In US units one square foot of roof can support 10 watts. So a kilowatt takes 100 sf of roof space. In much of the US you would generate 1,400 to 1,600 "AC su

In US units one square foot of roof can support 10 watts. So a kilowatt takes 100 sf of roof space. In much of the US you would generate 1,400 to 1,600 "AC sun hours" per year, so a 1 Kw system generates 1,400 to 1,600 kwhrs per year. If your grid electricity costs $0.20 per kwhr, 1 kwh then produces $280 to $320 worth of electricity per year.