off grid system

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jr4jc
jr4jc Registered Users Posts: 1
my wife and i have built a small [14x24] cabin in the woods of tennessee and want to be off grid.
the problems we see is we really need air conditioning, tennessee can be very hot and stay that way at night.
I am open to suggestions.
we do not have enough wind to make electricty that way.
no running dropping water.
we have thought about solar and propane generators and even read about wood gasification.
glad to find this web site and forum, we need help to make this descision.
jr

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
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    Re: off grid system
    jr4jc wrote: »
    my wife and i have built a small [14x24] cabin in the woods of tennessee and want to be off grid.
    the problems we see is we really need air conditioning, tennessee can be very hot and stay that way at night.

    You say you want to be off-grid. Does that mean that you have the option to be on grid, but would prefer an alternative for either philosophical or economic reasons? Or that you have to be off-grid?
    If you have access to grid and want to do air conditioning (a very heavy power drain on the scale of solar) you will be spending a fortune on panels and batteries with no economic return.
    SMA SB 3000, old BP panels.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
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    Re: off grid system

    Welcome to the forum.

    So far you've realized two very important things: you don't have reliable wind or water as a power source.

    The first thing that has to be asked is: why do you want to be off grid? If it's to save money, rethink the plan. If it's because the grid is so far away that connecting it to the cabin would be a huge expense, welcome to the world of solar. :D

    You need to determine a couple of things for off-grid. First would be the maximum power consumption at any given time, and second would be the total daily Watt hours used. This can be hard to come up with unless you already have the things you need to run, a source of power to run them with, and a Kill-A-Watt (or similar) meter to measure just how much power they use. You mention air conditioning. That is a big power consumer. There are a lot of threads/discussions about A/C (air conditioning as opposed to AC alternating current) on the forum. Look under the energy use and conservation section. Very long thread on the "mini-split" A/C units which are the easiest on the power draw.

    Another thing you want to do is look at the PV Watts http://www.nrel.gov/rredc/pvwatts/ site. Put in some numbers for a location near you and get an idea how much sun you can expect year-'round. You will probably find Winter in Tennessee is a bit short on sunlight. Your particular site will make a difference in this too.

    Once you have info on how much power you need to supply and what you can expect for sunlight you can design a system. We'll help; all of us who hang around here giving away thousands of dollars worth of engineering for free. :D

    You are going to want a generator anyway. No matter what power source you use it's good to have back-up. There's a couple of threads on gasification too, although it's not quite as promising as some would have you believe. Jaybird has a better understanding of it than most, and a realistic approach: http://forum.solar-electric.com/showthread.php?15990-Jaybird-s-wood-gas-thread

    Hope we can be of some help.
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Re: off grid system

    Is this going to be your residence, or weekend use?

    Solar is doable, but NOT cheap. For weekend use a small efficient generator (Like the Honda line) would be most cost effective. For a residence, it would be close to a draw dependent on how many years you foresee using the property.

    Remember, 'woods' and solar don't combine very well, I've taken down several trees and had a good size clearing already.
    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 backup...lol), 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.
  • Photowhit
    Photowhit Solar Expert Posts: 6,003 ✭✭✭✭✭
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    Re: off grid system

    ...need to add to what 'Coot said, conservation is always more cost effective than solar, so first you would want to 'super insulate' your cabin. Also when I did my off grid cabin, designing for solar, I found the extra solar array needed to run an A/C making winter cloudy days not a thing to worry about. ...but it's worth a check, I take it you'll heat with wood/gas...
    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 backup...lol), 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.
  • icarus
    icarus Solar Expert Posts: 5,436 ✭✭✭✭
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    Re: off grid system

    You can run a small energy star window unit on a Honda Eu1000 for a 1 litre (quart) of fuel every 6 hours or so. You may find it is m ich cheaper to use the genny for the A/C when it is essential rather that building a big enough system just to run it now and again. A small window unit will draw ~ 500 watts, 12 hours is 6kwh. You are going to need a big battery and lts of solr to do that on a regular basis.

    In the long term, conservation, extra insulation, shade trees awnings etc are way cheaper, followed by perhaps a efficient mini split system.

    Tony
  • ywhic
    ywhic Solar Expert Posts: 621 ✭✭
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    Re: off grid system

    I've got a 12 x 24 cabin down in TX..

    IM000022R.JPG

    I have 870 watts of panels.. hooked up like 24v.. an Classic 150 MPPT controller due in next Friday..

    I've spent $1720 thus far.. and that does not include the mounts, inverter, or battery bank..

    I'll be spending about another $1800 to get it done..

    How far from the OPEN are are you to get 100% sunlight with no shading??

    Longer wire runs will need special need to get the current to the charge controller..

    Notes to keep in mind.. 1 amp AC = about 10 amps DC +/-..

    To run an A/C with the sun out and on the panels I will need a 400-600 ah in a 12v battery bank to be safe..

    A 5000 BTU A/C uses about 450-500 watts (50 amps) per hour of DC.. (6000 BTU is 60 AMPS of DC, etc..)

    Granted if I want to do a 24v battery bank I can drop that to a 400ah battery bank..

    24v systems need less heavy wiring and are more effiecient than 12v systems..

    The 24V inverters cost about $300-500 more.. I went with a $340 (Xantrex) inverter.. the same size 2000w (Samlex) inverter in 24v is approx $750

    I had to sell my original controller (for a loss) because after all was said and done I decided I wanted the MPPT and not PWM..

    Is your setup for the weekends?? or going to be year round??

    And yes figure out your wattage needs 1st.. don't buy anything..

    Not to scare you but I'm going THRU this same thing currently..
  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
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    Re: off grid system
    icarus wrote: »
    You can run a small energy star window unit on a Honda Eu1000 for a 1 litre (quart) of fuel every 6 hours or so. You may find it is m ich cheaper to use the genny for the A/C when it is essential rather that building a big enough system just to run it now and again. A small window unit will draw ~ 500 watts, 12 hours is 6kwh. You are going to need a big battery and lts of solr to do that on a regular basis.

    In the long term, conservation, extra insulation, shade trees awnings etc are way cheaper, followed by perhaps a efficient mini split system.

    Tony
    I agree with Tony on this one, although I could not run my 5600 btu window air on a Honda 1000i I got an 8000btu to run on a Honda 2000i. Alot cheaper than a solar system.
    Larry