I have 4-100 watt solar panels mounted on top of my RV.
The panels are wired in series.
The battery bank is composed of 12-106 ah batteries, totaling 1260 ah.
The battery bank is at 81% SOC.
The MPPT controller is set for lithium battery charge algorithm.
Last year I routinely saw 75-78 volts and 350-400 watts being scavenged from the panels during peak hours. However, this year those numbers have changed.
Today, at the ON/OFF switch, incoming voltage from the panels is 79 volts. However, when I set the switch that connects the panels to the MPPT controller, to the ON position, voltage going to the MPPT controller walks down to 48. The wattage gauge shows just 220. This is in direct sun, midday.
I recently bought a new MPPT 100/50 controller, and the same reduced voltage and wattage is occurring again. So now I’ve tested both controllers and the system exhibits the same reduced voltage and wattage with either controller.
I would suggest that one of your panels has a fault in it or your wiring / connectors between the panels have a poor connection with a high resistance joint. You need to do check all your connections for tightness, corrosion, moisture etc. Try taking one panel out of circuit at a time if that does not help. Another way is get a piece of cardboard or thick blanket the size of 1 panel and cover them one at a time. If covering a panel makes no difference then the panel is suspect. Panels have bypass diodes so even if a panel gets a break in it, the others in the string can continue to work as the current goes through the bypass diode.
Another thing worth noting, what is the Voc voltage for your panels. Hopefully 4 in series stays below 100V in all conditions.
Thanks for your response. I have recently measured each panel’s output in volts and amps. They are uniform in that each panel displays between 19 and 19.5 volts. Amps were between 5 and 5.5, each.
As you think there may be connection issue, I’ll replace them all with new pieces.
At 19V oc, and 5A load on each module, this would indicate about 85W from each module.
Try measuring the short circuit current from each module, and compare with the value on the modules label.
Do also check the PV wiring for a high resistance somewhere - either a faulty connector or chafed wiring.