We get many enthusiastic calls and emails from people ready to get solar installed on their roofs. Their enthusiasm is exceeded only by their disappointment if I have to tell them their roofs don’t work. Here are some questions to ask yourself when evaluating if your roof is solar-friendly.
Can solar panels fit on my roof?
A good-sized residential solar system (e.g. a 5-kW system with 15 SunPower panels) can be installed on 300 square feet of roof. Square footage is length times height, so a 15’ x 20’ roof has 300 square feet.
A nice, clean rectangular roof is great, but hardly the norm. We design solar energy systems for all kinds of roof configurations. Dormers, vent pipes, chimneys and skylights take up valuable roof space and cast shade on panels, but solar still often works on those homes (see photos below). In most cases, we can move vent pipes.
Most roof shapes work for solar, although hip roofs lose some useable space due to their shape.
Can you put solar panels on a metal or rubber roof?
Solar panels are most easily installed on asphalt shingles and standing seam or corrugated metal roofs (but not metal shingles). They can also be installed on rubber roofs. (I’m talking New England now. In California, for example, clay tile roofs are the norm.) Cedar shingles or slate tiles typically cannot support solar energy systems.
Is my roof good for solar?
If your roof doesn’t have at least 10 years of life left in it, or if the shingles are cracked or in poor condition, I recommend replacing your roof before installing solar. Even with snow, roofs in New England are great for solar energy.
Which direction should solar panels face?
In the Northern Hemisphere, the sun is always to our south, so roofs ideally should face true south. (In solar terminology, the best “azimuth” is 180.) But, with today’s improved panels, a roof facing east, southeast, southwest or west also works.
Again using solar terminology, south facing roofs are 100% of ideal while panels on east or west facing roofs produce about 85% of the ideal amount. That’s still a lot of sun that can be captured and put to good use.
If you don’t know which direction your roof faces, go to Google Maps and type in your address. Click the “Earth” view in the box at the lower left. Zoom in using the + sign to find your roof. (The pin doesn’t always land on the right roof.) Google always opens with north at the top of the map.
Best pitched roof for solar panels?
Although a less significant factor than azimuth, the angle or “pitch” of a roof also needs to be considered. For a roof in the Northeast, because of the sun’s position, the ideal angle for maximum electricity production on a south-facing roof is 36 degrees. (This is also called a 9-pitch roof, but I’m going to talk in terms of angles or degrees – think back to your geometry days.) However, almost any angle can work, even a flat roof.
In fact, a steeper roof is not always better for solar, although certainly snow sheds faster off a steeper roof. If you put solar on a west (or east) facing roof, a lower pitch is better, because more morning (or afternoon) sun reaches over the peak than with a higher pitch. As you can see, the interplay between azimuth and pitch is an important factor in how good your roof is for solar.
And for those craving more detail on pitch, here’s how angles translate into roof pitch:
How much shade does my roof have?
Shade is, of course, the enemy of solar. Ideally, your roof should get full sun between 9 AM and 3 PM all year round. Many people think their roof is sunny all day, but have you really looked? Sometimes when you’re home all day, check your roof hourly to see how much sun it truly gets. Keep in mind that 40% of your solar production comes during the winter, so summer is not the only season that matters. (But don’t wait a year to call us while you check your roof seasonally. We have tools for that detailed analysis!)
Trees within 50 feet of your house will almost certainly shade a portion of the roof during the day. To estimate your roof’s shade, use the general rule that trees cast a shadow about three times their height. Also, shadows are longer during the winter as the sun is lower in the sky, so a roof that’s shade-free in the summer isn’t necessarily shade-free in the winter. This illustration shows the difference between the sun’s winter and summer paths.
Many customers trim or cut trees to maximize the production of their solar energy systems. If you’re curious about the environmental trade-off of cutting trees to install solar, see my “Tree Math” article (and watch for an updated version of that coming soon).
Still not sure if your roof is good or bad for solar? If you live in our service area of central Mass., southern NH and northern RI, give us a call, we’d be happy to have a look. If your roof space isn’t quite enough for your solar needs, you can install high-efficiency panels like SunPower to make the most of the space you do have. If your roof just doesn’t work at all but you have ample clear land, a “ground mounted” solar energy system can be installed to get you saving and making money with solar.
But if the answers to these questions suggest neither your roof nor your yard is good for a solar electric system, you can still install other cost-saving, environmentally friendly home improvements like air-source heat pumps or solar attic fans.
For more details on what makes a good solar roof (or a bad one), play our Good Roof Bad Roof game.
If you liked this article, you might also enjoy:
- How to Build a Solar-Friendly Home
- What’s in a Solar Production Estimate?
- Challenging the New York Times: Why Solar Panels Should Face South, Not West