# Correct angle for Solar Panels

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• Solar Expert Posts: 102 ✭✭✭✭
Re: Correct angle for Solar Panels

From what I have learned about all this so far is what you said is 100% correct, and I agree.

I did notice an increase of 1 Amp everyday at 12:00 since start up. I attribute that to the sun's position changing to a more direct hit on my panels. My southern panels are 44* facing south. My western panels are 42*. Can't do much there.

I was trying to find a good average angle for year round. As said, it's the cost justification. I was originally going to make an Awning with panels,that is where I wanted the angle. But my wife nixed it, saying itwould look ugly.
• Registered Users Posts: 12 ✭✭
Re: Correct angle for Solar Panels

BB - have you ever seen a calculator that can tell you what the resulting true slope and orientation of modules installed on an east facing roof, but tilted up to some degree to get them more south-facing?

It's not trivial trig so I would think someone would have invented such a calculator. We've installed arrays on sloped ground surfaces and tilted the array, then measured the orientation with a string & ball, and measured the slope with a level and inclinometer. But that's all "after the fact".

But do you know of anyone that has developed a calculator for this?
• Solar Expert Posts: 102 ✭✭✭✭
Re: Correct angle for Solar Panels

Interesting. I thought about that too. But my neighbors may complain about the look.

On another note, as the season progresses to summer, I see more and more current coming down the pipe. I actually saw my meter running backwards with the house running normally. Until the AC kicked in, And it was a partly cloudy day.
• Solar Expert Posts: 713 ✭✭
Re: Correct angle for Solar Panels

Here is the Excel equation I use for figuring the effective module angle given tilt and azimuth:
=IF(E27-180>0,ACOS(1-(1-COS(E26*PI()/180))*SIN((ABS(E27-180))*PI()/180))*180/PI(),-ACOS(1-(1-COS(E26*PI()/180))*SIN((ABS(E27-180))*PI()/180))*180/PI())
Definitely not trivial. I'd sell my proposer software, but the thought of having to provide maintanance makes me shudder.
• Registered Users Posts: 12 ✭✭
Re: Correct angle for Solar Panels
solarix wrote: »
Here is the Excel equation I use for figuring the effective module angle given tilt and azimuth:
=IF(E27-180>0,ACOS(1-(1-COS(E26*PI()/180))*SIN((ABS(E27-180))*PI()/180))*180/PI(),-ACOS(1-(1-COS(E26*PI()/180))*SIN((ABS(E27-180))*PI()/180))*180/PI())
Definitely not trivial. I'd sell my proposer software, but the thought of having to provide maintanance makes me shudder.

I'm not sure you understood the problem. Imagine an east facing 5/12 roof, modules mounted flush; simple & clean looking, absolutely, but then we know they will produce more if they were facing more south.....so to get a more south-facing azimuth on the modules, tilt legs on the north side of the modules could be added. So, with these tilt legs now in place, what is my resulting slope and orientation?

As a result, such a calculation would need to begin with at least three input parameters:
- initial roof slope
- initial roof azimuth
- tilt angle of the modules

The results of interest would then be two fold:
- the resulting slope and
- the resulting azimuth of the modules.
• Solar Expert Posts: 1,973 ✭✭✭
Re: Correct angle for Solar Panels
I'm not sure you understood the problem. Imagine an east facing 5/12 roof, modules mounted flush; simple & clean looking, absolutely, but then we know they will produce more if they were facing more south.....so to get a more south-facing azimuth on the modules, tilt legs on the north side of the modules could be added. So, with these tilt legs now in place, what is my resulting slope and orientation?

My pragmatic answer is this: Unless you are changing the azimuth angle by a large amount, the change in output that you will realize from such an arrangement will not pay for the added racking cost. And lifting the north edge of a module will shade the one to the north of it unless you move it back, so you'll need a lot more roof area for the same number of modules. Plus, you cannot get away from the fact that late in the day the modules will be shaded by the roof itself no matter how you orient the modules.

Also, have you explored the added exposure to wind loading that you would get from this strategy?

Overall, this sounds like a bad idea to me.

I know this does not address the theoretical math problem you presented, but I don't think it would be that tough if you used a spherical polar coordinate system. When I was in engineering school I probably could have solved it in a couple of minutes but many brain cells have fallen by the wayside since then.
• Solar Expert Posts: 115 ✭✭
Re: Correct angle for Solar Panels

Calculating panel angles down to a knat's knee is fine for us type "A" people, but after it's all said and done, my biggest problem with a flat summertime angle is...BIRD CRAP! Man, I'm telling you, as soon as I flattened out the panels around the equinox, these nasty little feathered miscreants took roost and negated any solar gain I might have realized. I actually raised them back up a bit to deter the wreaker's.
3500w solar, 800AH with Rolls Surrette, Magnum inverter, Midnite charge controller, Kubota 21kW diesel genset...private well...and just recently connected to city power for additional options...nice to have options
• Solar Expert Posts: 102 ✭✭✭✭
Re: Correct angle for Solar Panels
plongson wrote: »
Calculating panel angles down to a knat's knee is fine for us type "A" people, but after it's all said and done, my biggest problem with a flat summertime angle is...BIRD CRAP! Man, I'm telling you, as soon as I flattened out the panels around the equinox, these nasty little feathered miscreants took roost and negated any solar gain I might have realized. I actually raised them back up a bit to deter the wreaker's.

You had to break my bubble. Here I was planning on 2000 watts on my flat roof. But they only target my freshly waxed truck. LOL
• Solar Expert Posts: 630 ✭✭
Re: Correct angle for Solar Panels
plongson wrote: »
Calculating panel angles down to a knat's knee is fine for us type "A" people, but after it's all said and done, my biggest problem with a flat summertime angle is...BIRD CRAP! Man, I'm telling you, as soon as I flattened out the panels around the equinox, these nasty little feathered miscreants took roost and negated any solar gain I might have realized. I actually raised them back up a bit to deter the wreaker's.

I'm surprised. I would have thought the heat generated by solar panels would deter birds from landing on them. I have mine almost flat for a couple of months out of the year, and the heat gets through my soaked towel quick enough (when I dust them, never had any droppings).
• Solar Expert Posts: 115 ✭✭
Re: Correct angle for Solar Panels

Most of the pooping is going on during the morning and evening hours. I never see one there at night or the middle of the day. I have a great solution, but I'm not a good enough shot to risk putting a hole in a \$500 panel...LOL I also have a woodpecker that jackhammers my stone chimney. I hate birds...Man did this thread get off track...HA...
3500w solar, 800AH with Rolls Surrette, Magnum inverter, Midnite charge controller, Kubota 21kW diesel genset...private well...and just recently connected to city power for additional options...nice to have options
• Solar Expert Posts: 102 ✭✭✭✭
Re: Correct angle for Solar Panels

Now that a month has passed, . . .

I have been watching my current output. Not long after I installed the panels My current was going up, maxing at about 75% of their potential. But lately, it's either the overcast I can't see or the angle has caused the out put to fall to 50%.

Now I'm eye balling that 20' X 23' Flat roof. That's why I asked about those roll solar panels. Other than people saying they are short lived, I have not heard anything negitive yet. I can get 1600 on the flat if I use the rolls for a fraction of the cost of panels, and the installation is included. I am going to test run 3 of them. IF IT EVER STOPS RAINING!!!:grr