How Many Solar Panels Does It Take to Run a House?

An average American house needs about 17 to 27 solar panels of 400 watts to cover a year of electricity. The exact number comes from three figures: how many kWh your home uses (the EIA average is 10,791 a year), how much 1 kW of panels makes where you live, and the wattage of each panel. Divide, then round up.

The three numbers that set your panel count

Your yearly use. Add up 12 months of kWh from your electric bills. The US Energy Information Administration says the average residential customer bought 10,791 kWh in 2022, about 899 kWh a month. Homes vary widely: Louisiana averaged 14,774 kWh per customer and Hawaii 6,178 kWh, so use your own bills, not the national figure.

Your local production per kW. A kilowatt (kW) is the size of the system; a kilowatt-hour (kWh) is the energy it makes. A 2009 DOE consumer guide prepared by NREL says 1 kW of panels in a sunny climate such as California, with good orientation and tilt, makes about 1,400 to 1,700 kWh a year. Cloudier places make less: DOE’s 2022 consumer guide says a 7 kW system makes 20 to 35 kWh a day depending on climate, roughly 1,040 to 1,830 kWh per kW a year. The free PVWatts calculator from the National Laboratory of the Rockies (formerly NREL) estimates the figure for your address, roof angle and direction.

Panel wattage. Ratings vary by model, so check the spec sheet; this page uses 400 watts as a round example. Higher-wattage panels mean fewer panels for the same system size.

The math, step by step

1. Divide yearly kWh by kWh per kW. That is your system size in kW.
2. Multiply by 1,000 and divide by panel wattage. That is your panel count.
3. Round up.

For an average home in a place where 1 kW makes 1,400 kWh a year: 10,791 ÷ 1,400 = 7.7 kW. Then 7,700 ÷ 400 = 19.3, so 20 panels. DOE says NREL uses an average home system of 7.15 kW in its analyses, with a range of 3 to 11 kW, which fits this example.

The table runs the same average home through four levels of local sun. The production figures are examples to show the math; get your own from PVWatts.

The roof column uses the rule of thumb in the 2009 DOE consumer guide of about 100 square feet of unshaded, south-facing space per kW. The same guide says a southeast- or southwest-facing system performs about 5% lower, so a roof that does not face due south still works with a slightly larger array.

Covering all of your use or part of it

You do not have to cover 100% of your use. Many homeowners size for part of the bill because roof space, shade or budget limits the array. Cutting use first also shrinks the system: DOE notes that with Energy Star appliances and other efficient products, you need less solar energy to power your home. The EIA says air conditioning made up 19% of home electricity use in 2020, with space heating and water heating at 12% each, so cutting those loads can change your panel count more than a panel upgrade.

Online tools are a starting point, and DOE advises working with an installer for a custom estimate of how much power your system is likely to make. Use your own math to check it.

Running a house in a power outage

Panels that “run a house” on a sunny day usually stop in a blackout. A grid-tied system shuts down when the grid goes down unless it has a battery or a backup design built for that. The same rule applies to plug-in balcony solar, which state laws require to stop feeding power in an outage.

For outage power without a full home system, a large portable power station runs the essentials and charges from a few portable panels. Our guides to solar generators for home backup and what size solar generator you need size one by the appliances you want to keep running, a far smaller job than covering a whole year of use.

Before you count panels

• Gather 12 months of bills; one summer or winter month misleads.
• Run PVWatts for your address with your real roof angle and direction.
• Check shade from trees and neighboring buildings in winter, when the sun is low.
• Plan for loads you will add, such as an electric car or heat pump.

To price a system once you have a panel count, see the cost to install solar panels. More on panels for homes, balconies and power stations is in our solar panels section.