# Mount Panels @ What Angle?

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Solar Expert Posts: 116 ✭✭
At what angle should the PV panels be set? My latitude is 34.5 degrees N. The earth's axis is tilted 23.5 degrees. Ugh, the math....
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• Banned Posts: 17,615 ✭✭✭
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Re: Mount Panels @ What Angle?

My favourite solution to the problem: http://www.macslab.com/optsolar.html
• Solar Expert Posts: 2,397 ✭✭✭✭
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Re: Mount Panels @ What Angle?

While near 30 degrees is optimal, your loads should help dictate your angle. If you plan on running AC Or even a swamp cooler in AZ you might want to set them more shallow to get some better production in summer. I have mine on a 5/12 pitch roof and I think that is a pretty good compromise considering panel temps are also higher in summer. PVWatts shows my peak production in May but it holds up pretty well in June and July as well.
• Solar Expert Posts: 621 ✭✭
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Re: Mount Panels @ What Angle?
My favourite solution to the problem: http://www.macslab.com/optsolar.html

Why using that table look opposite for me at lat 30.69 ??

I used another site where you just punch in your city/state.. lets say Houston since its 30' N..

http://solarelectricityhandbook.com/solar-angle-calculator.html

It says 55 winter and 14 summer..

Then another site (which I am trying to find the link for) said 86 summer, 60 summer, & 36 winter..
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: Mount Panels @ What Angle?

it all depends on what they are referencing to for the angles. if they mean that a pv laying flat or horizontally it 0 degrees then is meshes with what we say because then as a side of the pv goes up the angle we would refer to is the point where it would meet the ground. this would also mean a pv standing straight up or vertical would be 90 degrees from the ground.

now recommending 86 degrees in the summer certainly would not mesh with what we are referencing to because the sun is nearly over head and would need to be flatter to the ground to point straight to the sun.
• Banned Posts: 17,615 ✭✭✭
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Re: Mount Panels @ What Angle?

I'll just quote their explanatory paragraph further down the page:

"The recommended angles can seem counterintuitive. For example, consider summer at 40° latitude. At noon on the solstice, the sun is 40° - 23.5° which is 16.5° from directly overhead. To capture the most sun at that time you would tilt the panel 16.5° to point it directly at the sun. On other days of the summer it is a bit lower in the sky, so you would want to tilt the panel a bit more. Yet we say to tilt it only 12.5°. The sun is never that high. How can that be right?

The answer is that we are considering the whole day, not just noon. In the morning and evening, the sun moves lower in the sky and also further north (if you are in the northern hemisphere). It is necessary to tilt less to the south (or more to the north) to collect that sunlight."
• Solar Expert Posts: 621 ✭✭
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Re: Mount Panels @ What Angle?

I got these numbers

Jan 36
Feb 42
Mar 51.4
Apr 63.5
May 74.1
June 81.2
July 82.4
Aug 77.5
Sep 67.9
Oct 56.4
Nov 45.1
Dec 37.6

I planned on hanging my panels on poles like this.. and be adjustable for tilt and turning.. pivot point up top..

Using this looks like 86' would be correct for summer as almost flat..
• Solar Expert Posts: 10,300 ✭✭✭✭
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Re: Mount Panels @ What Angle?

maybe this tool will show you better to understand.

http://www.sears.com/craftsman-magnetic-universal-protractor/p-00939840000P?prdNo=1&blockNo=1&blockType=G1

if as it appears in the picture and was on top of a pv laying flatly that the angle shown on the top would show the angle we refer to. trouble is this tool would show both angle references so you could get confused.

had another senior moment. sorry for confusion.
• Solar Expert Posts: 621 ✭✭
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Re: Mount Panels @ What Angle?

Using macslab numbers I get.. 26.4244 for my all around FIXED position.. which if you subtracted from 90' you'd get 32.57 which is close to the 60' the other site said..

For summer (using .93 - 21) would be 7.54.. for winter (using .875 + 19.2) it says 46.05..

Which works to 82.46 and 43.95 both which would match my numbers (for July and Feb) pretty close from that OTHER 3rd site I still can't re-find..

Ok.. just though I was nuts.. I guess all is well.. Thanks niel..

ETA: heres my TILT protractor that I'm going to use.. Flat side parallel to my pole in the ground.. I marked summer, winter, spring.. and on the back is each month listed in case I get bored.. this would be my 90' as on the post.. so 86' would be almost flat..

• Solar Expert Posts: 5,183 ✭✭✭✭
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Re: Mount Panels @ What Angle?

Pablo, here is a no math solution.

assuming you are going to, or will have adjustable angle PVs... use a gnomon
http://en.wikipedia.org/wiki/Gnomon,
ie a 90* carpenters square, set it on the panel at your optimal time of day, I used noon, and adjust the panels angle till there is no shadow cast by the gnomon, that is when the panel is pointed straight at the sun and is best for that time of day on that day.
So, the angle needs to be adjusted quarterly or each month of the year if you like, to optimize your capture.

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