Agree with Salvo except "12v" panel Isc will taper a little from about Vbat 13.5 to 14.5 before dropping off the cliff at 15v. So IMO observe the amps at say 14v then drop Vbat to 12.3 or what you can in a hurry and note the amps then, or else with PWM you will see a small change in the amps and get confused if it is MPPT or not..
Also nit-pic on Psolar/Vbat. I think Salvo means Psolar to be the power that's left from panel power at the controller's output. My controller displays watts as the product of Vbat (as seen at the controller end of the wires) and controller amps output.
You will see a jump in amps with the lower Vbat for sure. I have seen that doing tests with my "true MPPT" controller.
