Short answer: It depends on how much electricity you use, how much sun your roof gets and the wattage of the panels. Many homes need somewhere between about 15 and 30 panels. Start with your yearly electricity use from your utility bills, then an installer uses your location, roof direction and shade to size the system.
One of the first questions homeowners ask about going solar is how many solar panels do I need. This guide explains the simple math and the factors an installer uses to size a system for your home.
The three things that decide the number
- Your electricity use: shown in kilowatt hours, kWh, on your utility bills. Add up 12 months.
- Your sun: how many hours of strong sun your area gets, and how much your roof faces the sun without shade.
- Panel wattage: many home panels today are rated around 350 to 450 watts each.
A rough estimate
- Find your yearly use in kWh from your bills, for example 10,000 kWh.
- Estimate how much power 1 kilowatt of panels makes in a year in your area. Sunny states produce more than cloudy ones. Installers use tools like the National Renewable Energy Laboratory’s PVWatts calculator.
- Divide your use by that production to find the system size in kilowatts.
- Divide the system size by the wattage of one panel to find the number of panels.
For example, if 1 kilowatt of panels makes about 1,400 kWh a year where you live, 10,000 kWh needs about a 7 kilowatt system. With 400 watt panels, that is about 18 panels. Your installer will refine this with your exact roof.
Other factors
- Roof space: how many panels physically fit on the sunny parts of the roof
- Shade: trees and nearby buildings reduce output
- Your goals: covering all of your use or only part
- Future changes: an electric vehicle, heat pump or pool will raise your use
- Utility rules: how your utility credits power you send back can affect the best size
- Batteries: if you add a home battery, sizing may change
Reading your electric bill
Look for the kilowatt hours, kWh, used each month, often shown as a 12 month chart. Summer and winter can differ a lot, especially with air conditioning or electric heating. Add up a full year, or ask your utility for a usage history, so the installer sizes the system for your real use, not one month.
Should you size for all your use?
Not always. Some utilities credit exported power at a lower rate, so a system sized to cover most of your daytime use can make more sense. Your installer should explain how your utility’s rules affect the best size.
Read about home solar installation, including batteries and what installers check first.
Quick answers: how many solar panels do I need
How many solar panels does a house need?
Many homes need about 15 to 30 panels, depending on electricity use, sun and panel wattage.
How do I calculate how many solar panels I need?
Divide your yearly kWh use by the yearly production of 1 kilowatt of panels in your area, then divide by the panel wattage.
How much power does one solar panel make?
It depends on its wattage and your sun. A 400 watt panel may make several hundred kWh a year in many areas.
Will I have enough roof space?
An installer checks the sunny, unshaded roof area and panel layout during the site visit.
Who installs home solar?
A licensed solar installer. Sifixit can connect you with a local installer where solar is offered.
Related
This guide covered how many solar panels do I need. For more background, see the U.S. Department of Energy’s guide to going solar, and if you need help, Sifixit can connect you with a local provider.
This guide is general information for homeowners, not professional, insurance or safety advice for your situation.