Is My Roof Big Enough for Solar Panels?

How Many Solar Panels Can Fit on My Roof?

There are a few rules of thumb that can give you a general idea of how much roof space is needed for solar panels. These guidelines can also help determine how much roof space you have available for solar panel installation.

Generally, every square foot of roof space has the potential to generate about 15 watts of solar energy. Thus, a solar panel installation on a small home might need about 200 square feet of roof space, while a larger home can require more than 1,000 square feet of roof space to properly offset its electricity usage.

To offset an average amount of energy usage by the average American home, you’ll typically need 18-24 panels. That is, of course, if the panels are of a standard rating, their positioning is optimal, and the location gets adequate sunlight year-round. If you change any of those variables, the number of panels you need in your array is going to change as well.

If you want to get a sense of how many panels a roof can support, you don't need a fancy solar panel square footage calculator. Here’s an easy calculation you can do.

Multiply the square footage of your roof by .75 to account for the required solar setback. Take that number and divide it by 17.5, which is the average square footage of the standard solar panel size. The resulting number is the maximum number of solar panels you can fit on your home’s roof.

How Much Power Can My Roof Generate?

Let’s take a 24-panel solar array using 400-watt panels as an example. Pretty simple math here is 24 multiplied by 400 to total 9,600 watts.

A solar array's capacity is measured in watts. The electricity produced is measured in watt-hours or, more commonly, in kilowatt-hours (kWh). If a solar panel produces 400W of electricity for one hour, it is producing 400 watt-hours, or 0.4 kWh. So 24 panels, with ideal power-generating conditions, could produce 9.6 kWh in an hour.

Learn more about solar panel output with more detailed math and examples or use the National Renewable Energy Laboratory’s PVWatts Calculator to learn more.

How Close Can Solar Panels Be to the Edge of the Roof?

Most roof-mounted solar installations will need a “solar panel setback” for safety. This is one of the most common requirements for roof solar panels in local and state building codes. This setback is the open space between the edge of the solar array and the edge of the roof, and it provides an unobstructed pathway around your rooftop for emergency responders.

The minimum solar panel setback varies from state to state, but generally, the setback will take up about 25 percent of your roof’s usable space. This accounts for roughly 36-inch wide pathways that run along the edge of your roof. If your roof is more complicated with multiple faces or odd angles, your setback requirements may be different.

Factors to Determine How Many Solar Panels You Need

When determining how many solar panels you need, it’s important to start with your goals and why you want to go solar in the first place.

Energy usage

How many solar panels you'll need starts with an estimate of how much power your family uses in a given year. You can determine your annual energy usage by looking at your monthly energy bills over a year. A good starting number is that the average American home uses about 855 kWh of energy every year.

Location

Different parts of the US get different amounts of sunlight. The average across the US is 205 sunny days a year. If you live somewhere with lots of sun, you might need fewer solar panels. If you live in a location with fewer sunny days, you’ll need more solar panels to generate a similar amount of energy.

The direction of your roof also determines how many solar panels you need. In the northern hemisphere, southern-facing roofs are ideal, as they receive more direct sunlight.

Size and rating of your solar panels

Solar panels vary in efficiency. More efficient panels may be able to squeeze more energy out of a smaller space.

Your budget

Generally, larger systems are a great way to quickly offset your current electrical usage. However, larger systems are naturally more expensive. While you may have the roof space available, your budget may limit your options.

Is it Possible to Install Too Many Solar Panels?

It’s not always beneficial to install as many solar panels as you can. A good solar installation should offset as close to the exact amount of energy you use as possible.

How to Put Solar Panels on Your Roof

Your home’s roof space is just one of the factors that determine the optimum solar power system for your family’s needs. Palmetto can help figure out the precise number and type of panels that will work best for your roof and your family's needs.To find out how many panels you can put on your roof, get started with a free solar estimate or contact a solar advisor today

Frequently Asked Questions

What if my roof is too small for solar panels? If your roof is too small, high-efficiency panels or ground-mounted panels may be a better fit.

Are rooftop solar panels a good fit for everyone? No, there are circumstances when home solar panels aren’t the right choice. A home with low energy bills or an incompatible roof design may not be a good fit.