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small solar system for cabin

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  • small solar system for cabin

    Hello All,
    Would like to get some opinions. We have a new cabin in West Virginia. We get there for a weekend once a month. We have been using a generator. i ordered 2 100 watt panels from Renogy. I have 8 deep cycle flooded 12v 100AH batteries.
    My thinking is that the batteries will be fully charged each time we come down, and then we can drain them to roughly 70% each weekend (roughly 3KW plus what generate in the few days we are there), We will hardly use the generator much except for when we are running tools.

    We will probably upgrade the solar down the road so we can add things like refrigeration, but for now it's really just powering lights and charging electronics.

    What challenges do you see?

    Is it safe to leave the solar panels charging for the few weeks we are gone? Using the solar controller that comes with the Renogy pack, called the Wanderer.

    Is it ok to charge the batteries over several days?

    Thanks in advance for your advice

  • #2
    200w is not going to charge 800Ah 12V battery bank.

    You also would be far better off going with a 48V battery bank instead. You can wire the batteries as two strings of 4.

    send back the 200W solar modules and get a decent MPPT CC with a few ~250w PV modules.

    Now you have a system that you can expand.

    Get yourself a decent 48V 2kW inverter and you will be set for adding refrigerator latter.

    When you are not there disconnect the loads but leave the Charge controller.
    OutBack FP1 w/ CS6P-250P


    • #3
      As Butch indicates you have already shot yourself in the foot. Mistakes:

      1. Using 12 volt batteries and parallel Batteries. There is no excuse for doing that. Paralleling batteries is going to severely shorten battery life. If you need 800 AH battery Capacity, use 800 AH batteries like 4 or 6-volt cells.

      2. Using the wrong battery system voltage. You should be operating at 48 volts.

      3. Using wrong controller and panel type. You should be using a MPPT controller and grid tied panels. A PWM controller is going to force you to wire your panels in parallel and turn your 200 wat panels into 120 watts. Grid tied panels are much less expensive than low voltage battery panels, and when used with a MPPT controller you can wire the panels in series eliminating combiners, fuses, and 50 to 75% less wire and much smaller wire.

      4. You do not have near enough panel wattage for a 12 volt 800 AH battery. That will require at least a 1000 watt panel system with a 80 Amp MPPT controller.

      Basically you have trapped yourself inside a 12 volt toy box. To salvage your batteries, get rid of the panels, get you 4 x 250 watt and a 40 Amp MPPT Controler. Configure system for 48 volt batteries. That will allow you to grow system to 2000 watts and a 400 AH 48 volt battery.
      MSEE, PE


      • #4
        It's hard to build a system and plan to expand it later.
        But first, size your loads in Watt Hours. 5 watt light for 2 hours is 10 watt hours 50A battery @ 12V = 50*12=600 watt hours, 300 of which are useable. Adding a fridge is a whole new ball game, even most mini-firdges consume 1,000watt hours in a day, because of poor insulation. Full size energy star fridge is about 1,000wh day
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A



        • #5
          Thanks for the info. The Renogy kit just arrived. Haven't unboxed it yet. Bought through Amazon, will return.
          The batteries I got from my friend that owns an auto parts store and he can take the batteries back. He'll be frequent visitor to the cabin.


          • #6
            Do not use auto Starting Lighting & Ignition (SLI) batteries. They are not made for cycle applications. If you press them into cycle service will destroy them, and have a lot of new boat anchors.
            MSEE, PE


            • #7
              Originally posted by Sunking View Post
              Do not use auto Starting Lighting & Ignition (SLI) batteries. They are not made for cycle applications. If you press them into cycle service will destroy them, and have a lot of new boat anchors.

              Thanks. The ones we got were deep cycle. But still going back. He can get us the batteries we really need.


              • #8
                Listen to these guys closely and you'll save yourself a lot of cash , and grief. I'm attempting the same thing you are and have come to find out there is a lot more to it than I first imagined


                • #9
                  Sorry if this is in the wrong place, but does anyone know how to post a new topic? Thanks