Considering going solar? Here’s how many solar panels you really need

Key points

• The average U.S. home requires 18 solar panels to produce enough electricity.

• Electricity usage, sunlight and the power rating of your panels determine the number of solar panels you need.

• Eliminating your electric bill is only possible if you have access to net metering or if you install batteries alongside your panels.

Even if you were to get one of the better solar brands out there, it’s important to remember that installing solar panels can significantly decrease your utility bills and raise your property value by an average of $15,000, according to research done by the Lawrence Berkeley National Laboratory. Getting the correct number of solar panels for your home will help minimize the chance of over- or underestimating your system’s production. 

Start your research by reaching out to solar companies in your area. 

How many solar panels you need depends on how much electricity you use, the wattage of the solar panels you’re considering, how much sunlight your home gets and your solar panel efficiency. 

Undersizing your system could lead to production that’s less than your consumption, meaning you’d still have an electric bill to pay. Oversizing it means you’d pay more for your system than you need to. “Ultimately, you’ll avoid overpaying while maximizing your savings,” said David Schieren, CEO of EmPower Solar, a certified solar installer on Long Island in New York and vice chair of the Distributed Generation Division for the Solar Energy Industry Association (SEIA). 

The average number of solar panels you need is 18, based on average electricity consumption data and typical panel production in the United States. This number could be higher or lower, depending on where you live and how much energy you consume.

The right number of panels varies based on your situation, including factors like the “pitch and orientation of your roof, obstructions on your roof — chimneys or plumbing vent stacks — and shading from nearby trees or buildings. You’ll want to factor in future upgrades, such as the addition of an EV charger or air conditioner units. “Increased occupancy could also increase your energy consumption,” Schieren added.

How many solar panels does the average house need?

The average home needs 18 solar panels to offset its electricity usage. There are a few factors that go into that estimate.

First consider that your home needs an average amount of electricity. According to the U.S. Energy Information Administration (EIA), the average American household consumed 10,788 kilowatt-hours (kWh) of electricity in 2022. That estimate comes out to approximately 29.5 kWh of electricity per day.

The estimate is also accurate if you have a system made up of standard 400-watt panels and your system achieves 85% of its peak rating due to factors that range from weather to shade from trees. This solar panel quantity is based on the assumption that your home receives about five hours per day of direct sunlight.

These numbers are only applicable if you want to offset 100% of your electricity bill with solar power. Some homeowners choose to save money upfront and purchase a smaller system that only produces a fraction of what their home uses per day.

The next section includes a detailed calculation to help you apply these principles.

How do you calculate how many solar panels you need for your house?

The following numbers are the basics to perform the sample calculation:

• Electricity usage: 29.5 kWh per day or around 885 kWh per month
• Solar panel wattage: 400 W (per panel)
• System efficiency: 85% (note that this is the efficiency of reaching its peak power generation, not the efficiency of converting sunlight to electricity, which is much lower
• Desired electric bill offset percentage: 100%
• Peak sunlight time per day: Minimum of 5 hours (a conservative estimate based on nationwide data)

These assumptions were chosen because they represent reasonable averages across the United States. Your individual system’s performance, your home’s light exposure and your energy consumption may be significantly different. You should use numbers that work for your home and solar energy system to calculate the number of panels you need.

Since these calculations are challenging to get right and your long-term savings depend so heavily on them, the best-case scenario would be to work with a reliable solar installer.

Step 1: Determine the total amount of electricity you need

To determine the total energy output you need, look at the yearly consumption on your electric bill. If you want to offset 100% of your daily electricity usage, that means your solar panel system needs to produce an average of 29.5 kWh per day. Of course, if you want to offset a different percentage of your daily energy usage, you can adjust this number.

Step 2: Calculate the panel output you need

Once you know how much energy you use, calculate the total solar system size you need to produce that much energy. Since solar power systems don’t operate at their peak rating 100% of the time, you can’t just buy a system with a power output rating that matches your daily electricity usage.

Panels do not typically produce power at their maximum capacity, but under ideal conditions ,a system could approach maximum power capacity during certain times of the year and certain times of day, Schieren noted. Those ideal conditions include a south-facing panel orientation and the proper angle to receive direct sunlight.

To calculate the maximum potential energy output a solar system needs to produce 29.5 kWh of usable energy per day, divide the target energy output by 0.85 (estimate of 85% efficiency under real-world conditions).

29.5 kWh / 0.85 = 34.7 kWh

Step 3: Calculate the number of panels you need

We’ll assume that you’re installing 400-watt panels. You should perform your own calculation using the power rating of the panels you plan to install.

You need to estimate the number of peak sunlight hours your panels will receive per day. This number will vary quite a lot, but we’ll choose five hours of sunlight for simplicity. In reality, the amount of direct sunlight that hits your panels will change with the weather, seasons and shade from nearby plants and vegetation. You can use the solar irradiance map developed by the National Renewable Energy Laboratory (NREL) to get a good estimate for your area.

In average conditions, a standard 400-watt panel will produce 2 kWh in five hours. To reach our target value of 34.7 kWh per day, that means you need 34.7 kWh / 2 kWh / panel = 17.35 panels. That means an average of 18 panels is required if you want to offset 100% of your electricity usage.

What factors determine the number of solar panels your home needs?

The number of solar panels you need depends on several key factors that include:

Average electricity consumption

The amount of energy you consume to run your home is one of the primary determining factors that dictates the total size of the system you need. The more energy you use, the larger the system you’ll need to offset your usage. Larger systems require panels with higher wattages, more panels or both.

How much of your usage you want to offset changes the number of panels you need as well. You can get away with a smaller system if you only want to reduce your energy bill rather than eliminate it altogether.

The size of your system depends on how you plan to use it over the next 25 years, which is the average lifespan for residential solar panels. If you’re considering purchasing an electric vehicle in the future, for example, you need to factor in the increased electricity demand to keep it charged. 

Additionally, all solar panels degrade at an average rate of around 0.5% per year, according to the NREL, plus a first-year degradation rate that’s higher, which complicates the calculation. Reliable installers will account for this degradation to help you maintain long-term savings even as your panels produce less electricity over time.

Net metering availability

Another important consideration is the net metering (NEM) policy in your area. “Under net metering, the utility company will replace a customer’s traditional meter with a “net meter,” which is a meter that has the ability to “spin” both forward and backward,” Schieren explained. What this means: during high production months (summer) and in the middle of the day, the solar system may produce more energy than needed. At this time, the excess energy is sent back to the electric grid.. That excess energy is recorded on the customer’s electric bill in the form of a credit. Those credits are then used when your system fails to meet production needs, perhaps during the winter months or overnight.

With one-to-one net metering, every additional kWh you produce and don’t use can offset one kWh when you use electricity but can’t produce enough solar power in real time to offset it.

Some states have mandated one-to-one NEM programs. If that’s the case in your area, the calculations above will work. If you receive a below-retail rate for your excess energy, you’ll need to produce more energy when the sun is shining to offset the same usage when it’s not. “Ideally, your solar installer will size your system to produce exactly what your home requires,” Schieren added.

Solar panel wattage

“A typical residential-use solar panel has a power output capacity of somewhere between 400 and 440 watts,” Schieren said. Choosing a lower panel wattage means that you’ll have to purchase more panels to generate a given amount of electricity.

Regardless of the individual panel power rating you choose, your total system size doesn’t change. If you need a 9-kW system to meet your home’s energy needs, for example, it doesn’t matter if you get those 9 kW from more solar panels with 30 lower wattage 300-W panels, or 20 450-W panels.

Higher-wattage panels can be more space-efficient, which means they could be better if you don’t have a lot of roof space. “However, the most important factor is power density, or the power output per square inch,” Schieren said. “For example, a smaller solar panel may have a lower power output capacity, but it may have a higher power density than a larger solar panel.” 

Amount of sunlight

Consider your location. A house in sunny California is going to have different energy needs than one in rainy Seattle. The more sun your roof gets per day, the fewer solar panels you need to generate enough electricity to power your home because each panel will deliver higher rates of electricity production.

The solar energy availability in your area can be challenging to estimate. We recommend consulting a local solar installer. The solar providers with expertise installing solar arrays in your region will tell you how the local weather conditions and available sunlight affect the size of the system you need. That said, you can check NREL’s map of solar irradiance to estimate the total available solar energy where you live.

Can solar panels completely offset your electricity bill?

Yes, solar panels can completely offset your electricity bill if you size the system correctly. See the steps above to calculate how many panels you need to produce enough energy. 

Roof space is another consideration. If you don’t have enough roof space to fit all of the panels you need for a 100% offset, you’ll have to restrict your search to high-efficiency panels including those made by Maxeon for SunPower. High-efficiency systems are more expensive than systems with lower-efficiency panels, but they could be worth it in the long run if they let you reach a 100% offset for your electricity consumption.

Another component of offsetting your electricity bill is taking advantage of solar batteries and local incentives, including net metering programs. Net metering smooths out your savings. Rather than paying for power from the grid during periods of underproduction.

If you don’t have access to net metering, solar batteries can act as a substitute. Batteries raise the price of your system but let you store energy and effectively create your own net metering setup. You store excess energy when your panels overproduce with respect to your consumption and then tap into that energy when your panels underproduce. The electricity you store can always be called on for free, giving you an alternative to traditional net metering.

Even though they add to already high solar panel costs, solar batteries might be a good idea if you live somewhere without a net metering program. They also act as an emergency backup power source you can use during power outages.

What’s next?

The calculation we provided in this article can give you a good estimate of the number of panels you need, which is a good place to start before you reach out to solar companies. Having a ballpark estimate of the size of the system you need can help you avoid getting talked into a larger system than the one you need.

Research local solar companies to schedule consultations. Given how complicated sizing a solar array can be, it’s worth it to have an experienced professional by your side.

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