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Old 27-10-2013, 17:59   #1
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solar panels

Have a question, while we have started our refit already and have come to the conclusion that we will be drawing 260 amp hrs on a worst case bases in a 24 hr time frame. So we have decided on 400 watts of solar and a 600 watt wind generator. The question. Is there a difference in having 1 400 watt panel to save space or having multiple solar panels that equals 400 watts in different locations? We will be installing an arch and thought we could install the one 400 watt panel on top and a 100 watt flex panel on the hard top dodger. Pros and Cons on one panel verse multiple panels. Thanks and fair winds
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Old 27-10-2013, 18:20   #2
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Re: solar panels

Give some serious thought to the mounting locations with respect to shadows. Shadows formed on the panels will definitely compromise the amount of electricity they will generate. Assess if one large panel might be obstructed; and if so, would that obstruction be eliminated if you had multiple small panels.
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Old 27-10-2013, 18:31   #3
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The one panel will be mounted on the top of the arch aft of every thing 80" from the deck. multiply panels will be mount one on the arch and two on the side rails. So i dont know.
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Old 27-10-2013, 18:39   #4
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Re: solar panels

Shadows are the bane of solar panels on boats. And since it's hard to hold a particular angle at anchor...

Most modules are built of a number of cells in series (a string), and then there may be a number of strings in parallel. A hard shadow on one cell can take the entire string out of production. If your larger module has multiple strings then it may be about the same as a number of smaller panels. On the other hand, if your large panel is a single string then shadows can kill production. You'll have to look at the module specs to know if you have more than one string. Each (silicon) cell is nominally 0.5V, so a 72-cell panel with a 36V output is one string, but 72-cell 18V panel is essentially two modules in one frame.

My gut, given that shadows are so hard to control, is that you are better off with at least a pair of modules, but that will depend on where they can be fit.
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Old 27-10-2013, 19:06   #5
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Re: solar panels

I agree - shadows are a huge killer so I personally would opt for multiple panels. I have 3 - 140 watt panels on my boat and am really glad I did it that way.
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Old 28-10-2013, 14:53   #6
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Also have a think about adjustable panel mounts for best angle. You will get way way better performance but it can increase complexity, windage and requires operation. On my boat I have two solar panels on each side of the boat on the staunchions and they can swing up to the best angle and swing down when not in use or racing.
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Old 29-10-2013, 17:14   #7
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Originally Posted by Dsanduril View Post
Shadows are the bane of solar panels on boats. And since it's hard to hold a particular angle at anchor...

Most modules are built of a number of cells in series (a string), and then there may be a number of strings in parallel. A hard shadow on one cell can take the entire string out of production. If your larger module has multiple strings then it may be about the same as a number of smaller panels. On the other hand, if your large panel is a single string then shadows can kill production. You'll have to look at the module specs to know if you have more than one string. Each (silicon) cell is nominally 0.5V, so a 72-cell panel with a 36V output is one string, but 72-cell 18V panel is essentially two modules in one frame.

My gut, given that shadows are so hard to control, is that you are better off with at least a pair of modules, but that will depend on where they can be fit.
So is it worth the expense of a muti string solar panel, then one with just a single string. I mean is the extra cost worth it?
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Old 29-10-2013, 17:19   #8
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Also have a think about adjustable panel mounts for best angle. You will get way way better performance but it can increase complexity, windage and requires operation. On my boat I have two solar panels on each side of the boat on the staunchions and they can swing up to the best angle and swing down when not in use or racing.
Great idea on the tilting solar panels. Do you have a pic of how they are installed. After reading all the comments we have decided to go with one 200watt panel on top of the arch and two 100 watt panels. I am hoping by seeing a pic I can arrange a similar set up on the stern rails. Thanks
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Old 29-10-2013, 17:33   #9
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Re: solar panels

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Originally Posted by Autumns Wind View Post
So is it worth the expense of a multi string solar panel, then one with just a single string. I mean is the extra cost worth it?
Too general a question. This really depends on your installation specifics:

What battery voltage are you charging (and it's not just "12V" - the difference between charging at 13.8 vs. 14.4V can be significant as you move solar modules off their optimum I-V curve)?

What type of charge controller are you using? Can it do step-up or step-down voltage changes (most MPP controllers can do one or the other, usually step-down, but PWM controllers can't make voltage changes)?

What are the shading characteristics of your installation location? If you are installing two panels side-by-side, or a multi-string single module and they will likely both end up with hard shade at the same time then splitting up the system makes no sense. This can be particularly true of multi-string units, if two cells in different strings are right next to each other in the shade...

Really, the bottom line usually ends up installing as much solar as you can fit and then accepting the limitations that installation on a boat brings.
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Old 29-10-2013, 17:53   #10
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Originally Posted by Autumns Wind View Post

Great idea on the tilting solar panels. Do you have a pic of how they are installed. After reading all the comments we have decided to go with one 200watt panel on top of the arch and two 100 watt panels. I am hoping by seeing a pic I can arrange a similar set up on the stern rails. Thanks
Dont have any pics right now
But its a very similar settup in this video at 1:55. this is what inspired me to do it.

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