Calculate how many solar panels you need for your home

Updated

The average American home needs between 19 and 23 solar panels based on the average electricity usage of 877 kilowatt-hours (kWh) per month. Installing that many solar panels would cost between $13,000 and $16,200 after the federal solar tax credit

However, chances are your energy usage doesn’t line up exactly with the U.S. average, plus the number of solar panels you need depends on several other factors, like the location of your home and what kind of solar panels you choose. 

So how exactly do you figure out how many solar panels you need? We’ve got you covered. 

Calculate how many solar panels you will need to power your specific home

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Key takeaways

  • The average home in the U.S needs between 19 and 23 solar panels to cover its electric bills.
  • Three main factors impact how many solar panels you need: your energy usage, the sunlight in your area, and the solar panels you choose.
  • An average solar energy system will require between 335 and 405 square feet of roof space.
  • If you have limited roof space, high-efficiency solar panels let you install fewer modules while still covering your energy needs.

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    Factors that determine how many solar panels you need

    You may think that the size of your house determines how many solar panels you need, but it doesn’t! To really understand how many solar panels your solar energy system needs, you need to determine the following: 

    • Your energy usage: The more electricity you use, the more solar panels you need to cover your electricity costs
    • Sunlight in your area: Homes in areas that receive less sunlight will need more solar panels to eliminate their electricity bills than those in sunnier states. As a rule of thumb, the southwestern United States gets the most sun in the country, while the northeast gets the least
    • Panel wattage: The wattage of the solar panels you choose, also called the power rating, determines how much energy the panels will produce and most solar panels installed today have a power rating of about 320 watts per panel; fewer panels are needed when you install panels with high wattage ratings 

    How to calculate the number of solar panels you need

    Our solar panel cost and savings calculator is the fastest, easiest, and most accurate way to find out how many solar panels your home needs - and you don’t have to do any math. Plus, we’ll give you the average cost of a solar installation for your exact home and how much it’ll save you on your electric bills.

    Find out how many solar panels you need to eliminate your electric bill

    However, if you want to put pen to paper and work out the calculations for yourself, follow these four easy steps to find how many solar panels you need. 

    Step 1: Determine your energy usage 

    Check out your most recent power bill to see your monthly electricity consumption. In most cases, the total amount of electricity used will be shown at the bottom of the bill in kilowatt-hours (kWh).

    Your yearly energy usage will give you the best estimate for how many solar panels you need, as energy usage fluctuates in different seasons (think about how much electricity you use for air conditioning in the summer!). 

    Because monthly energy usage varies so much, it can be beneficial to dig up your monthly electric bills for the past year, add the electric usage together, and divide by 12. 

    But using just one utility bill to find your energy consumption is still enough for a ballpark estimate. 

    Step 2: Find how much energy solar panels produce in your area 

    Now that you know how much electricity your home uses in a month, you need to find the amount of sunlight your area receives. This is usually measured in something called ‘peak sun hours’, which is essentially the intensity of sunlight in your area. 

    You can find the average number of daily peak sun hours for your state here. This number is how much sunlight you receive daily, but we need to know how much you receive monthly. To do this, simply multiply your state’s daily peak sun hours by 30. 

    The monthly peak sun hours you get tells you how many kWh of electricity 1 kilowatt (kW) of solar panels will produce in your area in one day. So, if your state receives 150 monthly peak sunlight hours, 1 kW of solar will produce 150 kWh of electricity per month. 

    Not sure about the differences between kW and kWh? Read our guide about kW versus kWh and what they mean. 

    Step 3: Calculate solar system size you need 

    Since you now know how much 1 kW of solar will produce in your area, you can determine what size solar system you need to cover your electricity needs. 

    Divide your monthly electricity usage by the monthly peak sun hours in your area to find the system size you need in kW. 

    Step 4: Figure out how many solar panels you need 

    So, you know the size of the solar system you need to cover your energy usage. Now what? To figure out how many solar panels you’ll need, take the solar system size and multiply it by 1,000 to convert the size from kilowatts to watts. 

    Next, take the size of the system in watts and divide it by the wattage of the solar panels you want to install. 

    Voila! That’s the number of solar panels you will need to power your home. 

    How much roof space is needed for solar panels?

    The average solar installation will require between 335 and 405 square feet of roof space. To find out how much roof space your solar system needs, just multiply the number of panels you need by 17.55 square feet, which is the area of most residential solar panels sold today. 

    If you have limited roof space, you may need to get high-efficiency panels, or panels with a higher power output so you can install fewer panels while still covering your energy needs. You can use RoofingCalculator.com to get an idea of how big your roof is to help you figure out if you have enough room for your solar panels.

    Average number of solar panels needed based on system size

    The table below shows how many solar panels you need based on the size of the system, as well as an estimate of the amount of power the solar array will produce.

    Table 1. Number of panels and roof space required based on system size
    System size Estimated monthly energy production Number of panels* Roof space required
    4 kW 480 - 600 kWh 13 220 sq. feet
    6 kW 720 - 900 kWh 19 330 sq. feet
    8 kW 960 - 1,200 kWh 25 439 sq. feet
    10 kW 1,200 - 1,500 kWh 32 549 sq. feet
    12 kW 1,440 - 1,800 kWh 38 659 sq. feet
    14 kW 1,680 - 2,100 kWh 44 768 sq. feet

    *Assumes 320-watt panels

    Do solar panels make sense for my home?

    Some factors, like roof direction, roof shading, the solar inverter you choose, and whether or not you’re including a solar battery could also influence the number of panels you need. These factors, however, are hard to quantify on your own. 

    The best way to determine the ideal location for your home solar power system and how many solar panels you need is by getting quotes from qualified local solar companies. Solar installers will also be able to give you an idea of the upfront costs of solar for your home and what rebates, incentives, and tax credits homeowners in your area qualify for.  

    In the meantime, using the steps in this article can give you a rough estimate of how many photovoltaic solar panels you need to power your home with clean, renewable energy. 

    Is going solar worth it where you live?
     - 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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