The diagram, “What is Photovoltaics?” on Page 28 of “Photovoltaic Systems: Harnessing the Power of the Sun” (February 2004) incorrectly stated that the electricity from the photovoltaic array to the inverter is AC electricity and the electricity from the inverter to the electrical panel is DC electricity. The photovoltaic array produces DC electricity, which is converted to AC electricity by the inverter. EC&M regrets the error.