How Many Solar Panels Do I Need? | Solar Calculator

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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.  5bb Perc Solar Cell

How Many Solar Panels Do I Need? | Solar Calculator

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

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!

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.

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.

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.

Quotes from solar companies will always list the system size in kW, so it’s a good idea to have an estimate of what you need when talking to installers! 

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.

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.

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

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!

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!

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:

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. 

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. 

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:

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. 

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. At night, your home is likely using energy from the utility grid. 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 in the afternoon, so you have credits to offset your electricity costs later in the day.

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. 

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:

Larger homes tend to use more electricity for several reasons: they have more appliances, usually have more people living in them, and require more energy for heating and cooling.

A 2,000-square-foot house will likely need around 18 solar panels, while a 3,000-square-foot house typically requires closer to 30!

Home size shouldn’t be your main indicator of how many solar panels you need, but it can give you a general idea. The following table shows different home sizes and how many solar panels they typically need:

A solar installer can give you the most accurate estimate of how many solar panels you need. Not only do installers have access to highly accurate estimating software, but they’re also experts! Solar professionals know how solar works in your area and how to design the best system to meet your needs. 

Yes, you can go off-grid with solar panels. Keep in mind that off-grid solar systems need to be paired with enough battery storage to keep your home running when the sun isn’t shining.

It only makes sense to go off-grid if you don’t have access to a utility. Off-grid solar systems are very expensive because of the number of panels and batteries needed to keep a home running. 

Most homeowners don’t need solar batteries, especially if you have access to full retail net metering, but they can come with many benefits. Solar batteries can maximize the amount of solar energy your home uses, keep your lights on during a power outage, and potentially save you a little extra money on your electricity bill.

But, solar batteries typically cost a minimum of $14,000 to install. So, even if the battery provides some extra savings, it might not be enough to recoup the installation cost. 

Solar panels can’t run your home during a power outage. If you want backup power, you need to install a solar battery or a gas-powered generator.

Read more: What happens if you have solar panels and the power goes out?

Solar panels generate renewable energy, which is better for the environment than energy derived from fossil fuels. No harmful pollutants are released into the atmosphere when solar panels turn sunlight into energy.

But solar panels aren’t completely clean. Manufacturing and disposing of solar panels does have some harmful effects. But, as the industry matures and solar panel recycling becomes more established, we can hopefully achieve even greener solar panels!

Catherine is the Written Content Manager at SolarReviews, where she has been at the forefront of researching and reporting on the solar industry since 2019.

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