One of the first questions homeowners ask themselves when deciding to go solar is, “How many solar panels do I need?” The average home needs between 17 and 25 full-sized solar panels to meet its energy needs. However, many factors go into determining how many solar panels you’ll need for your home, including how much electricity your household uses, the amount of sun exposure your roof receives and the power output of the solar panels you’re planning to install.
This guide will help you make sense of each and walk you through the calculations to determine the number of solar panels you need.
Key takeaways:
The average home needs between 17 and 25 solar panels to offset energy costs.
Your energy usage, climate, roof and solar panel efficiency impact the number of panels you need.
To determine how many solar panels you need, start by determining how much energy you use per month.
When in doubt, contact a professional solar installer or use a solar calculator to determine how many solar panels you need.
Factors that determine how many solar panels you need
You may think, “Shouldn’t a 10-kilowatt system produce 10 kWh per year?” It doesn’t work that way.
How much energy your solar panels produce depends on several variables, including the amount of direct sunlight they receive daily, the tilt and orientation of the panels, the direction your roof faces and the type of panels. When a solar installer installs your solar panels, they calculate the actual estimated output of the system by considering all of these factors.
“It’s crucial to acknowledge that solar panels don’t function at maximum efficiency 24 hours a day,” said Aaron Nichols of solar system installation company, Exact Solar. “Weather conditions, for instance, can temporarily diminish a system’s efficiency.”
Experts advise including a 25% “cushion” to your target daily average to guarantee you can generate all the clean energy you need.
Production ratio
The production ratio is the estimated amount of energy in kilowatt-hours your system will produce divided by the total wattage of the solar system.
Most 10kW solar systems produce anywhere from 11,000 to 17,000 kWh per year, which would be a production ratio of between 1.1 and 1.7.
While you can’t make precise calculations for your system’s production ratio, you can make a rough determination based on where you live. Production ratios for homes in sunny locales, such as California, are typically between 1.4 and 1.8. In contrast, production ratios for the Northeast, which receives significantly less sunlight, are much lower at 1 to 1.3, according to EnergySage.
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Typical Production Ratio
|
|
|---|---|
| Southwest | 1.5 - 1.8 |
| West Coast | 1.4 - 1.8 |
| Mountain West | 1.3 - 1.6 |
| Southeast | 1.2 - 1.5 |
| Midwest | 1.1 - 1.3 |
| Mid-Atlantic | 1.1 - 1.35 |
| Northeast | 1 - 1.3 |
| Pacific Northwest | 1 - 1.15 |
Source: EnergySage
Household electricity usage
According to the U.S. Energy Information Administration (EIA), the average American household used 10,791 kWh of electricity (or about 900 kWh per month) in 2022. Start by determining how much energy your household uses each year.
Look at past electricity bills. The total of 12 months’ worth of energy use in kilowatt hours (kWh) is the amount of solar power you’ll need to generate annually to meet your household’s needs. Some electric companies conveniently print your 12-month usage right on each bill. If yours doesn’t, pull out all your bills — since your monthly usage can vary significantly from season to season, you’ll need them to reflect your annual energy usage accurately.
Local climate and sun exposure
How many hours of sun your panels get each day impacts how much energy they can generate and, thus, how many solar panels you need to meet your home’s energy demands.
Though there are typically 8 to 12 hours of sunlight daily, homes in the United States receive between four and six hours of direct — or peak — sunlight per day. Solar radiation is highest during these daily peak sun hours.
Here’s a look at peak sunlight hours in your state, according to the National Renewable Energy Laboratories’ (NREL) U.S. solar irradiance map.
Roof size and direction
Since your solar panels mount to your roof, the roof size limits how many solar panels you can fit on top. You can determine how many panels you can fit on your roof by measuring the area of the roof (length times width) and then dividing it by the area of the solar panels. So, if your solar panels are three feet by five feet (15 square feet) and your roof measures 1500 square feet, you can fit a maximum of 10 panels.
The direction your roof faces also matters; south-facing roofs are ideal, as they’ll get the most direct sunlight daily. “If roof space is limited and only faces north or is blocked by trees, you’ll need to invest in the highest-efficiency panels possible, and that still may not be enough to meet your needs,” said Nichols.
Solar panel size
When considering solar panel size and how it influences how many panels you’ll need, look at the number of cells in the panel. Most residential solar panels have either 60 or 72 cells. While both sizes of solar panels have the same width, 72-cell panel models are about a foot longer.
Larger 72-cell panels are ideal for homes with wide-open roof space, while smaller panels make sense for roofs, dormers and other architectural elements that make it more challenging to mount large panels.
Solar panel type and efficiency
Panel efficiency is another factor that impacts how many solar panels you need. The higher the solar panel’s efficiency, the fewer you’ll need to mount to your roof. “If you have a ton of roof space facing south, you can get away with a system made up of several low-efficiency panels,” Nichols said.
There are two main types of residential solar panels: monocrystalline and polycrystalline. Monocrystalline panels cost more but are also the more efficient of the two options. Polycrystalline panels have an average efficiency of between 13% and 16%, and monocrystalline panel efficiency ranges from 15% to 22%, which means you’ll need fewer monocrystalline panels to reach your target daily average.
How do I calculate the number of panels I’ll need?
To calculate the number of solar panels you’ll need:
- First, divide the target amount of electricity you need to generate each hour by the production ratio for your area.
- Next, divide that amount by the wattage of the panels you plan to install.
For example, we’ll assume you consume roughly 10,000 kW of electricity per year and live in sunny Southern California, which averages a high production ratio of 1.8.?If you’re using solar panels with a 300-watt output, you would need to install 19 solar panels to meet your home’s energy needs (10,000/1.8/300).
Average solar panel requirements per annual energy consumption
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Production ratio
|
Panel wattage (in Watts.)
|
Number of solar panels needed
|
|
|---|---|---|---|
| 10,000 kWh | 1.8 |
300 |
19 |
| 11,000 kWh | 1.3 |
300 |
28 |
| 11,000 kWh | 1.1 |
350 |
29 |
How much can I save by going solar?
How much money you save by going solar depends on a few factors, like your monthly energy usage, initial solar installation cost and state, local and federal incentives.
According to the EIA, the average U.S. household spent about $1,600 on electricity in 2022. While you can reduce that number significantly by going solar, it won’t drop to zero. Unless you purchase a solar battery and go off-grid, you’ll still need to buy electricity from your power company for use at nighttime and on cloudy days when your solar array isn’t generating electricity.
You’ll also still have to pay taxes, a delivery charge and the other fees you see on your monthly electric bill. With that in mind, you can expect to cut about 80% off your utility bill, saving you about $1,280 annually. That said, the average homeowner will see a return on their solar investment within six to 12 years of their installation.
How do I know if solar panels are right for my home?
Before deciding to go solar, Nichols advises evaluating your roof, considering your energy use and weighing the installation costs.
“Check if the roof is in good condition and has sufficient space and proper orientation for solar panels,” he said. “It’s a good idea to replace your roof before going solar so that you don’t have to have a contractor remove the panels before installing a new roof.”
If the roof is ideal for solar, Nichols suggests homeowners weigh the savings and costs to see if it makes sense. “Get quotes from several local solar companies,” he said. “Evaluate the cost of installation, the level of customer service, available incentives and the payback period to see if it aligns with your budget and financial goals.”
Bottom line
Determining how many solar panels you need for your home can be complicated. However, you can determine the number of solar panels you’ll need yourself by assessing your energy usage and making a few calculations.
If math isn’t your thing, you can still find out how many solar panels your home will need by using an online calculator, such as the one offered by the National Renewable Energy Laboratories, or by contacting a professional solar system installer and asking them to perform a free estimate.
