The first step in any homeowner’s solar journey is determining the number of solar panels needed to power your house. While the average household requires between 17 and 25 solar panels, the exact number is impossible to predict—you need to consider factors such as your home size, electricity usage, energy-saving goals, and your roof space.
You can reach out to any of the leading solar providers to determine how many panels you need. Keep reading to do the calculations yourself. Our guide includes a basic solar panel calculator to get you started.
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How To Calculate How Many Solar Panels You Need
EnergySage, an online solar comparison-shopping marketplace, estimates that the typical U.S. household will need 15–22 solar panels to meet its full energy needs.
According to EnergySage, you’ll need to know three key factors to calculate exactly how many solar panels you need to power your home:
- The wattage, or capacity, of the solar panels you’re considering: How much electricity each of your solar panels produces.
- Your annual electricity usage: How much electricity you use in a year, measured in kilowatt-hours (kWh). This number is also used to calculate the size of the battery storage, if any, your system requires.
- Your solar power system’s estimated production ratio: How efficiently your system operates in your specific climate.
Here’s the formula for calculating how many solar panels your home needs with EnergySage’s methodology: Number of panels = system size/production ratio/panel wattage
To get an estimate of how many solar panels you’ll need, divide your annual electricity usage by the estimated production ratio and divide that number by your solar panel’s wattage.
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 lights and appliances, such as air conditioning units, water heaters, and refrigerators.
The U.S. Energy Information Administration (EIA) reports that a U.S. residential customer’s average annual electricity consumption was 10,791 kilowatt-hours (kWh) in 2022, with an average of 899 kWh per month. Some electricity providers have an app or online portal where you can view your meter readings and track your monthly and annual electricity usage. Otherwise, you can calculate your annual usage by adding up the total kWh listed on your last 12 bills.
Note that usage can vary significantly by season. That’s why we recommend adding up your last 12 monthly statements rather than taking a single statement and multiplying by 12. This method takes a little more time but will give you a more accurate estimate.
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 watts (W). You might assume this is a simple 1:1 ratio, but 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 ratio might apply to a home in Arizona, which sees large amounts of sunlight all day, year-round. If your home is located somewhere that’s prone to cloudier weather and more rain, like New York, the production ratio might dip to 1.2.
This is a complicated ratio, so we advise you to contact a professional for the best results. EnergySage has also produced a helpful graphic showing the average solar production ratio by state based on its own marketplace data.
Solar Panel Wattage
You might think that the best solar panels are all built the same, but that’s not true. Different solar panels use different materials and designs, resulting in different energy outputs. A panel’s wattage is how much electricity it produces, and most residential solar panels range between 300 and 450 watts of power. The higher the wattage, the fewer panels you’ll need.
The Formula
The actual formula a solar installation company will use to design a solar panel system is as follows:
Number of panels = system size/production ratio/panel wattage
If we use a simplified version of some of the numbers we mentioned above, we get the following:
Number of panels = 11,000 kW/1.4/400
This formula equals approximately 20 panels. However, your home may require more or less depending on your energy consumption, the wattage of the panels you select, and the production ratio in your area. The National Renewable Energy Laboratory (NREL) maintains a PV watts calculator to help you estimate your needed system size.
Other Ways To Calculate How Many Solar Panels You Need
A simple alternative to the formula above is to figure out how much energy you use per day and multiply by the number of peak sunlight hours your area gets per day. Then, divide the result by the wattage of the panels you’re considering. Use this helpful NREL map to determine how many hours of peak sunlight you can expect.
Factors That Influence How Many Solar Panels You Need
Determining how many solar panels you need goes beyond simple calculations. Here are some additional factors that can affect the final number:
Roof Size and Layout
The size and shape of your roof can significantly impact your solar panel system. If you have a spacious roof, you can opt for less-efficient, larger panels and still meet your energy needs. On the other hand, if your roof is small or has unique architectural features, you’ll want to maximize efficiency with high-performance panels.
Shade and Sunlight Hours
The amount of sunlight your home receives is crucial to how much energy your solar panels can produce. If your house is surrounded by tall trees or buildings or is in an area with frequent cloudy weather, you’ll need more panels to generate the same amount of energy.
Sun-kissed areas like southern California often require fewer panels compared to places like Seattle or New York, where cloudier weather is common.
Types of Solar Panels
The type of solar panels you choose also influences how many you need:
- Monocrystalline panels: These are considered the most efficient, with efficiencies up to 24%. They require fewer panels but are typically more expensive.
- Polycrystalline panels: Less efficient at 13%–17%, you’ll need more of these to deliver the same energy output as monocrystalline options. However, they’re generally more budget-friendly.
- Thin-film panels: With efficiencies ranging from 10% to 20%, these panels are best suited for specialized projects, like powering an RV or small shed, rather than entire homes.
Other Energy Systems
If you’re considering adding a battery storage system for backup power or integrating your solar panels with other energy-efficient systems like smart thermostats or energy management software, these can also influence the number of panels you need.
Understanding these factors in detail helps you fine-tune your solar installation to match your home’s specific needs.
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 solar energy it captures is converted into usable electricity. A solar panel’s composition, roof placement, and design all affect its efficiency.
Opting for more efficient solar panels will cut costs in the long term. You’ll receive more energy savings over time and a higher return on investment (ROI).
Our Conclusion
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. 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 surveyed 1,000 homeowners who purchased a solar panel system, and 23% said a 10-kilowatt system was needed to power their home. Twenty percent of our survey takers said their home is between 1,000 and 1,500 square feet.
We recommend contacting a solar installer who services your address. A professional can evaluate your home and tell you exactly how many solar panels you’ll need, answering questions about 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. After choosing a solar installer, you can explore different types of solar financing that can make your investment more affordable.
FAQs About Solar Panels
Can I run my house on solar power only?
Yes, you can run your home on solar power only. However, you’ll need to install backup generators and solar batteries to run your home at night, on low-sunlight days, or during power outages. Systems that run your home exclusively on solar power are considered off-grid. These systems must be larger than average and are thus more expensive.
Are solar panels worth it?
Yes, solar panels are worth it when you consider how much they reduce your utility bills, increase your home value, and positively impact the environment. However, not all homes are suited for solar panels, so check with a professional. Our 2024 survey data shows that 96% of respondents have found going solar to be worth it, and 82% said installing solar panels increased their property value.
What happens if you have too many solar panels?
If you have too many solar panels, your system will produce more energy than your home needs. You can store this excess energy in a solar battery for later use, or you can feed it back into the power grid. Some states award solar renewable energy certificates (SRECs) for producing solar energy, which allows you to earn extra income from your system. Working with a professional solar company will ensure you order the correct number of solar panels for your project.