How to add onto my solar array

TomroupeTomroupe Registered Users Posts: 3
Hello all! Just joined and have a question for you all. I have an off grid cabin, cold climate with ridges and barely get direct sun in December and January. I have 300w solar panels,(increasing to 500w soon) 630ah bank and would like to add a small wind turbine. Would you all add a separate controller or buy one new controller to handle both sources? I am running a 30a Morningstar on my panels.


  • PhotowhitPhotowhit Solar Expert Posts: 5,804 ✭✭✭✭✭
    Small wind often comes with a charge controller. You would typically not want wind and solar on the same charge controller. wind will usually need a diversion load, you can't 'turn off' a wind generator like you can with a solar array. That said you will want a charge controller which can handle a diversion load. I think Schneider/Xantrex C40 can as well as Morning start TS45 and TS60 in PWM controllers.
    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, 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.
  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin
    edited January 2018 #3

    You did not say if you are living in the cabin during winter (batteries just "resting") or if you are actively using them. Also, what is the voltage of your battery bank?

    In general, if actively using the battery bank, you would want to recharge a lead acid battery bank back over 90% state of charge after 2-3 day of use (if no sun). And try to avoid going below 50% state of charge for long battery life (assuming full time usage).

    Roughly recommend 5% to 13% rate of charge, with 20-25% maximum (generally supported by genset and large AC battery charger--although, solar is pretty cheap these days and you could approach 25% rate of charge, assuming you have a remote battery temperature sensor and watch bank temperature. >13% rate of charge for solar usually does not help much unless you have few hours of sun per day and/or large daytime loads with Lead Acid batteries.

    For a 630 AH @ 12 volt battery bank (if 24 volts, simply multiply the answers by 2x). Just general rules of thumbs below (good starting points for discussion):
    • 630 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 539 Watt array minimum (weekend/non-winter cabin)
    • 630 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,186 Watt array nominal (full time off grid)
    • 630 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,542 Watt array "typical cost effective" maximum

    Lead acid batteries if left fully charged, with a little bit of "float charging", will generally do fine in a frozen winter climate. They will not freeze if full charged (if "warmer" than ~-77F), and the cold temperatures dramaticlly reduce self discharge and help extend battery life.

    If you are using power during the winter, alternative power sources are really needed (such as start genset at ~50% state of charge and end it ~80% state of charge, and a few times a month recharge >90% state of charge (helps conserve fuel / genset run-time). Lead Acid batteries charge much faster/more efficiently below ~80% state of charge and rather slowly/inefficiently >90% state of charge.

    And they tend to sulfate if left below ~75% state of charge for days/months at time (without cycling). If you are daily cycling, sulfating of the plates seems to be less of an issue (but still does occur- and will eventually kill your batteries no matter what over time).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • TomroupeTomroupe Registered Users Posts: 3
    Thanks Bill. This is a weekend use cabin. I have heat, propane, on at 45 degrees Fahrenheit. I have a LED display on my xantrex inverter and always charge when I hit 75% charge, with a small generator at about 15amps, when I lack the sun on my panels. I did build a solar tracker that works awesome, of course when I have sun.
  • TomroupeTomroupe Registered Users Posts: 3
  • BB.BB. Super Moderators, Administrators Posts: 32,599 admin

    The percent numbers of battery charge on various "meters" are, at best, rough estimates that can diverge over time from reality.

    If your batteries are flooded cell, get a hydrometer (glass or other direct reading, not a floating ball type) and see what your battery's state of charge really is. That is the "gold standard".

    You have a pretty large battery bank, and even at 5% rate of charge, that would be a (630 AH * 0.05=) ~31.5 amp charging current. Your 15 amp current is pretty small.

    If these are true deep cycle batteries, you can go below 75% state of charge when needed (50% is a good number to avoid going below in normal operation). If your batteries are "UPS" type, or other non-deep cycle, staying at 75% minimum state of charge will certainly help them last longer.

    I am all for a "balanced" system design... Loads define battery bank. Battery bank defines rates of charge. Loads * hours per day also help define the size of the solar array.

    And no-sun--No charging, the dark side of solar power. :s

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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