Horsefly
Solar Wizard
What you measure is certainly correct, at least at that very moment in time. ?
There are at least two things people use the spec voltages for. You would use the Vmp (voltage at max power) along with Imp (current at max power) to size your PV array, wire, and components for what your system needs are. The second thing is to use the Voc (open circuit voltage) to make sure however you plan to hook up your panels will not burn out your charge controller.
If you read the rest of the thread, you'll find discussion of how the voltage of the panels goes up as the temperature goes down, and so you need to account for that, not just counting on the measurement you take.
There are at least two things people use the spec voltages for. You would use the Vmp (voltage at max power) along with Imp (current at max power) to size your PV array, wire, and components for what your system needs are. The second thing is to use the Voc (open circuit voltage) to make sure however you plan to hook up your panels will not burn out your charge controller.
If you read the rest of the thread, you'll find discussion of how the voltage of the panels goes up as the temperature goes down, and so you need to account for that, not just counting on the measurement you take.