To determine your home’s average energy requirements, look at past utility bills. You can calculate how many solar panels you need by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage (150 W) and high-wattage (370 W) example to establish a range (ex: 17-42 panels to generate 11,000 kWh/year). Note that the size of your roof and how much sunlight your roof gets are factors as well.