The following are some of the most important factors to consider when figuring out many solar panels your house needs:
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 geographic 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 residential 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.
How Can You Estimate the Number of Solar Panels You Need to Power Your Home?
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: what is your energy use and how much energy your panels will produce. We dive into these in more detail below, but here are the general steps:
- Calculate how much energy your home uses
- Assess your roof space and the amount of sunlight your home receives
- Figure out the specific yield of solar panels in your area to estimate system size
- Check the wattage of the specific panels you intend to purchase
- Divide the wattage of your system by the solar panel wattage
Determine Your Home’s Electricity Needs
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 monthly electric 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.
Electricity Needs for Common Household Appliances
The size of your home is a major indicator of how many solar panels you need, but you also have to take into account your daily energy use. For instance, a household with common appliances — such as a refrigerator, dishwasher, stove, etc — will consume less electricity than a home that has an added heated pool, central air conditioner, hot tub and electric vehicle.
These additional appliances and systems will dramatically increase your daily energy use, which means you will need more solar panels to offset your total energy consumption. As you plan your home solar system, make a list of all your appliances and systems so that all are accounted for in your final design.
| Product | Average Annual Energy Use | Number of Solar Panels Needed |
| Television | 100 kW/year | 1 |
| Dishwasher | 360 kW/year | 2 |
| Oven | 410 kW/year | 2 |
| Dryer | 470 kW/year | 2 |
| Energy Star Refrigerator | 615 kW/year | 2 |
| Electric Vehicle | 4,000 kW/year | 12 |
| Electric Water Heater | 4,500 kW/year | 16 |
*assuming 350-watt solar panels are installed and average sun hours
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 hours of sunlight.
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’s energy needs are 15,000 kWh 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 power 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 utility bills adds up to 24,000 kWh, you’ll need a 20 kW system (24,000 / 1,200 = 20).
You can also visit this resource to get an idea of how solar panels may perform at your house.
Watch below for more info on how your solar panels may be producing less electricity (watts) than what their power rating claims.
How Much Roof Space Does Your Solar Panel System Need?
On average, a solar system requires between 280 square feet and 350 square feet of roof space. Considering the average square footage of residential home roofs in the United States is 1,700 square feet, most people will not have any issues with solar panel installation.
But if you have a smaller roof, it’s best to invest in higher efficiency panels because you will need fewer panels to cover your energy costs. To help estimate the required square footage for your home solar, we’ve created a table that estimates how much space you’ll need for the most common solar system sizes:
| System Size | Estimated Monthly Energy Production | Number of 350-Watt Solar Panels | Minimum Required Roof Square Footage |
| 3 kW | 200 – 520 kWh | 9 | 160 sq. ft. |
| 5 kW | 300 – 860 kWh | 15 | 265 sq. ft. |
| 7 kW | 430 – 1,210 kWh | 20 | 355 sq. ft. |
| 9 kW | 555 – 1,550 kWh | 26 | 460 sq. ft. |
| 11 kW | 678 – 1900 kWh | 32 | 565 sq. ft. |
| 15 kW | 924 – 2500 kWh | 43 | 760 sq. ft. |
*based on the installation of 350-watt panels and average sun hours
The above estimates are based on the installation of 350-watt solar panels. If you decide to go with panels rated for more or less wattage, the required roof space will differ. For instance, you will need more roof space for panels with less wattage and less roof space for panels rated for a higher wattage.
It’s fairly simple to determine how much roof space you need, just multiply the number of solar panels you need by their size. The industry average square footage of a solar panel is 17.55 square feet, but this number will vary depending on your panels.
Below we’ve provided estimates for the amount of roof space you’ll need if you install a 9 kW solar system but choose panels with a wattage other than 350-watts:
- 300-watt panels: 30 solar panels = 530 square feet
- 325-watt panels: 28 solar panels = 500 square feet
- 375-watt panels: 24 solar panels = 425 square feet
- 400-watt panels: 23 solar panels = 400 square feet
Conclusion: How Many Solar Panels Do You Need?
Once you know how much electricity you use and 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 energy 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.
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.