Updated 5 days ago

How many solar panels do you need to power your home?

Most homeowners need between 15 and 19 solar panels to cover their power needs. But how do you calculate the number of panels necessary to run your specific home? Solar expert Ben Zientara breaks down the calculations in the video below, or you can read on to find out how to estimate the amount of solar panels that are right for you. 

Use this calculator to find out how many solar panels you need for your specific home

Key takeaways

  • The average home needs between 15 and 19 solar panels to cover its daily electric usage.

  • You can calculate the number of solar panels you will need with your energy usage, the amount of sunlight you get, and the wattage of the solar panels you choose.

  • You can calculate the number of solar panels you will need with your energy usage, the amount of sunlight you get, and the wattage of the solar panels you choose.

  • The exact amount of solar panels needed for your home can vary with the characteristics of your roof, your local climate, your budget, and the size of your home.

How to calculate how many solar panels you need

You can get an estimate of how many solar panels you need by looking at three things:

  • Your monthly electricity usage

  • How much sunlight your home gets

  • The wattage of the solar panel

Let’s take a closer look at where you can find this information and how to use it to determine what solar system size is right for you!

Step 1: Find out how much electricity you use

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

Your electricity usage is the biggest deciding factor in how many solar panels you need. If you use a lot of electricity, you’ll need more panels to cover the costs!

According to the U.S. Energy Information Administration, an average home in America uses about 88 kWh of electricity each month. That’s a monthly electric bill of about $135.

Remember that electricity usage can vary widely depending on your home and where you live, so it’s essential to check your electricity bills to get the most accurate estimate possible!

Annual electricity usage will give a more accurate estimate. If you have access to your electricity bills from the last 12 months, you can better understand how many solar panels you’ll need. Electricity usage varies significantly from month to month (think about cranking the AC in the summertime), so your most recent bill might not reflect your all-time-high electricity usage.

Step 2: See how much sunlight your home gets

The amount of sunshine that hits your roof also plays a vital role in how many solar panels you need. Homes in sunnier areas need fewer solar panels than homes in overcast states.

How much sunlight an area gets is measured in peak sun hours. Sunny states like Arizona can get up to 210 peak sun hours monthly, while somewhere with more cloudy days, like Massachusetts, will only get 135 peak sun hours a month. The following map outlines the estimated monthly peak sun hours each state receives.

A map outline estimated monthly peak sun hours a state receives based on data from the National Renewable Energy Laboratory. The northeastern United States receives the least amount of sunlight with around 120 monthly peak sun hours, the south east, midwest, and north western U.S. receives between 135 and 165 PSH, and the south west and west coast receive upwards of 180 monthly peak sun hours.

Step 3: Determine what solar panel system size you need

Now that you know your electricity usage and sun exposure, you can calculate the size of the solar system you need in kilowatts (kW). Simply divide your household electricity consumption by the monthly peak sun hours to find the right system size for your home.

Graphic showing the equation for calculating solar system size. Monthly energy consumption in kilowatts divided by your area's estimated monthly peak sun hours equals the system size you need

Most solar panels installed today have power ratings of around 400 watts (0.40 kW). If you’re interested in a specific solar panel model, you can find its wattage on its datasheet, where it will usually be labeled as maximum power, rated power, nominal power, or “Pmax”.

Remember, for this calculation, you need to convert a panel’s power rating from watts to kilowatts by dividing the wattage by 1,000.

Step 4: Calculate how many solar panels you need

Finally, you can divide the system size by the power output of a solar panel to find out how many solar panels you need. The higher a solar panel’s power output, the fewer panels you need to install.

graphic showing the equation for calculating how many solar panels you need using the system size. Divide the system size in kilowatts by the power output of a solar panel in kilowatts to find out how many solar panels you need

Most solar panels installed today have power ratings of around 400 watts (0.40 kW). If you’re interested in a specific solar panel model, you can find its wattage on its datasheet, where it will usually be labeled as maximum power, rated power, nominal power, or “Pmax”.

Remember, for this calculation, you need to convert a panel’s power rating from watts to kilowatts by dividing the wattage by 1,000.

Skip the math and use our solar calculator for an accurate estimate of how many solar panels you need

Example: Calculating how many solar panels you need

Graphic outlining the steps for calculating how many solar panels you need and an example.

Let’s look at an example to illustrate how to estimate the number of solar panels you’ll need.

The Smiths are looking to install solar panels on their roof. They look at their most recent electricity bill and see that they used 1,100 kWh in one month. The map above shows their state receives about 150 monthly peak sun hours. This means the Smiths would need an 8 kW solar system to offset their electricity usage.

1,200 kWh usage / 150 monthly peak sun hours = 8 kW solar system

To determine how many panels are used in an 8 kW system, we need to know the panel wattage. For this example, we’ll use 400 watts or 0.40 kW. Now, we just divide the system size by the panel’s output for the number of solar panels needed.

8 kW solar system / 0.4 kW panel = 20 solar panels

Factors that determine how many solar panels you need

Many things can impact the right number of solar panels for you, including your electricity usage, the panel you use, your roof, and your budget!

Electricity usage

How much electricity you use has the biggest impact on how many solar panels you need. If you use a lot of electricity, you’ll need a lot of solar panels!

Energy consumption can vary with the number of people that live with you, how energy efficient your home is, the appliances you use, and the state you live in. For example, a home with an electric stove, water heater, and clothes dryer will have a higher electricity bill than a home with gas appliances!

Panel output 

The more powerful a solar panel is, the fewer you will need to run your home. The following table outlines how many solar panels you would need to cover an average household’s electricity usage, depending on the size of the panel:

Panel wattage

Panels needed for average electric usage

250 watts

26

300 watts

22

350 watts

19

400 watts

17

450 watts

15

Disclaimer! 250 watt solar panels are rarely used in new rooftop solar installations in 2024. You'll want to look for solar panels with a higher output to cover your basic electricity needs. 250 watt solar panels are useful in smaller-scale solar projects.

Sun exposure and climate

Solar panels need sunlight to generate electricity. You can install fewer solar panels to cover your electricity bills if you live somewhere with lots of sunshine. 

For example, one 400-watt solar panel in Arizona can produce almost 90 kWh of electricity in one month. That same panel could only generate 36 kWh in Alaska.

If your panels will get shaded at any point of the day, they can’t generate electricity. So, you may need to install a few more panels on a shady roof or cut down overhanging trees to ensure your panels can produce the most electricity. 

Roof angle and direction

Solar panels operate best on south-facing roofs at an angle between 30 and 45 degrees. This orientation maximizes the amount of sun exposure panels can get.  If your roof faces north, you can still install solar panels; you’ll just need to install more to cover your energy needs fully than if your roof faces another direction. 

Roof size

The size of your roof may limit how many solar panels you can install. A typical solar installation will need a minimum of 335 square feet of suitable roof space. For reference, an average roof is 1,700 square feet. 

If your roof can’t fit all the solar panels you need - that’s okay! You can install fewer panels that do fit on your roof, but the system will only cover a portion of your electricity needs. Those with smaller roofs should also consider high-efficiency solar panels, which can generate more electricity in a smaller space.

The following table outlines how much roof space is needed for different amounts of solar panels:

Number of panels

System size*

Minimum roof space required

10

4 kW

177 square feet

15

6 kW

265 square feet

20

8 kW

353 square feet

25

10 kW

442 square feet

30

12 kW

530 square feet

*Assumes 400-watt panels

Budget

A typical solar panel system costs about $20,000 before any incentives are considered. If that’s not in your budget, you can install fewer panels and still save on your electricity bills. However, the panels might not generate enough electricity to cover all of your electricity bills. There may also be solar incentives and rebates in your area that bring the cost of solar installations down!

You could get cheaper, lower-quality solar installation to save a little bit upfront, but we don’t recommend it. Low-quality panels might not last as long or operate well, and poor-quality workmanship can potentially damage your roof and system. If you are on a budget, we recommend installing fewer panels and exploring different solar financing options. 

Can solar panels power your entire house?

Technically, yes, solar panels can power your entire house. But it might not be in the way that you’re thinking.

For most home solar panel systems, your solar panels only run your house during the day, when the panels produce electricity. Solar panels don't produce energy at night, so your home is likely relying on the utility. So then, how do solar panels cover all of your electricity costs?

Well, many utility companies let solar homeowners send extra solar energy to the grid during the day in exchange for bill credits that cover the cost of electricity they take from the grid later. This process is called net metering. Solar bill credits can be worth the full retail rate of electricity, but sometimes it’s less.

Usually, a solar installer will install enough solar panels to generate your daily electricity usage during the aylight hours, so you have credits to offset your electricity costs later in the day. For example, read about how many solar panels you need for the average 2,000 square foot house.

If you want to run your house entirely on solar panels, install a solar battery. The battery can store your excess solar energy for later use instead of sending it to the grid for bill credits. 

Find a reliable solar company to install the solar panels you need

The best way to know how many solar panels you need is by talking to actual solar installers. Solar companies are the experts on all things solar in your area. They will know the climate conditions near you, the panels that operate best, and how all of the specific elements of your home will impact the number of solar panels you need.

This expertise is why SolarReviews recommends local solar installers - they know you’re neighborhood as well as you do! To get the best solar installation possible, you should:

  • Look for companies that have been in business for at least five years

  • Consider installers with good customer reviews

  • Get quotes from at least three companies to get the best deal

Get quotes from trusted local solar companies

How many solar panels do I need FAQ

Written by Catherine Lane Solar Industry Expert

Catherine is the Written Content Manager at SolarReviews, where she has been at the forefront of researching and reporting on the solar industry for five years. She leads a dynamic team in producing informative and engaging content on residential solar to help homeowners make informed decisions about investing in solar panels. Catherine’s expertise has garnered attention from leading industry publications, with her work being featured in Sola...

Learn more about Catherine Lane