However, a solar array on a rooftop in New England will generate a different amount of electricity than an identical one in Florida or California because of a factor known as the solar resource, or how much sun is available every day to a PV panel oriented due south. To find the solar resource in your area, check the solar maps produced by the National Renewable Energy Lab. Knowing the solar resource in your area and the amount of power you want to generate, you’ll be able to get a sense of what size system you need.