What Is the Perfect Roof for Solar—and How Does My Roof Compare?
If you’re looking to go solar at home, chances are you’re going to put those panels up on your roof. (A Ground-mounted solar is a great option—cheaper to install and slightly easier to maintain—but it’s uncommon to have enough space to put up a decent-sized system in your yard.) And if you’re going to get the most juice from your solar panels, having a good roof will make all the difference.
Let’s get this out of the way first: Almost no one has the perfect roof for solar. In the coming years, we will hopefully see homebuilders fully incorporate solar power generation into their projects, but for now, solar suburbs are rare.
That said, what are the factors that will make your roof a solar powerhouse? Here is the top six:
Orientation – also known as azimuth – is the direction your roof faces. For North American solar systems, facing directly south (an azimuth of 180 degrees) is ideal. Not having a south-facing roof is not a deal-breaker, however: Many roofs are multi-faceted, and if your roof is mostly west- and east-facing, you’re likely to only see a 10-20 percent reduction in the amount of energy you’re generating.
There’s been an ongoing debate about south-facing vs. west-facing panels over the last couple of years. While south-facing panels will generate the most energy, west-facing panels generate the most energy when demand is highest. That’s why some big proponents, including the California Energy Commission, encourage builders to include some west-facing solar panels in their developments.
In the end, south is best, but west and east are also good; having panels facing south and west will help you generate energy throughout the day.
Shade – Big surprise: Solar panels only work when the sun is shining directly on them. If you’re surrounded by tall trees and your roof and yard are shaded most of the day, your choices are limited to either a) getting out the chainsaw, or b) buying clean energy from a community solar system instead.
Material – What is your roof made of? The most common type of roofing material is asphalt shingles, but solar installers can put panels on just about any of the most common types of roofing materials, including tile, metal, slate and even wood shingle. Some roof types are more difficult to install on than others, and if your roof is made of trickier materials it will add to the cost of your solar installation.
Age – More important than the roof type you have is how old your roof is. According to a study by the National Home Builders Association, an asphalt shingle roof should last for around 20 years, while slate, copper, tile, and metal roofs can last 50 years or more. Meanwhile, most home solar systems are guaranteed to last for 20 years, and will likely last much longer.
So if your roof will need to be replaced in the next 10 years or less, consider doing so before your solar panels are installed. You can always replace the roof after your panels are in place, but it involves removing the panels and racks, replacing the roof, and then re-installing the panels, which adds more cost to the project.
Size – Along with orientation, the size of your roof will determine how many solar panels you can install. The average US home solar system size is 5 kilowatts or 20 250-watt panels. With solar panels requiring about 15 square feet each, you need about 300 square feet of (south- or west-facing) roof space to fit 20 panels on your roof.
Pitch – The slope of your roof isn’t as important as the orientation, but it can affect your solar energy output. The ideal roof angle for power generation is about 30 degrees, but roofs that are too steep make installation difficult, while flat roofs mean that you can set the panels at just the right angle, but you’ll be paying extra for the required racking.
In summary, here are the roof factors that affect your home solar panel performance:
- Roof orientation: South is best, west works well too, and a mix is OK too.
- Shade: The amount of energy each solar panel produces will be directly reduced by the amount of shade covering each panel, so less shade is always better. (Also, using microinverters instead of string inverters can help improve performance even when shady.)
- Roof material: Asphalt shingles or metal roofs are best, but almost any kind of roofing material will work.
- Roof age: As long as you have 10-15 years left in your roof’s lifespan, there’s no need to replace your roof before you go solar.
- Roof size: More space is better, but you will need 300-350 square feet for an average-size system.
- Pitch: 30 degrees is ideal, but as long as it’s not too steep to install safely, the pitch is relatively unimportant.
If your roof seems like a fit, use Solar.com to receive free, no-obligation bids on a solar installation for your home.