How Many Solar Panels Do I Need?

Updated: 2 days ago

One of the most common questions photovoltaic (PV) installers get during early consultations with customers is, “how many solar panels do I need for my home (or business)?” It’s a natural question since the number of PV panels directly impacts the total cost of the installation – not to mention variables like:

Monthly electricity bill savings
Carbon offsets from reduced fossil fuel use
Solar payback period

However, explaining technical terms like insolation, voltages, or kilowatt-hours to a homeowner used to thinking in dollars and cents can be challenging. If you’ve faced this situation before, use the guide below to make the solar consultation process easier to explain and easier for customers to understand.

How Many Solar PV Panels Do I Need To Power A House?

Every home is different, making it difficult to provide a universal answer that applies to all situations. But here are some useful guidelines to keep in mind:

The U.S. Census Bureau reports that the average single-family home is just over 2,300 square feet. This is a useful metric. But it’s not nearly as important as the next two points.
According to the U.S. Energy Information Administration, the average American home consumes 10,500 kWh of utility electricity each month.
The average residential solar energy system size in the United States is approximately 6 kilowatts (kW), according to data from EnergySage. This is based on the data from residential solar quotes requested through the EnergySage online marketplace.

6 kW is a good baseline, and most homeowners will understand it. Still, it’s important to correctly size every solar system so that it covers the amount of energy customers use today and tomorrow. For example, you might want to quote a rooftop solar system if the household plans to buy an EV or install heat pumps.

To understand how many solar panels to install, keep reading.

How To Determine How Many PV Panels Are Needed

When sizing a residential solar system, below are five of the most important variables that should factor into the decision-making process.

1. The Homeowner’s Solar Energy And Savings Goals

Adding just a single solar panel can help generate monthly electric bill savings. Installing more PV modules results in higher electricity bill savings. So, it’s important you consult with each customer to determine their energy and savings goals in advance.

For example, do they:

Want enough solar energy capacity to cover 100% of their electricity needs?
Plan on using net metering to sell excess power to their utility provider?
Need on-site batteries to store daytime solar energy for nighttime use?

Clearly defining these goals is crucial before moving on to the next steps.

2. Current Household Energy Usage Before Installing Solar Panels

With energy and savings targets in place, you’re ready to analyze the customer’s historic electricity consumption. Most homeowners focus on the dollar amount of past electric bills, but what matters more is the kilowatt-hours of electricity they consumed over the past year.

The higher their electricity usage, the more solar panels you’ll need to install to cover that energy consumption.

3. Power Needed For Common Appliances

The next step involves developing a clearer picture of the customer’s energy needs moving forward. Historic analysis already takes into account whatever power-hungry appliances already exist in the home. But with growing families and more electronic gadgets, it’s likely those power needs will grow over time.

In fact, “electrifying” one’s home is very common among solar power customers, whether they replace:

Gas-guzzling cars with electric vehicles (EVs) and plug-in hybrid vehicles (PHEVs)
Natural gas or propane furnaces with electric alternatives, such as heat pumps
Gas water heaters with an electric or hybrid water heater

The goal is to power more appliances with free solar energy instead of utility electricity made from fossil fuel. When talking with customers to determine how many solar panels they need, it helps to show charts and infographics so that they can better understand the effect that future purchases will have on their energy production and needs.

In addition, many customers can also make energy efficiency improvements throughout their homes. Swapping out incandescent lightbulbs with LEDs, for example, helps to reduce electricity consumption. And this allows you to install a slightly smaller solar panel system to cover that homeowner’s energy needs.

4. How Many Hours Of Sunlight Does The Area Receive?

Geography can have a huge impact on PV panel performance, with a state like Arizona receiving more direct sunlight than someplace like Massachusetts. The same is true of the changing seasons, which is why you want a year’s worth of electricity bills – and not just the past few months.

Fortunately, the National Renewable Energy Laboratory (NREL) publishes several solar radiation resources to help you determine the average amount of sunlight for each geographic region throughout the year. And these charts can help make your own sizing estimates far more accurate.

However, there is still one more piece of the puzzle.

5. Factors That Impact Solar Panel Efficiency

Solar PV panels are tested in ideal laboratory conditions. But the average home is in the real world, where constant exposure to UV light is impossible. Therefore, you’ll need to adjust your calculations to determine how many solar panels a home needs to reflect this.

Below are some of the most important factors to consider when determining system size and potential energy production:

Technology: The higher the quality (and wattage) of the panels, the fewer modules you’ll need to install.
Shading: If trees or buildings ever cast shadows over the installation, you may need to add more PV panels than normal. And it’s probably a good idea to use microinverters instead of string inverters to ensure partial shading doesn’t negatively impact total solar system performance.
Orientation: The direction of the installation also matters, with south-facing roofs receiving more sunshine than those pointing north (assuming you’re above the equator).
Temperature: Solar panels perform best when it’s cold. This means that, with all other things being equal, Massachusetts has a slight advantage over a warmer state like Florida.

How Many Solar PV Panels Will I Need?

The average home in the United States typically requires between 17 and 25 solar panels to fully power it. However, the exact number of solar panels needed can vary based on several factors, such as average household electricity usage, available roof space for PV panels, geographical location, and the solar panel's wattage output.

Solar panels are typically measured in watts, with most generating between 250 and 500 watts of power. To determine the number of solar panels needed for a specific home, calculate the household's total energy consumption and divide it by the average wattage output of the solar panels you are considering. Keep in mind that this calculation may also take into account factors such as shading, orientation, and efficiency losses.

Will I Need More Solar Panels for a Shaded Roof?

Having a shaded roof can indeed affect solar panel performance and efficiency. Shade reduces a solar panel system's overall energy output, as shaded panels receive less sunlight and generate less electricity. However, the impact of shade on a solar panel system can vary depending on several factors, such as the type of shade, the type of panel, and the system's design.

In some cases, you may need to install additional solar panels to compensate for the reduced solar generation caused by shading. The exact number of additional panels will depend on the severity and duration of the shade and the home's overall energy needs.

Do I Need Fewer Solar Panels If Using Higher Watt Modules?

Using higher-watt modules can potentially allow you to install fewer solar panels to meet a home's energy needs. Since higher-watt solar panels produce more energy per unit, a system comprised of higher-watt modules may require less overall panel surface area to generate the desired amount of electricity. This can be particularly advantageous in situations where space is limited, such as on residential rooftops or in densely populated areas. However, higher-watt solar panels sometimes have larger dimensions, requiring more roof space.