New system set up

BobblerBobbler Registered Users Posts: 1
Hi Everyone 
I recently purchased a hunting camp and set my system in place but not sure I am maximizing it potential 
I have two 245w panels going to eleven 40 Amp mppt charge controller going to two 6v 225ah golf cart batteries running to a 12 v 1000w inverter 
only draw in camp is led lights, one ceiling fan and television 
the camp is wire so I just feed into my distribution box which has 2 15 amp breakers
eve works fine 
I have 34.8v and 2.7amp 87.1 w going to batteries my batteries are at 14.6v 6.2amps my controller is currently set on manual default settings she I be setting my own peripherals in to controller if so what would be best for my set up
thanks any help would be appreciated 


  • wellbuiltwellbuilt Solar Expert Posts: 763 ✭✭✭✭
    I have the same set up on my trailer , the cc charges @ 14.6  and eq every month automatically  the battery’s are going on 6 seasons but sits Jan feb March . 
     My new system is charging at 14.8 and 14.9  with 2/3hr absorb  
     my battery’s seam to like more charge in the winter . 
       I don’t get a lot of sun this time of year , I have 3” of snow on them now.
    Out back  flex power one  with out back 3648 inverter fm80 charge controler  flex net  mate 16 gc215 battery’s 4425 Watts solar .
  • BB.BB. Super Moderators, Administrators Posts: 32,642 admin
    Welcome to the forum Bobbler,

    I am not quite sure what you intended here "two 245w panels going to eleven 40 Amp mppt"....

    Anyway... I am always a big fan of designing a "balanced" system... Loads->battery bank; battery bank->minimum solar array; loads/sun->array too...

    So, battery bank is the heart of your system. I will use our rules of thumbs for a full time off grid cabin. But, of course, we can adjust based on your needs (weekend summer usage, etc.)... A good optimum is to define the battery size based on 2 days of storage and 50% maximum discharge (longer battery life, good day to day operation):
    • 12 volts * 225 AH battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max planned discharge = 574 Watt hours per day battery power
    Then there is sizing the solar array... First based on amount of charging current for the battery bank. The second based is based on your daily loads and hours of sun per day based on your location...

    Charging the battery bank, 5%, 10%, 13%+ are common aim points. 5% can work for a summer/weekend cabin. 10% minimum for full time off grid (and good battery life). 13% or so is typically the cost effective maximum unless you have special needs (lots of power during the day, vs using batteries mostly overnight/cloudy weather):
    • 225 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.05 rate of charge = 212 watt array minimum
    • 225 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.10 rate of charge = 424 watt array nominal
    • 225 AH * 14.5 volts charging * 1/0.77 solar panel+controller deratings * 0.13 rate of charge = 551 watt array "typical" cost effective maximum
    And then sizing based on your hours of sun/seasons... Note, the panels must be free of any shade (trees, chimney, vent pipes, etc.) or the array output will be "killed" by shading from ~9am to 3pm minimum (facing array south west to avoid eastern trees, etc. are other possibilities as an example). Using a simple solar calculator for Ottawa Canada, fixed array:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 45° angle:
    (For best year-round performance)


    Lets say drop the bottom three months... assume you are not there, or us a genset when needed.... I will use the 25% per day battery capacity... But actual energy usage numbers are critical for system planning:
    • 574 Watt*Hours per day * 1/0.52 off grid AC system eff * 1/3.19 hours of sun per day (October) = 346 Watt array October "break even" month
    Now--you should plan on using 50% to 65% of the "planned/predicted" solar output for daily required "base loads" (lighting, cell phone charging, indoor water pump, etc.)... And plan on using larger loads during sunny weather (vacuuming, washer, laptop, etc.)...
    • guess 574 Watts daily base load * 1/0.52 off grid AC eff * 1/3.19 hours of sun (Oct) * 1/0.65 base load fudge factor) = 532 Watt array (65% baseload fudge factor--Reduce genset runtime/more solar power during poor weather)
    To predict your output by month:
    • 245 Watt panel * 2 panels * 0.52 offgrid system eff * 3.19 hours of sun (October long term average) = 813 WH per ave Oct day
    Regarding loads... More or less, the largest AC inverter recommended for your battery bank would be around:
    • 225 AH * 250 Watts/100AH (for 12 volt battery bank) = 563 Watt max suggested AC inverter for your bank
    Your 1,000 Watt AC inverter is a bit on the large size for "reliable" (over temperature/state of charge/age) for your system. A ~250 to 500 Watt AC inverter would be a better choice. Also--Large AC inverters can draw fair amount of energy just being turned on and no loads (tare losses)... A typical 300 Watt or so PSW inverter would draw around 6 watts... Larger inverters can draw 10-20 or more Watts tare (need to check the inverter specifications to be sure).

    If you want to add more panels/battery bank later to the existing controller... The typical "cost effective" maximum array would be:
    • 40 amps * 14.5 volts charging * 1/0.77 panel+controller derarings = 753 Watts (rough) maximum array for 40 amp MPPT controller
    That is the basic math based on my guesses about your system. Your thoughts/questions?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
Sign In or Register to comment.