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Old 06-06-2013, 23:06   #1
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300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Hi all,

To replace 2 old and inefficient 110W panels (that produce at most 9A), I've found a single solar panel that would fit perfectly on my davits. At 2m x 1m, it is compact enough, sturdy (5cm high frame) and coupled with a MPPT controller, it should produce at least twice as much amperes as the existing pair of 12V panels. However, it is a 36V unit. I've never seen nor heard of a single big 36V panel feeding a 12V lead acid battery bank (mine is 5 x 180Ah).
After reading a few threads here and discussing the matter with fellow sailors, here are my thoughts:
FOR
- 36V: the performance of the MPPT controller is enhanced by the difference in tension between the panels and the battery bank (the greater the better?)
- 36V: smaller cables
- one panel: easy connections, less weight, less windage

AGAINST
- 36V: less flexible than 12V or even 24V panels for a future upgrade
- 36V: demands an expensive MPPT controller to work with a 12V battery bank
- one panel: much reduced electricity production if there's any projected shade, no backup if damaged

So does it make sense? If not, where is the catch?
Thanks for your feedback
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Old 06-06-2013, 23:22   #2
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

MPPT is the catch.
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Old 06-06-2013, 23:27   #3
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Also, do you have a recommendation for a small output, 36V-compatible MPPT controller? The VICTRON 70V/15A is rather cheap and would be ideal if it could deliver more than 15A. The VICTRON 150V/60A (or MORNINGSTAR 150V/45A) are much heavier and expensive.
I guess I would need a 25A model as the 36V 300W panel I'm considering delivers 8,31A (i.e. potentially 24,93A into my battery bank, if I got it right).
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Old 06-06-2013, 23:36   #4
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Quote:
Originally Posted by Redcoat View Post
MPPT is the catch.
Could you please explain? Are these controllers more fragile? Or do you think that their 10-30% higher efficiency is not worth paying 2-3 times more than conventional PWM controllers? If I choose a 36V panel, I would have to go for MPPT
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Old 06-06-2013, 23:52   #5
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

A good charge controller will read the current. Spend the money.
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Old 07-06-2013, 01:30   #6
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

There is no problem using a 36v panel with a 12v boat system, this is done all the time.

You have summed up the For and against well, but a couple of minor points.

MPPT controllers are generally less efficient (not more) with high panel voltages. However, the difference is small and for most practical purposes you can pick what ever panel voltage you want. (providing you don't exceed the controllers max voltage, or go below battery voltage)

MPPT controllers are more fragile. One against with high voltage panels is if the controller fails a direct, get out of trouble, connection to the battery results in less than 1/3 of the normal power. If "12v" panels are used a direct connection will only cause a small loss (10%)
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Old 07-06-2013, 01:35   #7
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What are the current panels? How about connecting them in series on a good controller?
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Old 07-06-2013, 04:39   #8
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

I have a 36V 290W panel with an Outback FlexMax 60 controller and all is good.
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Old 07-06-2013, 05:41   #9
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Quote:
Originally Posted by Wellington View Post
Also, do you have a recommendation for a small output, 36V-compatible MPPT controller? The VICTRON 70V/15A is rather cheap and would be ideal if it could deliver more than 15A. The VICTRON 150V/60A (or MORNINGSTAR 150V/45A) are much heavier and expensive.
I guess I would need a 25A model as the 36V 300W panel I'm considering delivers 8,31A (i.e. potentially 24,93A into my battery bank, if I got it right).
Your 300w panel will have a Vmp somewhere around 26v to 30V allowing for heat Hence these panel current will be in the order of 12A , hence the smaller controller may do . ( if the Vmp is a bit lower it might just get a little tight , but I don't know where you got 24 A. , you don't use bat voltage , you use the curves and computation to derive Vmp and that's the max current )

Oh , Nolex , sweeping statements without a shred of technical factual backup data don't add much

Dave
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Old 07-06-2013, 06:13   #10
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

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Originally Posted by goboatingnow View Post
Your 300w panel will have a Vmp somewhere around 26v to 30V allowing for heat Hence these panel current will be in the order of 12A , hence the smaller controller may do . ( if the Vmp is a bit lower it might just get a little tight , but I don't know where you got 24 A. , you don't use bat voltage , you use the curves and computation to derive Vmp and that's the max current )
Solar cortrollers are rated for battery, current , so the the controller needs to be rated for around 24A, or above, for a 300w panel in a 12v system.

The Victron 15A model is too small.
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Old 07-06-2013, 06:26   #11
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Can you get the panel on and off of the bimini by yourself? I would go with two or more panels for this reason alone. The shading issue is real as well. All three of our panels can be removed and held by one person and taken below if needed.

Chris
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Old 07-06-2013, 06:41   #12
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Originally Posted by witzgall View Post
Can you get the panel on and off of the bimini by yourself? I would go with two or more panels for this reason alone. The shading issue is real as well. All three of our panels can be removed and held by one person and taken below if needed.

Chris
I think people with big panels do permanent installations instead of the out and in and out and back in - thing...
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Old 07-06-2013, 09:05   #13
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Quote:
Originally Posted by Don L View Post
I have a 36V 290W panel with an Outback FlexMax 60 controller and all is good.
Could you please tell me how many Amperes you typically produce around noon?
Also, may I ask what the dimensions of your panel are, and how much you paid for it? Thanks
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Old 07-06-2013, 09:46   #14
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Quote:
Originally Posted by witzgall View Post
Can you get the panel on and off of the bimini by yourself? I would go with two or more panels for this reason alone. The shading issue is real as well. All three of our panels can be removed and held by one person and taken below if needed.

Chris
Good point. Do sailors typically dismantle their solar panels and store them away if a hurricane or a tropical storm is forecast? One of the main reasons why I would choose a "small" - by catamaran standards - solar array (2m2) is precisely because of windage. But is it such an issue if the panel(s) are bolted horizontally?
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Old 07-06-2013, 10:33   #15
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Re: 300W 36V panel with MPPT controller for a 12V bank: does it make sense?

Quote:
Originally Posted by noelex 77 View Post
Solar cortrollers are rated for battery, current , so the the controller needs to be rated for around 24A, or above, for a 300w panel in a 12v system.

The Victron 15A model is too small.
Could I possibly "make do" with that VICTRON 70V/15A, that costs less than 1/4 of a 150V/45 or 60A?
Victron Energy Blue Solar MPPT 70/15 Solar Regulator
Would the only drawback be an electricity production limited to 15A rather than a maximum theoretical 25A? Or would it fry?
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