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Solar panel partial shading

1K views 13 replies 8 participants last post by  capta 
#1 ·
For the panels that are mounted on top of the dodger, for example, wouldn't the boom really kill the output due to partial shading? Does having two panels up their help? Does it help to use thin film amorphous panels? I want to sort out if a position under the boom is just not ideal, or really inefficient.
 
#2 ·
I have a panel on the dodger. Single older style 100 watt. When it's partially shaded, output is greatly reduced.

When at anchor or moored, which is most of the time, I move the mainsheet to the toerail which gets the boom shade off the panel and output is back where it should be.

I also have 2 50 watt panels on the Bimini, but haven't yet noticed if it's better than the single or not. These are the thin flexible variety.
 
#3 ·
I think the overshaddowing is a bit over rated. Yes its going to drop a bit of power but its better than nothing. Yes, hauling out the boom is going to be better, as is tilting panels towards the sun.
What about clouds? No need to shake a fist at them either imho.

But they only need a bit of sun and they still make power.
 
#4 ·
Solar panels consist of a bunch of small cells connected in series strings. Let's say your panel has 3 of these series strings. If a small area of the panel is shaded so that the shadow falls on only one of the strings, then you would lose up to 1/3 of your output. However, if the same small piece of shade falls across all 3 strings, then you will lose almost the entire panel output.

The type and style of cells makes no difference, so amorphous, thin film, etc are meaningless in this regard.

Most people just move their boom out of the way of bimini mounted panels whenever they can.

Solar mounted anywhere is better than no solar at all.

Mark
 
#5 ·
My anecdotal experience....

My 2 panels sit on the coach roof along side a hatch in the salon and DO get shade from the boom or the main at times. These panels (total 110watts) are for keeping the house bank (500 ah) topped up. I do not monitor their output. But they do the job... my bat voltage, if that's a measure... when I return to the boat (at anchor or moored) is pretty much 12.9 - 13.2). Since this is working for me... and has for 25 years, I don't see a problem. I do not have any continuous high amp loads like refer.

When sailing I have the instruments, and the AP... and at night we have LED lighting and maybe the PC. So if you are not needing a lot of charging (alternative) to satisfy hungry loads... then you don't need much solar power. When we do run our refer it is with the engine which also has a high output alternator. This works for me! YMMV
 
#12 ·
.....when I return to the boat (at anchor or moored) is pretty much 12.9 - 13.2).....
If you return during daylight, I'm guessing the panels themselves are keeping the voltage up. You'd have to disconnect everything and wait hours to know what resting voltage really is. Nevertheless, I'm sure your setup is working well. As I recall, you have substantially excess amp hour capacity for your usage and never draw down on it much. Excellent recipe for longevity, although, it comes at an acquisition, weight and space cost.
 
#6 ·
My 400 watt array consists of four separate panels. They are all run mid-ships, all under the boom. I definitely experience significant shading much of the time. But when thinking about my system I knew this would happen. I assume I'm exposing only 1/2 my panels most of the time.

All panels are parallel, which helps. And at anchor I swing the boom out to fully expose them. But underway we tend to get only 1/2 exposure most of the time.
 
#8 · (Edited)
Our panels do just fine on the bimini. The boom is only a few inches above the panels when we aren't sailing, so shading is minimized. They are separated significantly which helps for both shading and viewing the sails when sailing. It really doesn't matter where you mount your panels, unless you have a mechanism that keeps them facing the sun 100% of the time, you will rarely get full power out of them. And of course, there's clouds as Mark mentioned.
Plan for enough wattage to keep you batteries filled at 1/2 efficiency or even less over the daylight period where you intend to use your boat. Don't forget to leave an air space behind the panels if you mount them on your bimini, as heat also diminishes their efficiency.
Below is a pic of ours, 10 years trouble free and counting.
 

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