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Old 13-04-2013, 09:40   #1
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Splitting Solar Panels

I am trying to figure out the configuration of the pannels on top of the bimini.
I was thinking on getting two pannels one of 142 wats and another of 100 or 125 aprox. But I read the importance of splitting the surface in different panels specially in a boat.
Does it make sense two split the 142 w panels into 3 x 50 w panel ?, in the same surface area?

That will mean three controllers , and three cables etc ? right ?
Any opinions or sugestions on that ?
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Old 13-04-2013, 09:57   #2
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Re: Sppliting Solar Panels

The reason for splitting panels is that partial shade on any given panel will dramatically reduce the panel's output, considerably more than the percentage area that is shaded. For example, a panel that is in 20% shade will be more than 50% less productive. So the optimal configuration is going to be a function of where the panels are located and what shade they are subjected to from the mast, sails, radar mast, etc.

I have heard a number of people say that they have encountered issues running panels of different makes/outputs but I don't recall specifically what the problems were. I'm sure someone here can shed some more light on the subject.
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Old 13-04-2013, 10:08   #3
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Re: Sppliting Solar Panels

Okay, here's the best advice I can give: go for the three 50W panels, or whatever panels that are all the exact same brand and type and capacity. Now, check if these panels have built-in by-pass diodes. I believe all new panels (like within 10 years) have them but some here on the forum insist that panels without them are still sold. If the panels does not have them, you can easily add one per panel.

Now connect all three panels in series, so 3x 12V nominal panel gives 36V nominal. This allows you to use thinner wire and have less losses. Use a small battery switch in the positive line and connect this to a single MPPT controller. It will pull maximum power from the solar panels and outputs almost all of that as a charge current for 12V batteries (or 24V if you order for that).

Make the installation solid and safe because connecting in series means that you can get voltages as high as 3x 22V so in lethal range.

Modern panels have multiple by-pass diodes so they are really multiple smaller panels inside one panel. If a cell is shaded then the output voltage of the string (or panel if it has just one string) goes down and the bypass-diode will divert the current from the other panels. With all of them in series you keep more than enough voltage so that the others keep charging.
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Old 13-04-2013, 10:18   #4
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Re: Sppliting Solar Panels

The advice on shading was correct. But the advice on connecting three 50 watt panels in series has one big caveat: Most controllers are not designed for the 60+ V open circuit voltage that three panels will cause.

There are two specs that are important in selecting a controller: the maximum voltage and the maximum current that they will be subject to. When you connect panels in series the maximum voltage (Voc) is additive. When you connect them in parallel, the maximum current (Isc) is additive.

David
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Old 13-04-2013, 10:23   #5
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Re: Sppliting Solar Panels

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Originally Posted by djmarchand View Post
The advice on shading was correct. But the advice on connecting three 50 watt panels in series has one big caveat: Most controllers are not designed for the 60+ V open circuit voltage that three panels will cause.

There are two specs that are important in selecting a controller: the maximum voltage and the maximum current that they will be subject to. When you connect panels in series the maximum voltage (Voc) is additive. When you connect them in parallel, the maximum current (Isc) is additive.

David
?? I believe all MPPT controllers will take 60V input. Most take 150V max.
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Old 13-04-2013, 11:04   #6
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Re: Sppliting Solar Panels

In the series case, what happens when one panel is shaded?
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Old 13-04-2013, 11:13   #7
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Re: Sppliting Solar Panels

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In the series case, what happens when one panel is shaded?
Then it stops generating power. It becomes high impedance, blocking current flow from the other panels, which make the bypass diode kick in to divert the current around the shaded panel.

In this case, voltage goes down from 36V to 24V with current staying the same. The MPPT controller output will go down by 35%, to be expected from shading a third of the panels.
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Old 13-04-2013, 11:32   #8
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Re: Sppliting Solar Panels

There is a lot of debate about series/ parallel connection of solar panels.
If you are planning different wattage panels series connection of all the panels is not recommended.
With either series or parrallel connection multiple controlers and wiring back to the controller is not needed.

Multiple smaller panels will perform slightly better than one big panel of the same wattage, but the difference is small. Go with whatever gives you the easiest instalation, most watts, and cheapest price.

They can be connected in parrallel, but the panels need to have similar characteristics, but not wattage,to make maximium use of a MPPT controller.
The best guide is to look at the Vmp if the panels are within 0.5v ( preferably less ) parallel connection is acceptable.
For series connection they want to be the same wattage as well.
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Old 13-04-2013, 12:02   #9
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Re: Sppliting Solar Panels

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Originally Posted by noelex 77 View Post

Multiple smaller panels will perform slightly better than one big panel of the same wattage, but the difference is small. Go with whatever gives you the easiest instalation, most watts, and cheapest price.

They can be connected in parrallel, but the panels need to have similar characteristics, but not wattage,to make maximium use of a MPPT controller.
The best guide is to look at the Vmp if the panels are within 0.5v ( preferably less ) parallel connection is acceptable.
For series connection they want to be the same wattage as well.
Ok, So it looks than in the newest panels somehow they solve the SHADOWING PROBLEM pretty well, with build in diodes, is that correct ? . Because I want a system to be used only in summer, and be easy to place and remove....to me if not huge difference will be much easier to work with one pannel than three......Does it make sense ?
The voltage in a 150 panel would be the same as in 50x 3 in series , I think, so the controller should be the same correct ?
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Old 13-04-2013, 12:11   #10
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I'm looking at 4 x 50watt Aurinco panels - you can walk on them and no need for a custom stainless frame. Simply screw and glue to deck (in our case a hard dodger and aft cabin top).

http://www.aurinco.com/compact40_us.html

A little more than the regular panels, but the look and lack of additional 'toe stubbing' zones is a major attraction.
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Old 13-04-2013, 13:43   #11
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Re: Sppliting Solar Panels

Quote:
Originally Posted by 4fish View Post
Ok, So it looks than in the newest panels somehow they solve the SHADOWING PROBLEM pretty well, with build in diodes, is that correct ? . Because I want a system to be used only in summer, and be easy to place and remove....to me if not huge difference will be much easier to work with one pannel than three......Does it make sense ?
The voltage in a 150 panel would be the same as in 50x 3 in series , I think, so the controller should be the same correct ?
Shadowing still has a disproportionate effect on the output.
As you say one 150w panel is generally easier to mount and is usually smaller than 3x50w panels. 3x50w will give a little more output, but the difference is small.
Be aware that the delivery costs for large panels can be very high.

150w panels come is a various voltages. Most 50w panels are (nominal) 12v panels.
If connected in series they will be (nominal) 36v. A single 150w panel may have a higher or lower voltage than this. (In parallel the 3x50w voltage stays at 12v.)
The controllers will generally be the same (although parallel connection of 12v panels gives you the option of using a non MPPT controler). Check it any controller will cope with the voltage and power of the panel(s)
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Old 13-04-2013, 13:44   #12
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Re: Sppliting Solar Panels

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Then it stops generating power. It becomes high impedance, blocking current flow from the other panels, which make the bypass diode kick in to divert the current around the shaded panel.

In this case, voltage goes down from 36V to 24V with current staying the same. The MPPT controller output will go down by 35%, to be expected from shading a third of the panels.
Does the MPPT magic voltage tuning actually function in this shadow case with a series panel, i.e. will MPPT controller producer higher output than a standard controller?
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Old 13-04-2013, 13:50   #13
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Re: Sppliting Solar Panels

Can someone tell him what that popular MPPT controller is for his 150W array range. I even forgot the name but think it's BlueSky or something?

I think advice to buy different panels or to buy anything but a MPPT controller is wrong. Even if you don't care about more power output (but everybody should), why would one not buy a MPPT controller today? Why would you buy different panels if you don't have to?
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Old 13-04-2013, 13:59   #14
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Re: Sppliting Solar Panels

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Does the MPPT magic voltage tuning actually function in this shadow case with a series panel, i.e. will MPPT controller producer higher output than a standard controller?
Yes, it will always outperform a regular controller. Never get a regular controller.

In order from good to not so good:

1. Same (but can be different) high voltage panels (like 24V nominal for a 12V boat), each with it's own MPPT controller.

2. Same panels in series to a single MPPT controller.

3. Same high voltage panels in parallel to MPPT controller.

4. Same panels in parallel to MPPT controller.

Looking back at what the OP wants, it's best when he gets two identical 125W panels and either connect each to it's own MPPT controller, in which case he should buy 24V nominal versions of the panels, or connect both panels in series to a single MPPT controller, in which case either 12V or 24V nominal panels can be used.
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Old 13-04-2013, 14:06   #15
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Re: Sppliting Solar Panels

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