Battery charger

maas
maas Registered Users Posts: 1 ✭
in Off Grid Solar & Battery Systems #1
Living in the bush in sierra leone. I bought a complete solar system. 4 panels 250watt 4 batteries 200AH 1 hybrid inv 3Kw.
With a 24/7power in the house my 4 panels are not able to charge fully. Resulting in power shutdown in the morning.
Question.
-I have an 220v/ 24v battery charger. May I connect this to the battery bank without interfering with the hybrid charger which will also charge.
-And if so may I adding up the amperage of the seperate systems.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    #2
    Welcome to the forum Maas,

    First--Get your batteries charged quickly and fully (assuming they are some sort of Lead Acid chemistry batteries). Lead Acid batteries, if left under ~75% state of charge for days/weeks/months will quickly sulfate and die.

    Next--I like to talk about a balanced system design that meets your needs/loads. Either design the system to meet your loads, or define how much energy your system can produce per day/by season, then live within the means of the system (and/or use backup power sources such as a genset).

    Can you tell us more about your battery bank (Lead Acid, GEL, AGM, Li Ion, or what)?

    The short answer is you can (usually) parallel charging sources to one battery bank. The big things are 1) get the charging voltage settings correct, 2) make sure the charging current from both sources are not too much for the battery bank, 3) I suggest that each charging source be connected to the battery bus directly ("star" wiring) and not from charger A to charger B to battery bank (daisy chain) as the chargers sharing the same cable can confuse each other.

    More or less--As a warning to everyone reading here--I suggest that for a full time off grid power system--That the inverter be no larger than the solar array. If you have a 1,000 Watts of panels, generally, you would be looking at a 1,000 Watt maximum inverter.

    Anyway--I will type more--But I am heading out right now.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • 706jim
    706jim Solar Expert Posts: 523 ✭✭✭✭
    #3
    1000 watts of panels 1000 watt inverter.

    A great and easily understood "rule of thumb".

    Thanks for this Bill; makes complete sense.
    Island cottage solar system with appriximately 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing due south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter which has performed flawlessly since 1994. Outback Flexmax 80 MPPT charge controller four 467A-h AGM batteries. Insignia 11.5 cubic foot electric fridge 1/4hp GSW piston pump. My 31st year.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,637 admin
    edited February 2021 #4
    Hello again Maas,

    I will go through a design assuming you have a 400 AH @ 24 volt flooded cell lead acid battery bank...

    First, for a full time off grid home, suggest 2 days of storage and 50% maximum discharge. So, the daily battery bank usage would be (overnight, or 24 hours for a day with poor weather):
    • 400 AH * 24 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 max planned discharge = 2,040 WH per day from battery bank
    Lets say that you use the system 5 hours in the evening (lights, charging cell phone, laptop computer, RV water pump), that would be an average load of:
    • 2,040 WH per day from battery bank / 5 hours evening usage = 408 Watts average AC load (much less than a 3,000 Watt AC inverter)
    Now... To charge the battery bank. Two sets of calculations. First is assuming 5% to 13% rate of charge with solar--And suggest 10%+ for full time off grid solar. 5% for weekend and sunny season usage:
    • 400 AH * 29.0 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 753 Watt array minimum
    • 400 AH * 29.0 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 1,506 Watt array nominal
    • 400 AH * 29.0 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 1,958 Watt array "typical" cost effective maximum
    And sizing the array based on your daily energy usage, location, and seasonal sun. 
    http://www.solarelectricityhandbook.com/solar-irradiance.html

    Freetown
    Average Solar Insolation figures    Measured in kWh/m2/day onto a solar panel set at a 82° angle from vertical:

    (For best year-round performance)

    JanFebMarAprMayJun
    6.54
         		6.76
         		6.66
         		6.19
         		5.48
         		4.55
     
    JulAugSepOctNovDec
    3.76
         		3.68
         		4.65
         		5.47
         		5.81
         		6.25
     
    In general, you are in a very sunny climate... Lets take July as your "break even month" (may need a backup genset for a stretch of cloudy weather).
    • 2,040 WattHour load * 1/0.52 off grid AC system eff * 1/3.76 hours of sun per day = 1,043 Watt array July "break even"
    In reality--You want to use around 50% to 65% of your predicted solar harvest for "base loads" (those load you must run). The optional loads you only run on sunny days or with a genset (pumping to cistern, washing machine, etc.).

    As it stands right now... Your 400 Watt array in January would supply around:
    • 400 Watt array * 0.52 off grid AC system eff * 6.54 hours of sun per day = 1,360 Watt*hours per day
    Even in very sunny conditions, your solar array would not keep up with with using 1/4 of your battery capacity per day (2,040 WH).

    Most people overestimate how much energy their solar system can supply, and underestimate their daily loads.

    To make "best use" of your present battery system--I would be suggesting a 1,506 to 1,958 Watt array as a good match for your battery bank.

    However, the 3,000 Watt AC inverter suggests that you are planning on using a lot more than 2,040 WH of power per day, or more than ~408 Watt average loads for 5 hours per day... And your 400 AH @24 volt battery bank would not really (edit/addition - BB) "reliably" support around a 3,000 Watt AC inverter on a lead acid battery bank...

    Need to make a correction here... A common rule of thumb for a lead acid battery bank is a maximum inverter rating of ~500 Watts per 100 AH @ 24 volt battery bank. In this case a 400 AH @ 24 volt bank would support around a max 2,000 Watt inverter "reliably" (over battery state of charge/age/temperature). AGMs and Li Ion can support higher inverter ratings--But for a standard off grid home, the larger inverters tend to just waste power (tare losses--Using power just being turned on).

    Anyway... Lots of questions on my part (daily loads, details on the hybrid inverter/solar charger, etc.). The above is the basic math for your system as currently designed (relatively conservative--Solar panels are "cheap" these days and batteries are expensive--So adding more solar panels to keep the battery bank "happy" will save you money in the long run)...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • littleharbor2
    littleharbor2 Solar Expert Posts: 2,113 ✭✭✭✭✭
    #5
    How are you planning on powering the battery charger?

    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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