Wholesale Solar lits a bunch of different brands and key facts about each. They say they offer "all" brands but I wonder if that's true. Anyway, they liste quite a few brands, and the differences make interesting reading.
At the site I found a matrix of orientation factors in Los Angeles (similar latitude to San Antonio). A 7/12 pitch facing south has the best performance year round (yes I already posted a number very similar from a detailed calculator), and that's defined as 1.0. But straight up isn't awful either, you still get 0.89 efficiency. And straight up, the angle doesn't matter, and trees are less likely to interfere (but still can, if they cast shadow on the panel because the sun isn't straight up either). Facing east or west at 7:12 gets you 0.84, you might as well point straight up if you can. SE or SW at 7:12 gets you 0.96, backing down to 4:12 gets you 0.95. E or W at 7/12 gets you 0.84, so there flatter is better, 4:12 gets you 0.88, straight up 0.89 (again).
My take, as usual, is don't sweat the small stuff. Go for the 1.0 if you can but other orientations are quite acceptable from E-S-W. If you must put on E-N-W half, just point straight up. It's more critical to avoid actual shading. A full shade cast across the narrow dimension of solar panel can reduce output by 100%, even if it's just a few inches. Many other kinds of shadow, not going all the way across, get you down to 50%. Obviously, avoiding shading is the most important factor. The the "diffuse" shade from object in distance isn't as important.
Here's a great blog post on solar power from an independent consumer.
One interesting point in there is that temperature derating can be significant, you can lose 10% at 122 degrees F (and it can get that hot on roof).
At the site I found a matrix of orientation factors in Los Angeles (similar latitude to San Antonio). A 7/12 pitch facing south has the best performance year round (yes I already posted a number very similar from a detailed calculator), and that's defined as 1.0. But straight up isn't awful either, you still get 0.89 efficiency. And straight up, the angle doesn't matter, and trees are less likely to interfere (but still can, if they cast shadow on the panel because the sun isn't straight up either). Facing east or west at 7:12 gets you 0.84, you might as well point straight up if you can. SE or SW at 7:12 gets you 0.96, backing down to 4:12 gets you 0.95. E or W at 7/12 gets you 0.84, so there flatter is better, 4:12 gets you 0.88, straight up 0.89 (again).
My take, as usual, is don't sweat the small stuff. Go for the 1.0 if you can but other orientations are quite acceptable from E-S-W. If you must put on E-N-W half, just point straight up. It's more critical to avoid actual shading. A full shade cast across the narrow dimension of solar panel can reduce output by 100%, even if it's just a few inches. Many other kinds of shadow, not going all the way across, get you down to 50%. Obviously, avoiding shading is the most important factor. The the "diffuse" shade from object in distance isn't as important.
Here's a great blog post on solar power from an independent consumer.
One interesting point in there is that temperature derating can be significant, you can lose 10% at 122 degrees F (and it can get that hot on roof).
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