3 ms·

Side question, I've been thinking about adding on above my garage. One side of the new roof would face S-SW (currently the roof of our house only faces east and

Side question, I've been thinking about adding on above my garage. One side of the new roof would face S-SW (currently the roof of our house only faces east and west). How would I figure out the optimal angle to build the roof for my latitude so that solar panels would get the maximum exposure?

bityard 5y ago
The optimal angle is perpendicular to the sun at all times. Which changes throughout the day, and also throughout the year. My recommendation would be to let the structural, material, and economic factors determine the pitch of the roof, and let the installers determine the optimal angle of the solar panels.
LeifCarrotson 5y ago
Mathematically, you want to be perpendicular to the sun, so typically you'd take your latitude and set that as the angle to horizontal. Some systems allow you to adjust the angle seasonally, angling down to latitude+23 degrees for the middle of winter and up to latitude-23 for the middle of summer, but your roof probably doesn't support that. Also, you might want to bias a little towards the sky rather than the ground; on cloudy days the light comes from all over the sky (less comes from the low-albedo dirt), and if it's fixed year round, again bias it a little towards summer angles because there's less solar energy and more clouds in the winter. Realistically, though, the angle just doesn't matter that much. More silicon area covers a multitude of inefficiencies. You're already proving this by setting a constant azimuth of S-SW because that's where the house aims, doing that again with the angle of elevation isn't that bad. A conversation with a roofer/contractor might go something like this: "Not sure what this nonsense about the arctangent of the latitude is, but you want a slope of 13 7/8 in 12?!?! That's ridiculous, I don't know if I could even get a permit for that, much less trusses or shingles. I did hear of a guy who did something like that for a custom house, he's probably booked out for 20 months and I hear he charges $900/square, talk to him not me if you really, really want that. I can do 9/12 pitch [36.87 degrees] at $600 per square [hundred square feet]. If you go down to 6/12 [26.57 degrees] my guys can walk it and get the job done faster, I'd go $550/square, final offer." Just match existing architecture and reinvest the savings in more panels. Here's an excellent article with some links to papers and calculators: https://www.thesolarnerd.com/blog/optimal-solar-panel-tilt-most-calculators-are-wrong/ https://www.thesolarnerd.com/blog/optimal-solar-panel-tilt-m...

bityard 5y ago

The optimal angle is perpendicular to the sun at all times. Which changes throughout the day, and also throughout the year. My recommendation would be to let the structural, material, and economic factors determine the pitch of the roof, and let the installers determine the optimal angle of the solar panels.

LeifCarrotson 5y ago

Mathematically, you want to be perpendicular to the sun, so typically you'd take your latitude and set that as the angle to horizontal. Some systems allow you to adjust the angle seasonally, angling down to latitude+23 degrees for the middle of winter and up to latitude-23 for the middle of summer, but your roof probably doesn't support that. Also, you might want to bias a little towards the sky rather than the ground; on cloudy days the light comes from all over the sky (less comes from the low-albedo dirt), and if it's fixed year round, again bias it a little towards summer angles because there's less solar energy and more clouds in the winter. Realistically, though, the angle just doesn't matter that much. More silicon area covers a multitude of inefficiencies. You're already proving this by setting a constant azimuth of S-SW because that's where the house aims, doing that again with the angle of elevation isn't that bad. A conversation with a roofer/contractor might go something like this: "Not sure what this nonsense about the arctangent of the latitude is, but you want a slope of 13 7/8 in 12?!?! That's ridiculous, I don't know if I could even get a permit for that, much less trusses or shingles. I did hear of a guy who did something like that for a custom house, he's probably booked out for 20 months and I hear he charges $900/square, talk to him not me if you really, really want that. I can do 9/12 pitch [36.87 degrees] at $600 per square [hundred square feet]. If you go down to 6/12 [26.57 degrees] my guys can walk it and get the job done faster, I'd go $550/square, final offer." Just match existing architecture and reinvest the savings in more panels. Here's an excellent article with some links to papers and calculators: https://www.thesolarnerd.com/blog/optimal-solar-panel-tilt-most-calculators-are-wrong/ https://www.thesolarnerd.com/blog/optimal-solar-panel-tilt-m...