Photovoltaic device

The photovoltaic system (20) has reference solar generator-inverter module (28,30) that is operated at maximum operating point, to generate electric power from solar radiation. The generator-inverter module is operated at throttled operating point, to generate throttled electric power is less than electric power generated at maximum operating point. The generator-inverter module is operated at relative operating point, and the power relationship between electric power generated at relative operating point and electric power generated at maximum operating point is determined.