While residential solar panels are – on average – 20 square feet each, the average home in the U.S. has a roof area of at least 1500 square feet, which intuitively seems like more than enough space to install all the solar panels that you need.
However, the square footage of a roof is not the only thing that matters when it comes to solar panels. This is because solar panels only perform as they should if they’re installed on roof sections that get enough sunlight.
So the real question is, how much of that space is really available for solar panels?
In this article, I’ll discuss a few of the factors involved in this, and I’ll show you an easy way to estimate the number of solar panels and the size of the system that you can fit on your roof.
How many solar panels will fit on my roof?
In the U.S. (or the northern hemisphere in general) Solar panels are preferably installed on south-facing roof sections. North-facing roof sections and any areas on your roof that experiences shading is generally avoided.
If the south-facing section of your roof is prone to shading or is simply too small, southwest or southeast-facing sections are the next best bet. If those are also unavailable or non-existent, west and east-facing roof sections are used.
In any case, Google’s Project Sunroof will give you a pretty good idea of how much of your roof is actually usable for solar panels. All you have to do is submit an address.
Based on 3D modeling of your roof and nearby trees, the tool will estimate how much of your roof is available for solar panels.
The estimate might not be 100% accurate, but it absolutely beats doing all calculations manually, especially if your roof structure is as complicated as the ones shown in the image.
Based on the available space on your roof, the calculator below will estimate the number of solar panels and the size of the system (in kilo-Watts) that can fit.
For example, based on the square footage from the example above, that particular roof can fit as much as 84 solar panels. Which is equivalent to 25.2 kW of solar power:
Chances are the available space on your roof is more than enough to install all the solar power you need. A better approach would be to determine how much solar power you need first.
Related: How many solar panels do I need?
Another important thing to mention is Fire Setback codes.
Fire Setback codes
When installing solar panels, you might be required to leave a certain amount of space for firefighter access and smoke ventilation in case of a fire.
In most cases, these requirements won’t have much impact on your ability to install all the solar panels that you need.
But in general, you might be required to leave a 3ft wide vertical access from each side of the roof, and a 3ft wide horizontal space down from the ridge for smoke ventilation.
For example, these are the setback requirements from the city of Manteca, California:
Disclaimer: The purpose of the example is to give you a better understanding of setback codes, and to help you make estimations. Make sure to contact your AHJ (Authority having jurisdiction) before making any decisions.