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Old 31-01-2013, 16:17   #16
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Re: PWM VS MPPT TROPICS

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Originally Posted by Sumner View Post
I'm interested in your setup. How many panels? 12 volt or 24 volt (final voltage)? Total wattage? Controller?

I keep seeing the power to operate a MPPT coming up but the Blue Sky controllers we have (25 amp and 30/40 amp) both say
We have 4 Kyocera 120W panels (nominal 12V) feeding a Morninstar Tristar 60 MPPT controller. The panels are mounted on our bimini - 2 per side - and are wired so that two the two panels on each side are in series and the two sides are in parallel. In this configuration, there isn't any partial shading of a series string.

In the tropics, we have no measurable gain in daily output vs. our old PWM controller when all panels were wired in parallel. We see a 25% increase in output when the MPPT is used with the series/parallel panels. We don't really see higher peak amperages from the MPPT vs. the PWM, so the gain must be from getting more usable power from the morning and evening lower light periods.

Our controller uses 1.3-2.5W, as per the spec sheet. The heat sinks are warmish, but not anywhere near hot, during the highest output. The heat sinks on the previous Trace C40 PWM controller got hotter. I don't know how much power the old controller used.

We get no SSB interference at all on any band from it. Our old Trace C40 PWM controller used to cause high interferences on many bands.

Mark
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Old 31-01-2013, 22:27   #17
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Re: PWM VS MPPT TROPICS

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What sized solar panels?
We are looking at 2 X 130W panels total 260W.
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Old 31-01-2013, 22:45   #18
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Re: PWM VS MPPT TROPICS

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We have 4 Kyocera 120W panels (nominal 12V) feeding a Morninstar Tristar 60 MPPT controller. The panels are mounted on our bimini - 2 per side - and are wired so that two the two panels on each side are in series and the two sides are in parallel. In this configuration, there isn't any partial shading of a series string.

In the tropics, we have no measurable gain in daily output vs. our old PWM controller when all panels were wired in parallel. We see a 25% increase in output when the MPPT is used with the series/parallel panels. We don't really see higher peak amperages from the MPPT vs. the PWM, so the gain must be from getting more usable power from the morning and evening lower light periods.

Our controller uses 1.3-2.5W, as per the spec sheet. The heat sinks are warmish, but not anywhere near hot, during the highest output. The heat sinks on the previous Trace C40 PWM controller got hotter. I don't know how much power the old controller used.

We get no SSB interference at all on any band from it. Our old Trace C40 PWM controller used to cause high interferences on many bands.

Mark
Thanks, that is good useful information. I might think about taking our six 80 watt panels and wiring them in 3 sets of 2 at some point and see if we get an increase. I hadn't really thought of an option like that before,

Sum
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Old 31-01-2013, 23:05   #19
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Re: PWM VS MPPT TROPICS

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Originally Posted by BriRich View Post
We are looking at 2 X 130W panels total 260W.
The best controler at this size is the Rogue
http://www.roguepowertech.com/documents/MPT3024C1.pdf

They are just about to release a new model which promises to be better again so it may be worth waiting if you can.
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Old 01-02-2013, 04:50   #20
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Re: PWM VS MPPT TROPICS

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Originally Posted by sailorchic34 View Post

One other thing, while you can put panels in series and use a Mppt controller, any shading on one panel would effect the output on all panels in series. In parallel you only loose 70-80% of the one panel. As someone who spends a whole lot of time at anchor, there will be parts of the day when one or more panels will be shaded...
Yes this is the question! . Im wondering what is the best thing to do here, My pannels will be 3- 36 volt pannels,280 watts each- on an arch- I would think im going to get some shading here if the sun comes from the bow- is it better to run them in series or parallel , anyone??
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Old 01-02-2013, 09:26   #21
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Re: PWM VS MPPT TROPICS

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Yes this is the question! . Im wondering what is the best thing to do here, My pannels will be 3- 36 volt pannels,280 watts each- on an arch- I would think im going to get some shading here if the sun comes from the bow- is it better to run them in series or parallel , anyone??
You need an MPPT controller due to the voltage for sure. Parallel is going to be best since the amps won't be flowing through the whole string where reduction in one would choke them all down. Then the very best would be to have a separate controller for each as each controller would maximize the output of the panel it is controlling and there again not be compromised by the shaded panel/panels.

Now what is practical price wise might be different but for a minimum use the MPPT controller and run them in parallel. If I knew that shading was going to be a constant problem like under the boom then I'd go with multiple smaller controllers. If it is occasional and I had quite a bit of solar (our case with both boats) I'd use one controller,

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Old 23-02-2013, 16:44   #22
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Re: PWM VS MPPT TROPICS

I'm ready to purchase a controller myself and I was looking hard at the Morning Star Tristar TS45 MPPT. Question: I've heard some of the controllers are producing lots of RFI/EMI noise in SSB and even VHF's...Is there a controller out there that has a history of little to no noise??
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Old 23-02-2013, 17:17   #23
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Re: PWM VS MPPT TROPICS

And here we go again with the shading and series vs parallel.

So let me start it off again by mentioning that only ancient panels in series have this problem. For the last 25 years or so the panels have internal diodes that take care of the problem and which makes series a better option.

With 2 panels, partial shading and parallel, you lose 1/2 output. With the two panels in series, you only lose the shaded partitions so 1/6th - 1/3rd output (most panels have three sections IIRC).

p.s. I swear by the Outback MPPT controllers but they are for bigger arrays.

cheers,
Nick.
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Old 23-02-2013, 18:25   #24
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Re: PWM VS MPPT TROPICS

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Originally Posted by s/v Jedi View Post
And here we go again with the shading and series vs parallel. With 2 panels, partial shading and parallel, you lose 1/2 output. With the two panels in series, you only lose the shaded partitions so 1/6th - 1/3rd output (most panels have three sections IIRC).
Hum....I'm thinking that might not be quite correct.

Below is a rather nice abstract on the subject. For those without an interest in the math, scroll down to 6. Conclusions. Oh it talks about large land based systems, but it should apply to marine systems as well.

https://docs.google.com/viewer?a=v&q...yh33s2VuygFPPQ

Oh and another link with a little easier to follow description.

Photovoltaic Panel Efficiency, Inherent and System Constraints

While shading is less an issue on a powerboats. For a sail boat at anchor, shading is an issue. You have the mast, boom, rigging, flags, etc all trying to reduce the power. In my mind, for a sailboat, parallel works better overall. Because there will be shading every day. Well almost every day...
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Old 23-02-2013, 19:11   #25
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Re: PWM VS MPPT TROPICS

Hello, every one has their likes and dislikes but I've bought panels from lensunhk.com , they pay import charges and offer free delivery and their products are good, I use their MPPT controller with no problems at all with interference etc. I also use a 4KW inverter bought from DHGate.com again with free delivery but you have to pay import duty but even so it's all at a very keen price.
I hope this helps someone.
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Old 23-02-2013, 20:54   #26
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Re: PWM VS MPPT TROPICS

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Originally Posted by sailorchic34 View Post
Hum....I'm thinking that might not be quite correct.
There is a lot of incorrect data on-line. Here is a site that does know about the existence of bypass-diodes: Bypass Diodes | PVEducation

check out your panel owners-manual, it will tell you about these diodes. Here is the shortest way to explain how it works:

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Old 23-02-2013, 21:21   #27
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Re: PWM VS MPPT TROPICS

I am still not convinced sure which is best series or parrallel.

Thanks for the link Sailorchick. I will have to work my way through the maths.
As nick says all panels have bypass diodes, but that does not mean series connection is best.

In the example shown with 8 cells in sun and one shaded the output would be significantly higher with parallel connection than with series connection with the bypass diodes shown as arranged. (The example is not great one for yachts because the voltage of cells would be too low for a 12v system)
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Old 23-02-2013, 21:28   #28
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Originally Posted by noelex 77 View Post
I am still not convinced sure which is best series or parrallel.

Thanks for the link Sailorchick. I will have to work my way through the maths.
As nick says all panels have bypass diodes, but that does not mean series connection is best.

In the example shown with 8 cells in sun and one shaded the output would be significantly higher with parallel connection than with series connection with the bypass diodes shown as arranged. (The example is not great one for yachts because the voltage of cells would be too low for a 12v system)
Ehrmm.. These are strings within a single solar panel... In parallel, partial shading of a panel will take out the whole panel because it's voltage drops too far. In series you have plenty voltage so that only the shaded strings are lost.
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Old 23-02-2013, 23:43   #29
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Re: PWM VS MPPT TROPICS

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Ehrmm.. These are strings within a single solar panel... In parallel, partial shading of a panel will take out the whole panel because it's voltage drops too far. In series you have plenty voltage so that only the shaded strings are lost.
Hum...I still say not exactly.

First as you indicated there are bypass diodes on each series string of cells in the panel. For 12V panels, that's normally 2 for the two separate circuits. For 24v panels there are normally 3 diodes for the three separate circuits. This mainly as the higher voltage panels are larger and have one more string of cells.

Now weather the panel is parallel or series wired, the percent loss of the panel output from shading is the same. This as the panels are strings of series cells in 2 to 3 circuits.

Anyway, So lets take a three panel 17V system putting out oh 7.5 amps each. Two are in bright sunshine and one is in shade (due to boom, mast or some dude standing in front of it).

In parallel your getting oh 17V's and 15 amps from the two panels assuming the other panel is fully shaded or shaded across both strings of cells.

In series with the one panel shaded your getting 7.5 amps but only 33.5 volts, Not 34V's from the two panels. The bypass diodes have a 0.5V forward voltage drop across them. So in series the bypass diodes when the panel is shaded place a drop across the other two panels of .5 volts. If you have two panels shaded then the third panel is only putting out 16V at 7.5 amps.

OK it's only a 3% or 6% loss of power but its a loss. So I still say Parallel is better. Also if the bypass diode fails say by excess heating then you'll still loose a good part or most of the output of the series string.

Now the other issue is thermal runaway of the bypass diodes. If that happens the Diode fails and you'll most likely loose the whole sets output or a fair amount of it anyway when wired in series.

Now if you have a cheap panels from oh say china without bypass diodes and your wired in series, when one gets shaded then you pretty much loose most of the output of all the panels. I've actually read of a fellow on here a few years back, complaining that his panels were not working right...

Speaking of bad information on the web, A web site I visited had a diagram as shown at the bottom. I thing Jedi pulled a link from on another page from this site, so maybe he knows about it. The problem with the diagram is its not correct. The two diodes on the left the each panel don't daisy chain as shown on the left, but each bypasses a single set of cells in the panel.

While it mentions heating and runaway thermal overload being a parallel problem, the problem is really a series issue. That as each bypass diode in parallel only sees the current and voltage of that panels cell string. It does not see the other panels wired in parallel current or voltage.

In a series set of panels all the watts of the unshaded string passes through the two shaded panels diodes. Which can cause thermal runaway. Thermal runaway will burn up the bypass diodes and then the whole output in series dies. So if someone has series wired panels and the out drops to near zero, you need to change out the fried bypass diodes.

Here's another link discussing parallel and serial Serial vs. Parallel - Shading

Plus while its possible for only one string of cells to be shaded in a panel, My experience is if there is shading on a boat, it generally crosses all sets of cells on a panel. Least wise more times then not from what I've seen.

Oh here is the link to the site with the bad diagram: http://www.pveducation.org/pvcdrom/m...ects-in-arrays

While is says the problems in parallel, its really showing panels in series. Plus it's showing the bypass on the non shaded panel, where the bypass would be on the shaded string of cells only which is on the right. Gee does anyone check this stuff.....

Ok time for me go spend time with my grumpy cat...
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Old 24-02-2013, 06:02   #30
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Hmm yes but now you are shading 1 panel out of 3 panels, which is NOT partial shading.


Do the example for 1 panel full sun and two that are partially shaded, let's say one of their two strings are shaded. In parallel, you loose 2/3 of the output because both partially shaded panels loose half their output voltage so can charge at 13-14V anymore.

But the series setup is happily charging away with only a 1/3rd reduction in output. Pretty cool huh
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