Declination, Elevation, Complication -

18 Posts
Aug 27, 2008 04:33 am
Declination, Elevation, Complication -

What is the optimum angle to mount PV panels . . .? . . .

I am in the far North West US (Olympic Peninsula).  I have a flat roof install, its actually a peaked roof but the peak runs North/South, 3/12 pitch.  What is the optimum angle for the PV panels to get the most energy from summer to winter?. . .  How would I calculate that?. 
I figure to mount them all on the West slope, with X amount of space between rows to allow for the Southern most angle of the sun over the top of the first row to the bottom of the next row and so on. 
Thank you.
 
Aug 28, 2008 06:15 pm
Re: Declination, Elevation, Complication -

By any chance is there an end wall facing solar south or close to solar south, that you could mount the array onto? Imagine a long awning, with the top of the array frame(s) attached to the wall at the same height as the top plate, to give a good solid hold for lag bolts, and brace arms holding the bottoms out at the desired angle, preferably were there is wall studs. You might even be able to get an awning company, if there is one near you, to make a frame to your spec.s and mount it.
http://www.sunwize.com/info_center/pdfs/HomePwr_sanyobifacial_11-07.pdf

Some of these pictures make an application of this sort look expensive I know, but, like the old saying goes, "you get what you pay for."

As for the "right" angle(s)
http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/

Once you are at the web site above, just follow the directions, but try a few different things. You will be dealing mostly with one of the three "flat plate tilted" settings. Those hours it gives you, will be an pretty decent approximation of the equivalent number of hours of full rated power from a PV module.

I hope this helps in some way. Good luck!
 
18 Posts
Aug 30, 2008 02:01 am
Re: Declination, Elevation, Complication -

Thank you, Thomas.  Here's a little more information. . .

Mounting an "awning" on the south wall would be too low - the sun would be blocked by the 100' trees in the winter. . . just. . . about 3+ months.  My best chance is to mount the panels on the West pitch of the roof facing south - in rows.
I need to figure out the optimum angle for the best over-all Southern exposure.  How low does the sun track in winter?  30*? 35*? - In the summer its pert near straight up.  These are going to be "fixed" in place.  So. . . should I split the difference between 30*-35* and 90* and go for 60*?  Or should I angle more to the horizon to get more winter exposure (45*or lower)?. . .

Thank you.
 
351 Posts
Aug 30, 2008 11:35 am
Re: Declination, Elevation, Complication -

Here is an article on the optimum orientation of panels.
http://www.macslab.com/optsolar.html
Take a look at the last graph that show the difference between a fixed angle, adjusting four times a year, and tracking.
 
Aug 30, 2008 01:04 pm
Re: Declination, Elevation, Complication -

Latitude at the Olympic Peninsula is around 47 to 48 degrees, add 15 degrees to that for 62 to 63 degrees, and in the months of December and January, you might get as much as 3 hours of equivalent full rated power.
If you have time prior to installing the PV array, and you want to experiment for yourself, find a piece of plywood about 12"x12" and a block of 2"x4" about 10" long with both ends cut square, attach the one end of the 2x4 to the plywood. Take it and an angle finder onto the roof December 21 at 12:00 noon (winter solstice). Hold one side of the plywood to the roof (to approximate a PV module) move it back and forth while holding the angle finder to the plywood until the shadow of the 2x4 block goes away. This will be the perfect angle for the shortest day of the year. You'll find that it will be somewhere near 60 degrees. If you could do the same thing on June 20 at 12:00 noon (summer solstice) it would be somewhere near 30 degrees. The difference between the two falling on both the vernal and autumnal equinoxes.
The autumnal equinox is just around the corner. You could see if I'm right or not this way. It should be somewhere near 45 degrees on September 22 at 12:00 noon.
http://www.almanac.com/astronomy/seasons/index.php
 
462 Posts
Sep 5, 2008 02:16 pm
Re: Declination, Elevation, Complication -

Jack, is the roof the only location you have? If you have a good ground location you can mount the panels so you can change the pitch throughout the year. If you have a flat roof, you can purchase or fabricate racks/mounts that are adjustable also.....
 
Sep 12, 2008 10:45 am
Re: Declination, Elevation, Complication -

After re-reading these postings, I glimpsed a mental picture of what might be your predicament.
Its not just the angle to the horizon you are wanting to know because that angle is compremised by the pitch of the roof as well being on the westerly side of that pitched roof.
In my area, I have noticed this same predicament on several homes with solar water heater panels.
Again, it would take time, but I believe a, full sized plywood mock up of, one of the PV modules you would like to use, would give you a first hand, clear result of the best angles. It would also cast a shadow from the top of it, onto the roof behind it, so that you know exactly where to start the next row.

Another alternative, although very costly, would be to frame and finish, two walls that would saddle the roof. One wall would sit parallel to and over top of, the end wall. It would support the bottom of the array The other wall would run parallel to the first and sit just behind the first. It would support the adjustable or fixed brace arms of the array.

This what I "had to" do on my roof, almost.
I built out short walls, 6' long and about 20" high, leveled off of the peak and at an angle from the peak that put the array facing solar south. Since the weight of the array has the tendency to push the wall away from itself, towards solar south, I pitched that side down to the roof, creating a valley. The back or north side just goes straight up. The walls are finished with; plywood, flashing's, siding and shingles to compliment the rest of the house. Of course it all still looks like a big "billboard" on top of my home but I don't care. Even though the PV "harvester" is by no means free, I am getting the most photonic particle electrons I can from our Sun.
 

Disclaimer and Disclosure

The Alternative Energy Store, Inc reserves the right, within its sole discretion, to refuse or delete any posting or portion thereof, or terminate or block the access to this forum.

The opinions and statements posted on this forum are the opinions and statements of the person posting same, and do not constitute the opinion or act of the Alternative Energy Store, Inc (AltE). The Alternative Energy Store, Inc does not endorse or subscribe to any particular posting. No posting shall be construed as the act or opinion of the Alternative Energy Store, Inc.

Click here for BBB Business Review

McAfee SECURE sites help keep you safe from identity theft, credit card fraud, spyware, spam, viruses and online scams
Desktop Website | Mobile Website

Share

Click on an icon to share! If you don't see the method you want, hover over the orange "+".

Feedback

What can we do to help you?

Please enter a summary
Sorry, the copyright must be in the template.
Please notify this forum's administrator that this site is using an ILLEGAL copy of SMF!
Copyright removed!!