Should I Parallel or Series? Please advise.

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drew4justice
drew4justice Solar Expert Posts: 36 ✭
in Solar Beginners Corner #1
Hello. I have two 24v SUN SV-T-200HV panels.
Specs are:
33.20 Voc
8.25 Isc
27.50 Vmp
7.28 Imp

I've wired these in parallel and I'm funneling through a Morningstar MPPT 45 controller and terminating into 4 series wired Trojan T105RE's. Monitoring is acheived via Trimetric equipment.

Being 225aH batteries, I suppose I should have at least 22A output from my solar farm, but I'm simply not there yet and will just have to wait longer for my batteries to recharge before drinking power from the bank again. I will monitor carefully and won't let the SOC drop more than 70-80%.

The problem I see; In full sun I was only seeing 4 amps into the batteries. The ambient temperature was hot (~95F) so I blasted the panels with the hose and the current rose a few amps but quickly settled back down as the water evaporated rapidly from the scortching panels. I can't imagine what the temperature was on the roof in full sun but I do have my panels sitting off of the roof so air can circulate under/around them.

From what I've learned on here, I should be seeing 80% of Imp. In parallel, that's 7.28x2*80% = 11.65A. The panels were hot and their not "A" rated panels--would I have high expectations to ask to see more than 4 amps?

I'm trying to determine wether I should series these or parallel them? The way I understand, if I series the panels, the MPPT should convert the extra voltage to current. If I parallel them, well, I don't have so much voltage overhead but I should have the raw current available.

I called Morningstar support and was advised to series connect my panels but it didn't seem to make much difference. Perhaps it was just too hot outside?

One side note; I picked up the Tojans at a local dealer who had a Trojan rep. deliver them to his business. When I loaded them into my truck I immediately called Tojan to understand what the datecode "J0" represents. Much to my suprise, the 0 represents 2010 and the J is the 10th letter in the alphabet resolving to the 10th month = October. Essentially, I just bought batteries that are almost a year old. I called the dealer and they are going to get me some newer batteries, hopefully they will be in today but we're expecting rain for the next decade right now. Ugh! :p
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: Should I Parallel or Series? Please advise.

    You have a 24 Volt system (four T105's in series). You have no choice but to wire these panels in series to feed the charge controller as the Vmp on the panels (27.5) is too low to achieve proper charging Voltage for those batteries (29.6). The Morningstar MPPT 45 will handle it.

    What you will probably see from your panels: 400 Watts @ 77% efficiency = 308 Watts / 29.6 = 10 Amps peak current (rough calculation: not exact numbers). Also remember the panels will only put out what the batteries need, so to speak; charged batteries will not draw much current.

    Your 400 Watts of panel should deliver a charge rate just around 10 Amps peak, which is a tad under the 5% recommended minimum. But you could get lucky with insolation and efficiency and maybe just make the mark.

    And yes, always try to get "fresh" batteries; no sense paying full price for ones that have already sat a year.
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  • drew4justice
    drew4justice Solar Expert Posts: 36 ✭
    #3
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    Re: Should I Parallel or Series? Please advise.

    Ahh, yes. Duh! Certainly true! Sometimes putting thoughts down on paper, or in this case electronically; helps to see simple and obvious that is otherwise right in front of my face! :blush:

    Thanks for taking the lead on replying. I've seen many of your posts and appreciate your feedback. You're very helpful.

    Drew
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: Should I Parallel or Series? Please advise.

    You're welcome.
    That's what we're here for.
    That and the free donuts.
    Hey! Who ate all the donuts? :grr (don't look at me as i'm not allowed to eat them.:-):p niel)

    :p
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