What is the Module Maximum Power Voltage (VMP)?
This is the voltage that the panel produces when exposed to sunlight and a complete circuit with a load impedance is attached in such a way that power produced by the panel is at its maximum. This voltage is again determined using the Standard Test Conditions, and like the Open Circuit Voltage, is highly dependent on the temperature of the panel. Like the Open Circuit Voltage the Maximum Power Voltage is reduced with increases in temperature. (Taken from SMA-America ’07.