12 X 100W panels in series/parallel on roof of motorhome. 12V batt bank. Inside the shop with ceiling lights on, the PV open voltage is showing 75V. But when I connect it to the controller, it drops to 12.5V. The batteries are at 12.6V. Should it not be able to charge the batts ? Thanks.
Your shop lights will trigger some voltage, but not enough energy to drive output from the panels.
If you took a 100W bulb, and 20% of it's total output landed on the panels, which are 20% efficient, that's 100W x 0.2 x 0.2 = 4W. That's not entirely accurate, but you see where it's heading.
