The “alternative energy” literature often states: “One hundred square miles of the Arizona desert, if devoted to photovoltaic electric generation, will furnish all the electricity used in the U.S.” Let’s see. A square meter (about 10 square feet) of sun energy at high noon is about 1 kilowatt. The best mass-produced photovoltaic array will convert about 10 percent of this incoming solar energy into electricity. If the sun provides high-noon energy one-fourth of the time, then that one square meter will supply about 200 kilowatt-hours of electric energy per year. U.S. electric energy use is about 4,000 billion kilowatt-hours per year. We need about 20 billion square meters to generate our electricity. A square mile covers about 2.6 million square meters. We need nearly 10,000 – not a hundred – square miles of Arizona desert. The “alternative energy” press often confuses 100 square miles with a 100 mile-square.