Highlights
The average home requires between 15 and 34 solar panels.
The average solar panel produces between 250 and 400 watts.
Annual energy use, panel wattage, and panel production all determine the final count.
You may be able to send extra power back to your local grid for a rebate.
A solar engineer will help you determine the number and placement of panels.
The time has come: you've decided to take the next step and commit to a solar-powered home. When estimating your solar power calculations, assume that you will need between 15 and 34 solar panels to meet your needs. The wide range accounts for the type of solar panel you choose, how much energy you use in your home, and your solar system's production ratio—AKA how much sun actually reaches those panels. If you’ve ever asked yourself, “How many solar panels do I need?” here's what you need to know.
How Do Solar Panels Work?
First things first: how do solar panels work and how does this info help you determine how many solar panels you need?
As explained by the U.S. Department of Energy, the solar panels we use to power residential homes use photovoltaics (PV). The panels use a series of technologies to convert photons from the sun into electricity. An inverter then transforms the direct current into power that keeps the lights on and the dishwasher running.
Today, you have the option of three types of panels:
Monocrystalline
Polycrystalline
Thin Film
In addition to affecting the cost of your solar panel design, each type of solar panel features a different level of efficiency. As you'd expect, the higher the percentage of sunlight converted to energy, the fewer panels you'll need on your home.
In spite of their dependency on sunlight, solar panels can work in nearly all climates. However, a local professional solar panel team may determine how many solar panels are necessary to power your house if it sits in significant shade.
How Many Solar Panels Do You Need?
Let's jump into the mathematics of solar power calculations. While you may think that the size of your home determines how many solar panels you need, this isn't always a dependable indicator. Think about it—both a small one-bedroom apartment and a large two-bedroom home will still likely have the same kitchen appliances and entertainment center that use up a good deal of power.
While home size will have some effect on solar panel count, it's inconsistent. Here are the top three numbers you need to do that math.
Home Energy Usage
The 2021 average for home electricity usage in the U.S. was 10,632 kilowatt hours, according to a report by the U.S. Energy Information Administration. To estimate your personal usage, take a look at Energy.gov's energy calculator.
Your solar panel system must be able to create the amount of power your home uses each year. If it produces more than necessary, which is common, you may be able to send the extra power back to the grid and even receive compensation from your utility company.
The solar panel team may also recommend scheduling a home energy audit to study the efficiency of everything from major appliances to your HVAC system.
Solar Panel Power
Depending on the type of solar panel you choose, each panel will produce between 250 and 400 watts. These numbers indicate how much the panel can produce on a sunny day with between five and six hours of light.
Home Production Ratio
The production ratio takes all the most common solar panel questions into account. What if you have trees over your roof? What if I live in a cloudy area? The production ratio is the estimated output divided by your solar panel's size in watts. The most common ratio in the U.S. falls between 1.3 and 1.6.
Solar Panel Equation
Once you have these three numbers, divide the system size in kWh by the production ratio and then again by the panel wattage. The resulting number will provide an estimate of how many panels you need on your home. Let's use a standard estimate for each as an example.
10,632 kilowatt hours / 1.4 / 300 W = Between 25 and 26 panels
If you land on installing 25 panels, each of which produces 300 watts, you'll need a 7,500-watt system, typically defined as a 7.5 kW system.
Measuring Your Home for Solar Panels
Home measurements are a significant part of solar power calculations. A professional solar panel installer will work with you to measure your home for solar panels. The process, it turns out, comes down to far more than just the area size of your roof. Here are some stats to keep in mind:
A 250-watt solar panel measures about 17.5 square feet.
A 400-watt solar panel measures about 21.5 square feet.
A standard solar panel measures 40–50 pounds.
If you need 25 solar panels, you'll need just under 500 square feet of space on your roof and the capacity to hold between 1,000 and 1,250 pounds. Both factors fall well within the capacity of a standard roof.
To maximize sun exposure, solar panels work best on the south-facing side of a roof. Even the pitch, or steepness, of the roof plays a role. Pitches between 15 and 45 degrees catch maximum sunlight throughout the day. The amount of shade and average hours of sunlight in your area will also come into play.
In other words, even if you have the space to put solar panels on your roof, it's important to chat with a professional. If your roof is not ideal for hosting the right number of solar panels, mounting them on the ground is also an option.
Solar Panel Costs Per System Size
The cost of solar panel installation typically ranges between $2.50 and $3.50 per watt when you include the cost of materials and labor. Higher prices include panels with higher efficiency or those with special structural features like thin film panels. Using our equation above, you'll pay between $18,750 and $26,250 for your system.
Your solar panel mount type, the access to your roof, and the cost of an inverter—about $1,500—will add to your final price tag.
Keep in mind that federal tax rebates, local incentive, and long-term cost savings on solar panels can balance the investment.
Frequently Asked Questions
The average-sized home in the U.S.—typically around 2,500 square feet—will require between 15 and 34 solar panels to power the whole home. The specific number, however, will have less to do with home size, and more to do with how much energy you use each year and the amount of sunlight in your region.
Solar panels have a lifespan between 10 and 40 years depending on the type of panel. For example, monocrystalline panels can last up to 40 years while thin-film ones only span between 10 and 20. The longevity also comes down to keeping up with solar panel repairs and their related costs.
While you can minimally overshoot the number of solar panels you need for your home, it's not smart to go too far. Not only is the extra cost unnecessary, but your state may put caps on how much energy your home can produce and send back to the grid. It is always best to work with a solar energy professional to determine the best system size for you.
