6. Solar BP Solar advertises that \"a 600 sq. ft. array [of photovoltaic cells] rated about 3.3 kW . . . would generate about 3640 k'Wh per year. Our highest efciency technology (also the roost expensive) would generate about double this. The typical cost for a single residential system is about $10,000 per kW\"5 3. Using the solar array advertised, determine the cost per kilowatt-hour over a 30-year period of use. b. Compare the energy output of this solar array to the energy needed by a water heater using 400 k'Wh per month