Have you ever wondered how much electricity you could produce from solar? In this article, we’ll walk through how to calculate the amount of solar power you can generate on your roof based on its size, orientation, and angle – as well as the solar panels you choose to install.
How much solar energy can you generate on your roof?
The short answer? Probably way more than you need! According to our calculations, if you used every square foot of roof space on the average U.S. home, you could fit about 97 solar panels on an average roof – resulting in about 31 kilowatts (kW) of solar panels on your roof. That translates to roughly 57,000 kilowatt-hours (kWh) of solar electricity throughout the year! Considering the average U.S. home uses about 10,600 kWh of electricity annually, this is more than five times the amount you’ll probably need to run your whole home on solar.
Calculating solar generation potential
To get the numbers above, we took several factors into account that are explained in much more detail below. There are a few assumptions baked in:
A roof size of 1,700 square feet (U.S. average)
320-watt solar panels that are 17.5 square feet in size
U.S. average 5 hours of direct sunlight (known as sun-hours), per day
First, you need to determine how many solar panels you can fit on your roof. Assuming all of the roof space you’ve got is usable for solar, that’s 97 panels (1,700 square feet divided by 17.5 square feet per panel). Multiplying that number of panels by the 320-watt power output of each panel gets us a system size of about 31 kW. Finally, 31 kW translates to roughly 80,000 kWh of production per year when you factor in total sunlight hours throughout the year (31 x 5 hours x 365 days). More on production ratios below.
Importantly, these numbers are for a perfect roof with nothing but open space on it. In reality, roofs have chimneys, vents, and more that reduce the overall space available for solar panels. Plus, most installers won’t install panels right up to the edge of your roof, which reduces the available space even more.
How many solar panels can you fit on your roof?
On average, solar panels measure about 17.5 square feet in size. To calculate how many panels can fit on your roof, simply divide your open roof space by 17.5 square feet (or however large your particular solar panels are). For example, if you have 1,000 square feet of open, available roof space, that works out to enough space for about 57 solar panels.
How much solar power can you generate by state?
Of course, there are many assumptions that we used that differ for every solar panel system. One of the major difference-makers is geographic location, which directly impacts the hours of quality sunlight your solar panel system will get. We used 5 hours per day as our average above–here’s how that number (and our end estimate) changes geographically, while still assuming an average roof size of 1,700 square feet and 320 watt solar panels:
How much solar energy can you generate on your roof by state? StateAverage peak sun hoursApproximate total yearly kWh of energy Arizona6.574,000 kWh California5.8266,000 kWh Colorado5.3761,000 kWh Florida5.4462,000 kWh Massachusetts445,000 kWh Maryland4.4751,000 kWh New Jersey4.2148,000 kWh Nevada6.270,000 kWh New York3.5841,000 kWh North Carolina5.0157,000 kWh Pennsylvania3.641,000 kWh Texas5.6464,000 kWh Virginia4.1347,000 kWh Washington4.3850,000 kWh
*Assumptions: 1700 square foot roof, 17.5 square foot/320-watt solar panels
How much solar power can you generate based on your roof size?
Another way to segment solar generation potential is by roof size. Below is a chart comparing solar generation potential based on roof size, assuming all of the same metrics as before: 320-watt solar panels, 17.5 square foot panels, and using every inch of roof space available for solar. The last assumption here is important to call out, because in reality, you can’t use every inch of space on your roof for solar. Panels can’t go out to the very edge of your roof, and you’ll more than likely have obstructions like vents or chimneys that take up space as well.
Bear with us here, these numbers are about to get a little bit silly.
How much energy can differently-sized roofs produce? Roof size (square feet)Number of solar panelsApproximate total yearly kWh of energy 5002845,000 10005791,000 150085136,000 2000114182,400 2500142227,200 3000171273,600
*Assumptions: 17.5 square foot/320-watt solar panels, 5 sun-hours per day
Key variables to consider when calculating your solar generation potential
Of course, it’s never quite that simple. There are a few factors to keep in mind that will adjust your personal solar generation potential: roof space, location, and equipment specs.
You guessed it–a primary indicator for how much energy you can generate on your roof is the size of the roof. The more usable space you have, the more solar panels you can feasibly add to your system. More panels = more energy production, so a larger roof means more capacity to generate solar electricity.
Location/amount of sun
You can put all the solar panels you want on your roof, but at the end of the day, they will only produce electricity when the sun shines above. As such, the amount of sunlight that hits your solar panels is a key factor to understand when calculating how much solar energy your roof can generate.
The amount of energy your system produces relative to the actual rated size of the system is known as the production ratio. A solar panel system’s production ratio is the ratio of the estimated energy output of a system over time (in kWh) to the 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, but also influenced by things like roof angle and directional orientation), 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 1.1 and 1.6.
Want to learn more about production ratios and how installers calculate them? We have a whole blog about it–check out our piece on production estimates to learn more. Spoiler: it’s a lot more complicated than we made it sound in this piece. When you register for solar quotes on EnergySage, our qualified installer network will take the time to actually calculate a true production estimate for your property so you can best understand your solar potential.
What about panel orientation and tilt?
To produce the most electricity, solar panels should be installed on a south-facing roof at an angle of about 30°. In our calculations in this piece, we didn’t take that into account. So, while you may live somewhere with almost six peak sun hours (like California), your entire roof almost definitely doesn’t face directly south at the correct angle. So, take all of the calculations here with a grain of salt. Want an accurate estimate for your unique home? Check out our solar calculator, or register for free quotes on our marketplace.
Equipment size, performance, and power
Solar panels with a larger power to size ratio will produce more electricity per square foot they take up on your roof. As panel technology continues to improve, it’s likely that the amount of space you need to produce enough energy for your home will decrease, potentially significantly, throughout the next several years. High-quality solar panels have their drawbacks, however. Usually, the higher efficiency and wattage solar panels cost more money.
Start your solar journey today by comparing personalized quotes
We made a lot of assumptions above, and things in the real world get much more complicated. Weather patterns, roof irregularities, equipment preferences, and more play into the amount of energy you can actually produce on your roof. If you want to start seeing how many solar panels you need to cover your electricity needs, register for free on the EnergySage Marketplace, where our pre-screened solar installers will provide customized solar quotes based on your unique property.