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Old 08-10-2012, 14:52   #1
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Thumbs up Wiring up to 8 small panel system help?

Hi I hope I haven't missed this information as my search is acting funny.
I have just purchased 8 X 50watt 17.5 VOC Sunpower semi flexible panels apearantly they have 2 bypass diodes.

My plan is 2 across davits 4-6 on Bimini (boom extends over so half could be fully partially shaded) possibly take 2 and mount of stern rails or keep as portable to place on deck.

Okay so I was thinking to wire all as parallel. If I wire all into a single MPPT controller how will the shaded cells effect the system? My concearn is more about hinderence than lack of contribution. (Most info I found only adressed a shaded string in series)

At the moment our house battery bank is 2X230AH AGM 12VDC in Parallel with use of an isolation switch.
I will add a start battery soon. So what's the best way to ensure all batteries are being charged?

FYI
I'm trying to balance the system with our current bank. I may or may not add
Another house battery. I'm holping that since our main consumption is during the day we will be back to 100% in our bank early and run off excess panel power for the main of the day.

Thanks in advance for everyones valuable insight.
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Old 08-10-2012, 16:45   #2
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Re: Wiring up to 8 small panel system help?

Do you have a reason for wiring your panels in parallel? (I guess the way I wired my 2x40W panels directly to the + and - terminals on the charge controller is parallel, the voltage stays the same, the amps get doubled)

Can your MPPT controller handle 24 Amps?

Wiring your batteries in parallel would be a good idea I think. Or breaking apart the two systems and have one starter battery and one 50W panel charging it, then the 7 other ones charging the house bank.

Do people wire them in series if their battery packs are 24V or 48V?
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Old 09-10-2012, 14:26   #3
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Re: Wiring up to 8 small panel system help?

The reason I choose parallel is because it is more shade tolerant when one panel is effected by shade. (This is how I understand it)
Where I am unsure is; when there is shading on select panels how or if it effects the other panels.
For example if I have 7 of 8 panels running at 17.5v and 1 at 12v what are the effects on the single MPPT controller? What if that same panel is at 2v

As far as my MPPT controller goes, we'll I haven purchased one yet, until I understand more how it will work with my new panels. Then I will need to find the best one to do the job.

Cheers
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Old 14-10-2012, 11:49   #4
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Re: Wiring up to 8 small panel system help?

We have MPPT controllers on both boats, one with 200 watts and the other with 480 watts. I'd normally recommend them but in your case maybe not unless you had quite a bit of money to spend on them. Notice the "them".

Our panels on both boats really aren't subject to shading or if so very little for maybe a very short time of the day. If you have read some of the other threads here and elsewhere on shading you can see it can significantly reduce power and yes wiring in parallel will help to reduce that but still not eliminate it.

In your case where you know you are going to get shading maybe break the array down into 3 separate arrays. One is off the stern with very little if any shading and the other two are the ones that get shade. Hopefully one will be in shade and one won't.

Buy 3 PWM controllers and use one for each array. 3 of them will be about the same price as one MPPT. Now hopefully at least 2 of the arrays will be producing most of the time.

3 MPPT controllers would be better yet if you could afford them, but if not I think the 3 PWM controllers would out produce the 1 MPPT controller if some of the panels are in shade.

Morningstar has some nice PWM controllers and the 10 amp are about $45 and the 20 amp about $77. Use two of the 10 amp for the shaded panels (2) for each controller (4 total) and the 20 amp for 4 panels on the back for a total of $167.

If you went the MPPT route you could get something like a Blue Sky 2512i for around $180. We have one of those on our smaller boat. They are rated to 25 amps, so you would have to see what those panels are putting out and you might have that controller maxed out (there again I'd call them).

Once again normally I'd recommend and use the MPPT, but in this case the 3 PWM controllers might be the best deal. If money is available you could replace all with MPPT or maybe the one with the 4 stern panels.

I talked to a tech the other day at Blue Sky Energy and they recommended breaking an array up with multiple controllers if you knew you were going to get shading.

Blue Sky Energy Inc. - Industry Leaders In Solar Boost Charge Controllers and Maximum Power Point Tracking (MPPT)

Call them and talk to them about your situation or call one of the other manufactures of quality controllers.

Personally I'd just try and permanently mount all the panels. You will soon tire of trying to move them around and then you also have the wiring to deal with doing that.

Good luck,

Sum
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Old 30-10-2012, 05:24   #5
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Wink Re: Wiring up to 8 small panel system help?

So just an update.....
I energy ahead and bought 6 Genasun MPPT controllers one for each panel.
Now I just have to wait for them to arrive and then they are about fourth on my list of big tasks. Four out of about 30 other things I want to finish ASAP.
Cheers
Shawnee
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