How many solar panels do I need?

Updated

House with solar panels on the roof
The amount of solar panels your home needs depends on the amount of energy your home needs, as well as the efficiency of your panels.

A typical American home will need between 21 and 34 solar panels to cover its electricity bill

Chances are your energy usage doesn’t quite line up with the U.S. average, and how much sunlight your home gets probably varies quite a bit, too. So, how exactly do you figure out how many solar panels you need? We've got you covered.

In this article, we’ll go over the ways in which you can get an idea of how many solar panels your home needs, based on different factors like where you live, your electricity usage, and what solar panels you choose. 

Calculate how many solar panels you need for your home

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    How many solar panels does the average home need?

    Like we said earlier, the average American home will need anywhere from 21 to 34 solar panels to cover its monthly electricity bill. That’s a minimum of 369 square feet of roof space to accommodate the solar panels. 

    This calculation is based on the U.S. Energy Information Administration’s average monthly electricity usage of 877 kilowatt hours (kWh) and assumes the system is made of 280-watt solar panels. We also assume the utility company offers full-retail net metering.

    However, these averages probably don’t give you the best snapshot of how many solar panels you need for your specific home because there are so many factors to consider. 

    What’s the easiest way to find how many solar panels I need?

    Many factors go into determining how many solar panels you need. That’s why the easiest way to figure out how many solar panels you need to power your home is by using a solar calculator. Otherwise, you’ll have to do some research and a bit of math to find the number of solar panels that is right for you.

    So instead of putting time and effort into calculations, you can put your address and monthly power bill into the below solar calculator to find out how many solar panels you need. Our state-of-the-art solar panel calculator is powered by artificial intelligence that will tell you the number of panels recommended for you. Plus, we’ll give you a free quote for how much a solar panel installation will cost you, so you can decide if solar is a cost-effective investment. 

    What factors influence the number of solar panels your home needs?

    To really understand how many solar panels your solar energy system needs, you need to determine: 

    1. The amount of energy your home uses: Look at monthly kWh usage on your electric bill
    2. The average amount of sunlight in your local area: As a rule of thumb, the southwest gets the most sun in the U.S., while the northeast gets less sun
    3. The wattage of the panel you purchase: This determines how much energy the solar panels produce

    How to calculate the number of solar panels you need to power your home

    There’s a pretty simple formula to help homeowners figure out how many solar panels they need: 

    how many solar panels do i need formula

    Let’s break this formula down a little further, so you can get a better idea of how to use it. 

    Step 1: Determine how much electricity your home uses 

    Check out your most recent power bill to see your monthly electricity consumption. With most bills, the total kWh of electricity you used will be shown at the bottom, with the cost of electricity multiplied by that amount

    how many solar panels do i need - electric bill example

    In the above example, you can see that 1,000 kWh were used over the course of the month.

    Step 2: How much sunlight does your area receive? 

    To figure out how many solar panels you need, you need to know how many peak sun hours your area receives. Peak sun hours aren’t just the number of hours between sunrise and sunset - they are each hour that the sun’s intensity reaches an average of 1,000 watts per square meter. 

    To put it plainly, peak sun hours are the hours when sunlight is most powerful and when your solar panels will be the most productive. The more peak sun hours you have, the higher a solar array’s energy production will be. This directly impacts what size solar panel system you will need. 

    If you live somewhere with lots of sunlight, like Arizona, you will need a smaller solar panel system. But if you live somewhere like Massachusetts, where there is less sunlight available, you’ll need a bigger system to produce the same amount of electricity. The direction of your roof and how much shading there is can also change the number of solar panels that you need. 

    The table below lists some of the average daily peak sun hours for different regions of the U.S. You can find the average number of daily peak sun hours for each state here, or you can check out solar irradiance maps from the National Renewable Energy Laboratory (NREL). 

    Table 1. Number of peak sun hours in different regions of the United States
    Region and state Average daily peak sun hours
    West: California 6.7 hours
    South: Texas 5.6 hours
    Midwest: Illinois 4.3 hours
    Northeast: New Jersey 4.1 hours

    Step 3: Calculate what size solar system you need 

    Now that you know the amount of power you use and have an idea of how much sunlight your area receives, we can figure out what size solar panel system you need. 

    First, we need to figure out how many peak sunlight hours you get in a month. To do this, just multiply your daily sun hours by 30. I live in New Jersey, so I would multiply 4.1 by 30, to get a ballpark estimate of 123 hours of sunlight per month. 

    Next, you take your monthly kWh usage and divide it by those monthly sun hours. We can use 1,000 kWh for this example, and we’ll stick with 123 hours of sunlight. So, 1,000 kWh divided by 123 hours gives you 8.13. That means you would need an 8.13 kW system to produce enough solar power to cover your monthly energy consumption. 

    Table 2. Solar system sizes needed in different regions to cover 1,000 kWh of electricity
    Region and state Average daily peak sun hours Average monthly peak sun hours Solar system size
    West: California 6.7 hours 201 hours 5 kW
    South: Texas 5.6 hours 168 hours 6.2 kW
    Midwest: Illinois 4.3 hours 129 hours 7.8 kW
    Northeast: New Jersey 4.1 hours 123 hours 8.1 kW

    As you can see from this table, the more peak sun hours you receive, the smaller the solar system you need. Areas with less sunlight require larger systems. 

    Find out how long your solar panel payback period will be 

    Step 4: Calculate how many solar panels you need 

    Now, the moment you’ve been waiting for, how to figure out how many solar panels you need. 

    The first thing we need to do is convert the size of the system you need from kilowatts to watts. To do that, all you have to do is multiply the system size in kW by 1,000. For our example, that would be 8.13 kW times 1,000, which comes out to 8,130 watts. 

    Next, you divide the system size in watts by the wattage of the solar panels you choose. Most solar panels have a power capacity of 280 watts. Again, sticking with our same system, you divide 8,130 watts by 280 watts per panel to get 29 panels needed to cover the total electricity usage. Easy as that!  

    The table below shows how the amount of sunlight hours you receive influences the number of 280-watt panels you need to cover 1,000 kWh of electricity usage: 

    Table 3. Number of solar panels needed in different regions to cover 1,000 kWh of electricity
    Region and state Average daily peak sun hours Solar system size Number of solar panels needed
    West: California 6.7 hours 5 kW 18
    South: Texas 5.6 hours 6.2 kW 21
    Midwest: Illinois 4.3 hours 7.8 kW 28
    Northeast: New Jersey 4.1 hours 8.1 kW 29

    The power capacity rating of the solar panel system you choose will also influence the number of solar panels you need. If you choose a solar panel with a higher power rating, you’ll need fewer solar panels, because each panel can produce more electricity. 

    The table below shows you how the wattage of panels impacts how many solar panels you’ll need:

    Table 4. Number of solar panels needed for a 7 kW system, based on the wattage of the panel
    Solar panel wattage Number of solar panels needed
    250 W 28
    280 W 25
    330 W 21
    375 W 19

    As you can see, if you choose 250-watt panels, you will need more solar panels than if you chose a higher capacity, 375-watt panel. 

    How many solar panels do I need for a 2,000 square foot home?

    You may think that the size of your house determines how many solar panels you need, but it doesn’t! The number of solar panels you need depends on how much electricity your home uses. In general, a larger home will use more electricity because it’s bigger, so it will need more solar panels. 

    But, that’s not always the case! Smaller homes can have much higher monthly electric bills than large homes, depending on the types of appliances, the number of people living there, how well-insulated the home is, the location of the home - the list goes on and on. 

    So, you shouldn’t rely on the size of your home to find the number of solar panels you will need. But, based on the median U.S. home size and average household electric usage, you can get a ballpark estimate of how much electricity a home will use based on its size, and thus, a rough idea of how many solar panels the home might need: 

    Table 5: Number of solar panels needed based on monthly power usage and home size
    Home size Estimated monthly electric usage Estimated number of solar panels needed*
    1,000 square feet 380 kWh 12
    1,500 square feet 570 kWh 17
    2,000 square feet 760 kWh 23
    2,500 square feet 950 kWh 28
    3,000 square feet 1,140 kWh 34

    *Assumes 4 daily peak-sun hours and 280-watt solar panels

    How much roof space do I need for solar panels?

    Given that the average solar panel system requires between 21 and 34 solar panels, you can expect to need anywhere from 369 to 598 square feet of roof space for a solar system. 

    Of course, the amount of roof space you need will depend on how many solar panels you install. The more solar panels you have, the more roof space you’ll need. To find out how much roof space your solar system requires, just multiply the number of panels you need by 17.55 square feet, which is the area of almost all residential solar panels sold today

    If you have limited roof space, you may need to get high power and efficiency panels, so you can purchase fewer panels but still meet your energy needs. A solar installer can help you determine what type of solar panels are best for you based on the size of your roof. 

    Do solar panels make sense for my home?

    Ultimately, most homes have enough roof space to accommodate a solar panel system that will cover their electricity usage. Some factors, like roof size, direction, the solar inverter you choose, and whether or not you’re including a solar battery could also influence the number of panels you need.

    In some cases, things like the shading and direction of your roof could impede the power output from the solar installation. 

    These factors, however, are hard to quantify on your own. Getting solar quotes from qualified solar companies is the best way to determine the ideal location for your home solar power system and how many panels you will need. Solar installers will also be able to give you an idea of the upfront costs of solar for your home and what rebates and tax credits you qualify for.  

    In the meantime, using the steps in this article can give you a rough estimate of what to expect. 

    How many solar panels will cover your electric bill?

    Key takeaways

    • The average American home needs 21-34 solar panels to cover its monthly utility bill.
    • To calculate the number of solar panels you need, simply divide your monthly electricity usage in watts by the number of sunlight hours your area gets in a month, divided by the wattage of the solar panel you are using.
    • If you live in a sunnier state, fewer solar panels are needed to produce electricity for your home.
    • Using higher wattage solar panels means less solar panels are needed to reduce your utility bill expenses.
    • If you have limited roof space, high-power, high-efficiency solar panels are best to help you cover your energy needs.
     - Author of Solar Reviews

    Catherine Lane

    SolarReviews Blog Author

    Catherine is a researcher and content specialist at SolarReviews. She has strong interests in issues related to climate and sustainability which led her to pursue a degree in environmental science at Ramapo College of New Jersey.

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