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Off grid occasional use cabin - sanity check

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  • Off grid occasional use cabin - sanity check

    I have been searching this forum for a while and learning lots. Hoping to ask my situation specific questions to get people's inputs.

    I am about to start building a 2200 Sq/ft house that will be off grid ($40k to bring in power lines and I cannot get permission even if I wanted to). Thus looking to build/install a solar setup. As of now I am thinking a ~7kW array with a 40,000 Wh battery bank. This will be located in central Virginia, I intend on ground mounting panels (<100' from house) so that they get max sun (will cut trees if needed). Will also have generator for surge support/backup but not trying to run it daily.

    I plan to heat the house with a wood-stove so winters will not be an issue, my concerns are the hot/humid summers. I was leaning towards putting in a few mini-split systems for A/C versus a traditional ducked HVAC. - This the right answer? I certainly do not expect to run the A/C 24/7 and keep house 68* or anything but do want some cooling.

    Other loads will be typical of a house, fans, LED lights, fridge, well pump, small appliances as needed.

    House will typically be used on the weekends so we will have the week to cool house during full sun hours, recharge battery bank, etc. If the weather is calling for storms then we will likely not be up there anyway.

    Is this the best way to go? Is this reasonable? I know it will be a $30k system but it is the only option I have

  • #2
    Start by reading "Solar Power Your Home for Dummies". ~ $20 at bookstores/Amazon. A free but slightly dated version is available online.

    After that, get as best a numerical handle/est. on loads as possible and build w/ conservation/low use in mind. You don't pay or oversize for what you don't use. Conservation first. Then plan to use other sources for loads such as propane, etc., as much as popssible, especially for water heating.

    You'll need load reduction even more than other situations if you plan off grid. Don't know your situation, but most folks are unaware of what's involved in an off grid lifesytle. If you grew up on the grid, you're in for some surprises.

    My guess is without a lot of load reduction your $30K buidget # will be more than difficult to reach even with DIY, mostly due to battery and associated equipment costs. Also, get ready for a part time job caring for a battery system.

    Then, get familiar w/PVWatts. Read all the help/info screens a couple of times, get your orientation as close as possible and make a few runs.

    The more (self) informed you are, the better prepared you'll be and that will make for a better outcome. You sound like you have a lot to learn.

    Welcome to the neighborhood. Read the book. Get your own information and avoid peddler's hype.

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    • #3
      Is this the best way to go? Is this reasonable? I know it will be a $30k system but it is the only option I have
      Or even more ! If it's worth doing, it's worth overdoing. I think several mini-splits are the way to go. you may need 240vac for them and your well pump
      If you are an engineer, you can brave mixing manufacturers, otherwise, stick to a uniform brand.



      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
        I think you have the right ideas, one decision will be if running a (probably 48V) DC well or
        a 240VAC well. That in turn may drive your cooling and the rest. There are minis that will
        run direct from panels, but do check their COP/SEER ratings, and the temp range to be
        covered. Some run on 48VDC. If you succeed in the hottest weather, the same equipment
        can cover at least part of your heating season at no extra cost, greatly reducing wood use.

        One approach is use a generator to occasionally to fill a water reservoir, catching up on
        batteries at the same time as needed. Lining up larger loads with time of good sun would
        drastically reduce battery requirements.

        Running 4 extremely satisfactory mini splits here. good luck, Bruce Roe
        Last edited by bcroe; 07-11-2019, 07:05 PM.

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