White home with black roof covered in solar panels.

How Many Solar Panels Do I Need?

6-Minute Read
Published on September 21, 2022
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More American homeowners are considering investing in a solar energy system to provide electricity to power their homes.

There are many factors to consider when purchasing a home solar array, but the most important question is “How many solar panels do I need for my home?” The cost of the actual solar panels, along with the installation of the system, are by far the two major expenses in the conversion to home solar power. Determining how many solar panels are required, then, is of the utmost importance.

How Many Solar Panels To Power A House?

When determining how many solar panels are needed to power a house, it’s important to look at many things, including your local weather, how many watts the panel you choose can generate and the average electricity consumption of your particular household.

Use this table to determine how many solar panels you need:

Home Size

Average Monthly Energy Consumption

Estimated Number Of Panels Needed

1,500 sq. ft.

633 kWh

14 – 17

2,000 sq. ft.

967 kWh

19 – 25

2,500 sq. ft.

1,023 kWh

24 – 30

3,000 sq. ft.

1,185 kWh

27 – 30

*Info pulled from the EIA’s Residential Energy Consumption Survey.

Here’s a further break down on how consumption, wattage and weather affect the number of panels you need.

Consumption

To understand your own usage, look back at your total energy consumption from the last 12 months on your utility bills. A typical electric bill will state the total amount of electricity you consumed that month in terms of kilowatt hours (kWh) and then charge you per kWh. For reference, in June 2022, the average cost for electricity in the United States was 15.42 cents/kWh.

Since usage varies depending on time of year and other factors, you can add the kilowatt hours used for all 12 months together to get your annual electricity needs. According to the U.S. Energy Information Administration (EIA), the average annual consumption of electricity in 2020 was 10,715 kWh.

Wattage

There are three main types of solar panels – monocrystalline, polycrystalline and thin-film, with the differences among them more thoroughly discussed here. All have varying levels of efficiency and cost. For deciding how many solar panels you’ll need to power your home, it comes down to how much power the panels can generate.

The wattage rating on a solar panel reflects the panel’s expected power production under ideal sunlight and temperature conditions. In 2022, most panels are rated at 250 – 400 watts, with the higher watt panels preferable but almost always more expensive.

This wattage rating multiplied by the number of panels is part of what is known as the system power. Every home has a different exposure to peak sunlight, and that must be factored into figuring the total power of the system.

There’s a distinction between system power, measured in watts, and the amount of energy the house will consume, which is measured in kilowatt (kW) hours. A 5 kW system will always be a 5 kW system. But, it might produce more or less power depending on a number of outside factors chief among them how much peak sunlight the panels receive. Thus, the exact same system might be enough for a 14,000 kWh home in one state, but only for a 10,000 kWh home in another.

Weather

Since solar panels don’t fully operate 24 hours a day, the weather and the seasons play a big role in their efficiency when producing solar energy. The amount of power a solar system generates fluctuates depending on sunlight exposure and time of year. If both have a 5 kW solar array, a home in California will receive far more sunlight during the course of the year and produce more kilowatt hours of electricity than a similar-sized house in Michigan.

The difference between the system’s estimated energy output over time, measured in kilowatt hours, and the actual system size, measured in kilowatts, is called the production ratio. For example, a 10 kW system that produced 14 kWh of electricity in a year has a production ratio of 1.4 (14/10-1.4).

For most U.S. locations the production ratio is 1.3 – 1.6. In the case above, the California home has a higher production ratio and the Michigan house has a lower one. This doesn’t mean that a solar system at the Michigan house cannot produce all the power the house requires. It just means it needs more solar panels and a larger system, probably closer to 6,000 watts, to produce the same amount of solar power as the California house with 5,000 watts.

Your solar installer will have specific data that will help determine the production ratio for a solar panel array in your exact location.

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How To Calculate How Many Solar Panels You Will Need

To calculate your total system size, we’ll need three piece of data: how much sunlight you get, your average energy requirements and the wattage of the solar panels you use.

Assess How Much Sunlight You Get In Your Area

You’ll need to calculate how many peak solar hours you can expect to receive on an average day where you live. This number reflects an average day because some days are sunnier than others, and because sun exposure is longer and more direct in summer than in winter.

The number of peak solar hours you receive will vary widely depending on where you live. A home in sunny southern California gets far more sun exposure than one in northern Michigan, which has more cloudy days. Further, time of day is significant — the intensity of sunlight is different depending on whether it’s 9 a.m. or 12 p.m. or 4 p.m. — as is the angle at which the sun’s rays are reaching a solar panel.

Technically, a peak solar hour occurs when the intensity of sunlight reaches 1,000 watts of energy per square meter. This sounds complex to figure, but, fortunately, science has done this difficult research for you so you don’t have to work this out for yourself. Researchers have determined peak solar hours for any part of the U.S., and the data are readily available.  Most parts of the U.S. receive 3 – 6 peak solar hours per day.

To begin calculating how many solar panels you’ll need, first determine the number of peak solar hours you receive in a month. To do this, simply multiply your peak solar hours (for example, 4.6 hours) x 30 (the average number of days in a month):

4.6 x 30 = 138 solar hours

Determine Your Average Energy Requirements

Next, to determine how many kilowatts of power our system needs in a month, we take the estimated annual kilowatt hours needed and divide it by the number of months. You can get your usage info from your electric company, but for this example we’ll use 10,715 kWh, the U.S. average:

10,715 kWh/12 = 893 kWh

To determine how many watts of power our system needs, we divide monthly kilowatt hours needed by the number of peak solar hours we receive in a month:

893 kWh/138 hours = 6.47 kW

Now we’re getting somewhere. We’ve determined that we need a 6.47 kilowatt solar system to meet our energy needs. This number is sometimes referred to as system size. To calculate how many panels we will need to build a system of that size, we first convert 6.47 kW to watts:

6.47 x 1,000 = 6,470 W

Choose Your Solar Panel And Calculate How Many You Need

Let’s say you choose a high-efficiency monocrystalline 340 Watt pane. While this will be a more expensive panel, it offers a lot of power. Here’s how you determine how many you need. Divide the total system wattage by the wattage in one solar panel, like this:

6,470 W / 340 W = 19.02

So, 19 solar panels with 340 watts of power should do the job for this particular home. Professionals will often suggest rounding up, and indeed most homes in the U.S. require 20 – 30 solar panels to meet all of their electricity needs.

The Bottom Line: How Many Solar Panels You Need Depends On Many Factors

The calculation to determine how many panels you will need is really pretty simple, once you’ve accounted for the three principal factors, which include the wattage rating of your solar panel, the total number of annual kilowatt hours you will need the system to provide for, and the peak solar hours you receive where you live.

In order to have enough solar power to meet your home’s electricity needs, as well as to not overpay for expensive solar panels, it’s important to have a strong estimation of how many panels you need before investing.

For further information on the kinds of solar panels available in today’s market, read our discussion here.

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David Collins

David Collins

David Collins is a staff writer for Rocket Auto with experience in publishing as well as communications, public relations, and web content creation for automotive manufacturing. He has a B.A. in English from the University of Michigan.