Next, you'll need to figure out how much energy an individual solar panel will generate. A simple way to estimate it is to multiply the panel wattage by the average peak sun hours and multiply that by the system efficiency. For example, a 400W panel in a location with 4.5 peak sun hours and 80% efficiency would result in the following equation: 400 × 4.5 × 0.8 = 1,440 Wh. To discover how many peak sun hours your location receives, check a peak sun hours calculator. Finally, divide the energy usage of your household by the output of an individual panel to determine the number of panels you'll likely need to supply your home.