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Solar Panel Shading tollerance?

Solar/Wind/Charging/Batteries

Solar Panel Shading tollerance?

by Jaga » Fri Sep 29, 2006 8:50 am

I understand the difference between the amorphous (shade tollerant) and high output (shade intollerant) types of panels, and that the high output ones produce nearly twice the energy per square foot of deck space. However, I've read a lot in the literature about partial shading significantly reducing the output of the high output ones.

My question is what are peoples real world experience with these? How shade intollerant are they? How far away does a shroud or mast have to be before it's shadow is no longer a problem? My ketch does not have a nice area on the back to hang panels so wherever they go will likely have some sort of wire casting a light shadow across them. Lifeline mounting might work but wouldn't be my preferred spot (esthetics and tangling with sheets while sailing).

Scot
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by paulmelliott » Fri Sep 29, 2006 9:01 pm

I have three 100W (Shell/BP mono-crystaliine) panels above the dodger of VALIS, and before I installed them did some experiments to find out how a panel is affected by shadows:

Each panel has two strings of 36 cells, and each string is in parallel using built-in combining diodes -- this is for connection to a 12V battery bank, using a simple (non-MPPT) charge-controller. If a shadow covers 1/2 of a cell, available current from that string drops to about 1/2. Smaller shadows reduce a string's current proportionally to the cell area covered. If a cell is completely shaded, that cell's string will have no output. Each string operates independantly.

It is possible that a shadow will only hit one string of the panel, but it is more likely that both strings in the panel will be equally affected. In my panels, alternating columns of cells are are connected as strings. Other panels may have a different arrangement. If the panel is wired for 24V output, I suppose that there will be only one long string of cells.

One test I didn't record is to partially block multiple cells in a string, but I recall that the output was reduced to the level of the most-shaded cell. There is probably an asymptotic cumulative effect but it seems that the "weakest link" cell dominates.

In practice, small shadows from shrouds only have a small effect. Clouds, and the shadows from the mainsail will cut the output significantly, and the large shadows from the mast and boom can reduce the output to practically nothing. The dodger is actually a pretty bad place to put the panels (and I was fully aware of this when I did it), but all things considered, including esthetics, it is still my preferred location for my boat.

I plan my power budget assuming that only two out of the three panels will be delivering power, and this seems to be a decent approximation (unless there are long periods of overcast skies). A stern-mount for the panels would suffer less from shadows.

-Paul
S/V VALIS - Pacific Seacraft 44 #16 - Sausalito, California
www.sailvalis.com
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by Vessel Hannah » Mon Oct 02, 2006 12:09 pm

I am going to purchase solar panels soon and am thankful for all the good info here on solar panels. If we were to mount panels on each side of the cockpit on the stanchions are there brackets sold by the solar panel companies to do this? I could not find any info on this on the internet. I have noticed many boats with solar panels mounted this way but have not have had a close look at them. When mounted as such do they pivot up on the side that the sun is not on so they can be in direct sunlight? How do solar panels hold up to rough seas when mounted this way, do you take them off before seas get big or can they take a beating? I wish we could mount them over the bimini but the boom is too long for that.
Thanks
Steve.
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by paulmelliott » Mon Oct 02, 2006 3:09 pm

Here is a link to one company's solution -- I have not used this product, but it is an example of what is out there: http://www.emarineinc.com/products/mounts/hardware.html

A friend had a home-made solution, using plastic rail clamps (the above site has them, and I have seen them elsewhere). He made a strut that would hold the panel up, or let it hang down when not in use. He got from San Francisco to Fiji with the system, but I would expect that any really heavy seas would rip the panel loose, and possibly the stanchion as well.

The rail location can also cause a problem by snagging the jib sheets. Make sure that you have it all figured out before you commit to a solution.

The stern pushpit is a decent place to put a panel, using an articulating bracket of some sort. I've got too much stuff hanging there already, but I've seen it done well.

-Paul
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Deck

by Sandero » Mon Oct 02, 2006 5:28 pm

I have 2 55 watt panels which are about 13x48" and keep them on the coach roof. I inserted 4 eye bolts in to the bottom of the frame/flange and they act as feet and raise the panels up about 1.5" and the running rigging lines to the cockpit run underneath. Offshore I use the screw eyes as lashing points. When sailing under typical conditions the 8 loop grad rails prevent them from sliding to leward and a raised profile of the coach does the same for the windward side.

Since I can easily move them I can repostion them when at anchor.

This location gets reasonable sun, although the boom can cast a shadow on one or the other panel. I do have to be careful, of course, to not step on them.... but I rarely walk where the panels sit except to put on the sail cover and then the boat is pretty flat and I can step around them. I am not completely happy with this compromise but there are few options on my boat. If the weather and seas are really nasty I can easily take them below and stow them for safe keeping. !5+ years and no problems. I recently upgraded the wire and they keep my 2-8Ds topped up... after a weekend of use.

Solar decks anyone?

Jef
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by Vessel Hannah » Mon Oct 02, 2006 10:06 pm

Thanks for the advise. Sounds like this is not as easy as I once thought. I now realize that if I put them on the stanchions on each side of the cockpit the Bimini top will block the sun on one and sometimes both. Sun cancer or power that is the question. Today, found brackets on line for the top of the bimini that mount at the stern end of it. But between the Moniter, Kato pole with outboard davit, outboard and radar, things are getting crowded back there. The coach roof would be ok except that is where our Avon fits perfectly. The modern day sailing vessel must look like a space ship to local folks around the world. No wonder we have become such a temptation to rob with all the stuff we have hanging off out boats.
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by mlc101 » Mon Oct 02, 2006 10:40 pm

Yeah. The best place for solar panels is probably an arch. Never thought I'd say that.....

Since we don't have an arch, we put one panel on a custom bracket on top of each of our davits. under certain circumstances, we can still get some shadows from the mast or wind generator pole, but its mostly clear, and boats are compromises....
Mark
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by Jaga » Tue Oct 03, 2006 10:13 am

Here's another source for ready-made brackets:

http://www.hamiltonferris.com/solar-power.html#mount

I'll probably do some sort of a home-brew stanchion mount as I don't have davits/arch/stern pushpit, but would probably only have the panels up while at anchor. I think some of the dodger frame components and tubing should work well plus some of the plastic mounting brackets mentioned above. Also, the plastic brackets for mounting bbqs on the stanchions nicely.

Scot
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by Vessel Hannah » Tue Oct 03, 2006 11:12 am

Thanks Scot,

After looking at the different websites that carry frames for solar panels I worry about getting the right measurements and having a lousy fit. Now that we found a slip up in Seattle I will go to one of the companies in Ballard that make custom frames to do the task and make one up. I'd like to beef up the bimini frame a bit anyway and maybe that can be done in congunction with the solar frame. It may cost a bit more but it will be done right.
Hope you are enjoying all the great sailing weather of the last few weeks we have had in the PNW.
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by mlc101 » Tue Oct 03, 2006 11:56 am

If you only use the panels at anchor, and don't mind "setting them up", a lot of boats have been successful mounting the panels on the lifelines. They stow by swinging them down against the stanchion and deploy by swinging them up and out from the lifelines, held up by some kind of bar.
Typically people run a stainless pipe either parallel to the lifeline or replacing the lifeline, between two stanchions. Then some kind of stainless connection to the bar, like a clamshell. Mount an aluminum angle iron to the panel and the clamshell fitting to the angle iron.
This is hard to describe, but rather easy to build and mount. It gets the panels out away from the majority of shadow-casting items on the boat when deployed.
For what its worth.....
Mark
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Solar panel mounting

by Delezynski » Fri Oct 06, 2006 2:05 pm

You might want to take a look at how we mount our panels on Guenevere.

We have WEB page about it at: http://www.svguenevere.com/2006/gear/solar.html

We also talked about how much power we need one page up.
http://www.svguenevere.com/2006/gear/gear2.html

Greg
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Re: Solar Panel Shading tollerance?

by betwithserejohn » Wed Jul 26, 2017 7:42 am

Hello,
Solar panels work best when there is no shade cast upon them. In fact, a shadow cast on even just part of one solar panel in your solar array can potentially compromise the output of the whole system. What are some strategies for dealing with potential shading of solar arrays?
Why does shading have such a dramatic impact on energy production?
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