As the sun was shining much more brightly today I decided to repeat my measurements of the solar cell (Solar Cell Maximum Power Output (Hazy Sunshine) ) to try and obtain a more detailed view. This time I only took measurements in the range 600 Ohms to 10 Ohms, in steps of 100 Ohms down to 200 Ohms and then in steps of 10 Ohms. The graph is displayed below and seems much better.
This has produced a much better curve and shows that the peak power output of 426 mW is at 60 Ohms load, comprising 83 mA at 5.1 V, which is pretty impressive for such a small solar cell. Nearly 0,5 Watts. That's enough to run a small mobile robot, albeit on a very sunny day. Still, two of these solar cells would be more likely to work better and three would be even better.
These solar cells have an area of 0.12 x 0.038 = 0.00456 square metres
Now work out how many of these solar cells are needed to make one square meter
Number = 1/0.00456 == 219.3
So if I have 219 of these solar cells I should be able to obtain a total power of:
Power = 219 x 0.428
= 93.9 W
I have had difficulty finding the average solar irradiation (insolation) in the south of the UK in May but I thought that it was about 800 Watts per square metre (some sources put it as low as 200 W m−2 ), but assuming 800 Wm−2 this would imply an efficiency of this solar cell of:
Efficiency = 93.9/800 x 100%
= 11.3 %
which seems about right for this type of solar cell.