Sizing solar watts to battery bank

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Comments

  • bigbillsdbigbillsd Registered Users Posts: 27 ✭✭
    @Mountainman,  its December,  I was wondering what you are experiencing on the charging front?   Are you able to charge those batterys fully in 4 hours of sun?   -Bill
    4 each Renogy 160w Solar Panels mounted flat on RV roof, Serially connected @ ~80v,  Victron 100/50 MPPT controller.  520AH LA batteries @ 12volt, 2800w PSW Magnum Inverter.   Bogart Trimetric. 
  • mountainmanmountainman Registered Users Posts: 161 ✭✭
    edited December 2018 #33
    14 days into this month and only 2 or 3 days of sun. My generator ran so much it needs an oil change. Pv watts says 4 hrs the only way to get 4 average sun hours per day  this month is if the next 2 weeks brings 8 hrs a day.  If I have a couple days of sun maybe  I can do some testing.Rolls formula says not.. absorb time 80 to 100% 416×0.42÷55 amps=3 hrs 17 mins?
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • mike95490mike95490 Solar Expert Posts: 8,172 ✭✭✭✭✭
    When you talk solar, nobody thinks bad weather !
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mountainmanmountainman Registered Users Posts: 161 ✭✭
    Probably a crazy question.  A 200 watt 30 vmp 6.66 imp panel vs a 200 watt 18.9 vmp 10.58 imp panel. Mppt cc @ 12 volts would would there be an amp advantage with the grid tie panel? 
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • EstragonEstragon Registered Users Posts: 3,342 ✭✭✭✭✭
    Maybe.  If the 12v panel got hot, or the gt panel got cold, assuming the mppt works as it should?
    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
  • mountainmanmountainman Registered Users Posts: 161 ✭✭
    But  at 77f 200 watts is 200 watts.no matter how you slice it?
    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • EstragonEstragon Registered Users Posts: 3,342 ✭✭✭✭✭
    True, but how often will a panel be 77°f?

    When it sits in the sun, a 12v panel may drop enough in voltage that mppt controller could have trouble bucking to battery voltage.

    Depending on distance and wire size, there may also be a bit of difference in line losses with higher current / lower voltage into the controller.

    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
  • BB.BB. Super Moderators, Administrators Posts: 28,633 admin
    With an MPPT charge controller you want a minimum of 1.3x max battery voltage or 1.3x15v=19.5 Vmp-array suggested minimum MPPT controller voltage.

    Running a Vmp~18 volt panel (the "12 volt" solar panel spec) on an MPPT controller will not gain you much of anything, and could cost you energy (hot/sunny day, 18 Vmp-std becomes ~Vmp-hot~14.4 volts). If the panel was exposed to sub freezing temperatures in full sun, perhaps a MPPT controller might give you a bit of better performance (something like ~10% +/-  -- Pure Guesswork).

    The minimum array would be 2x Vmp~18 volt panels in series, or a single Vmp~30 volt panel would be better for MPPT. I don't think you would "see" any difference between 2x100W "12 volt" panels vs a single 1x200W "31Vmp" panel) on a MPPT controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • littleharbor2littleharbor2 Solar Expert Posts: 1,185 ✭✭✭✭
    edited January 29 #40
    But  at 77f 200 watts is 200 watts.no matter how you slice it?


    A solar panel, correctly oriented, on a sunny 77 degree day will have a considerably warmer surface. Cell temp and air temp. are two different things. Have you ever picked up a crescent wrench that has been lying in the sun for a while? Same idea. 

    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, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • EstragonEstragon Registered Users Posts: 3,342 ✭✭✭✭✭
    It's pretty amazing watching steam rise off panels with ambient <0°f temp air when the sun hits and melts remnants of ice and snow, even in weak winter sun.
    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
  • mountainmanmountainman Registered Users Posts: 161 ✭✭

    @Estragon what are your nominal and peak amps from a 1000 watt array with 12 volt bank?

    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • EstragonEstragon Registered Users Posts: 3,342 ✭✭✭✭✭

    IIRC, the best I've seen is ~80a on a cool breezy day with broken cloud. In normal conditions more like 50-60a.

    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
  • mountainmanmountainman Registered Users Posts: 161 ✭✭
    edited February 28 #44

    Thanks So normally 55 amps 10 % charge rate on a 550 amp hour 12 volt bank with around c/7 when it's putting out 80. But On a 450 ah @ 12 volts 55 amps = 13% with a max of 80 roughly c/6. A 624 bank @55 amps puts me at 9℅ And with 80 amps c/7.8 charge rate. looks to me a 550 is the best match for a 1000 watt array. Question is could I squeak by on a 624 ah bank by doing some bulk if needed. I only have a 300 watt inverter for TV dvd and charging phones. So I normally crank the generator each morning for making toast and using the Microwave and the S.O. blow drying etc. Or would it be a better match with 550 or the 450 battery bank. Suggestions?

    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • mountainmanmountainman Registered Users Posts: 161 ✭✭
    edited February 28 #45

    Being that im in RV and want to stay 12 volt. With 600 + ahs im thinking for 30 minutes running a 800 watt washer. 5 or 10 minutes of Microwave 900 watts. and a 830 watt toaster 4 slices 5 min. Does it Sound doable ? I'd have 1200 watt hrs available with a 3 day reserve. With 5 avg sun hrs from April - aug would a 1000 watt array produce 3500 watt hrs per day ? Anyone

    Blue ridge mts. Renogy 400 watts manual tracking . Epever mppt 30. 2 GC 208 [email protected] volts 300 watt psw inverter. 2 kw genny. Iota 45.
  • EstragonEstragon Registered Users Posts: 3,342 ✭✭✭✭✭

    3500wh/(sunny)day is roughly right for a 1kw array most of the year in many locations, IMHO.

    I wouldn't run more than one of the heavy (toaster/microwave) loads at the same time on a 12v system, but one at a time should be doable. Running the genny for heavy loads in the morning sounds like a good plan to me.

    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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