Calculate how many solar panels you need for your home
The average American home needs between 15 and 19 solar panels based on the average electricity usage of 893 kilowatt-hours (kWh) per month. Installing that many solar panels would cost between $12,000 and $17,000 after the federal solar tax credit.
But, 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. When trying to find the right solar system size for you, you need to ask yourself a few questions:
- How much electricity do I use?
- How much sunlight does my house get?
- Is my roof big enough?
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How many solar panels you need at a glance
|Monthly electric bill*||System size**||Number of solar panels needed|
*Based on average U.S. electricity rate. Source: EIA
**Based on 4 daily peak sun hours. Source: NREL
The average home in the U.S. needs to install between 15 and 19 solar panels to cover a $140 monthly electricity bill.
The actual number of solar panels needed to run a house varies depending on where the house is located, the home’s energy usage, and the size of the solar panels.
Factors that determine how many solar panels you need
To really understand how many solar panels your solar energy system needs, you need to know 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 370 watts per panel; fewer panels are needed when you install panels with high wattage ratings.
Below, solar expert and SolarReviews Founder Andy Sendy breaks down everything you need to know about how many solar panels you need to power your home.
How to calculate the number of solar panels you need
Figuring out how many solar panels you need is easier than you think. Once you know how much energy you use and the amount of sunlight you get, you can get a good idea of the number of solar panels to put on your roof.
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).
If you can, compile your electricity bills for the last 12 months to see how much energy you use yearly. Annual energy usage gives you a better estimate of how many solar panels you need, as energy fluctuates with the seasons. The average U.S. household electricity usage is about 900 kWh of electricity per month or 10,800 kWh yearly.
If you only have one utility bill on hand, it’s still enough for a ballpark estimate. Remember, if you’re using your yearly or monthly electric usage - it’s important later!
Step 2: See how much sunlight your home gets
The map above shows how many peak sun hours different areas of the United States receive daily. Image source: NREL
Now that you know how much electricity your home uses in a month, you need to find the amount of sunlight your area receives. How much sunlight an area gets is measured in peak sun hours, which represents the intensity of sunlight at a given location.
On average, the U.S. gets about 4.2 peak sun hours daily or about 128 monthly, but how much sunlight you get can vary quite a bit. Arizona, for example, can get upwards of seven daily peak sun hours. On the other hand, Alaska gets an average of two peak sun hours.
The more sunlight your home gets, the fewer solar panels you need to cover your energy bills. The following table outlines the estimated average peak sun hours for different regions of the United States:
|Region||Daily peak sun hours||Monthly peak sun hours|
Tip! Peak sun hours are often listed as daily values. You need to convert this to monthly or yearly hours, depending on if you’re looking at your monthly or yearly energy consumption. These must match to estimate how many solar panels you need accurately!
Step 3: Find out how much energy solar panels produce near you
Use how many peak sun hours you get to determine how many kilowatt-hours of electricity a solar panel can produce in your area.
Take the size of a solar panel in watts and multiply it by the number of peak sun hours you get in a month to see how much electricity a solar panel in your area will produce monthly. You’ll have to convert this from watt-hours to kilowatt-hours by dividing it by 1,000 to match your energy consumption from your electricity bills.
Here’s an example. Most solar panels today are 400 watts in size. If you installed a 400-watt panel in an area that gets 121 peak sun hours per month, that solar panel will generate about 48 kWh of electricity:
400 watts X 121 peak sun hours = 48,400 watt-hours generated monthly
48,400 watt-hours / 1,000 = 48.4 kilowatt-hours
Solar panels with lower wattages will generate less electricity than those with high wattages. Also, panels installed in areas with more sunlight can generate more electricity.
Step 4: Calculate how many solar panels you need
Now you know how much energy you’ve consumed and how much energy a solar panel can produce where you live, you’re ready to figure out how many solar panels you need.
All you need to do is divide your energy usage by the amount of solar energy generated by one solar panel. This will tell you how many solar panels you need to install to generate that much electricity.
For the average home in the U.S., the calculation would look something like this:
900 kWh consumed / 48.4 kWh electricity generated = 19 panels
Voila! That’s the number of solar panels you need to power your home.
How much do solar panels cost?
Solar panel systems usually cost between $12,000 and $17,000 after the federal solar tax credit. But, answering “how much do solar panels cost?” is a lot like answering “how many solar panels do I need?”. The truth is - it depends.
The total cost of a solar panel system will vary based on how many solar panels you install, where you live, and the installer you choose. The following table outlines the estimated cost of installing different-sized solar panel systems based on the average cost of solar in the U.S.:
|System size||Number of solar panels||Installed cost before incentives|
*Assumes 400-watt panels
How many solar panels do you need based on your house size?
The most accurate way to calculate how many solar panels you need is by basing it on your energy usage rather than your home size. You could have a huge house and use very little electricity, thus needing fewer panels. But, in general, bigger houses tend to use more electricity. We made a table that gives a general idea of how many solar panels are needed on average to run different home sizes:
|Home size||Estimated monthly energy usage||Number of solar panels needed*|
|1,000 square feet||440 kWh||9|
|1,500 square feet||660 kWh||14|
|2,000 square feet||880 kWh||18|
|2,500 square feet||1,100 kWh||23|
|3,000 square feet||1,320 kWh||27|
*Based on 400-watt panels and 4 daily peak sun hours
How many solar panels can fit on your roof?
The average solar installation will require between 260 and 340 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. The following table outlines how much roof space different system sizes use:
|System size||Number of panels*||Approx. roof space required|
|4 kW||10||176 sq. feet|
|6 kW||15||264 sq. feet|
|8 kW||20||351 sq. feet|
|10 kW||25||439 sq. feet|
|12 kW||30||527 sq. feet|
|14 kW||35||615 sq. feet|
*Based on 400-watt panels
If you have limited roof space, you may need high-efficiency panels or panels with a higher power output to install fewer panels while still covering your energy needs.
Your roof matters! Not all roofs are good for solar. Depending on your roof direction, shading, and tilt, you may need to install more solar panels. Ideally, solar panels should be installed on south-facing roofs that get lots of sun. These factors are harder to quantity on your own, but we take them into account in our solar panel calculator.
Do solar panels make sense for my home?
Solar panels are a great investment for many homeowners and can often significantly reduce or even eliminate monthly electricity costs.
The best way to determine how many solar panels you need to lower your utility bill is by getting quotes from qualified local solar companies. Solar installers can look at your home's characteristics and determine exactly how many panels you need and how much they can save you.
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. You can also use our solar calculator to find reliable installers near you and get on your way to savings.
- The average U.S. home will need between 15 and 19 solar panels to cover its electricity 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 system will cost between $12,000 and $17,000 and require between 260 and 340 square feet of roof space.
- Larger homes typically use more energy and therefore need more solar panels.