Why do installers put the panels at roof angle instead of optimal angle?

[tradergordo]

Seems to me based on videos I've seen of installs (lots of them on youtube) and pictures I see, that most installers just mount the rails/panels at whatever angle the roof happens to be at. I've read that in a fixed position install, the panel angle should be equal to your latitude. In my area latitude is 40 degrees and the most common roof angle is 30 degrees. Does it make sense to have the panels at 30 degrees? How much difference does it make in efficiency? I know they make adjustable rails or mounts, just wondering why they don't seem to be commonly used (cost?).

[Sunking]

To low ball the bid.

[peakbagger]

Generally when the panels are not at the same pitch as the roof, they dont look good. Aesthetics is important in some areas and to most owners. There are also some design issues that need to be addressed when the panels are at a different angle then the roof due to potential wind uplift.

There are also shading effects that can occur with multiple rows of pitched panels. In areas with low winter sun angles it can really reduce the availlable roof space for panels as each row has to be set back to clear the shadow from the previous panel. I expect that the loss in efficiency on a year round basis for a less than optimum angle is less than the loss of generating capacity due to a lower square footage of installed panel for optimally pitched panels where roof space is limited.

[russ]

Using Sharps calculator http://sharpusa.cleanpowerestimator.com/sharpusa.htm this is the better calculator I have seen on the net.

I looked at the monthly output for a 3kW DC array at 45 degrees north location - changing the tilt from 0 to 60 degrees and

For example there is little difference between 25

[tradergordo]

Cool, thanks for the info guys. I decided to plug my numbers into PVWatts:

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/code/pvwattsv1.cgi

And even though my latitude is about 40 degrees, after a bunch of trial and error and one degree increments I found that the ideal tilt according to PVWatts for my location is 34 degrees. Since my roof is 30 degrees, I calculated the difference, it it amounts to just 20 kw per year (energy value of about $3) so it isn't very significant.

I looked at azimuth too (i.e. what if it was mounted to point directly south instead of flat on my roof) and this amounted to 27 kw per year, so also pretty small. Add them both up and its 47 kw per year I'm missing out on or about $8 in energy savings. I should be more concerned with the 185 kw per year loss I'll have because of the installer NOT using more efficient inverters, but that's another story

Next time I'll probably self install, but that probably won't happen in the next 20 years.

Did I mention installer put his foot though my ceiling because he apparently didn't know how to work in an unfinished attic? Hah. I've been up there at least 20 times doing all sorts of work (4 ceiling fans, attic vent fan, antenna mount, wiring cable and power, fixing a flashing problem, installing junction boxes, etc) never had a problem, this guy goes up and decides to walk on the drywall.

[russ]

Hope he fell with one leg on each side of the truss!

The bird stuff or tree fuzz will cost more kW than that.

For the 3 kW DC system I compared simply adding one panel would make up the difference in some cases. Better to have the angle and orientation that looks best if that is important.

Russ