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Old 19-12-2011, 18:05   #1
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solar set-up

I am about to install 3 40W solar panels on very bad places (two on dodger, one in front of dodger) (Ganz 40). I understand that I should use three individual MPPT's (Genasun GV4).
I have two identical house batts (200Ah each) and one starting batt (100Ah). I have a fourwinds windgen that feeds the housebatts. (Windgen is off when I am off the boat.) I also have a battery combiner between house batts and starting batt.
Instinctively I would link one solar panel to the starting batt and the other two to the house batt.
Is there anybody with a similar kind of situation? Am I overlooking stuff?
Thanks!! Arjan
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Old 19-12-2011, 18:40   #2
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Re: solar set-up

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Originally Posted by arjand View Post
I am about to install 3 40W solar panels on very bad places (two on dodger, one in front of dodger) (Ganz 40). I understand that I should use three individual MPPT's (Genasun GV4).
I have two identical house batts (200Ah each) and one starting batt (100Ah)... I also have a battery combiner between house batts and starting batt. Instinctively I would link one solar panel to the starting batt and the other two to the house batt. Is there anybody with a similar kind of situation? Am I overlooking stuff? Thanks!! Arjan
Hi Arjan - you'll probably want a way to pull your boom off to the side so your panels can get as much sunshine as possible. Shading just 1 cell will effectively shut the whole panel down (unless you wire your panels in series to your MPPT). You certainly don't need individual MPPT controllers on each panel! One controller should easily handle your 120W. Or you can go with a cheaper controller, but you should really have a controller between panels & controller, for a long list of reasons.

Not knowing how you use your boat, connecting 1 panel to the starting bank & the other 2 on the house makes a certain amount of sense, assuming you're off the boat for extended periods & can't manage panel output yourself.

You might want to read the page we published on solar panels for more info, including more mounting options.
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Old 20-12-2011, 02:01   #3
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Re: solar set-up

MPPT controllers can mistrack if panels are experiencing very different conditions with one in sun and one in shade. Individual controllers will give more power output in these conditions, but this increases expense considerably. The other problem is when the solar panels are small, or the output is low, the self consumption of the controller can become significant.
I think with small 40w panels the gain you will get from individual controllers is likely to be small and I would use a single controller.

The start battery normally has very little discharge. Starting a typical diesel only uses a couple of amp hours. Most installations therefore connect all the solar output to the house bank.

There are a few reasons to connect solar to start bank

  • To compensate for self discharge if the boat is left for long periods
  • If running the anchor winch or bow thruster from the start battery with only short motoring periods
  • To occasionally charge the start battery up to 100% which is difficult to do if you are using only short engine runs.

If you could elaborate the reason for wanting to attach the solar panels to the start battery and outline how the start battery is normally isolated it would help in recommending the best wiring options.
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Old 20-12-2011, 06:52   #4
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Re: solar set-up

Jon and Noel,
Thank you very much for your replies. Using one MPPT does save money and offers a more simple set-up. I ,might as well try that first and see the results. I will basically be living on the boat which makes the connection to house batteries indeed the logical choice. Thank you again! Arjan
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Old 20-12-2011, 07:08   #5
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Re: solar set-up

I would use one controller and put diodes in-line with the output of each panel, so a shaded panel can't draw-down the power from the others. You'll loose a little efficiency when all are in full sun, but the real world on a sailboat is there is usually partial shading. You should also fuse the outputs and do all those connections on a terminal strip inside the boat.

Your start battery is always being charged by the engine alternator when motoring, and you have a battery combiner that will take care of distribution between banks anyway. The house bank is much more likely to be drawn-down and therefore they will charge at a much higher acceptance rate than your start battery in typical use, so it will be far more efficient to use solar on a house bank.

One other thing -- the Ganz panels are lighter than most and could go airborne above a dodger unless you mount them securely. Being semi-rigid they could also flap and flex in high-wind storm conditions so you may want to consider a mounting frame.
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Old 20-12-2011, 07:25   #6
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Re: solar set-up

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I would use one controller and put diodes in-line with the output of each panel, so a shaded panel can't draw-down the power from the others. You'll loose a little efficiency when all are in full sun, but the real world on a sailboat is there is usually partial shading.
The diodes are not necessary, with most controllers, and will reduce output. In simple terms a deeply shaded panel develops high resistance, so it does not transmit or consume (almost ) any power. If connected in series (which is not what the OP is planning) then extra bypass diodes can be helpful , but these are wired differently.
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Old 20-12-2011, 07:32   #7
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Re: solar set-up

Use bigger panels. Just work backwards with the math to find the optimum wattage.
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Old 20-12-2011, 07:33   #8
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Re: solar set-up

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The diodes are not necessary, with most controllers, and will reduce output. In simple terms a deeply shaded panel develops high resistance, so it does not transmit or consume (almost ) any power. If connected in series (which is not what the OP is planning) then extra bypass diodes can be helpful , but these are wired differently.
My understanding is different from yours: A shaded panel will draw power from others and become hot if they are in series or parallel, unless they are diode-isolated from each other.

The OP did not say whether he was planning to wire them in series or parallel, but he said he has 3 Ganz panels so I assume he plans to wire them in parallel. I could be wrong on the specs, but I believe if the OP checks the specs he'll find he can't wire more than 2 Ganz panels in series without going over the max voltage rating of the panels. That would dictate parallel. A parallel setup would also be more efficient if partial shading were to occur.
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Old 20-12-2011, 07:37   #9
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Re: solar set-up

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Originally Posted by noelex 77 View Post
The diodes are not necessary, with most controllers, and will reduce output. In simple terms a deeply shaded panel develops high resistance, so it does not transmit or consume (almost ) any power. If connected in series (which is not what the OP is planning) then extra bypass diodes can be helpful , but these are wired differently.
Perhaps you're confused. Controllers keep the the panels from becoming a load in darkness, and therefore the controller literature usually says no blocking diodes needed. However, I was writing about shaded panels drawing from unshaded panels. In that case diodes are beneficial.
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Old 20-12-2011, 07:46   #10
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Re: solar set-up

I have gone into the subject EXTENSIVELY in past posts, with decades of intense research, boatbuilding / repair, and liveaboard / cruising as a reference. You may look up the information in my past posts... I found the process of explaining this subject to others, frustrating enough, that I prefer not to repeat the experience.

Best regards,
Mark
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Old 20-12-2011, 07:57   #11
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Re: solar set-up

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My understanding is different from yours: A shaded panel will draw power from others and become hot if they are in series or parallel, unless they are diode-isolated from each other.
That is not correct for a parallel connection. If it was we could not connect a solar panel to a battery without it drawing power and becoming hot.
The in line diodes you describe are blocking diodes as you correctly point out the only need for these is to prevent a very slight discharge at night. Most controllers do this automatically anyway.
The diodes used to prevent hot spots are only necessary for series strings of solar cells and are fitted within the panel by the manufactures. They are called bypass diodes and are not wired in line.
There is some argument that extra bypass diodes may be beneficial for series connection, but never for a parallel conection.
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Old 20-12-2011, 08:10   #12
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Re: solar set-up

I recommend Mark's and Noelex's many posts (via the search). They both have good advice.

Our set up is 3 panels wired in parallel, no extra diodes, 1 MMPT controller, wired to the house bank. We can charge the starting battery via the isolator, or not, as desired.

If one panel is shaded we still get full output from the other two. Check out the photo in my profile gallery to see the panels on our bimini. We have two 43W and one 130W Kyoceras.
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Old 20-12-2011, 16:19   #13
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Re: solar set-up

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I recommend Mark's and Noelex's many posts (via the search). They both have good advice.

Our set up is 3 panels wired in parallel, no extra diodes, 1 MMPT controller, wired to the house bank. We can charge the starting battery via the isolator, or not, as desired.

If one panel is shaded we still get full output from the other two. Check out the photo in my profile gallery to see the panels on our bimini. We have two 43W and one 130W Kyoceras.
I still believe Noelex is wrong, and suspect you have output diodes on your Kyocera panels that are built-in. Ganz panels do not come equipped with output diodes in the junction box. Don't take my word for it. Check with Ganz.
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Old 20-12-2011, 16:33   #14
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Re: solar set-up

I decided to look up the specs for the Ganz panels, and the best I could come up with was a data sheet. http://computarganz.com/file.cfm?id=639

Here's a quote: "Includes a 10’ power cable, blocking diode, fuse, fuse case, connectors and terminals (preconnected)."

They wouldn't include the diode if it was built in.

Here's a simple explanation of why you use diodes on the outputs of each panel on parallel installations. http://www.absak.com/tech/diodes.pdf

Believe what you want or do your own research, but my advice is good.
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Old 20-12-2011, 23:59   #15
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Re: solar set-up

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I still believe Noelex is wrong, and suspect you have output diodes on your Kyocera panels that are built-in. Ganz panels do not come equipped with output diodes in the junction box. Don't take my word for it. Check with Ganz.
Skepticism is often good with advice given on the internet.
You can do a simple practical test. Hook the solar panel up to a battery without the extra diodes and without any blocking diodes and measures the discharge current when in darkness. It will be very tiny. You can increase the battery voltage with a charge source if you like it will make little difference.
The solar panel will behave exactly the same way hooked up in parallel to another solar panel. Voltage is voltage the panel does not know, or care, if the voltage is from a solar panel, or battery, the discharge current will be the same.
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