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Help figuring out and sizing off-grid solar system

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  • Help figuring out and sizing off-grid solar system

    Hi all - I hate to come here and dump this all over you to help me figure out, but I realize that some of you REALLY know your stuff and like sharing your knowledge, and I'd find myself far less confused and frustrated if I could enlist help instead of trying to figure it all out myself.

    I have a property in the mountains of Northern California, off-grid, with a well. My goal here is to install some panels and batteries and use it to make my property a bit more comfortable, AND to *potentially* eliminate the need to run my loud and obnoxious generator to power the well pump. It's a property I cannot access in the winter, so I'd bring the batteries up to the property in the spring and bring them home in the late fall. I also only go there off and on throughout the times of year I can access it. Given how much I'd use it, I know this is going to be inefficient.

    There are a few things I'd like to be able to run:

    1. 4.5 cubic foot fridge/freezer. The one I'm looking at refuses to show a consumption value other than 235 kWh per year. Or, .62 kWh per day.
    2. Washing machine. Maybe two loads per week, air dry on a line. Let's say 500 watts for two hours per week. What is that, 1 kWh per week, or .15 kWh per day on average
    3. TV: 100 watts, 2 hours per day. 1.4 kWh per week, .2 kWh per day.
    4. Lights: let's say 100 watts max, 4 hours per day. .4 kWh per day

    So, I'm looking at what, 1.4 kWh per day. At any one time I could potentially be running all of those things at once.

    I can get used Sharp NT-175U1 panels for fairly cheap. Can we assume I'll use these?

    Electrical Characteristics
    Maximum Power: 175 Watts
    Voltage at Pmax: 35.4V
    Current at Pmax: 4.95A
    Short-circuit current: 5.40A
    Open-circuit voltage: 44.4V

    The panels would be approximately 30' from where I'd have the batteries and charge controller and inverter.

    Using the battery sizing tutorial in the stickies:

    1400 watt hours X 1.5 (using an inverter) X 2 days of reserve. 4200 watt hours. 4.2 kWh
    I don't THINK I'll need more than 1000 watts of panels, so, 12V?
    4200 / 12 = 366 amp hours.

    Would I want one big battery or multiple smaller ones? If I only need 12v, then I would think a 12v battery or two, wired in parallel?


    Without this question being too broad, what should I do?
    How many 175w panels do I need? What size/type of charge controller? Inverter?

    Thank you for taking the time to read all of this!

    Chet

  • #2
    Oh, one other variable I'm thinking about is if I ditch the generator that powers the well pump (into a pressure tank), and run that off batteries too. I know that changes things considerably given it's a 240v 1 HP well pump. Is it fairly unrealistic to think I can run that off of a couple of batteries too? It would run something like 30 minutes a day, IF that.

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    • #3
      > 240v 1 HP well pump. Is it fairly unrealistic to think I can run that off of a couple of batteries too?

      That's going to be killer. That will need a BIG inverter to spin up the motor. What about weekly pumping into an above ground storage tank of 2,000 gallons, and using a 12V RV pump to pressurize your house ?
      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

      solar: http://tinyurl.com/LMR-Solar
      gen: http://tinyurl.com/LMR-Lister

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      • #4
        Originally posted by Mike90250 View Post
        > 240v 1 HP well pump. Is it fairly unrealistic to think I can run that off of a couple of batteries too?

        That's going to be killer. That will need a BIG inverter to spin up the motor. What about weekly pumping into an above ground storage tank of 2,000 gallons, and using a 12V RV pump to pressurize your house ?

        That's one reason I kind of want to keep the well pump separate from this conversation, because I likely will do something like what you mentioned. I don't quite have enough slope to put a tank in the back of the property and gravity feed everything I need, but maybe a pump like you said would work. I don't know enough about it. I also don't know how I'd tie that into the existing system which is really just a well connected to a pressure tank which leads to a series of a couple of hose spigots. I guess a check valve would be needed to prevent it from interfering with the pressure tank and well?

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