We estimate that a typical home needs between 20 and 24 solar panels to cover 100 percent of its electricity usage. The actual formula to find out how many solar panels you need can be found by the system size divided by the production ratio, divided by panel wattage.
The actual number you’ll need to install depends on factors including geographic location, panel efficiency, panel rated power, and your personal energy consumption habits. Importantly, the number of solar panels you need for your home directly impacts the price you pay for solar. While the answer isn’t always simple, we’ve put together some example cases to help you understand, at a high level, how many solar panels you need to install an effective solar array.
How many solar panels power a house? Key takeaways
- An average home needs between 20 and 24 solar panels to fully offset utility bills with solar.
- The number of solar panels you need depends on a few key factors, including geographic location and individual panel specifications.
- You’ll need more solar panels for the same output if you live in Massachusetts compared to California.
- Compare free, custom solar quotes on the EnergySage Marketplace.
What’s in this article?
- How to calculate how many solar panels you need
- Main considerations to determine how much solar you need
- Frequently asked questions
How to calculate how many solar panels you need
In order to calculate how many solar panels you need, you need to divide the total system size by the production ratio by the panel wattage. Calculating how many solar panels you’ll need to meet all of your energy needs depends on several factors. The easiest way to find out how many panels you’ll need is to use our Solar Calculator. By putting in your address and estimated monthly power bill, we do all of the math for you so that you can make an informed decision. If you’d like to do those calculations for yourself, we’ve explained our formula below to help.
You can calculate how many solar panels you need by taking into account three main factors:
- Annual electricity usage
- Solar panel wattage
- Production ratios
The formula we used to estimate the number of solar panels you need to power your home depends on these key factors. Here are the assumptions we made, and how we did our math:
Annual electricity usage
Your annual electricity usage is the amount of energy and electricity you use in your home over a full year. Measured in kilowatt-hours (kWh), this number is influenced by the appliances in your home that use electricity and how often you use them. Refrigerators, air conditioning units, small kitchen appliances, lights, chargers, and more all use electricity.
According to the U.S. Energy Information Administration (EIA), the average American household uses 10,715 kWh of electricity per year, so we’ll use that number as the ideal solar panel system or solar array size, which would mean you could offset 100 percent of your electricity usage and utility bill with solar panels (in practice, it’s not this neat, but bear with us here). If you’re interested in getting a more exact number based on your personal energy usage, check last year’s utility bills to find out how much electricity you used. Once you have that number, feel free to plug it into the equations below.
Solar panel wattage
Also known as a solar panel’s power rating, panel wattage is the electricity output of a specific solar panel under ideal conditions. Wattage is measured in watts (W), and most solar panels fall in the range of 250 – 400 W of power. We’ll use 340 W as an average panel in these calculations because the majority of the most popular solar panels on the EnergySage Marketplace are at least 340 W.
A solar panel system’s production ratio is the ratio of the estimated energy output of a system over time (in kWh) to the actual system size (in W). These numbers are almost never 1:1 – depending on how much sunlight your system will get (which is primarily based on your geographic location), your production ratio will change accordingly.
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 is an entirely realistic production ratio to see out in the real world. In the U.S., production ratios are usually between 1.3 and 1.6, so we’ll use those two numbers as the high and low estimates for our calculation.
Now, let’s work out the math
We have our three main assumptions (energy use, solar panel wattage, and production ratios) – now how do those numbers translate to an estimated number of solar panels for your home? The formula looks like this:
Number of panels = system size / production ratio / panel wattage
Plugging our numbers in from above, we get:
Number of panels = 10,715 kW / 1.3 or 1.6 / 340 W
…which gives us between 20 and 24 panels in a solar array, depending on which production ratio we use (20 for a 1.6 ratio, and 24 for a 1.3 ratio). So, 20 panels at 340 W each result in a total system size of about 6.8 kW!
Main considerations to determine how much solar you need
Calculating how many solar panels you need can be done with the three inputs above, but digging deeper, there are many more factors at play in determining your ideal solar panel system size. Understanding production ratios, the relationship between system size and the number of panels, and the impact of home size can all be important when you’re designing your ideal solar panel setup.
How many kWh can your solar panels produce?
The amount of power (kWh) your solar energy system can produce depends on how much sunlight exposure your roof receives, which in turn creates your production ratio. The amount of sunlight you get in a year depends on both where you are in the country, and what time of year it is. For instance, California has more sunny days annually than New England. But in either location, you’ll be able to produce enough power to cover your energy needs and say goodbye to your utility bills–if you live in an area that gets less peak sunlight hours, you’ll just need to have a larger solar array system installed at your home. Thus, production ratios differ according to geographic location and a lower production ratio (because of less sunlight) means you’ll need more solar panels to get the amount of energy production you need.
Here’s an example: two comparably sized households in California and Massachusetts consume the average amount of electricity for an American household, which is 10,715 kWh annually as mentioned above. The California household needs about a 6.8 kW system to cover 100 percent of their energy needs. By comparison, the comparable household in Massachusetts needs about an 8.2 kW system to cover their energy needs. Solar panel systems in California are smaller than solar panel systems in Massachusetts but are able to produce the same amount of power because they’re exposed to more peak sunlight hours each year. Homeowners in less sunny areas, like Massachusetts, can make up for this disparity by simply using more efficient panels or increasing the size of their solar energy system, resulting in slightly more solar panels on their rooftop.
How many solar panels do you need for specific system sizes?
In our long example at the beginning of this piece, we determined that a 6.8 kW system would probably cover the average energy use for an American household if you live in an area with a production ratio of 1.6, which might be a realistic number for homes in most parts of California.
Let’s extend that a little further, and look at a few more examples. In the table below, we’ve compiled some solar panel estimates for common system sizes seen on the EnergySage Marketplace. Again, the big caveat here is that we’re using 1.6 as the production ratio of choice. For California shoppers, this might actually be realistic, but for folks in the Northeast or areas with less sun, these estimates might be a bit high on the production end and low on the number of panels needed.
Number of solar panels needed for specific system sizes
|System size||Number of panels needed||Estimated annual production|
|4 kW||12||6,400 kWh|
|6 kW||18||9,600 kWh|
|8 kW||24||12,800 kWh|
|10 kW||29||16,000 kWh|
|12 kW||36||19,200 kWh|
|14 kW||42||22,400 kWh|
The table above again assumes that you’re using a 340 solar panel again – however, the number of panels you need to power your home and the amount of space that your system will take up on your roof will change if you’re using lower-efficiency panels or high-efficiency panels (which generally correlates to low and high power rating, respectively).
Below is a table that will give you a sense of how much space your system will take up on your roof, depending on the power output of the solar panels you select:
Square footage of different size solar panel systems
|SYSTEM SIZE||300 W PANELS (SQ. FEET)||340 W PANELS (SQ. FEET)||360 W PANELS (SQ. FEET)||400 W PANELS (SQ. FEET)|
Perhaps one of the most difficult aspects of sizing a solar panel array is estimating the annual amount of energy usage for your household. A number of larger consumer products or add-ons can significantly change your annual kWh requirements and greatly impact how many panels you will need. For example, if you’re running central air conditioning or powering a heated swimming pool in your backyard, the size of your solar panel array could be drastically altered. To get a feel for the size you’ll need, you should evaluate the energy impact of various products you own or are considering for your home.
If your home is small or has an unusually shaped roof, the size of solar panels can be very important to consider. While those who have a large roof may be able to sacrifice some efficiency and buy larger panels to achieve the ideal energy output, homeowners with a smaller roof must be able to use fewer small high-efficiency panels – like those from SunPower, LG, or REC – to get optimal output. For those atypical roofs, you might end up getting a system design like this:
Today, the average size of solar panels for a residential home is about 65 inches by 39 inches or 5.4 feet by 3.25 feet.
How does my home size affect the number of solar panels I need?
While solar panel dimensions have more or less remained steady over the past several years, the power output within the same area has dramatically increased. In fact, many manufacturers like SunPower have reduced the size of gaps between panels and use invisible framing and mounting hardware to keep the panels tight, efficient, and aesthetically pleasing. Check out the table below for a ballpark estimate of how many solar panels your home would need based on its square footage.
Home square footage compared to the number of solar panels needed
|Home Size||Estimated Annual Electricity Needed||Number of Solar Panels Needed|
|1,000 sq. feet||4,710 kWh||14|
|2,000 sq. feet||9,420 kWh||29|
|2,500 sq. feet||11,775 kWh||35|
|3,000 sq. feet||14,130 kWh||42|
How many solar panels do I need for common appliances?
By reviewing the various kWh requirements for everyday household appliances and products, one thing is clear: certain add-ons will dramatically change monthly energy use and can have an outsized impact on the size of the solar panel system you should install. For example, pairing your electric vehicle with solar panels is a great way to reduce carbon emissions and improve energy efficiency; however, it should be planned accordingly, considering it could potentially double the size of your PV system.
Though it is certainly possible to install a solar system and then have a solar installer add more panels later to accommodate increased energy needs, the most pragmatic option is to size your system as accurately as possible based on your expected purchases–such as an electric vehicle, swimming pool or central air system. Asking yourself, “how many solar panels will I need for my refrigerator, my hot tub, etc.” is a great habit for any new solar homeowner.
Solar panel requirements for individual appliances
|Product||Average Annual Electricity Needed||Number of solar panels needed|
|Window air conditioning||215 kWh||1|
|Central air conditioning||1,000 kWh||3|
|Electric vehicle||3,000 kWh||9|
|Heated swimming pool||2,500 kWh||8|
|Hot tub (outdoor)||3,300 kWh||10|
Frequently asked questions
Once you install solar panels, you’ll still receive a monthly electricity bill. However, it should be lower, close to zero, or even negative! If you’re still experiencing high utility bills after installing solar panels, you may need to reconsider the size of your system. Especially if you have added electricity loads since your solar installation (like an electric car), your current system size just might not cut it anymore.
The two main disadvantages of solar energy are the high upfront costs and intermittency, meaning that solar energy isn’t available 24/7 because the sun doesn’t shine at night. Luckily, that problem can be partially sorted with solar energy storage. Check out our article about the advantages and disadvantages of renewable energy to learn more.
Depending on your electricity prices, your energy needs, your desire to be eco-friendly, and your home’s geographic location, solar panels are definitely worth installing. While the initial investment in solar panels is high, they do pay off over time by cutting down on your electricity bill. On average, EnergySage solar shoppers “break even” on their solar investment in about eight years.
Start your solar shopping on the EnergySage Marketplace
There are multiple variables to consider when seeking out the best solar panels on the market. While certain panels will have higher efficiency ratings than others, investing in top-of-the-line solar equipment doesn’t always result in higher savings on your utility bills. The only way to find your property’s “sweet spot” is to evaluate quotes with varying equipment and financing offers. If you want quotes from local contractors today, check out our quote comparison platform.