15 degrees off of south

[petect]

As I  prepare for my summer pv build I've measured the orientation of my house and found the roof where the panels will be mounted (probably 6) faces about 15 deg east of solar south. How much of a loss in performance can I expect if I don't correct the orientation of the panels? It seems that most of the makers of quality panels tout their glass as being forgiving to off angle light, but I have no idea how much off angle light they capture.

Changing the orientation of the entire rack is not an option, but adjusting each panel individually  might be o.k, if it doesn't make things too complicated - I don't remember ever seeing this on commercial installs.  Of course buying one more panel might prove to be the easiest, and possibly cheapest solution.  Any thoughts will be greatly appreciated.
Pete

[SparWeb]

15 degrees east = 30 minutes early.  No biggie.

The sun's inclination in the sky varies by 56.5 degrees during the year, and it traces a 180 degree arc across the sky during the day on the equinox.  In context the 15 degrees won't make that much difference.
Some sites actually have better sun in the morning, depending on shading or weather.

[birdhouse]

+1 on what spar said. 

if it were my install, i wouldn't worry about 15 degrees. 

i can almost certainly say that one more panel will be cheaper than individually tilting each panel. 

adam

[Rob Beckers]

Petect, as mentioned, 15 degrees won't make much of a difference.
You can actually get a very good idea of what energy output to expect for your pitch and orientation by using the free PVWatts calculator at http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/
I use "0.75" as the "DC to AC derate factor" for grid-tie, that gives a pretty accurate number for long term PV production (panels will produce a little more the first few years, a little less at the end of a 20-year period). In the same calculator you can play with 'perfectly south' vs. your actual orientation, and see how little difference that makes.

-RoB-

[petect]

Thanks guys.  It's nice to have this part of the puzzel just fall into place.

Rob   Pvwatts is an interesting site. If nothing else, it reminds me of the losses I can expect as I add components. Something I should have known - but sometimes it's easy to miss the obvious.
 Pete