How much solar power can my roof generate?

Have you ever wondered how much electricity you could produce from solar? 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 install.

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. That translates to roughly 57,000 kilowatt-hours (kWh) of solar electricity annually! The average U.S. home uses about 10,600 kWh of electricity annually, more than five times the amount you'll probably need to run your home on solar.

Calculating solar generation potential

To get the numbers above, we considered several factors 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, 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 57,000 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 only open space. 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 open space even more.

On average, solar panels measure about 17.5 square feet in size. To calculate how many panels can fit on your roof, 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's enough space for about 57 solar panels.

Of course, we used many assumptions that differ for every solar panel system. One of the significant 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?

*Assumptions: 1700 square foot roof, 17.5 square foot/320-watt solar panels

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 you can't use every inch of space on your roof for solar. Panels can't go out to the edge of your roof, and you'll more than likely have obstructions like vents or chimneys that also take up space.

Bear with us here; these numbers are about to get slightly silly.

How much energy can differently-sized roofs produce?

*Assumptions: 17.5 square foot/320-watt solar panels, 5 sun-hours per day

Of course, it's never quite that simple. There are a few factors to consider that will adjust your personal solar generation potential: roof space, location, and equipment specs.

Roof space

You guessed it–a primary indicator of how much energy you can generate on your roof is the size of the roof. The more usable your space, 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 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 rarely 1:1 - depending on how much sunlight your system will get (primarily based on your geographic location but also influenced by 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 much 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 calculate an accurate production estimate for your property so you can best understand your solar potential.

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 consider that. 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, the amount of space you need to produce enough energy for your home will likely 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.

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 how much energy you can produce on your roof. Register for free on the EnergySage Marketplace, where our pre-screened solar installers will provide customized solar quotes based on your unique property if you want to start seeing how many solar panels you need to cover your electricity needs.