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, 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.
- The average home in the U.S needs between 15 and 19 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 260 and 340 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 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
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 specific home and how much it’ll save you on your electric bills.
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.
We have a complete list of the average number of daily peak sun hours for each state. This is how much sunlight your area receives daily, be we need to know how much you receive monthly. To do this, simply multiply your state’s daily peak sun hours by 30. On average, the U.S. receives between 120 and 150 peak sun hours per month.
The monthly peak sun hours you get tells you how many kilowatt-hours of electricity 1 kilowatt (kW) of solar panels will produce in your area in one month. So, if your state receives 150 monthly peak sunlight hours, 1 kW of solar will produce 150 kWh of electricity per month.
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. For the average home in the U.S. the calculation would look something like this:
893 kWh consumed / 135 monthly peak sun hours = 6.61 kW of solar
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. Let’s use the same example as before:
6.61 kW of solar x 1,000 = 6,610 watts of solar
Next, take the size of the system in watts and divide it by the wattage of the solar panels you want to install. The average solar panel in the U.S. is about 370 watts in size. For the sake of our example, that means you would need 18 solar panels to cover your energy usage.
6,610 watts of solar / 370-watt solar panel = 18 solar panels
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 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.
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.
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.
|System size||Estimated monthly energy production||Number of panels*||Approx. roof space required|
|4 kW||480 - 600 kWh||10||176 sq. feet|
|6 kW||720 - 900 kWh||15||264 sq. feet|
|8 kW||960 - 1,200 kWh||20||351 sq. feet|
|10 kW||1,200 - 1,500 kWh||25||439 sq. feet|
|12 kW||1,440 - 1,800 kWh||30||527 sq. feet|
|14 kW||1,680 - 2,100 kWh||35||615 sq. feet|
*Assumes 400-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.