The number of panels installed is based upon factors such as; the structure and size of the roof or mounting system, the required amount of energy, and the orientation and location of the roof. Each roof is unique regarding these factors mentioned, therefore, the number of panels will vary.
Solar panels come in wattages ranging between 150 watts to 370 watts per panel. (See Average kWh solar panels.). The number of solar panels is not an accurate determination of how much energy a roof can obtain, but rather the amount of wattage of each panel and the required energy consumption.