A few more questions about solar panels...

CA Traveler wrote:

time2roll wrote:
Put a 20 amp load on the battery and test again.

X2 Your 2 parallel panels can deliver 5.4A+5.17A = 10.57A at 17.6V (the lower voltage panel). This power loss from the higher voltage panel will not be a factor for a PWM controller as long as your wiring losses do not limit the maximum charge rate the battery will accept, ie the absorb voltage for flooded batteries.

:h

Hmm, not so sure about that.

In parallel the combined voltage will result in a lower voltage than the highest panel voltage rating which does affect PWM output. Some of the voltage (hence some of the wattage) developed is wasted (IE is lost) as heat in the lower voltage panel.. The lower voltage panel due to additional heat may result in a further reduction of harvest.

This is the same thing as paralleling old wornout battery(ies) with new batteries.. The old batteries will draw down the voltage of newer batteries until they reach equilibrium in voltage..

Mismatched voltage panels for maximum harvest are better suited to be combined in series and use a MPPT controller.

There is a considerable 5.2V difference between the two panels open voltage rating, that is about 11 - 12 cells difference (each individual solar cell in a panel develops about .5V).. My guess is the max harvest might be in the range of 7A-8A at best, not 10.57 as it isn't going to be a linear addition of current.

This is why adding isolation diodes might prove beneficial since Schottky diodes only drop .3V and would help maximize the harvest in parallel with mismatched panel voltages with PWM controller.

I would agree that if the OPs batteries are already charged and topped off, they will not see more than a couple of amps.. In this case for testing purposes they need to turn on at least a 10A "load" then check the current being harvested from the panels.