Advice on setting up solar array

cdrudgecdrudge Registered Users Posts: 5
I have a flexmax 60 cc with a 12volt battery bank. I have (8) 145 watt solar panels- Pmax: 145W * Vmp: 18.7V * Imp: 7.75A * Voc: 22.3V * Isc: 8.37A.
I also have (2) 100 watt panels- Power Temperature Coefficient 12V Voltage Temperature Coefficient 18V Current Temperature Coefficient 5.56A Nominal Voltage 21.5V Operating Voltage (Vmp) 6.06A.

In addition I have a 3024il Bluesky mppt cc that will accommodate up to 500 watts pv and (3) 15 watt harbor freight panels that can be use.

My run from combiner box to disconnect 30 ft. I would welcome and appreciate your help and advice.


  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Re: Advice on setting up solar array

    What battery bank do you have (AH, voltage, series/parallel connected?).

    The Bluesky + Harbor Freight 15 watt panels are not even worth connecting (the 15 watt panels will not add significant current to the battery bank).

    Are you in upper Michigan area?

    And, have you measured/estimated your daily power needs yet (Watt*Hours/Amp*Hours at what voltage per day)?

    Will this be seasonal usage (summer weekends/spring/summer/fall) or full time?

    Do you have/need a backup generator?

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • cdrudgecdrudge Registered Users Posts: 5
    Re: Advice on setting up solar array

    Hi Bill,
    Thank you for your response. My present battery bank is made up of (5) 105ah batteries for a total of 525ah.
    These batteries are wired in parallel.
    I am located in mid Michigan. My usage will be determined by ah available in battery bank. I am not off grid but have isolated outlets tied to battery bank.

    My solar is not grid tied, but is an independent system that I am looking to expand as I am able.

    I do have a 8500 watt generator.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice on setting up solar array

    In addition to Bill's questions, I can give you some idea of what to expect based on the info you've supplied:

    You have 1160 Watts of panel on your FM 60. It can't handle that much on a 12 Volt system. It will be "clipping" some of the Watts much of the time. If you could exchange the FM60 for an FM80 you'd be okay. As is, the array has a potential peak output current around 74 Amps, and the FM60 will only pass 60 Amps.

    That is enough array to recharge about 740 Amp hours of battery. This would necessitate some rather large batteries to prevent too many parallel connections. It is also more than 4kW hours of stored capacity. If you need that much power you should consider a 24 Volt system instead. Once you go to 24 Volts your FM60 becomes viable again, as the peak output current will halve. But it is the same amount of power. See this thread:

    I wouldn't waste any time with the notoriously over-rated HF panels, and the BlueSky controller is probably best sold as you've got quite a bit of capacity potential as it is.

    Five parallel batteries is a mistake; they will not share current evenly, no matter how well done the wiring is.
  • BB.BB. Super Moderators, Administrators Posts: 32,004 admin
    Re: Advice on setting up solar array

    Regarding battery wiring, here is a good explanation of how to make the best of it.

    There are several ways of determining the "optimum" power output of your system... I always like to come back to the battery bank. Batteries treated well will (usually) last pretty well... Treated badly, they will commit suicide (or is it murder :confused::p).

    Normally, we recommend 1-3 days of "no sun" storage and 50% maximum discharge... A good nominal number is 2 days of storage and 50% maximum discharge--or using 25% of the bank's energy per day:
    • 525 AH * 12 volts * 0.85 inverter eff * 1/2 days * 0.50 max discharge = 1,339 Watt*Hours of 120 VAC power per day

    Next, is how much panel and sun you have, using PV Watts for Alpena Mich., fixed array, tilted from horizontal to Latitude (45.1 degrees), using 1.16 kW of solar array and 0.52 system efficiency (yes, about 1/2 of your panel "rating" is "lost" through various factors):
    "Station Identification"
    "Lat (deg N):", 45.07
    "Long (deg W):", 83.57
    "Elev (m): ", 210
    "PV System Specifications"
    "DC Rating:"," 1.2 kW"
    "DC to AC Derate Factor:"," 0.520"
    "AC Rating:"," 0.6 kW"
    "Array Type: Fixed Tilt"
    "Array Tilt:"," 45.1"
    "Array Azimuth:","180.0"

    "Energy Specifications"
    "Cost of Electricity:"," 8.3 cents/kWh"

    "Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
    1, 2.72, 52, 4.32
    2, 3.88, 68, 5.64
    3, 5.04, 95, 7.89
    4, 5.37, 94, 7.80
    5, 5.32, 92, 7.64
    6, 5.52, 90, 7.47
    7, 5.72, 94, 7.80
    8, 5.10, 85, 7.06
    9, 4.40, 72, 5.98
    10, 3.37, 58, 4.81
    11, 2.35, 39, 3.24
    12, 2.07, 38, 3.15
    "Year", 4.24, 876, 72.71

    So, you will average around 38-95 kWH per month, or ~1-3 kWH per day.

    Nominally, for an "off grid" system, I typically assume the lowest 3 months will require a generator backup (poor weather/sun angle), which leaves you with October at 3.37 hours of sun as a "break even" point between generator/no generator use. Another way to manual calculate system output for 9 months a year):
    • 1,160 Watts of panel * 0.52 off grid system derating * 3.37 hours of sun = 2,033 Watt*Hours for 120 VAC power average in October (or better).

    Yes, you will lose some power because of "too small" of charge controller current rating--But it probably is not enough to make it worth the extra time/money to replace your controller just yet... And, eventually, you might want to consider that 24 volt or larger battery bank anyway (I am not a fan of paralleled battery strings for many reasons).

    Some suggestions... Lots of reading:

    Battery FAQ
    All About Inverters
    Choosing an inverter for water pumping
    A Thread with lots of information/links/etc. for solar power and conservation

    I am a big believer in "balancing" load to battery bank, and charging sources to battery bank (i.e., as Marc mentioned, the 5% to 13% rate of charge to the battery for optimum life/service).

    And that includes the genset. An 8.5 kW genset is pretty large and can really gulp down the fuel if used to recharge a "smaller" battery bank... Most gensets are fairly fuel efficient at 50% to 100% or rated output, below ~50% rated output, the fuel flow stays at ~50% of rated GPM while the energy used falls.

    So, for many folks, it is worth while to plan loads (use washer/drier/well pumping while charging battery bank) or to use a smaller genset when just recharging the battery bank... Here is a nice thread that delves into the question of optimizing the charger for a small genset.

    Question about battery charger selection with EU2000 generator.

    And, some suggested tools:

    Hydrometer (assuming flooded cell battery bank)
    Kill-a-Watt type meter (measure your plug-in AC loads/general conservation use around home)
    DC Current Clamp Meter (really a DMM+AC/DC current clamp)
    Battery Monitor (Victron another good brand) (makes managing a battery bank much easier, very helpful for spouse/kids/guests in off grid home/cabin)

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Advice on setting up solar array

    "My usage will be determined by ah available in battery bank."

    now this makes me think your loads could possibly go higher in overall amp hours than you should for your battery bank capacity. one should not, as a rule of thumb, exceed 50% of the battery capacity used. with this in mind a battery monitor should be purchased to track things better.
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