Number size of battery bank

lipets
lipets Solar Expert Posts: 61 ✭✭
edited March 2017 in Off Grid Solar & Battery Systems #1
Doing a new project on an an RV I have 4 265 watt panels to go on the roof flat.

I'll be using an mppt controller the roof distance to the battery bank is about 10-12 feet

I don't want to under utilize the array, was thinking six 6 volt  batteries, I have access to Trojans at wholesale pricing.

Your opinions?


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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,100 ✭✭✭✭✭
    #2
    Those panels x4 will give you close to 80 amps of charging into a 12 volt bank. What controller are you planning to use?

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric,  460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.

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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #3
    Depending on location, you may find you need more panel for that much battery.  Unless you're pretty far south, flat mounting can cut production a lot.  You could start by looking at a solar calculator like http://pvwatts.nrel.gov/

    Assuming you got 700w for 4 hours, that would be around 2800w, about 1/4 of capacity, back into the bank.  You need to estimate loads, including inverter losses, to get a sense of battery size need.

    In a mobile application, available space for panels is usually a limiting factor.  A second charging source is usually necessary.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
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  • lipets
    lipets Solar Expert Posts: 61 ✭✭
    #4
    Well i'm based in Fl but travel all over, last RV had 600 watts 4 6 volt batteries was almost enough 95% of the time would reach full charge early afternoon most most of the time.
    For our needs so on the new rv I wanted to up it a bit that's why 1,000 watts with six 6 T105's looked reasonable.

    I planed on using two Kids stacked, the old RV used one worked great, it maxed at times but the Kid protected the bank

    When there was lite cloud cover or early morning the Kid utilized it well

    I can use another controller if need be



    Thanks
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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #5
    If you have another charging source (generator?), you could probably get away with it.  Sounds like your loads are reasonable and you know how to control them based on battery status etc. 

    With 3 parallel strings, you may want to read http://www.smartgauge.co.uk/batt_con.html

    I don't know why you would need to use something other than a pair of Kids if you liked them.  I've been happy with my Classics for the most part.  The Kids apparently do "true paralleling", but I'm not sure what that means exactly.

    Off-grid.  
    Main daytime system ~4kw panels into 2xMNClassic150 370ah 48v bank 2xOutback 3548 inverter 120v + 240v autotransformer
    Night system ~1kw panels into 1xMNClassic150 700ah 12v bank morningstar 300w inverter
    · Share on Twitter

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