The first step in any homeowner’s solar journey is determining how many solar panels it will take to power your house. The average household needs between 17 and 25 solar panels, but the exact number depends on several variables, such as your average electricity usage, home size, and local climate. Any of the leading solar providers can help you determine how many panels you need, but our guide includes a basic formula to get you started.

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How To Calculate How Many Solar Panels You Need

EnergySage, an online solar comparison-shopping marketplace, estimates that the typical U.S. household will need 17–25 solar panels to meet its full energy needs. Houses with that are well positioned for solar, and thus have a high sun number score can benefit more from each panel. You’ll need to know three key factors to calculate exactly how many solar panels you need to power your home:

• Your annual electricity usage
• Your solar power system’s estimated production ratio
• The wattage of the solar panels you’re considering

You’ll then divide your annual electricity usage by the estimated production ratio, and divide that number by your solar panels’ wattage. We’ll break down these factors and the formula in more detail below.

Annual Electricity Usage

Your energy consumption is the amount of electricity your home uses annually. This number is measured in kilowatt-hours (kWh) and includes all lights and appliances, such as air conditioning units, water heaters, and refrigerators.

The U.S. Energy Information Administration (EIA) reports that a U.S. residential customer’s average annual electricity consumption was 10,791 kilowatt-hours (kWh) in 2022, with an average of 899 kWh per month. Some electricity providers have an app or online portal where you can view your meter readings and track your monthly and annual electricity usage. Otherwise, you can calculate your annual usage by adding up the total kWh listed on your last 12 bills.

Note that usage can vary significantly by season. That’s why we recommend adding up your last 12 monthly statements rather than taking a single statement and multiplying by 12. This method takes a little more time but will give you a more accurate estimate.

Production Ratios

A solar panel system’s production ratio is its estimated energy output over time (in kWh) compared to its actual system size in watts (W). You might assume this is a simple 1:1 ratio, but complex variables come into play, such as the amount of sunlight your home receives versus the amount of shade.

For example, a 10-kW system that produces 14 kWh of electricity in a year has a production ratio of 1.4 (14/10 = 1.4). This ratio might apply to a home in Arizona, which sees large amounts of sunlight all day, year-round. If your home is located somewhere that’s prone to cloudier weather and more rain, like New York, the production ratio might dip to 1.2. 

This is a complicated ratio, so we advise you to contact a professional for the best results. EnergySage has also produced a helpful graphic showing the average solar production ratio by state based on its own marketplace data.

Solar Panel Wattage

You might think that the best solar panels are all built the same, but that’s not true. Different solar panels use different materials and designs, resulting in different energy outputs. A panel’s wattage is how much electricity it produces, and most residential solar panels range between 300 and 450 watts of power. The higher the wattage, the fewer panels you’ll need. 

The Formula

The actual formula a solar installation company will use to design a solar panel system is as follows:

If we use a simplified version of some of the numbers we mentioned above, we get the following:

This formula equals approximately 20 panels. However, your home may require more or less depending on your energy consumption, the wattage of the panels you select, and the production ratio in your area. The National Renewable Energy Laboratory (NREL) maintains a PV watts calculator to help you estimate your needed system size.

Other Ways To Calculate How Many Solar Panels You Need

A simple alternative to the formula above is to figure out how much energy you use per day and multiply by the number of peak sunlight hours your area gets per day. Then, divide the result by the wattage of the panels you’re considering. Use this helpful NREL map to determine how many hours of peak sunlight you can expect.

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Factors That Influence How Many Solar Panels You Need

Though the three key factors above can give you a general idea of how many solar panels you’ll need, other factors can influence the final result.

Roof Size and Layout

If your roof is small or unusually shaped, you need to choose the number and type of solar panels more carefully. Homeowners with large roofs may choose to sacrifice efficiency and buy larger panels to achieve the ideal energy output. Those with smaller roofs must use a smaller number of high-efficiency panels to produce enough energy to power their homes.

Your roof’s layout and design may also limit the size of your solar system. For example, chimneys or unique roof designs might mean you can only install a certain number of panels.

Hours of Sunlight

The amount of energy you’ll get from your solar panels is directly related to how much sun your home receives. If your home receives limited sunlight due to its location, the weather, tall neighboring buildings, or trees, it will require more panels.

Solar Panel Type

The type of solar panel you choose affects how many solar panels you order. For example, you’ll need more polycrystalline panels than monocrystalline to power your home because polycrystalline panels are less efficient. These are the three main types of solar panels:

• Monocrystalline: These are the most efficient and cost-effective solar panels. They’re most commonly offered by solar panel companies, and you can order fewer of them than other types given their high efficiencies of up to 24%. 
• Polycrystalline: These panels are less efficient than monocrystalline panels, with average rates of 13%–17%. You’ll have to buy more panels to match the output of a monocrystalline system, but polycrystalline solar panels cost less than monocrystalline ones. 
• Thin-film: Thin-film solar panels have a broad efficiency range of 10%–20% and are used for more specialized projects, such as converting a shed, recreational vehicle (RV), boat, or small guest house.

For more information about choosing the right solar panels for your home, check out this video with heating expert Richard Trethewey and Mark Trout, Group CEO of Sunworks (formerly Chief Technology Officer of Vivint Solar):

Solar Panel Efficiency

Solar companies use efficiency to measure a solar panel’s ability to convert sunlight into usable electricity. Efficiency ratings are expressed as a percentage to help you quickly compare different solar panels’ performance. For example, if a solar panel has a 25% efficiency rate, 25% of the solar energy it captures is converted into usable electricity. A solar panel’s composition, roof placement, and design all affect its efficiency.

Opting for more efficient solar panels will cut costs in the long term. You’ll receive more energy savings over time and a higher return on investment (ROI).

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Our Conclusion

Though the formulas provided in this article can give you a general idea of how many solar panels you’ll need, they don’t provide a definite answer. The number of solar panels you need is highly individual and depends on various factors, such as your roof layout and the panels’ size, efficiency, and cost. We surveyed 1,000 homeowners who purchased a solar panel system, and 23% said a 10-kilowatt system was needed to power their home. Twenty percent of our survey takers said their home is between 1,000 and 1,500 square feet.

We recommend contacting a solar installer who services your address. A professional can evaluate your home and tell you exactly how many solar panels you’ll need, answering questions about solar batteries and other components. Solar installers can also help you access the federal tax credit and local incentives to reduce costs and maximize your savings. After choosing a solar installer, you can explore different types of solar financing that can make your investment more affordable.

Use our tool below to connect with reputable solar installers that offer solar panel installation in your area.

FAQ About Solar Panels

Can I run my house on solar power only?

Yes, you can run your home on solar power only. However, you’ll need to install backup generators and solar batteries to run your home at night, on low-sunlight days, or during power outages. Systems that run your home exclusively on solar power are considered off-grid. These systems must be larger than average and are thus more expensive.

Are solar panels worth it?

Yes, solar panels are worth it when you consider how much they reduce your utility bills, increase your home value, and positively impact the environment. However, not all homes are suited for solar panels, so check with a professional. Our 2024 survey data shows that 96% of respondents have found going solar to be worth it, and 82% said installing solar panels increased their property value.

What happens if you have too many solar panels?

If you have too many solar panels, your system will produce more energy than your home needs. You can store this excess energy in a solar battery for later use, or you can feed it back into the power grid. Some states award solar renewable energy certificates (SRECs) for producing solar energy, which allows you to earn extra income from your system. Working with a professional solar company will ensure you order the correct number of solar panels for your project.

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