I completed the testing this morning:
- Conditions were ideal with a clear blue sky and 24°C temperature.
- After some experimenting with positions, I ended up using an east-west facing setup as this aligned the panels best with the sun.
- One panel was fully illuminated while the other was only receiving ambient light. No shading was present.
- Both panels (HSL60P6-PC-1-260) are almost new, from the same batch and have no defects.
- The panels were cleaned with a microfibre cloth prior to testing.
- The battery had been run down prior to the test, and had approximately 150W resistive load across it to ensure the voltage didn't rise to a point where the charge controller would limit output.
- The MPPT used during the test was an EPever Tracer 2210AN, which is a 20A, 100V unit. The tests were all within specification of the MPPT, with the second parallel power test approaching its maximum output current.
I followed the test procedure
documented above and produced the following results:
| Parallel | Series |
VOC | 34.2V | 68.6V |
MPPT Output Amps | 18.5A | 12.9A |
MPPT Output Volts | 14.5V | 14.3V |
Output Watts | 268.25W | 184.47W |
Result: This test showed a 45.4% higher power output when the panels were wired in parallel.
The tests were then repeated in reverse to ensure no time-related factors influenced the results:
| Parallel | Series |
VOC | 34.2V | 68.6V |
MPPT Output Amps | 19.7A | 13.5A |
MPPT Output Volts | 14.6V | 14.5V |
Output Watts | 287.62W | 195.75W |
Result: This test showed a 46.9% higher power output when the panels were wired in parallel.
To be sure of the results I also swapped the position of the panels and repeated. The results were the same with 46% more output in parallel.
The temperature difference between the panels was substantial during the tests, with one being almost too hot to touch, while the other wasn't much above ambient temperature.
I've also attached a photo of the test setup to show that it did in fact happen
To be honest I wasn't expecting such a large difference. If anyone has any feedback, suggestions or questions I'd be happy to follow up.