Impact of Solar Panel Orientation

You are losing a lot of power. IF it was me, I would definitely put them on racks facing south. I would make them adjustable racks so that I could change the tilt angle a couple of times a year.

Here is a good article on tilt optimization.

http://www.macslab.com/optsolar.html

Ken

Oops! That should read - "number of hours of full rated output."
I miss the editing part of this forum. Geuss I will have to start reading what I type more closely.
Something else to consider id the deviation of magnetic south from true solar south if you really want to "dail in" that PV array. Set them as close as possible to true solar south on Dec. 21.
Cut a piece of 2x4 square on both ends about 8 inches long and place one end of it on a moveable flat surface. Move the surface until the 2x4 does not cast any shadow at all on Dec.21 at 12:00 noon. Thats the direction and angle you want your PV array in. If the direction is fix and the PV array is lowered for a summer Sun this will not happen until about 1:30 on June 21.

Thanks for the links to those sites guys, those should help a lot.  I am seriously considering reorienting the panels, but I have two concerns. 

I looked at the adjustable mounting racks on this site.  I was thinking the low profile design might be best, as they will be on a roof, and I think having solar panels sticking 5 feet up in the air might be kind of weird.  But I was wondering just how easy it is to adjust these racks.  It looks like they are of fairly basic design (I won't go so far as to say crude), and I was wondering with the weight of several panels on them how hard it would be to adjust them.  Would it require two people, one holding the panels in place while the other unbolts and rebolts the rear support in order to adjust its length? 

My other concern is how to figure out how far apart I'd need to place the racks so they don't end up shading each other in the winter (when there will be the combination of steepest angle of panels, and lowest angle of sun).  There is limited room on the roof, so if I have to space the racks out too much it might be counter productive.  As an example, if I lose too much space, I might be better off just resorting to brute force by putting up more panels, albeit in terms of expense that option will probably be a lot higher. 

I would suppose in terms of shadowing, I should be most concerned about the middle of the day when most generation occurs.  The whole fact that the roof is not completely flat so there will be some east/west tilt of the installation makes figuring out shadowing a little more difficult. 

Hi David - I ran the model for a home in Memphis (you didn't say where you were located, but my uncle has a home similar to yours in Memphis!).  Anyway, it turns out that, on an annual basis, panels facing due east or due west in Memphis at a tilt angle of 35 degrees will have an overall net efficiency of 80% of those facing due south. Definitely not as bad as I thought before running the model.  While purists will argue that this is unacceptable, all the other issues mentioned (and a bunch not mentioned) probably make the case for staying with simple, low profile, aesthetic flush mounting on the west and/or east facing roofs.  With (relatively) low tilt angles, be sure to keep all the collectors clean so that you maximize the performance with what you have.  I would also recommend evaluating overall energy use and work to increase efficiency (you are using CFLs everywhere for example?) before I would start working up a rack system for the panels.

Best regards -

Tom Hardy, PE
HVTA, Inc.

I am in San Diego, just about as far South and West as you can get, without either ending up either in Mexico or the Pacific.   

Some of the links provided above have been very helpful in assessing my situation.  I tend to agree that being in a relatively southern latitude, the less then ideal placement of my panels is not that dire.  I do believe that reorienting the panels to the south would be worthwhile, and it's something I plan to do eventually, but I am not going to treat it as an emergency. 

I have already more or less optimized my power usage with CFLs, energy efficient appliances, etc, so there is not much more I can do in that area (although always striving for improvement).  The balance of my generation to usage is already generally positive, but then again it never hurts to have a little bit of extra cushion, and in the end if I don't use the power I suppose I can rest easy knowing I have displaced a little bit of polluting power from the grid. 

I would consider putting them on the ground, but it simply is not practical due to space constraints.  I would not be struggling with the whole east/west orientation issue if the ground was an option.  Unfortunately, it's just isn't. 

It has been my experience that orientation doesn't matter as much as the pleasent look on the roof. Why align the panels at latitude plus 15 degrees to maximise the sun for the one day of the year that the angle will be perfect (dead of winter). My modules work great and perform above the rated amps set 5 degrees below latitude at 4500 ft ASL. Rain won't wash them as well at the lower angle but I just spray them with a hose from the ground.
more later..

You might want to check out my free solar panel simulation on YachtSoftware.org.  It will predict the output of an array for a user specified orientation at any time of the day, for any cloud cover, and for any latitude.  Although it was designed for a boat installation you can simply set the boat heading to the orientation of the house.  If after using it you find the software useful we ask for a small donation.