How many solar panels does the average house need? How many solar panels do I need for a 3-bedroom house? How many solar panels do I need for a 2000 sq. ft. home? These are all common questions for an aspiring solar homeowner. Determining how many solar panels you’ll need for your home requires first knowing what your goals are.
Do you want to minimize your carbon footprint? Maximize the return on your investment? Save as much money as possible?
Most people want to save money while minimizing their environmental impact.
To calculate how many solar panels you need, you need to understand:
Your home's average energy requirements
Your current energy use in kilowatt-hours (kWh)
The climate and amount of sunlight in your area
The efficiency of the solar panels you’re considering
The physical size of the solar panels you’re considering
One simple way of answering the “How many solar panels do I need” question is to consult a professional solar installer, who can give you a free home solar evaluation.
To determine your home’s average energy requirements, look at past utility bills. You can calculate how many solar panels you need by multiplying your household’s hourly energy requirement by the peak sunlight hours for your area and dividing that by a panel’s wattage. Use a low-wattage (150 W) and high-wattage (370 W) example to establish a range (ex: 17-42 panels to generate 11,000 kWh/year). Note that the size of your roof and how much sunlight your roof gets are factors as well.
Look at your electricity bill for average usage. Look for “Kilowatt Hours (or kWh) Used” or something similar, and then note the length of time represented (usually 30 days). If your bill doesn’t show kilowatt hours used, look for beginning and ending meter readings and subtract the previous reading from the most recent one.
You want daily and hourly usage for our calculations, so if your bill doesn’t show a daily average, just divide the monthly or annual average by 30 or 365 days, respectively, and then divide again by 24 to determine your hourly average electricity usage. Your answer will be in kW. (And just in case you’re wondering, a kilowatt-hour is how much power you are using at any given time multiplied by the total time the power is being used.)
A small home in a temperate climate might use something like 200 kWh per month, and a larger home in the south where air conditioners account for the largest portion of home energy usage might use 2,000 kWh or more. The average U.S. home uses about 900 kWh per month according to the EIA. So that’s 30 kWh per day or 1.25 kWh per hour.
Your average daily energy usage is your target daily average to calculate your solar needs. That’s the number of kilowatt-hours you need your solar system to produce if you want to cover most if not all of your electricity needs.
It’s important to note that solar panels don’t operate at maximum efficiency 24 hours a day.
Weather conditions, for example, can temporarily reduce your system’s efficiency. Therefore, experts recommend adding a 25 percent “cushion” to your target daily average to ensure you can generate all the clean energy you need.
For more information on that topic you can read our Solar 101 article: What is Solar Energy and How Do Solar Panels Work?
The peak sunlight hours for your particular location will have a direct impact on the energy you can expect your home solar system to produce. For example, if you live in Phoenix you can expect to have a greater number of peak sunlight hours than if you lived in Seattle. That doesn’t mean a Seattle homeowner can’t go solar; it just means the homeowner would need more panels.
The National Renewable Energy Laboratory (NREL) provides sunlight information by state and for major cities.
Now multiply your hourly usage (see question No. 1) by 1,000 to convert your hourly power generation need to watts. Divide your average hourly wattage requirement by the number of daily peak sunlight hours for your area. This gives you the amount of energy your panels need to produce every hour. So the average U.S. home (900 kWh/month) in an area that gets five peak sunlight hours per day would need 6,000 watts.
Here’s where solar panel quality makes a difference. Not all solar panels are alike. Photovoltaic (PV) solar panels (most commonly used in residential installations) come in wattages ranging from about 150 watts to 370 watts per panel, depending on the panel size and efficiency (how well a panel is able to convert sunlight into energy), and on the cell technology.
For example, solar cells with no grid lines on the front (like SunPower® Maxeon® cells) absorb more sunlight than conventional cells and do not suffer from issues such as delamination (peeling). The construction of our cells makes them stronger and more resistant to cracking or corrosion. And a microinverter on each panel can optimize power conversion at the source, in contrast to one large inverter mounted on the side of the house.
Because of these wide variations in quality and efficiency, it’s difficult to generalize about which solar panels are right for you or how many you’ll need for your home. The main takeaway is that the more efficient the panels are, the more wattage they can produce, and the fewer you will need on your roof to get the same energy output. Conventional solar panels usually produce about 250 watts per panel, with varying levels of efficiency. In contrast, SunPower panels are known to be the most efficient solar panels on the market.*Based on datasheet review of websites of top 20 manufacturers per IHS, as of April 2021.
To figure out how many solar panels you need, divide your home’s hourly wattage requirement (see question No. 3) by the solar panels’ wattage to calculate the total number of panels you need.
So the average U.S. home in Dallas, Texas, would need about 25 conventional (250 W) solar panels or 17 SunPower (370 W) panels.
If you have a small or unusually shaped roof, solar panel size and numbers are important considerations. With a large usable roof area, perhaps you can sacrifice some efficiency and buy larger panels (at a lower cost per panel) to get to your target energy output. But if your usable roof area is limited, or if it’s partially shaded, being able to use fewer smaller high-efficiency panels may be the best way to make the most possible power over the long term, ultimately saving you more money.
Typical residential solar panel dimensions today are about 65 inches by 39 inches, or 5.4 feet by 3.25 feet, with some variation among manufacturers. SunPower panels are 61.3 inches by 41.2 inches.
These dimensions have remained more or less unchanged for decades, but the efficiency and output from that same footprint have changed dramatically for the better. In addition, SunPower designs entire systems to have virtually no gaps between panels and uses invisible framing and mounting hardware to keep the rooftop footprint as tight, efficient, and attractive as possible.
If you’re planning on installing a rooftop solar system, understanding the weight of your solar panels is another key factor to consider. Knowing a solar panel’s weight is the best way to be certain that your roof can support a full installation.
While panel weights vary from brand to brand, most panels weigh about 40 pounds.
SunPower panels are the lightest of all major brands*Energy Sage, July 2021, https://news.energysage.com/average-solar-panel-size-weight/, with some of our panels weighing as little as 33 pounds. For comparison, at the top end of the range, some conventional panels weigh as much as 50 pounds.
Knowing the answers to the above questions will give you an idea of the ideal number of panels for your electricity generation needs, or at least a realistic range. Next, a professional installer needs to assess your roof architecture, angle to the sun, and other factors to see if and how you’d be able to physically arrange the right number of panels on your roof to achieve your daily energy production goals.
You should also consider net metering as you’re considering how much money you’ll save and make from your solar system. Net metering is how your utility company credits you for producing excess solar energy when the sun is shining and then lets you draw from those credits when you’re using a conventional power grid at night if you don’t store your excess solar energy in a battery storage system.
Ready to learn more about saving with solar panels?
SunPower is changing the way our world is powered by making solar and storage more accessible to everyone. With nearly 40 years of dedicated solar experience, we're the top-rated U.S. solar company with over 15,000 five-star reviews.*Based on public solar providers in the U.S. Includes average of BBB, Yelp, ConsumerAffairs, BestCompany, Google, Solar Reviews and Energy Sage review scores as of 10/22/23. If you're considering installing solar panels, energy storage, or EV charging at your home, make sure you talk to SunPower.
Schedule your free, no-obligation consultation with SunPower by calling 1-800-SUNPOWER. Or click the Get Started button and we'll get in touch with you! Our team of Solar Advisors is here to help make your transition to a sustainable lifestyle.
Calculating the output of your solar panels isn’t as simple as you might think.
While the rated power (e.g., 100W or 400W) indicates the maximum amount of electricity a PV panel can generate per hour, many factors come into play that affect how much power output you’ll actually get.
The truth is, there are so many variables involved in how much electricity a solar panel produces hour by hour that there’s no way to predict exactly how many watts a PV panel will produce. Even panels from the same manufacturer, with the same rated power, on the same rooftop will generate slightly different amounts of electricity.
However, once you understand the various factors that impact a solar panel’s performance, you can come up with a reasonably accurate estimate of the average amount of electricity each PV panel should produce per day.
If you’re considering switching to solar and shopping for a PV panel array, a rough estimate of real-world electricity production in your location is essential — and much more likely to be accurate than simply adding up the rated power of each panel.
Here’s what you need to know to estimate solar panel output in real-world conditions.
Factors to Consider When Calculating Real-World Solar OutputThe benefits of solar energy are numerous, but building your own solar power system requires advanced planning to ensure it meets your family’s unique electricity consumption needs.
One of the most crucial factors to consider when planning a switch to solar is also one of the least understood: The difference between a solar panel’s rated power wattage and its real-world electricity output.
Every PV panel comes with a rated power wattage. Likely, this is between 100W and 400W per panel. Rated power indicates the maximum amount of electricity your panels can produce (in watts) under ideal or Standard Test Conditions.
However, in the real world, conditions are rarely perfect, and numerous factors affect how much electricity a PV panel will actually produce. And it’s never a constant. The wattage your solar panels generate will vary from hour to hour — even minute to minute.
For example, EcoFlow 400W Rigid Solar Panel has a rated power spec of 400W. But you’re more likely to produce an average of 300W of electricity per hour over the course of a day.
On average, you’ll get about 75% of the rated power in actual output with EcoFlow rigid, portable, and flexible PV panel options.
Keep in mind, that’s a daily average. Some hours, your panel might produce close to 100% of its rated power — other hours, it might produce 60%, all on the same day.
Here are the crucial factors that impact the real-world output of your solar panel array.
Solar Panel EfficiencySolar panel efficiency measures the percentage of direct sunlight a PV panel receives that gets converted into electricity. Again, the listed specification is calculated based on ideal conditions — rare in practice.
Factors that impact the real-world efficiency of your solar panels include temperature, panel age, and cleanliness.
Having said that, a brand-new PV panel’s efficiency should not vary much from its listed rating.
The higher a solar panel’s efficiency, the more electricity you will generate from available sunlight.
Understanding what “efficiency” measures as a PV panel spec helps you make a more informed purchase decision.
High-quality monocrystalline PV panels typically average around 20% efficiency. EcoFlow solar panels, like the 400W Rigid Solar Panel, the 220W Bifacial Portable Solar Panel, and even the 100W Flexible Solar Panel, achieve 23% efficiency — an industry best.
Polycrystalline PV panels are a cheaper option and tend to achieve between 10-15% efficiency. Thin-film panels can fall between 7-18% efficiency.
The lower the efficiency rating, the less electricity you’ll generate from the sunlight your location receives.
Orientation and LocationWhat direction are your PV panels facing? The orientation relative to your geographic location significantly impacts your solar array’s energy production. You want your solar panels to be facing the equator for maximum output.
Tilt also matters when positioning panels to receive the maximum amount of sunlight. The best way to get the most output out of your panels is to set the tilt of your panels at an angle equal to the latitude of your location. You can leave your panels at this angle year-round or adjust them for maximum optimization a few times each year.
The goal is to position your panels to receive maximum sunlight. Of course, the ideal tilt varies over the course of a day as the Earth orbits the sun. To get the most out of your solar panel array, consider a solar tracker so your panels can follow the sun automatically.
Degradation RateLike everything else, photovoltaic panels degrade over time. You’ll find that your solar panel loses around 0.5-1% of its rated output with each passing year.
Half a percent is not a significant amount. At that rate, you can still expect your solar panels to work at 90% capacity even two decades later. Still, the degradation rate is worth remembering because it will eventually reduce overall output and affect how long your solar panels last.
You can extend the lifespan of your panels by keeping them clean and free of dirt and debris. Routine maintenance and cleaning help ensure you get the most juice out of your PV panels.
Solar Panel Output CalculationsNow, it’s time to combine everything you’ve learned to estimate how much power your solar power array can generate.
The formula to estimate your solar panel output is below:
Output = STC Rating (rated power under Standard Test Conditions, in watts) x Peak Daily Sunlight Hours x .75
To calculate your solar panel output, take the power rating and multiply it by the peak hours of sunlight and multiply by .75.
Why .75? That’s to help account for all of the factors we discussed above that can decrease your solar panel’s electricity output.
Here’s an example. The EcoFlow 400W Rigid Solar Panel has a 400W rated power output. Let’s say you get an average of 5 hours of daily peak sunlight where you live.
If you enter that into the formula, you get the following:
Output = 400W rated power x 5 Peak Daily Sunlight Hours x .75 = 1,500Wh
You can estimate that a 400W panel will produce 1,500 watt-hours per day, or 1.5 kWh, under those real-world conditions.
Why Is Solar Panel Output ImportantUnderstanding the output of your panels is essential for calculating energy production in real-world conditions. It will only ever be an estimate. But still, it enables you to plan for how much power you can rely on your panels to produce on average — and if that’s enough for what you want them to power.
Suppose you’re trying to power a refrigerator using your solar panels. You’ll want it running around the clock to keep perishable items stored at a safe temperature. In this case, understanding the output of your panels lets you determine whether your setup can meet the electricity consumption demands of your refrigerator.
Remember, solar panels don’t work on their own. You’ll need a portable power station or other balance of system to convert and store the solar energy your panels capture into household (AC) electricity.
Determining your PV panel output lets you estimate how long it will take to charge your portable power station with solar power.
What Are the Standard Test Conditions for Solar Panels?As discussed above, the rated power wattage of PV is determined in a laboratory under Standard Test Conditions. It indicates the maximum amount of electricity a solar panel can produce under ideal circumstances.
So what are the “ideal conditions” for maximum electricity output (wattage) from a solar panel?
Here are the most critical conditions that testers rely on to determine rated power:
Unsurprisingly, these conditions rarely exist all at the same time in the real world.
Understanding rated power is crucial to ensuring your solar panel array meets your electricity consumption needs.
Final ThoughtsNow, you should have all the information necessary to estimate the average amount of electricity your panels should produce per day. From there, you can determine how many PV panels you need to accommodate your desired electricity consumption.
Other crucial things to keep in mind when purchasing solar panels and a balance of system include:
EcoFlow has a wide range of award-winning plug-and-play solar power solutions for almost any use case — from backpacking to whole home generators. Check out EcoFlow today to meet your off-grid electricity needs.
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