Which controller

lipets
lipets Solar Expert Posts: 61 ✭✭
in General Solar Power Topics #1
I have 2 265W panels are Hyundai, voc, 37, isc,8.6, vmp 31

I'm in the sunny state of FL

Maybe a Kid?

But some newer ones with phone app are kinda nice.

What models might you suggest

----
Next question is batteries thinking T105's GC with carbon

maybe 4 or 6, is there really a limit as to how many?

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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #2
    Before your pick the hardware, it is better to design your system on paper to meet your needs.

    Regarding battery banks, generally you look at a 12 volt battery bank for up to 1,200 to 1,800 Watts

    24 volt battery bank up to 2,400 to 3,600 Watts peak.

    And over that, a 48 volt bank is recommended. You want to keep the DC Battery bank current below ~100-200 Amps, and voltage drop low (short, heavy copper cables).

    And suggest to keep battery bank below ~800 AH in capacity (i.e., a 950 AH @ 12 volt battery bank should be changed to a 425 AH @ 244 volt battery bank). One main reason is that solar charge controllers are rated for maximum output current at "any voltage" (12/24/48 volt battery bus).

    And if you want to charge at ~10% rate of charge (recommended minimum for Lead Acid batteries)--The typical "high end" controllers are around 80 amp output limited... If you want more charging current (larger solar array), you either bump the battery bank up in voltage (i.e., charging at 80 amps @ 12 volts is the same Watts as charging at 40 Amps @ 24 volts). Allows you to use a smaller or avoid buying a second solar charge controller in many cases.

    So... 6 volt @ 200 AH "golf cart" batteries are generally cheap and rugged. A very good bank to "learn on" (many people kill their first bank or two). 

    And your series/parallel connections. Your bank voltage 2x6 volt, 4x6 volt, 8x6 volt series gives you a 12/24/48 volt battery bank.

    And there is paralleling your bank for more AH capacity... 1x parallel = 200 AH bank; 2x parallel = 400 AH; and 3x parallel = 600 AH battery bank...

    So, for a 24 volt @ 400 AH battery bank, 4x6 volt batteries in series by 2x 200 AH batteries in parallel for 400 AH battery bank (@ 24 volts).

    I highly suggest that you do not connect more than 3 parallel strings together for your battery bank... It is a personal suggestion that usually results in less maintenance and fewer things to go bad. There are lots of people that parallel more strings--But I would avoid it.

    If you need more AH capacity... You start to look for different battery configuration... For example, 3 cells in series @ 200 AH for 6 volts at 200 AH (remember "battery" is a grouping of cells... 3x for 6 volt, 6x for 12 volts, etc.). But you can find, for example, a 2 volt cell * 600 AH--Basically the same size and weight (and total energy storage) when compared with 6 volt @ 200 AH (3 series cells).

    Power=Voltage*Current... So, if you have 1/3rd the voltage and 3x the Amps (or AH), you have the same power/energy (Watts or Watt*Hours).

    "Cheap" golf cart batteries can be found for $100 or less (in USA). And will typically last around 3-5 years. Hot weather/hot battery bank, deep cycling, etc. gives shorter battery life. Cold conditions (winter mountains) & shallower cycling, etc. gives longer life.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    A second post to talk about "the system". Generally, I like to start with your loads (DC or AC, voltage, wattage, hours per day of use, etc.).

    However, you can start with another major component like your solar panels. And design your system around it.

    To use your solar panels, we need to know more about your panels. Taking some guesses:
    • 265 Watts; 37 Voc; 8.6 Isc; 31 Vmp
    • Imp = Pmp / Vmp = 265 Watts / 31 Vmp = 8.55 Amps (your Isc sounds more like Imp)
    For a typical off grid power system, we suggest 5% rate of charge minimum for weekend/summer usage, and 10%-13%-20% for full time off grid usage. Say 12 volt battery bank:
    • 2 * 265 Watt panels * 0.77 panel+controller deratings * 1/0.05 rate of charge * 1/14.5 volt battery bank = 563 AH @ 12 volt battery bank maximum
    • 2 * 265 Watt panels * 0.77 panel+controller deratings * 1/0.10 rate of charge * 1/14.5 volt battery bank = 281 AH @ 12 volt battery bank nominal
    • 2 * 265 Watt panels * 0.77 panel+controller deratings * 1/0.13 rate of charge * 1/14.5 volt battery bank = 216 AH @ 12 volt battery bank minimum suggested
    So, if you where using this off grid full time... I would be tending towards the ~216 AH @ 12 volt battery bank (2x golf cart batteries in series). If this was a weekend/summer cabin or emergency backup system, the ~281 to ~400 AH @ 12 volt battery bank could be interesting (2x golf cart batteries in series, times 2 parallel strings for a 12 volt @ 200 AH battery bank).

    A fixed solar array facing south around Orlando FL would produce average hours of sun per day, by month:
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Orlando
    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 62° angle from vertical:
    (For best year-round performance)

    JanFebMarAprMayJun
    4.29
         		4.76
         		5.36
         		5.79
         		5.75
         		4.99
     
    JulAugSepOctNovDec
    4.96
         		4.87
         		4.74
         		4.89
         		4.55
         		4.16
     

    Say December, 4.16 hours of sun on average (some days better, some days worse):
    • 2 * 265 Watt array * 0.52 off grid system eff * 2.16 hours of sun (ave Dec) = 1,146 WH per day
    That is enough energy to run a laptop, some LED lighting, and charging your cell phone. Perhaps a small fan, RV water pump, etc. (the more you draw, the more careful you have to be to not over discharge your battery bank and "murder it").

    A 12 volt @ 200 AH battery bank would support an AC inverter rated at:
    • 200 AH (at 12v) * 250 Watt inverter * 1/100 AH (at 12 volts) = 500 Watts maximum
    And 1/2 that would be really nice (around 250 Watt AC inverter rating)... More than that, and FLA batteries will not "reliably" support that large of load.

    And we see another "battery bank sizing question"--What are your peak loads--Large peak loads require a larger battery bank (or different battery chemistry--Another post).

    I will stop here... Lots of information and questions/guesses as to your power needs... And I have yet to even discuss what solar charge controller you should get... (design overall system first, then pick hardware to support your needs).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • lipets
    lipets Solar Expert Posts: 61 ✭✭
    #4
    Thanks but a bit to complex to follow

    I spoke to Midnite they recommended a KID controller
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    What size array and what voltage battery bank.

    Are you getting a second charge controller?

    Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • lipets
    lipets Solar Expert Posts: 61 ✭✭
    #6
    I have 2 265W panels are Hyundai, voc, 37, isc,8.6, vmp 31
    He said the KID is good to about 475 watts but most systems work ay about 75% and if it went over the KID will just ignore the excess
    12 volt system
    the batteries I'm thinking are 8 T 105's



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  • Estragon
    Estragon Registered Users Posts: 4,496 ✭✭✭✭✭
    #7
    Keeping it simple (assuming 12v system), 8xT105s,  is 4 strings in parallel.  Each string should be fused, and keeping balanced can be an issue.  If you really need that much storage, bigger and/or lower voltage batteries would be better than 4 strings of T105s. 

    Anyway you'll have a ~850 amp-hour bank.  This would normally want ~80+ amp charging capacity.  For that, you'd need 3 kids or a classic.  With 1 kid at 30a it's ~3.5% of bank capacity - not enough for most use cases.

    Too much battery for available charging = recipe for undercharging and reduced battery life.  Depending on your application, a single kid and a couple panels would be good for a single string of 2xT105s, maybe 2 strings for a weekend cabin sort of use.
    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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  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #8
    lipets said:
    "maybe 4 or 6, is there really a limit as to how many?"
    lipets said:
    the batteries I'm thinking are 8 T 105's

    No "rules" but a balanced system would be able to charge at a 10-13% of the capacity of the battery bank if in daily use. or as low as 5% for weekend use.


    With 2 - 265 watt panels through a MPPT type charge controller, you could expect about 530 watt array x .75(to adjust for Normal Operating Cell Temperature values) = 398 watts under normal conditions ÷ 12 = 33 amps (the kid would be limited to 30) or 10% of 330 amp battery bank. That's pretty squarely between 2 and 4 batteries. 

    If you intend to use the system infrequently or plan to expand, I'd go with 4 batteries.

    If you intend to use the system daily cycling, I'd suggest sticking with 2 batteries.

    8 batteries would be a mess, too many strings of batteries, hard for them to share the load or charging.
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
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