Let’s face it, few of us bought our current home because of its unobstructed and ubiquitous south facing roof potential for solar. Most of us are stuck with what we happened to walk into when we bought our last home. The best residential solar roof is one that is composition shingle, south facing, at least 500 sqft of available space, one big single solar array and no shade. If your roof doesn’t fit into this profile, it does NOT mean that you have a bad roof for solar. But the more factors in the negative column that add up, it does reach a point where the value proposition will be difficult. Let’s take a deeper look at each of the variables mentioned above and five questions to consider when evaluating whether you have a good roof for solar panels:
1. What direction is your roof facing? (Roof orientation):
A south facing roof gives you the largest solar window during the day. A solar system of identical size and components will generate a very different value proposition based on which direction it faces and potential shade implications. As I mentioned, South facing is typically best unless you have time of use implications (TOU) or geographic implications like morning fog on the West coast or afternoon showers in the Rocky Mountain regions. You can expect to see 10% to 15% less energy production from an East or West facing solar panel.
2. What type of roof surface do you have? (Roof type):
Some roof surfaces are easier to install on than others. Easier = cheaper and composition shingle is the easiest. Given that your solar power plant will live on your roof for a few decades, you want to make sure there is plenty of life left in those shingles so keep that in mind. Wood shake and stone coated steel are pretty much out of the question. Spanish tile is significantly more challenging than flat tile roofs. Slate is also challenging and expensive to install on. If you happen to have a standing seam metal roof, there is a great application for that and I do like the fact that you have a lifetime roof under your solar power plant. Corrugated metal roofs are possible but require some additional mounting considerations. There are some really creative solutions out there for different roof applications but creative typically means more expensive.
3. How big is your roof? (Roof Space):
You want at least 500 sqft of available roof space. That may not sound like a lot but when you add in all the chimneys, dormers, roof vents, skylights and other shade obstacles, it does make that more challenging. Some roof vents can be relocated but the gas vents are tougher than the PVC vents. Just about anything is possible when it comes to moving obstructions around but it adds to the cost of the project. One of the biggest challenges with small solar arrays is that a significant portion of the cost for your solar system is a sunk cost. Meaning you will pay that for a 3kW system as well as a 10kW system. The ability to spread those costs over a larger array dramatically improves the return on investment. So it’s not that you can’t install a smaller array with less than 500 sqft of available space, it just impacts the value proposition.
4. Is your available roof space spread out over multiple roofs? (Number of solar sub-arrays):
You may have the roof space if you consider all of your available roof planes but they are spread out. 200 sqft facing East, another 200 sqft facing West and another 200 sqft facing South. No problem. I’ve seen homes with 5 or more different sub-arrays. But as you can imagine, that costs more in labor, materials and time. It can also start to look really bad from an aesthetic perspective. So the fewer sub-arrays the better.
5. How much shade do you have on your roof? (Shade):
I want to point out something obvious but important. Shade on a solar panel is bad. Another obvious but important factor is that the sun moves throughout the sky during the year. What looks perfect in the summer may be totally shaded in the winter. Shade does not have to be a deal killer but it does need to be quantified and included in the overall assessment. It’s also worth considering if removing trees will have a significant impact. If that is your situation, it is best to assume you would need to completely remove a tree vs just cutting back branches. It is usually the height of the tree that is problematic, not the width, and topping a beautiful tree can look really bad. There are design considerations to make that will help mitigate seasonal shade on a roof but that will be for another post. Product does matter because all solar is NOT created equal.
The Takeaway
There are a number of factors that will determine if you have a good roof for solar. Few homeowners have the perfect roof but you want to have more variables in the plus column than the negative column. For those homeowners interested in going solar and the financial value proposition isn’t the primary driver, you can make a lot of roofs work just fine even with less than ideal solar conditions.
