How Many Solar Panels Do I Need? (2023 Guide)

Solar panels are an eco-friendly way to upgrade your home, reduce energy bills, and positively impact your community through clean, renewable energy production. If you’re thinking of going solar, you’re probably wondering how many solar panels it takes to power a house. 

The answer changes for every homeowner depending on several variables, which this guide breaks down in clear, easy-to-understand language. Using one of the best solar companies helps guarantee you’ll get the correct number of solar panels, professional installation, and maximum savings.

You’ll need to know three key factors to calculate how many solar panels you need: your annual electricity usage, the solar panel’s wattage, and the entire solar power system’s estimated production ratio. Below is a breakdown of each.

Annual Electricity Usage

Your energy consumption is the amount of electricity your home uses annually. This number is measured in kilowatt-hours (kWh) and includes all home sources. Sources might be appliances, air conditioning units, lights, water heaters, etc. The U.S. Energy Information Administration (EIA) reports that a U.S. residential customer’s average annual electricity consumption was 10,632 kilowatt-hours (kWh) in 2021, with an average of 886 kWh per month.

Solar Panel Wattage

You might think that the best solar panels are all built the same, but that’s not true. There are different solar panels for different projects with different energy outputs. A panel’s wattage is how much electricity it emits, and most residential solar panels range between 250 and 400 watts of power. The higher the wattage, the fewer panels you’ll need. 

Production Ratios

A solar panel system’s production ratio is its estimated energy output over time (in kWh) compared to its actual system size (in W). Though you might assume this would be a simple 1:1 ratio, complex variables come into play, such as the amount of sunlight your home receives versus the amount of shade.

For example, a 10 kW system that produces 14 kWh of electricity in a year has a production ratio of 1.4 (14/10 = 1.4). This applies to a home in a sunny state like Arizona, where there are large amounts of sunlight all day, year-round. If your home is located somewhere like New York, where it can be cloudier and there’s more rain, this production ratio might dip to 1.2. 

Due to how complicated this ratio can become, we advise you to contact a professional. 

The Formula

The actual formula a solar installation company will use to quote you a solar panel system is as follows: 

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

If we use a simplified version of the numbers we listed above, we get the following:

• Number of panels = 11,000 kW/1.4/300

This formula equals approximately 25–27 panels. However, you may require fewer or more solar panels depending on your specific home.

Alternative Formula

A simple alternative to the formula above is to look at your monthly electric bills and determine how much energy you use. Then, multiply your energy usage by the hours of sunlight your home gets, and divide that result by the wattage of the panels you’re considering.

Though the three factors above can give you a general idea of how many solar panels you’ll need, other factors can influence that total. Read about some other important considerations when building a solar panel system below. 

Home Layout

Your home’s layout and roof design determine your solar panel system’s size. For example, chimneys or unique roof designs might mean you can only install a certain number of panels.

Hours of Sunlight

The amount of energy you’ll get from your solar panels is directly related to how much sun your home receives. If your home is in an area with limited sunlight, it will require more panels. 

Solar Panel Cost

According to the Center for Sustainable Energy, the average cost of solar panels is $3–$5 per watt, totaling $15,000–$20,000 for a typical 5 kilowatt (kW) system. You’ll have some wiggle room with cost depending on which type of solar panels you choose, but this will also affect how many solar panels you order. For example, you’ll need more polycrystalline panels than monocrystalline to power your home because polycrystalline panels are less efficient.

Solar Panel Efficiency

Solar companies use efficiency to measure a solar panel’s ability to convert sunlight into usable electricity. Efficiency ratings are expressed as a percentage to help you quickly compare different solar panels’ performance. For example, if a solar panel has a 25% efficiency rate, 25% of the sun’s energy it captures is converted into usable electricity. A solar panel’s solar cell composition, roof placement, and design all affect its efficiency.

Opting for more efficient solar panels will cut costs long-term because you’ll receive more energy savings over time and a higher return on investment (ROI).

Solar Panel Size

If your home is small or has an unusually shaped roof, solar panel size is crucial. Homeowners with large roofs may choose to sacrifice efficiency and buy larger panels to achieve the ideal energy output. Those with smaller roofs must use a smaller number of high-efficiency panels, such as SunPower’s panels, to produce enough energy to power their homes.

Solar Panel Type

There are three main types of solar panels: monocrystalline, polycrystalline, and thin film. Below is a breakdown of each solar panel type:

• Monocrystalline: These are the most efficient and cost-effective solar panels. They’re most commonly offered by solar panel companies, and you can order less of them than other types given their high efficiency of 15%–25%. 
• Polycrystalline: Also called poly solar panels, these panels are a bit less efficient than monocrystalline panels, with average rates of 11%–17%. You’ll have to buy more panels to match the output of a monocrystalline system, but polycrystalline solar panels cost less than monocrystalline ones. 
• Thin film: Thin-film solar panels may be a better fit if you have a lot of roof space or require limited energy for your solar project. These panels have a broad efficiency range of 10%–20% and are used for more specialized projects, such as converting a shed, recreational vehicle (RV), boat, or small guest house.

Though the formulas provided in this article can give you a general idea of how many solar panels you’ll need, they don’t provide a definite answer. This is because the number of solar panels you need is highly individual and depends on various factors, such as your roof layout and the panels’ size, efficiency, and cost.

We recommend contacting a solar installer that services your address. A professional can evaluate your home and tell you exactly how many solar panels you’ll need in addition to solar batteries and other components. Solar installers can also help you access the federal tax credit and local incentives to reduce costs and maximize your savings.

Use our tool below to connect with reputable solar installers that offer solar panel installation in your area.

The This Old House Reviews Team is committed to providing comprehensive and unbiased reviews to our readers. This means earning your trust through transparent reviews and data to back up our ratings and recommendations. Our rating system for solar providers is on a 100-point system based on five factors:

• Payment options (40 points): Options include purchase, loan, lease, and Power Purchase Agreements (PPAs). Companies receive points for each of the four options they provide.
• Solar services (30 points): Does the company provide in-house installation of solar panels and battery backups? Can the company also monitor energy production and perform energy-efficiency audits to ensure system performance? The more options available, the higher the score. 
• Warranty options (10 points): The success of a residential solar system depends on the workmanship, performance guarantees, and length of product coverage. The more warranties a company offers, the higher the score it receives. 
• State availability (10 points): We award the most points to companies with the broadest service area and state availability.
• Reputation (10 points): We factor in how the Business Better Bureau (BBB) scores each company. We deduct points for any alerts or pending lawsuits.

To share feedback or ask a question about this article, send a note to our Reviews team at reviews@thisoldhousereviews.com.