How Many Solar Panels Do I Need to Power My Home?

Here’s what we’ll cover in this guide:

  • How to calculate the number of solar panels you need
  • What factors influence your installation size
  • How panel efficiency differs
  • How specific yield plays into system size
Ecowatch Author Leonardo David

By Leonardo David

Updated 6/26/2022

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How Many Solar Panels Do I Need to Power My Home?

Making the switch to solar energy can help you lower or even eliminate your monthly electric bills while reducing your carbon footprint. However, before installing a clean energy system in your home, you must first answer an important question: “How many solar panels do I need?”

To accurately calculate the ideal number of solar panels for your home, you’ll need a professional assessment. However, you can estimate the size and cost of the system based on your electricity bills, energy needs and available roof space. Here are the general steps:

  1. Calculate how much energy your home uses
  2. Assess your roof space and the amount of sunlight your home receives
  3. Figure out the specific yield of solar panels in your area to estimate system size
  4. Check the wattage of the specific panels you intend to purchase
  5. Divide the wattage of your system by the wattage of your panels

Read on for a full explanation of each step of the process. Or, to consult with a professional and start designing your system right away, you can click the buttons below to get connected with one of the best installers in the nation.

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Factors That Influence How Many Solar Panels You Need: Size and Output

To determine how many solar panels are needed to power a house, several factors must be considered. For example, if there are two identical homes powered by solar energy in California and New York, with exactly the same energy usage, the California home will need fewer solar panels because the state gets more sunshine.

The following are some of the most important factors to consider when figuring out many solar panels you need:

Size of Your Home and Available Roof Space

Larger homes tend to consume more electricity, and they generally need more solar panels. However, they also have the extra roof space necessary for larger solar panel installations.

There may be exceptions to this rule — for example, a 2,000-square-foot home with new Energy Star appliances may consume less power than a 1,200-square-foot home with older, less-efficient devices. When it comes to installation, solar panels can be placed on many types of surfaces.

However, your roof conditions may limit the number of solar panels your home can handle. For example, if you have a chimney, rooftop air conditioning unit or skylight, you’ll have to place panels around these fixtures. Similarly, roof areas that are covered by shadows are not suitable for panels.

Also, most top solar companies will not work on asbestos roofs due to the potential health risks for installers.

Amount of Direct Sunlight in Your Area

Where there is more sunlight available, there is more energy that can be converted into electricity. The yearly output of each solar panel is higher in states like Arizona or New Mexico, which get a larger amount of sunlight than less sunny regions like New England.

The World Bank has created solar radiation maps for over 200 countries and regions, including the U.S. The map below can give you an idea of the sunshine available in your location. Keep in mind that homes in sunnier regions will generally need fewer solar panels.

© 2020 The World Bank, Source: Global Solar Atlas 2.0, Solar resource data: Solargis.

Number of Residents and Amount of Energy You Use

Households with more members normally use a higher amount of electricity, and this also means they need more solar panels to increase energy production.

Electricity usage is a very important factor, as it determines how much power must be generated by your solar panel system. If your home uses 12,000 kilowatt-hours (kWh) per year and you want to go 100% solar, your system must be capable of generating that amount of power.

Type of Solar Panel and Efficiency Rating

High-efficiency panels can deliver more watts per square foot, which means you need to purchase fewer of them to reach your electricity generation target. There are three main types of solar panels: monocrystalline, polycrystalline and thin-film.

In general, monocrystalline panels are the most efficient solar panels, followed closely by polycrystalline panels. Thin-film panels are the least efficient.

If you want to know for sure how many panels you need, you can click below to connect with an EcoWatch-vetted installer and get a free estimate.

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How to Estimate the Number of Solar Panels You Need

So, based on these factors, how many solar panels power a home? To roughly determine how many solar panels you need without a professional assessment, you’ll need to figure out two basic things: how much energy you use and how much energy your panels will produce.

Calculating How Many Kilowatt-Hours Your Home Uses

According to the latest data from the U.S. Energy Information Administration (EIA), the average American home uses 10,649 kWh of energy per year. However, this varies depending on the state. For example:

  • Louisiana homes have the highest average consumption, at 14,787 kWh per year.
  • Hawaii homes have the lowest average consumption, at 6,298 kWh per year.

To more closely estimate how much energy you use annually, add up the kWh reported on your last 12 power bills. These numbers will fluctuate based on factors like the size of your home, the number of residents, your electricity consumption habits and the energy efficiency rating of your home devices.

Solar Panel Specific Yield

After you determine how many kWh of electricity your home uses annually, you’ll want to figure out how many kWh are produced by each of your solar panels during a year. This will depend on the specific type of solar panel, roof conditions and local peak sunlight hours.

In the solar power industry, a common metric used to estimate system capacity is “specific yield” or “specific production.” This can be defined as the annual kWh of energy produced for each kilowatt of solar capacity installed. Specific yield has much to do with the amount of sunlight available in your location.

You can get a better idea of the specific yield that can be achieved in your location by checking reliable sources like the World Bank solar maps or the solar radiation database from the National Renewable Energy Laboratory. To estimate how many kW are needed to run a house, you can divide your annual kWh consumption by the specific yield per kilowatt of solar capacity.

For example, if your home needs 15,000 kWh of energy per year, and solar panels have a specific yield of 1,500 kWh/kWp in your location, you will need a system size of around 10 kilowatts. Paradise Energy Solutions has also come up with a general formula to roughly ballpark the solar panel system size you need.

You can simply divide your annual kWh by 1,200 and you will get the kilowatts of solar capacity needed. So, if the energy consumption reported on your last 12 power bills adds up to 24,000 kWh, you’ll need a 20 kW system (24,000 / 1,200 = 20).

So, How Many Solar Panels Do I Need?

Once you know the system size you need, you can check your panel wattage to figure how many panels to purchase for your solar array. Multiply your system size by 1,000 to obtain watts, then divide this by the individual wattage of each solar panel.

Most of the best solar panels on the market have an output of around 330W to 360W each. The output of less efficient panels can be as low as 250W. So, if you need a 10-kW solar installation and you’re buying solar panels that have an output of 340W, you’ll need 30 panels. Your formula will look like this: 10,000W / 340W = 29.4 panels.

If you use lower-efficiency 250-watt solar panels, you’ll need 40 of them (10,000W / 250W = 40) panels. Keep in mind that, although the cost of solar panels is lower if you choose a lower-efficiency model over a pricier high-efficiency one, the total amount you pay for your solar energy system may come out to be the same or higher because you’ll have to buy more panels.

Conclusion: Are Solar Panels Worth it for Your Home?

Solar panels produce no carbon emissions while operating. However, the EIA estimates fossil fuels still produce around 60% of the electricity delivered by U.S. power grids. Although the initial investment in solar panels is steep, renewable energy systems make sense financially for many homeowners.

According to the Department of Energy, they have a typical payback period of about 10 years, while their rated service life is up to 30 years. After recovering your initial investment, you will have a source of clean and free electricity for about two decades.

Plus, even if you have a large home or find you need more solar panels than you initially thought you would, keep in mind that there are both federal and local tax credits, rebates and other incentives to help you save on your solar power system.

If you want to know for sure how many panels you need, you can click below to connect with an EcoWatch-vetted installer and get a free estimate.

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FAQ: Solar Panels Needed to Power a House

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Leonardo David

Solar Expert

Leonardo David is an electromechanical engineer, MBA, energy consultant and technical writer. His energy-efficiency and solar consulting experience covers sectors including banking, textile manufacturing, plastics processing, pharmaceutics, education, food processing, fast food, real estate and retail. He has also been writing articles about energy and engineering topics since 2015.