# efficiency problems connecting multiple solar panels

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.

• What is the "load" - is it just the shunt of the multimeter in 20A mode? Are you measuring the voltage and current at the same time (with two different meters)? Jul 5, 2013 at 10:27
• yes, the load is the shunt of the multimeter, I'm measuring the both - Amps & Volts simultaneously Jul 5, 2013 at 10:36
• electronics.stackexchange.com/questions/73226/… Jul 5, 2013 at 11:41
• I've constructed a dummy load with a replaceable 10W resistors. By controlling a current through MOSFET I was trying to find that particular threshold where current starts to drop and the voltage it at its maximum. Didn't work - peak wattage was 3W most from the two panels. Tried replacing resistors with 3W+3W LEDs, brushed motors etc. Then, I've plugged-in 7.4V LiIon battery. Inrush suddenly current peaked at [email protected] resulting in 24Watts total, or 12Watts per panel! Jul 6, 2013 at 11:07