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  • Oxygen Concentrator off-grid?

    So, I was asked by someone(since in my extended familly, I am the solar fanatic), to come up with a solar panel system, for an RV, that will run a Oxygen Concentrator off-grid.
    The idea(these are the prepper-type people), is that they want it for a SHTF scenario, they want it to run without any access to grid power, gas generator or propane. 24 hours a day.
    I was not told how much power the concentrator users, however, based on my reading, they range anywhere from 180W for a small unit to 600W for a large unit.

    The concentrator that I was tasked with powering is probably a medium unit, with a power consumption of ~400W.
    Now, the problem is, based on my calcs, 24 hours a day * 400W = 9,600Wh/day. So, 9.6kWH per day, in an area that receives 4.5 peak sun hours per day on average, should require a 2,200W solar array. And of course, this will require at least a 9.6kWh battery for storage. For Lead-Acid, I want at least double that capacity, so 19.2kWh of Lead-Acid battery. Lastly, in order to have some reserve for cloudy days, I will multiply by 3, so I need 57.6kWh of battery.

    I highly doubt this is a realistic number. 57.6kWh of Lead-Acid battery will weigh well over 3,100lbs if I use 2V deep-cycles...
    Do you have any pointers for what can be done, to either reduce the amount of battery that I need, or reduce the weight of the batteries?
    Preferably, these batteries should be able to sit for a while in storage, since I doubt that the scenarios that they envision(SHTF) will ever actually happen.

  • #2
    Until you know the wattage the unit uses, and any starting surge, you are DOA.

    Lead acid batteries have a shelf life, about 2 years max, and a lifetime of proper care might get you 10 years with a generously sized bank, that weighs half a ton ! And there better not be 8 cloudy days in a row, because the power is going off. A generator converted to run on propane and broken in with 30 hours of use, and a dozen changes of oil, is going to be needed. Propane can be stored as long as the tank metal holds out.

    You could look into LFP lithium batteries, but they too, have a lifetime clock that starts ticking, and can maybe go 10-15 years, before their chemistry fails too.
    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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    • #3
      For a SHTF situation I would find a pair of sunglasses and watch the show. But if you want to live a full life after the world goes to hell then have at it.

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      • #4
        Originally posted by mzs112000 View Post
        I highly doubt this is a realistic number. 57.6kWh of Lead-Acid battery will weigh well over 3,100lbs if I use 2V deep-cycles...
        That's right, and that looks like a realistic number. If you have a constant load of a few hundred watts you want to power, and you do the math, and the battery size you come up with shocks you - you've done the math right.

        You will at least need a generator as backup, and you'll want an array big enough to maintain that battery size.

        If you want a science project, and you have the space, you could make and store the oxygen (actually enriched air) for use at night. To store enough air for 24 hours, you'd need a plastic bag 11 cubic meters in size (a cube about 7 feet per side.) You could do that in a big room. Or you could compress it and store it, but that takes a lot more energy.

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        • #5
          Originally posted by mzs112000 View Post
          Now, the problem is, based on my calcs, 24 hours a day * 400W = 9,600Wh/day. So, 9.6kWH per day, in an area that receives 4.5 peak sun hours per day on average, should require a 2,200W solar array. And of course, this will require at least a 9.6kWh battery for storage. For Lead-Acid, I want at least double that capacity, so 19.2kWh of Lead-Acid battery.
          You are so far off on calculations that it is laughable. At 9.6 Kwh per day will require a 4000 watt panel system operating into a 48 volt 1000 AH, 3000 pound, $9000 battery. When SHTF your best bet is to save the last bullet for yourself.

          I suggest you go over to the Arizona Wind and Sun Forum where they will coddle you and worship Preppers. They will tell you what you want to hear, then sell it to you. FWIW a 2-volt 1000 AH cell weighs 130 pounds x 24 cells = 3120 pounds, and each cell will cost you roughly $400 each x 24 units = $9600. I will not even address the $200 per unit shipping cost and fork lift rental. That is reality, deal with it.
          Last edited by Sunking; 09-12-2018, 01:54 PM.
          MSEE, PE

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          • #6
            Originally posted by SunEagle View Post
            For a SHTF situation I would find a pair of sunglasses and watch the show. But if you want to live a full life after the world goes to hell then have at it.

            This is not for me. I am not really worried that much about SHTF, because IMO the largest potential causes of SHTF would be: Solar Superflare(Carrington Event), EMP Attack, Economy/currency collapse, huge earthquake, or a supervolcano
            In 2 of those scenarios, it's unlikely a solar array of any size would still function anyways, and even if it did, it's still useless because all of the devices that you would run, would be fried.
            In an economic collapse, or currency collapse, anything of value(like a $70,000 solar system), would be looted or destroyed in short order anyways. A supervolcano would likely put so much ash into the atmosphere that food would not grow, water would be poisoned, and in that case, without food or water, all the solar in the world doesn't help you.

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            • #7
              Originally posted by mzs112000 View Post
              In 2 of those scenarios, it's unlikely a solar array of any size would still function anyways, and even if it did, it's still useless because all of the devices that you would run, would be fried. In an economic collapse, or currency collapse, anything of value(like a $70,000 solar system), would be looted or destroyed in short order anyways. A supervolcano would likely put so much ash into the atmosphere that food would not grow, water would be poisoned, and in that case, without food or water, all the solar in the world doesn't help you.
              The most likely SHTF event is when WW-III officially begins. Both Russia and China will hit the free world with EMP attacks over the free world, and take out military satellites. These will be the opening shots. With just two devices required will collapse the USA economy instantly. You will not have any money as anything and everything electronic is now a brick. No TV, No phones, no internet, no electricity, your autos will be worthless junk, no communications, no water or sewer, no refrigeration, nothing. It will be the 1800's in the USA. Unfortunately many of you will live to see it happen. So if you really want to be prepared, convert all your assets to gold and silver, make a fort, stockpile weapons, and see how long you can stay alive. But sooner or later you will run out of Ammo, so save the last round for yourself right after you shoot the rest of your family and save the last round for yourself. The USA will loose WW-III

              MSEE, PE

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              • #8
                Originally posted by Sunking View Post

                The most likely SHTF event is when WW-III officially begins. Both Russia and China will hit the free world with EMP attacks over the free world, and take out military satellites. These will be the opening shots. With just two devices required will collapse the USA economy instantly. You will not have any money as anything and everything electronic is now a brick. No TV, No phones, no internet, no electricity, your autos will be worthless junk, no communications, no water or sewer, no refrigeration, nothing. It will be the 1800's in the USA. Unfortunately many of you will live to see it happen. So if you really want to be prepared, convert all your assets to gold and silver, make a fort, stockpile weapons, and see how long you can stay alive. But sooner or later you will run out of Ammo, so save the last round for yourself right after you shoot the rest of your family and save the last round for yourself. The USA will loose WW-III
                So, what's your point ?

                After that, maybe the aliens will show up with brooms.
                They've been here for a long time, just waiting. I've even been for several rides with them. The anal probes are tough, but at least they let me drive the spaceship.

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