Need help with solar angle

[WaltL]

Hi guys. I need some mathematical help here. I have my solar panels on the south side of the roof of my cabin. My problem is I don't know what angles they should be at for optimum sunabilty. My roof is 68 inches long to center by 35 inches high. The top slope is about 72 inches. These are approximate dimensions. I would upload a picture if I knew how. The cabin is in central Pennsylvania. I believe because of the slope I cannot lay the panels flat enough for dead of summer but as we get closer to winter I would like to know how high to raise them. The bottom of the panels are mounted on 4" pipe so I can raise the top.  

There was supposed to be a drawing here but it didn't take.

You can try this link until the bandwidth is exhausted: http://ee.domaindlx.com/wlonger/dsc00026.jpg

Thanks in advance

Walt

[MelTx]

   Someone said last week to put a nail or screw in the side of the frame then turn the panel till you dont see no shadow....It works good for my carry around panel.

                                                          MelTx

[Oso]

Your optimum angle for year-round use is your latitude. For central Pennsylvania, this is about 41 degrees.  If you take a piece of plywood and place the 90 degree corner to your left, measure over 1 foot and make a mark. With a protractor centered on this mark, lay out a 41 degree angle going back towards the left. Cut the angle off, and label the 3 angles, 41, 90 and 49 degrees.  Place this angle on the solar panel with the 41 degree angle towards the top of the panel and the 49 degree angle towards the bottom. Put a level on the top edge. Center the bubble and you are aligned.  

If you are going to adjust the angle for summer and winter, you need two more triangles. A 26-90-64 (summer) and a 56-90-34 (winter). These are 41 degrees minus 15 degrees for summer and 41 degrees plus 15 degrees for winter.  (The 41 degree triangle becomes your spring setting.) Construct these in the same way you did the first, laying out the 26 degrees and the 56 degrees from the one foot mark, respectively. Align the panel the same way.  

To check your roof for the summer setting put the 26 degree angle towards the top of the roof and the 64 towards the bottom and level. If the lower angle (the 64 degrees) is in contact with the roof when the upper edge is level, you are OK with your current set up. If the upper end (26 degrees) is in contact when level, measure the gap between the lower point and the roof. If your solar panel is 5 feet long, multiply the measurement by 5 and that is how far the lower panel mount must be raised. (This is the reason for setting the exact 1 foot measurement off of the 90 degrees, before laying out the angle.)

If you do need to block up the lower mount, I would give it a little bit of a fudge factor, just to be on the safe side.  

[geoffd]

I used this link to calculate mine.

http://www.wattsun.com/resources/calculators/photovoltaic_tilt.html

Cheers

Geoff

[mungewell]

I also found this link:

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

Which is interesting as it claims to increase the power generation by optimising over the whole day, not just optimising for 'solar noon'.

Simon.

[K3CZ]

With all due respect to those who carefully calculate panel angles, I submit that a few moments experimentation moving the panel around, with the panel charging a battery thru an appropriate ammeter on a cloudless day , at noon +/- a couple of hours, that you will discover that the angle is not critical at all; 20 deg. off axis produces only a very slight change in amperage.  The biggest loss will come in the summer from the very wide angle that the sun traverses; insolation of the panel may only be 8 hrs/day, even with 16 hrs of direct sunlight available.  You will probably need most power in the winter; if so, elevate the panel to just under the elevation of the sun at high noon.  This is way below best angle for the summer, but you probably won't need as much solar power in the summer! Also, this near-vertical angle will have less problem with snow accumulation.

[Tom in NH]

I'm inclined to agree with K3CZ. Output is dramatically greater when a panel is perpendicular to the sun, but other variables tend to reduce the need to be absolutely precise with sun angle. How much battery capacity do you have? How much load? This will influence the amount of electricity you will need to charge your batteries. If your panels have to go all out to charge the batteries then sun angle is more important than  if you have ample generation capability.

An exception to this would be when you have a large dump load such as a hydrogen generator or something. In this case you will want all the power you can get from your system, and you may even wish to incorporate some sort of tracking mechanism to follow the sun as it moves across the sky. --tom