How Many Solar Panels Do I Need For My House? The answer will depend on 10 key factors: 1. how much electricity (kilowatt-hours) you use each year. 2. which ways your roof(s) are facing (also known as azimuth; southwest at 135 degrees, south at 180, southwest at 225, and west at 275 degrees are the most solar-friendly directions). Ground or patio mounts can usually be installed to face south at 180 degrees. 3. the tilt of the roof faces (the angle or slope of the roof). 4. how much space there is on your roof or property for solar panels? 5. how much shade hits the spots where solar panels would go and for how long? 6. local building and fire codes. 7. the watt size and efficiency ratings of the solar panels. 8. the watt size and efficiency ratings of the solar inverters. 9. the distance from the solar panels to the main electrical service panel. The longer the run, the more loss of energy. Applies mostly in the case of ground and patio mounted solar power systems. 10. the net metering...