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Old 20-11-2011, 12:58   #31
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Re: Solar Panel: Too Big?

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Originally Posted by noelex 77 View Post
There has been a lot of debate about series or parallel connection for a boat, but IMHO if you do connect the panels in series I would not look at connecting more than 2, nominally 12v panels, in series for a 12v battery.

Be careful about the risk of lethal shocks if you wire a lot of panels in series.
huh? Do I read this wrong or are you implying that anything over 24V DC is potentially lethal? The Internationally accepted value for that is 48V DC, and I think nobody ever died of electrocution from 48V DC or less.

Why would you hesitate to put 48V into a MPPT controller, but go for 24V instead? I mean in case one has 4x 12V panels?

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Old 20-11-2011, 13:12   #32
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Re: Solar Panel: Too Big?

I should have qualified my statement. The Outback, Midnight and others are 60 and 80 amp units. That is huge overkill and requires greater boat space. Additionally, the parasitic losses of any of these devices is some percentage of its rating. We generally only need 15 to 20 amps output so the smaller SB3048 unit is the better size. And please talk the tech guru. They were quite specific regarding the series format for boats. It will give you the ability to charge in lower light than parallel. You will recoup more of the advertised 30% increase in total output of your panel rating only if the input voltage to the MPPT is above the ouput voltage for the longest time. When your 19 volt panels drop to 12 there is no power out of the MPPT. If you have them in series, the voltage input is 24 or 36 etc. and the MPPT is still putting out amps. AND -yes, you will not need as heavy a wire but that is not so important for 20 ft leads.
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Old 20-11-2011, 13:53   #33
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Re: Solar Panel: Too Big?

A 12v solar panel will deliver a higher voltage than 12v

I was recommending staying with a maximum of 2 nominally 12v panels for safety.
Once you have 3 you have Voc of about 66v (Vpm about 54v) . Four is Voc 88v (Vpm 72v)

In term of efficiency there is a lot of debate about the relative benefits of series or parallel connection, particularly with regard to the performance when one or more panels is shaded.
Once the Vpm is significantly above the battery voltage, adding more panels in series introduces more of the drawbacks of series connection without IMHO further benefits.

If you have 4 solar panels connecting 2 strings of 2 panels in series I think will be more efficient than 4 in series, but we really need some practical tests to establish the optimum configuration. Staying with a maximum of 2 panels in series also keeps the voltage below the potentially lethal level which I think is an important consideration, especially around salt water.
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Old 20-11-2011, 14:24   #34
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Re: Solar Panel: Too Big?

Strange... my mppt controller says it will output from 7v, it steps up the voltage, i would never do solar in series for the loss of shading of a single part, in parallel shading is so less an issue, one large bird pooh and your series system is not worth S*&t
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Old 20-11-2011, 14:24   #35
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Re: Solar Panel: Too Big?

Yes, safety is important. However, Voc is not gonna kill anybody, because the human body will close the circuit and form a load to the panel. We can take thousands of Volts without harming ourselves, like demonstrated with static sparks etc. (we feel it alright). But yes, 54 Vpm is not inherently safe so you're right in case it needs to be safe to touch bare wires.

When we have new, modern panels that have all the bypass diodes etc., I am pretty convinced there is a wide consensus that series connection is the way to go, especially if up to 4-6 panels and the controller can handle the voltage. Performance will be better in both low light and shading.

It is the relatively new MPPT controllers that enabled us to do these series configurations and parallel was the rule before that. It's always difficult to break away from how it's been done when new ways/methods come up and still in this thread there are poster(s) who don't know about the MPPT controllers and voltage conversion they do, let alone the impedance matching for better efficiency, which is so substantial that it completely ridicules the "parasitic" power usage from the controller itself.

ciao!
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Old 20-11-2011, 14:28   #36
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Re: Solar Panel: Too Big?

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Originally Posted by stevensuf View Post
Strange... my mppt controller says it will output from 7v, it steps up the voltage, i would never do solar in series for the loss of shading of a single part, in parallel shading is so less an issue, one large bird pooh and your series system is not worth S*&t
Sorry, the opposite is true. Series connection completely outperforms parallel in shading conditions. Your information is true for the very first generations of solar panels, but this has been fixed well over 10 years ago. (search the forum for "bypass diodes" to find the earlier discussions)

About the 7V... you are referring to what is called "buck boost". What brand and type of controller do you have?

ciao!
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Old 20-11-2011, 14:49   #37
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Re: Solar Panel: Too Big?

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Sorry, the opposite is true. Series connection completely outperforms parallel in shading conditions. .
Nick I think the Jury is still out on the efficiency gains of series and parallel connections of solar panels on a boat..
I was planning to do some tests myself, changing my existing parellel arrangement to series, but these tests will need to wait for some more stable sunlight conditions than we get at this time of year.



Comments like this from the designer of the Rogue MPPT controllers put me off making the effort to change the connections and control the variables, while the measurements are made.


A partially shaded array, especially an array that has panels wired in series, will
result in substantially less output and less-than-optimal tracking of the maximum
power point. If your PV array experiences partial shading for much of the
day, and you are unable to relocate it to a better site, it is best to wire your
modules in parallel so that those modules which may be receiving full illumination
will not be hampered by shaded modules.
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Old 20-11-2011, 15:01   #38
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Re: Solar Panel: Too Big?

ok correct me if i have it wrong, if i put 4 panels in series, and one is shaded ,will it not drop the output of all 4, but if in parallel then i will only loose the output of the shaded panel?
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Old 20-11-2011, 15:14   #39
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Re: Solar Panel: Too Big?

http://us.sunpowercorp.com/cs/BlobSe...ble=MungoBlobs

check out these SunPower panels. I plan two in series. 19% efficiency and good low light performance. 64.8 volts open circuit. Even in parallel, you need a high voltage MPPT. The Blue Sky 3048 is 140 VOC.
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Old 20-11-2011, 15:26   #40
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Re: Solar Panel: Too Big?

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Originally Posted by stevensuf View Post
ok correct me if i have it wrong, if i put 4 panels in series, and one is shaded ,will it not drop the output of all 4, but if in parallel then i will only loose the output of the shaded panel?
In series, the panel that becomes shaded will be bypassed (by diodes that are inside all modern panels). This means that the array will maintain the same current but drop the voltage 25%.

So when full array delivers 48V at 5A, it will deliver 36V at 5A when one panel is shaded.

In parallel it's the other way around: 12V at 20A and when one panel gets shaded you get 12V at 15A.

This all doesn't matter on which setup is best as you can see from results: 36x5 equals 12x15 so both provide the same power when one panel becomes shaded.

The series connection wins because of the lower current which gives less losses, the higher voltage which makes it easier for the controller to work efficiently, and the fact that we often have partial shading. It's in partial shading that series connection wins. When every panel in a parallel setup gets 10% shading, it's doomed, while the series connection only looses 10% voltage (depending on panel design this can be more, the cells are grouped) which leaves enough voltage for the controller to work with.

Always remember that you always have series connections as your panel is really 36 or so little panels (cells) all connected in series.

ciao!
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Old 20-11-2011, 15:34   #41
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Re: Solar Panel: Too Big?

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Originally Posted by noelex 77 View Post
Nick I think the Jury is still out on the efficiency gains of series and parallel connections of solar panels on a boat..
I was planning to do some tests myself, changing my existing parellel arrangement to series, but these tests will need to wait for some more stable sunlight conditions than we get at this time of year.
The difficulty is that most who change to series, also change to MPPT controller at the same time... so indeed you are in a perfect situation to do the test :-)

Quote:
Comments like this from the designer of the Rogue MPPT controllers put me off making the effort to change the connections and control the variables, while the measurements are made.
Yep, that is info that disregards the diodes in the panels (or is just old, from the time those diodes were not in the panels).

When a panel can only be installed in a partially shaded location, I recommend to NOT buy and install the panel. Partial shading should only happen in rare or short duration circumstances. At some level of shading, it makes no sense (economically nor environmentally) to install the panel.

cheers,
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Old 20-11-2011, 15:53   #42
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Re: Solar Panel: Too Big?

Jedi,

So all panels now have the diodes.

That means that only the cells that are shaded are bypassed and all the rest are pumping full out?

Thanks.
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Old 20-11-2011, 16:43   #43
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Re: Solar Panel: Too Big?

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Jedi,

So all panels now have the diodes.

That means that only the cells that are shaded are bypassed and all the rest are pumping full out?

Thanks.
Bypass diodes are fitted to all rigid panels that are likely to be used on a boat (and have been for as long as I can remember). They are necessary to prevent damage, so its difficult to imagine a poly or mono cell of 12v or above could be constructed without them.
The better panels do tend to have more bypass diodes which helps in both the shade tolerance and the durability of the panel. Most of the Kyocera panels have 8 bypass diodes fitted, cheaper panels often only have 2 or 3.
If connecting panels in series there is some theoretical advantage to fitting extra bypass diodes between the panels. This reduces the voltage loss that can occur with shaded panels connected in series.
Unfortunately most of the research and data on solar systems is directed to domestic systems where partial shading of some panels in a string is rare. On boats it is very common, so we are left to ponder such fundamental questions.
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Old 20-11-2011, 16:56   #44
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Re: Solar Panel: Too Big?

Just a comment on MTTP units. Check to make sure radio interference is not an issue!!
I was extra cleaver in using 80V supply from solar & used an outback mx60 to do the charge job. All very good for charging BUT THE RADIO INTERFERENCE IS BAD!!! (VHF wipe out.) I would opt for a simple 12v panels & NO MTTP if starting today. In the mean time still investigating how to fix the RFI problem I have - before making it a part of my ground tackle!!

My advise KISS

Regards Bill
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Old 20-11-2011, 17:06   #45
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Re: Solar Panel: Too Big?

There are panels made now with zones on diodes. typically 3 zones. Not all are made that way
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