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Old 22-11-2018, 13:13   #1
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Question about partial solar shading

All the tests Iíve seen done on shading with solar show testers placing an item directly ON the solar panel. In real world conditions where the boom or sail partially shade a panel, they are quite a distance away and there is still bounce light hitting each cell even when direct sunlight is blocked. What are the real world negative effects of this kind of shading in terms of output reduction? Does a partially shaded cell that is still receiving bounce light limit the electrical production of every cell in its series (even those in direct sunlight) to the output of that shaded cell?
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Old 22-11-2018, 14:56   #2
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Re: Question about partial solar shading

No.

There are so many variables, need to test a given setup, each will vary widely.

But generally, partial shade even as you describe, affect total output much higher than just proportionally.

The ideal would be each cell getting its own IC-level MPPT controller.

Next best is a series of inexpensive small SCs, each with one panel, matched so as to optimize Watts per dollar spent.

Next up is an SC handling a group of panels likely to be in the same state of un/shaded, e.g. one port group one starboard group.

Worst is a large set of panels all over the boat, all hooked up to one huge controller.
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Old 22-11-2018, 15:00   #3
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Re: Question about partial solar shading

Example, Victron MPPT 75/15 model ~$120

Look for a panel high watts per square area, rated @ 30+ Voc, ideally 200-220W per single panel, but from 160W is OK, could go to 300W if crazy cheap, like $150.
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Old 22-11-2018, 16:32   #4
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Re: Question about partial solar shading

Quote:
Originally Posted by Thalas View Post
All the tests Iíve seen done on shading with solar show testers placing an item directly ON the solar panel. In real world conditions where the boom or sail partially shade a panel, they are quite a distance away and there is still bounce light hitting each cell even when direct sunlight is blocked. What are the real world negative effects of this kind of shading in terms of output reduction? Does a partially shaded cell that is still receiving bounce light limit the electrical production of every cell in its series (even those in direct sunlight) to the output of that shaded cell?
I don't know if you have seen this video, and I'll be the first to admit that I really don't like "U" Tube stars, but they do simulate exactly the kind of shading you are talking about.

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Old 22-11-2018, 20:41   #5
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Re: Question about partial solar shading

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Originally Posted by john61ct View Post
No.

........

The ideal would be each cell getting its own IC-level MPPT controller.

....
If you are going to offer unsolicated advice to posters on what is optimal, at very least it should be feasible on a cruising boat.
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Old 23-11-2018, 09:28   #6
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Re: Question about partial solar shading

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I don't know if you have seen this video, and I'll be the first to admit that I really don't like "U" Tube stars, but they do simulate exactly the kind of shading you are talking about.

Agreed about youtube stars, but at least these guys from time to time provide some useful, practical info, not theoretical BS or videos showing the equivalent of people on vacation.
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Old 23-11-2018, 11:37   #7
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Re: Question about partial solar shading

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Agreed about youtube stars, but at least these guys from time to time provide some useful, practical info, not theoretical BS or videos showing the equivalent of people on vacation.
No disrespect to these guys but they only learned to sail when they took off and now we are bombarded by their constant knowledge of all things electrical, sailing and you name it , it is not that hard to go onto the internet and find this information and therefore getting a more rounded response than coming on here
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Old 23-11-2018, 11:51   #8
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Re: Question about partial solar shading

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No disrespect to these guys but they only learned to sail when they took off and now we are bombarded by their constant knowledge of all things electrical, sailing and you name it , it is not that hard to go onto the internet and find this information and therefore getting a more rounded response than coming on here
At least they went out and actually set sail as live a boards and have made it as far as the Pacific starting out in Fla. I think they spent a number of years living in a RV which has some carry over.

Maybe they are not helpful if you are an old salt, but for those that have not sailed much and want to become live a boards I think they are offering some value added to get an idea of what is involved.

Agreed only a little of these type of youtubers is enough. There is an easy solution to that. All you need to do is click on the X at the upper right of your screen.
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Old 23-11-2018, 11:54   #9
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Re: Question about partial solar shading

I've spent years experimenting with panel placement on my own boat.

My 26 foot Pearson Ariel has very limited deck space. Still I managed to mount 290 watts of panels. Instead of installing one set of panels that have a nominal horizontal alignment (pointed straight up), I installed 150 watts of panels on the deck aligned to vessel-vertical (not visible in the photo), and 140 watts on the port and starboard shrouds. My design goal was to produce power throughout the day's arc of the sun without the effort and mechanical complexity of a single large adjustable panel on a vessel that continually rolls in swells and changes orientation (especially when tacking). I've spread out the panel orientations as much as possible.

Conventional wisdom says that the panels on the shrouds, which are polycrystalline type, should produce very little power except when the sun is near the horizon. In fact, those two panels, which comprise less than 50% of the total capacity, generate more than half the power output.

The shroud panel that is facing away from the sun still produces about 25% of its capacity due to bounce-light off the water, and the array performs very well in diffuse light conditions (overcast skies).

The panels were chosen to have very similar Vmp (maximum power voltage), and all of the panels are wired in parallel through steering diodes for each panel. I have a single MPPT controller. Individual MPPT controllers would improve performance, but only by a few percent (partially negated by multiple controller operating currents), and I traded that off for simplicity, space, and cost. Vmp does not change substantially with illumination. If parallel-configured panels have closely matched Vmp values and reverse currents are blocked by steering diodes, implementing multiple MPPT controllers achieves very little.

I have people who are indoctrinated in the belief that panels have to be horizontal tell me that my shroud panels can't work - until I demonstrate that my polycrystalline panels aligned 45 degrees off axis to the Sun still produce 75% of maximum power and the panel facing away from the sun still produces 25% capacity when on the water. There is very little data provided by panel manufacturers on panel performance in overcast conditions (which predominate here). My testing indicates the optimum configuration in that condition is a electrically parallel panel configuration in a hemisphere arrangement. I've done as much as I can to replicate that configuration.

I've also been challenged by claims the windage introduced by the shroud panels will disrupt handling of the boat. Since the panels are within inches of the center of lateral resistance, they have no practical effect on yaw stability, and are low enough to not substantially effect roll stability. With wind abeam, they probably increase leeway slightly, but I can't detect the effect. Finally, as panels heat up, their output declines. The suspended panels receive maximum possible airflow.


The panels have so far survived 45 knot winds and 6 years of continuous exposure. I did reinforce the frames with aluminum flat stock to prevent twisting (racking).
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Old 23-11-2018, 12:03   #10
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Thumbs up Re: Question about partial solar shading

Quote:
Originally Posted by Augi View Post
At least they went out and actually set sail as live a boards and have made it as far as the Pacific starting out in Fla. I think they spent a number of years living in a RV which has some carry over.

Maybe they are not helpful if you are an old salt, but for those that have not sailed much and want to become live a boards I think they are offering some value added to get an idea of what is involved.

Agreed only a little of these type of youtubers is enough. There is an easy solution to that. All you need to do is click on the X at the upper right of your screen.
May I suggest that you read proper sailing books and blogs and other useful information if you want to go sailing and learn something,to these 2 which all they do is regurgitate what they find out on the internet anyway , the reason I dont need to press X is I have a life and do not need to watch a mini soap opera on a u tube channel if you feel the need to watch 2 people getting drunk and laughing and really putting not much input their trip (i.e talking about the sea and its wildlife the people they meet the cultures then by all means) , I never slated you , so dont slate me , if you would like to defend them that is ok but do it civilly and you wont receive my catty reply
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Old 23-11-2018, 12:05   #11
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Re: Question about partial solar shading

I don't have a specific answer to your question, but thinking beyond that I went with the strategy that if you are installing solar put up as many watts as you can afford. With virtually every solar installation there will be a time of some shadowing over the panels so the more panels you have the better functioning system you will have.


My boat has 4 x 140W panels (560W) mounted over the dodger and stern arch. They are fixed and I never worry about shading as at least one of them will always be fully charging.


~ ~ _/) ~ ~ MJH
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Old 23-11-2018, 12:18   #12
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Re: Question about partial solar shading

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May I suggest that you read proper sailing books and blogs and other useful information if you want to go sailing and learn something,to these 2 which all they do is regurgitate what they find out on the internet anyway , the reason I dont need to press X is I have a life and do not need to watch a mini soap opera on a u tube channel if you feel the need to watch 2 people getting drunk and laughing and really putting not much input their trip (i.e talking about the sea and its wildlife the people they meet the cultures then by all means) , I never slated you , so dont slate me , if you would like to defend them that is ok but do it civilly and you wont receive my catty reply

That is actually exactly what I do(read sailing books and seek out sources other than youtubers content). I did not think my post was the least bit a slight to what you posted or even contrary to what you posted.

I agree your post was catty, and unjustifiably so.

Nothing stated was uncivil. You obviously have watched enough sailing youtubers to know you do not like them much. Nothing wrong with that. So I guess clicking on the X in the upper right corner of the screen came in handy. Nothing wrong with that either.

But I have no idea why you took offense and slighted me since I said in my post I can only take the Wynns or similar in small doses

The bit about catty responses works both ways.
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Old 23-11-2018, 12:24   #13
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Re: Question about partial solar shading

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That is actually exactly what I do(read sailing books and seek out sources other than youtubers content). I did not think my post was the least bit a slight to what you posted or even contrary to what you posted.

I agree your post was catty, and unjustifiably so.

Nothing stated was uncivil. You obviously have watched enough sailing youtubers to know you do not like them much. Nothing wrong with that. So I guess clicking on the X in the upper right corner of the screen came in handy. Nothing wrong with that either.

But I have no idea why you took offense and slighted me since I said in my post I can only take the Wynns or similar in small doses

The bit about catty responses works both ways.
Hee Hee got you back up then
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Old 23-11-2018, 12:57   #14
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Re: Question about partial solar shading

i bet it makes a difference whether you are using "12V" panels or "20-30V" far as the shading goes
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Old 23-11-2018, 13:01   #15
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Re: Question about partial solar shading

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Hee Hee got you back up then
Thanks. Good one! I am pleased you are not actually offended.
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