Little confusion about panel tilt

ramiws

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Hi,

I am at 60 degrees altitude. I have checked that sun elevation during summer is around 40-50 degrees. So I thought if I want to have some days with 90degree angle between sun rays and my panels then I have to tilt them 40 degrees. I got this by ( 180 minus sun angle 50, minus 90 to be perpendicular that leaves 40)

But this website says:
"Tilting the module to the incoming light reduces the module output."

What am I missing ?

 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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This link http://www.solarelectricityhandbook.com/solar-angle-calculator.html will give you the correct angles for the various seasons. March & December are the Median Months so if you have a fixed Ground Mount for example, that is the angles to pick for maximum average generation through the seasons. Manually Adjustable Mounts typically have provision for 3 settings, Mid-Winter, Spring/Fall and Mid-Summer.
 

ianganderton

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There are a number of blog posts from australian installers looking at the cost vs benifit of tilting solar panels.


I saw a link the other day on here that discussed how cloud reflection makes a big difference to the irradiance solar panels get in the winter but I cant find it now, wish I'd saved it :/
 

svetz

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But this website says:"Tilting the module to the incoming light reduces the module output."What am I missing ?
I think they mean you lose power when not tilted perpendicular to the sun, the problem is the sun's angle changes throughout the seasons, so the panel's tilt would need to adjusted to stay perpendicular to it.

Try SAM for something very accurate and hard to use, or an online calculator for quick and easy. If you're off-grid, you might want to have enough power when the sun is least effective for you (e.g., rainy season or winter) or optimize when you use the most power; if you're net-metering it might make sense to maximize the annual output. If it's a manual system perhaps you want to seasonally adjust the tilt? Lots of options!
 
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ianganderton

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This is interesting

Quote:- “We found that on sunny days, solar collectors with a DTS (Direct Towards Sun) configuration captured more solar energy in accordance with the well-known cosine dependence for the response of a flat-surfaced solar collector to the angle of incidence with direct beam radiation. In particular, a DTS orientation was found to capture up to twice as much solar energy as a horizontal (H) orientation”

But....

Quote:- “ During cloudy periods, we found that an H configuration increased the solar energy capture by nearly 40% compared to a DTS configuration during the same period, and we estimate the solar energy increase of an H configuration over a system that tracks the obscured solar disk could reach 50% over a whole heavily-overcast day.”

From https://www.researchgate.net/public...ltaic_energy_capture_on_sunny_and_cloudy_days
 

HaldorEE

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This link http://www.solarelectricityhandbook.com/solar-angle-calculator.html will give you the correct angles for the various seasons. March & December are the Median Months so if you have a fixed Ground Mount for example, that is the angles to pick for maximum average generation through the seasons. Manually Adjustable Mounts typically have provision for 3 settings, Mid-Winter, Spring/Fall and Mid-Summer.
I am still confused.

Here is what the website said.

Phoenix
Optimum Tilt of Solar Panels by Month​

Figures shown in degrees from vertical

JanFebMarAprMayJun
41°
49°
57°
65°
73°
80°
JulAugSepOctNovDec
73°
65°
57°
49°
41°
34°

Winter 34°, Spring/Fall 57° and Summer 80°

I understand the Spring/Fall angle recommendation, but I am puzzled by the angles suggested for Winter and Summer. These would only be optimal for Jun and December and would be less optimal for the rest of the season. Wouldn't it be better to use an inbetween angle for this season instead?

Winter 37.5°, Spring/Fall 57° and Summer 76.5°?

Or to do it as a chart:

November - January: 37.5°
February - April: 57°
May - July: 76.5°
August - October: 57°

I can see the concern about winter due to short days and cloudy weather, so that could be an issue. However, we get over 300 days of sunshine a year in Phoenix, so cloudy days don't really matter here.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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If you have a non-adjustable Fixed Mount then you would want the panels at 57 degrees because that is the average set for yearly production.
If you have adjustable mounting you could move the setting for every month, if you wanted to. . If you want optimal production always, then a Solar Tracker is the solution and those are not cheap by any means. Siimply put, double the cost of the installation by the time your all said & done..
 

rin67630

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Apr 29, 2020
Messages
810
Hi,

I am at 60 degrees altitude. I have checked that sun elevation during summer is around 40-50 degrees. So I thought if I want to have some days with 90degree angle between sun rays and my panels then I have to tilt them 40 degrees. I got this by ( 180 minus sun angle 50, minus 90 to be perpendicular that leaves 40)

But this website says:
"Tilting the module to the incoming light reduces the module output."

What am I missing ?

The panel slope perpendicular to the max sun apex is not everything.
The higher in latitude you are, the more the sun will turn around your panel. By reducing the slope you will get a little more chance to catch more early and late sun rays. You also increase the harvesting of diffuse light.
The optimal really depends on how sunny or cloudy your location is and what are your objectives:
-Maximize the production during sunny hours (if you have a usage of that energy maximum) .
-Maximize the average production also during cloudy days (if you frequently get in situations where you can't store all the energy for later use)
 
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chrisski

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I am in the Phoenix valley also and I noticed quite a few North Facing panels when I walk around the neighborhood. I think that's an awful way to put a panel, but in the longest days of the year, it probably gives a good Angle to catch the sun Since it rises more or less in the North East, is about overhead at noon, and then sets in the North West. To me that describes the dancing in the sky of the sun. This will get more extreme the further North you go.
 

Zil

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Those Phoenix, Az charts have little to no application to Seward, Al.
 

HaldorEE

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For a space limited application (like the top of my Van), tilting my single 300 W panel could make sense since I can't add a panel and don't have to worry about panels shading each other.

I have designed a DIY tilting mount that will let me tilt the panel in one direction (towards the front), which means as long as I can park facing South I will be able to use tilt. I was going back and forth on if doing this is worth it.

The confusion for me came from all the comments about tilting not being worth it. But now I understand that is only true for the situation where it is possible to add more panels if you install them flat. I don't really have that option.

I am going to move forward with my tilting mount. I can operate it from the ground which is important to me (I am not climbing up on the roof every time I want to move the van)..
 

Zil

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I have tilting panels on my van. I built so they tilt up from the right side. I intended to park with the left side to the sun. I found the panels flat to the roof were suppling all the power I needed.
 

HaldorEE

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I have tilting panels on my van. I built so they tilt up from the right side. I intended to park with the left side to the sun. I found the panels flat to the roof were suppling all the power I needed.
Got a pic of your tilting mechanism? I am open to alternatives to what I have come up with (concept, not even a drawing yet).
 

chrisski

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I used the Renogy Tilt Mount:

Tilt Mount.jpg
These are installed:
100 Watt Panels Tilting Mechanism.jpg
Note the picture shows a boot width between panels because the hardware needs to come off to tilt.

This pictures shows since the roofs aren't flat, I had to cut the mounting rails. Without cutting its like trying to warp a flat ruler onto a basketball.
Tilt Mounting Rail.jpg
I also mounted in "portrait" mode not landscape, and unfortunately this means the panels won't tilt as high as I had mounted the tilt mounts in "landscape" mode. There's six nuts and bolts to loosen and tighten each panel each time I tilt the panels, 36 total nuts and bolts, so that's about an hour at least start to finish.
 

HaldorEE

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I used the Renogy Tilt Mount:

View attachment 26409
These are installed:
View attachment 26410
Note the picture shows a boot width between panels because the hardware needs to come off to tilt.

This pictures shows since the roofs aren't flat, I had to cut the mounting rails. Without cutting its like trying to warp a flat ruler onto a basketball.
View attachment 26411
I also mounted in "portrait" mode not landscape, and unfortunately this means the panels won't tilt as high as I had mounted the tilt mounts in "landscape" mode. There's six nuts and bolts to loosen and tighten each panel each time I tilt the panels, 36 total nuts and bolts, so that's about an hour at least start to finish.
I will continue to explore my idea. I was thinking about mounting the panel sideways across the front of my van with a roof rack ahead and behind.

The leading edge of the panel is connected to the front rack with hinges. A pair of 8020 extrusions are mounted front to back inside the panel (the panel is 65" in that dimension). A pair of hinged slides are connected by 8020 extrusions to a rotating member located behind the panel in front of the middle roof rack. When I want to tilt the panel I rotate the rear cross member which lifts the panels from the middle, the slide moves up and back until it reaches the rear of the panel at which point the panel is at maximum tilt. I expect I might need to help lift the back edge of the panel at the beginning of the lift.

Here is an example of the slides I am thinking of.


Here is the round member I am thinking of using to rotate the struts.


This will rotate in a pair of these bearings.


I will use these brackets to attach the round member to the struts.


I still haven't worked out all the details. A picture will help, but I need to draw one (I will do so and post it tomorrow). This is still very much a work in process, a process that I am probably 40% of the way through.
 

chrisski

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If I had it to do again, I would not put the tilts in I did, and I would measure the roof space much better and match available roof space to panels. Properly planned, I could have put 1000w -1200w of panels on my roof just on the right side and leaving the left side for walking space.

If I did go with tilts, I'd mount the panels 90 degrees of what I did to maximize the tilting angle.

You're certainly planning it good.

Seems like so much of these builds we do it seems its the first time anyone has ever done it, and feels like there should be more complete off the shelf.
 

chrisski

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My tilt mounts are not faster and not easy and I have to go to the roof, Which means after the novelty wears off, I won’t tilt them,
 

HaldorEE

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I created a thread about my tilting mount in the Vehicle forum.


Let me know what you guys think. There will be some kind of handle on the end of D28 round extrusion so I can rotate the tube more easily. I figure I will probably have to help lift the back end of the panel by hand when I first start to deploy the tilt mechanism, but once it is up it should be very solid. Bringing it back to the travel position should be very easy since gravity will be assisting me.

There will need to be some kind of a hold down (retaining clips) so the the panel won't flap up while I am driving down the road.
 
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