How Many Solar Panels Do You Need to Power Your Home?

Based on a monthly power usage of 877 kilowatt-hours (kWh), the average American home requires between 20 and 24 solar panels to pay 100 percent of the cost. After the federal solar tax credit, installing that many solar panels would cost between $13,000 and $16,200.

However, your energy use is likely to differ from the national average, and the quantity of solar panels you require is determined by a variety of other factors, including the location of your property and the type of solar panels you select.

So, how do you calculate the number of solar panels you require? We've got your back!

How to Determine the Number of Solar Panels Needed

Several factors influence how many solar panels you'll need to satisfy all of your energy demands. A Solar Calculator is the simplest method to determine how many panels you'll require. It handles all of the math for you by entering your address and expected monthly electricity cost so you can make an informed decision. If you want to conduct the calculations yourself, we've included a formula below to assist you.

The method we used to determine the number of solar panels you'll need to power your house is based on three major factors: yearly energy consumption, panel wattage, and production ratios. What does that exactly mean? Here are our assumptions and how we calculated them:

Annual Electricity Consumption

The amount of energy and electricity you consume in your house over the course of a year is referred to as your annual power usage. This quantity, measured in kilowatt-hours (kWh), is impacted by the items in your home that utilize power as well as how frequently you use them. Electricity is used by refrigerators, air conditioners, small kitchen appliances, lights, chargers, and other devices.

According to the United States Energy Information Administration (EIA), the average American household uses 10,715 kWh of electricity per year, so we'll use that number as the ideal solar panel system or solar array size, which would mean you could offset 100 percent of your electricity usage and utility bill with solar panels (in practice, it's not quite that simple, but bear with us here). If you want a more precise figure depending on your own energy use, see-through once you have that number, enter it into the formula below.

Solar panel wattage

Panel wattage often referred to as the solar panel's power rating is the electrical production of a certain solar panel under ideal conditions. Wattage is measured in watts (W), and most solar panels provide between 250 and 400 W of power. In these calculations, we'll assume 340W as an average panel because most of the popular solar panels on the Marketplace are at least 340W.

Production ratios

The production ratio of a solar panel system is the ratio of the estimated energy output of a system over time (in kWh) to the actual system size (in W). These ratios are virtually never 1:1 — your production ratio will vary depending on how much sunshine your system receives (which is mostly determined by your geographic location). A 10 kW system that generates 14 kWh of power per year, for example, has a production ratio of 1.4 (14/10 = 1.4) — this is a completely realistic production ratio to observe in the real world. Production ratios in the United States are typically between 1.3 and 1.6, therefore we'll take those two figures as the high and low estimations for our computation.

Now, let’s do the math

We've established our three primary assumptions (energy usage, solar panel wattage, and production ratios). But how do those figures convert to an anticipated quantity of solar panels for your home? The formula is as follows:

Number of panels = system size / production ratio / panel wattage

Using the numbers given above, we get:

Number of panels = 10,715 kW / 1.3 or 1.6 / 340 W

...which provides us between 20 and 24 panels in a solar array, depending on the production ratio we select (20 for a 1.6 ratio, and 24 for a 1.3 ratio). So, 20 panels at 340 W each equal a total system size of around 6.8 kW!

Finally, efficiency and size must be considered.

After determining the size of your system, it's useful to understand basic details about the solar panels themselves. If your solar panels are more efficient, you will probably need fewer of them, and your solar array will take up less area.

The quantity and size of solar panels may not be an issue for homeowners with a spacious roof and plenty of useable space. However, for households with limited space, it is critical to balance efficiency and size with what you have available or consider solar shingles or a ground-mounted system.

How much roof space do solar panels need?

Solar installations typically require between 335 and 405 square feet of roof area. To get the amount of roof space required for your solar system, multiply the number of panels required by 17.55 square feet, which is the size of most residential solar panels offered today.

If you have a small roof, you may need to acquire high-efficiency panels or panels with a higher power output so you may install fewer panels while still meeting your energy demands.

Number of Solar Panels needed based on the System Size

The table below indicates how many solar panels you'll need based on the size of your system, as well as an estimate of how much electricity the solar array will generate.

Figure 1. Depending on the system size, the number of panels and roof space required will vary.

System size	Estimated monthly energy production	Number of panels*	Roof space required
4 kW	480 - 600 kWh	13	220 sq. feet
6 kW	720 - 900 kWh	19	330 sq. feet
8 kW	960 - 1,200 kWh	25	439 sq. feet
10 kW	1,200 - 1,500 kWh	32	549 sq. feet
12 kW	1,440 - 1,800 kWh	38	659 sq. feet
14 kW	1,680 - 2,100 kWh	44	768 sq. feet

How To Think About Scaling a Solar System to Meet Your Needs

One of the things that homeowners commonly wonder about when they’re considering going solar is how many solar panels they’ll need to have installed. What’s behind this question is often concern about whether their home has enough “solar potential” to get a good return on investment from going solar.

To figure out the scale of the solar system you will need to achieve your financial and energy generation goals, you first need to understand your own energy needs. When our energy consultants talk with homeowners about whether going solar is right for them, we recommend they find their annual average energy consumption by looking at the electricity usage from their utility bills from the previous 12 months. Then, consider any changes in lifestyle you anticipate in the near future that might impact your energy consumption – such as purchasing an electric vehicle.

Using this information, we can determine the amount of electricity your solar panels will need to generate to meet your energy needs. You should understand that depending on the incentives available in your state, it may make financial sense to continue to buy some of your electricity from your utility rather than to install a solar system that generates 100%+ of your anticipated energy usage.

The next factor to consider is the unique characteristics of your home. Obviously, sun exposure is crucial for generating electricity from solar panels. The directional orientation of your home and shading from trees, hills, or other nearby buildings all impact how much sun your solar panels can soak in and how much energy they’ll be able to produce. The square footage of available space on your roof also determines how many panels can be installed.

Google has created an excellent tool called Project Sunroof that will give you an idea of how much sun exposure the roof of your home gets. You simply type in your address, and get an estimation of the solar energy capacity of your home.

Now that you’ve considered your energy needs and the structural and environmental factors, you can actually answer the question of how many solar panels you need in your residential solar system. Solar panels are classified by the wattage of the electricity they can generate, which is in turn determined by their physical size and the efficiency of their design.

If you have limited roof space, then it might be necessary to use a smaller number of higher-wattage panels. On the other hand, if you have abundant roof space to place panels on, then a larger number of cheaper lower-wattage panels might be a smarter buy. Another scenario may be that you have plenty of roof space, but expect to increase your usage in the years to come – perhaps by installing a swimming pool or buying an electric vehicle. In this case, you may opt for higher wattage panels to leave adequate space to add more panels down the road when your usage is higher.

In the end, the actual number of solar panels installed on your home isn’t very important in and of itself. The more pertinent consideration is how much energy do you need to generate, and how much roof space do you have available to use. Still, thinking about this question can be a useful starting point for understanding the factors you need to consider when deciding whether going solar is the right decision for you.

Not all roofs are ideal for solar panels.

In addition to evaluating the number of solar panels required, you need to consider the weight of the panels themselves.

A single panel weighs roughly 40 pounds on average, adding around 2.8 pounds per square foot to a standard pitched roof and 5 pounds to a flat roof. As a result, you must ensure that your roof can withstand the extra weight. You should also evaluate your roof's material, age, and construction.

According to the United States National Renewable Energy Laboratory, Energy Department, almost half of all residences cannot accommodate rooftop solar panels. Many homes, companies, and renters use community solar initiatives to go solar without ever putting anything on their rooftops. Participants can subscribe to a neighboring solar farm and pay less for the power generated by it.

Finally, the amount of solar panels you'll need to achieve potential savings is dependent on your home's energy use. Do you want to find out how much money you may save by putting solar panels in your home? Contact us by visiting our page or by calling 1-714-694-2262.