 limit of expected performance, while the readings taken in water with a 2.5-ft visibility (0.75 

 m) are the lower limit. The upper limit could logically represent visibility attained by water 

 in tropical and polar regions, while the lower limit could represent visibility encountered in 

 estuaries of rivers, shallow bays, and polluted harbors. The readings taken in water with 16.5- 

 ft visibility (5 m) are conservative values of solar cell performance in seawater near wave- 

 battered shores. To maintain reasonable comparability between the readings taken at different 

 locations, they were taken only at noon when the solar insolation measured at the horizontal 

 water surface was in the 75- to 85-mW/cm- range. 



