It’s no use installing just one solar panel–you’ll need more than that to reap the financial benefits of a solar panel system. While the answer isn’t always so simple, we’ve put together some example cases to help you understand, at a high level, how many solar panels you need to install.
How many solar panels power a house? Key takeaways
- An average home needs between 20 and 25 solar panels to fully offset electricity bills with solar
- This number depends on a few key factors, including geographic location and individual panel specifications
- Compare solar quotes on the EnergySage Marketplace, customized to your property and energy needs
How many solar panels do I need to power my house?
We estimate that a typical home needs between 20 and 25 solar panels to cover 100 percent of its electricity usage. 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.
How to calculate how many solar panels you need
The formula we used to estimate the number of solar panels you need to power your home depends on three key factors: annual energy usage, panel wattage, and production ratios. What does that mean exactly? Here are the assumptions we made, and how we did our math:
Annual electricity usage: Your annual electricity usage is the amount of 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 10,649 kWh of electricity per year, so we’ll use that number as the ideal solar panel system size, which would mean you could offset 100 percent of your electricity usage with solar panels (in practice, it’s not this neat, but bear with us here).
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 watts of power. We’ll use 320 watts as an average panel in these calculations.
Production ratios: 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 used those two numbers as the high and low estimates for our calculation.
And finally, let’s do 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 = 10,649 kW / 1.3 or 1.6 / 320 W
…which gives us between 20 and 25 panels, depending on which production ratio we use (20 for a 1.6 ratio, and 25 for a 1.3 ratio). 25 panels each at 320 W results in a total system size of 8 kW, which is right around the average for EnergySage shoppers. Tada!
How many kWh can your solar panels produce? The complexities of production ratios
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–if you live in an area that gets less sun, you’ll just need to have a larger 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 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 10,649 kWh annually as mentioned above. The California household needs about a seven kW system to cover 100 percent of their energy needs. By comparison, the comparable household in Massachusetts needs about a nine 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 sunlight 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 an 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.
How many solar panels do I need for my house? System size comparison
|System size||Number of panels needed||Estimated annual production|
|4 kW||13||6,400 kWh|
|6 kW||19||9,600 kWh|
|8 kW||25||12,800 kWh|
|10 kW||32||16,000 kWh|
|12 kW||38||19,200 kWh|
|14 kW||44||22,400 kWh|
The table above assumes that you’re using a 320 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.
How many solar panels can I fit on my roof? System size compared to square footage
|System size||Low power panels (sq. feet)||Average power panels (sq. feet)||High power panels (sq. feet)|
Perhaps one of the most difficult aspects of sizing a solar panel system is estimating annual 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’ll be 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.
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 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 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.
How many solar panels do I need for individual electricity loads?
|Product||Average Annual KWH Required||Estimate number of solar panels needed|
|Air Conditioning Unit||215||<1|
|Central Air Conditioning||1,000||3|
|Heated Swimming Pool||2,500||8|
|Hot Tub (outdoor)||3,300||11|
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. The only way to find the “sweet spot” for your property is to evaluate quotes with varying equipment and financing offers.
For any homeowner in the early stage of shopping for solar that would just like a ballpark estimate for an installation, try our Solar Calculator that offers upfront cost and long-term savings estimates based on your location and roof type. For those looking to get quotes from local contractors today, check out our quote comparison platform.