I cannot understand why doubling the amount of solar panels gives only a few percent increase in total amount of power.
Here are the test results of a single 10-cell panel:
Single solar panel efficiency tests http://imageshack.us/a/img43/6561/nlgd.png
Here are the test results of two panels connected in series:
And here are the test results of two panels connected in parallel:
My expectations were:
- to see the voltage of 9.3V under load in serial connection, yet I've
got 4.3 - to see the current of 5.2A under load in parallel connection, yet I've got 2.6
- to see the wattage doubled in both serial and parallel connection, yet I've got 10%,20%
Can someone explain the reasons behind such a weirdness?
The tests we repeated with the two different multimeters swapped in places to measure voltage and amperage.
The tests were conducted 1.5 – 1.0 hour before the noon, on a clear sky conditions, so there's a bias of few percent in measurements due to increase solar elevation angle.
Best Answer
http://en.wikipedia.org/wiki/Solar_cell_efficiency#Maximum_power_point
If you draw too much current from solar cells their overall efficiency falls. This is evidently affecting all three configurations to different extents. If you test with a set of resistors in the 1 - 20 ohm range you'll get different results. Given the power dissipation it may be easiest to do this with automotive lightbulbs of different wattage ratings (higher wattage rating for same rated voltage = smaller resistance). Ideally you'd want an adjustable 20W dummy load.