Self- Sustainability

Discussion in 'Earth Science' started by quinnsong, Feb 21, 2014.

  1. billvon Valued Senior Member

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    Storing it as heat is several orders of magnitude easier and cheaper than storing it in a battery.

    Beyond some very esoteric/fragile/expensive vehicles like a Sunraycer, putting solar on a vehicle does a few things for you:

    1) Increases drag
    2) Increases weight
    3) Tempts you to park it in the sun. Parking vehicle in the sun = hotter vehicle, shorter battery life
    4) Gets you a little power. 20-30 watts for a scooter, 200-500 watts for a vehicle.

    From experiments a lot of people have done, putting solar on a mainstream vehicle reduces its range overall, and makes it less effective as a vehicle. (Not to say you can't try it but I suspect you will end up learning the same thing.)

    All that sounds great, but again, you don't need a solar heating system if the sun is already coming in the window and hitting the wall. You've got one already. A friend of mine did that and can grow tomatoes year-round now. It's San Diego, granted, and we only have about a dozen freezes a year, but she still sees a 20-30F gain at night.

    Why? In most places, go down a few feet and the soil never freezes. It's a good way to "back up" solar heat if you run into a cloudy spell.
     
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  3. billvon Valued Senior Member

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    That might work - but - if you have the solar power from the panel it's always better to use it directly than try to store it and use it later. You would be pretty lucky to get 50% efficiency out of such a system, which means that if you generated a kilowatt-hour, you could either use a kilowatt-hour now or use half a kilowatt-hour later. About the only place I've seen this done to good effect is in places that already have water turbines, and during the summer (when the source stream dries up AND solar is plentiful AND there is another source of water, like a lake) they use the extra power to pump water up to the penstock/catchment.

    What most people who live "off the grid" do is use stored energy in their batteries for their 'background' power - lights, radios, TV, computer - and save the big energy users (clothes washing, water pumping etc) for days when the sun is out or they have to run their generator anyway.
     
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  5. Trippy ALEA IACTA EST Staff Member

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    Tomatoes require a minimum temperature, and I was expecting Dunedin to be too cool:

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    And from what I can see your winter temps are warmer than ours, and you are ten degrees closer to the equator, but then, you're in a different environment.

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    But now you've got me thinking that the brick wall might be enough.
     
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  7. KitemanSA Registered Senior Member

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    There is a varient of the Arch-screw tht is made of a bent pipe. It is what I think of as an Arch-spiral since the pipe spirls around the axis of rotation of the unit. Since it doesn't have the sliding joint of a typical Arch-screw, it tends to be more efficient, and the more hydro-phobic you can make the pipe walls, the more efficient.
     
  8. KitemanSA Registered Senior Member

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    624
    Whoever said that storing energy as heat is more effective is correct, if you define the desired output as both electricity and low temperature heat. This dual need is true of most house-holds. And the split between the two can be somewhat adjusted by the temperature of fusion of the phase change material (typically a salt eutectic of some variant). The higher the Tf, the higher the electricity output percentage but the more expensive the system.
     
  9. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    edit made new next post, so killed this one.
     
    Last edited by a moderator: Mar 11, 2014
  10. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    I only knew of the bent helix tube type, but going to your link I saw this:

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    and was reminded of my energy free way to lift fresh water out of the deep ocean:

    A long vertical tube, filled with fresh water and closed at the bottom with osmotic membrane will float in the salt water if diameter is large enough* with open upper top of the tube well above the ocean surface. The pressure on the fresh water side of the membrane is less than that on the salt water side. Thus "reverse osmosis" will occur sending fresh water across the membrane into the tube. That fresh water influx, if tube top is not floating too high above the ocean surface** will force fresh water to over flow the top an fall into the ocean. If want more than just fresh water in the middle of the ocean with no energy cost from salt water, don't let the overflow water just fall - let it for example turn an Archimedes screw, driving a power generator.

    Almost seem to violate conservation of energy. I taught college physic and usually asked my students to explain why it does not - You want to try?
    Or do you think there is a "free lunch" with fresh water to drink with it, after all?

    * I.e. The upward force on the bottom of tube area increases with the square of the OD radius but wall weight only with the mean radius.

    ** Make tube with slightly higher density material than water. It must have thick walls in the deeper part to not collapse radially inward. Thus it will naturally float stably with the heavier end down. Most of the tube can have a very much smaller OD but large area at the bottom does make more fresh water each minute. If top ID is only a mm or so, the osmotic pressure entering flow acting on a large bottom will send a water jet into the air!
     
  11. KitemanSA Registered Senior Member

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    624
    No, the fresh water will flow OUT thru the bottom membrane until the physical pressure difference is something like 400psi. only after the differential increases further will the flow go from salty to fresh.
    If you put a pipe filled with salt water in a lake of fresh, and narrowed the top you would get a fountain, but not the other way.
     
  12. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Seawater has an average density of 1.027 gm/cm3,... http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/seawater.html (Perhaps 1.03 near the equator with greater salt concentration.)

    Each gram (near earth's surface) weight 0.0022 pounds so a layer of water 1 cm tall on top of one square inch (6.4516 cm^2) weighs 0.01419 pounds. Thus the pressure one meter deep into fresh water is 1.419psi or at 1000 meters depth it 1419psi but the difference between fresh and salt water pressure 1000 meter deep is only 1419x0.0022 = 3.1218 psi so you need 128.13 km depth to get your 400 psi differential. (which I don't know where that comes from and think it may be less for some membranes, but not enough to make system actually work.)

    "How many miles in 1 km? The answer is 0.621371192237." So you need point of ocean 79.6 miles deep. Unfortunately even the Mariana Trench is known to be only 36,200 feet deep, or only 6.856 miles deep. - too shallow for one to actually make this flow of fresh water to the surface actually occur by a factor of 11.6, but that is a "technicality." One still needs to explain the reason why it would work continuously if the ocean were deeper without violation of conservation of energy.
    Anyone wanting and willing to try?

    Or if one does not want to deal with that ocean depth limited question where does the energy come from to make the jet of salt water you describe, which will soon stop as vertical tube fills with fresh water, come form?
     
  13. quinnsong Valued Senior Member

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    I just emailed him another batch of thread discussion, thanks guys! He did say he would try to email me in the next day or so some responses to what he has read so far,btw all we talked of when we skyped last was the discussion on this thread, he is loving it.
     
  14. scheherazade Northern Horse Whisperer Valued Senior Member

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    One of my co-workers ran his own solar business for many years doing remote installations for various government and private projects. Given the current efficiency of solar panels and deep cycle batteries etc., it is not a cheap undertaking. Additionally, all of the components do have a service life, and need regular attention, eventually replacement and the used components either recycled or disposed of.

    Personally, I have lived many years of my life in remote locations without electricity or running water. We had creek or well water, heated with wood and used candles, coal oil, white gas or propane lighting, depending on how far we were from the nearest town at the time. At one location, we rendered fat from the fatty tissue of the beaver we trapped and used this rendered oil and a string wick as a light.

    I agree with billvon that being more energy efficient will save you more money than attempting to be self sufficient where energy is concerned.
     
  15. scheherazade Northern Horse Whisperer Valued Senior Member

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  16. KitemanSA Registered Senior Member

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    I was wondering if someone would actually do that calc. Assuming it is correct (feels about right), it still wouldn't work in that, IIRC, the osmotic membranes we make stop working under a hydrostatic pressure MUCH shallower than that. Indeed, I doubt they would work in the Mariannes Trench. ICBWAT.
     
  17. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    They could, if made the way submarines get their fresh water needs. I. e. not a large area even with perforated metal sheet support, but very many tiny tubes bent into U shape sticking into the salt water. Hugh surface area compared to the (pi)R^2 area of the pipe these U-tube emerge from. It is very hard for the high pressure difference to radially collapse a tube, only 0.01 mm or less in OD.

    Again the whole point is not whether or not it could actually be done, but where does the energy it could produce in principle come from?
    Why I gave it as a puzzle for my physic students to explain. The correct answer is amazing.
    Here is a hint: Consider two "salt domes" deep in the earth.
    One is filled with oil and the other with solid NaCl - which has more stored solar energy?
     
  18. KitemanSA Registered Senior Member

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    624
    It is not the pressure DIFFERENTIAL I mentioned, it is the basic hydrostatic pressure. Under enough pressure, the membranes STOP being osmotic, IIRC. So my issues is not that they will bust, it is that they won't BE.
     
  19. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Yes I misunderstood what you were saying. Do you have any link telling more? I can imagine that the pressure could increase the density and that reduce the permeability but it would surely depend on the atomic structure of each different membrane. For example I bet carbon nano-tubes would be permeable even with huge external pressure acting on them.
     
  20. KitemanSA Registered Senior Member

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    624
    Sorry, no, I don't have a reference. I had been reading something about why abyssal fish can't survive shallow open ocean and vice versa when the difference in membranes under pressure was mentioned and the author mentioned that man made membranes don't work very deep. It made sense at the time. This was... 20(?) years ago.
     
  21. Billy T Use Sugar Cane Alcohol car Fuel Valued Senior Member

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    Your admission made me search to see is your 400psi differential was correct. It seems not. Only 1psi differential is used for home drinking water system:
    That was my first "hit." Here is a better one:
    Now the deep ocean is typicall at 4C, (277K) water's greatest density state. So if the bottom end of the long vertical pipe is in that "max density" with 33g/L salt the equliprium pressure (no net flow either way is 27.8x277/300= 25.67 bar and the flow of fresh water production increases linearly with higher pressures. One bar is 14.50 psi.

    In post 69 I showed that: "the difference between fresh and salt water pressure 1000 meter deep is only 1419x0.0022 = 3.1218 psi" So 25.67x14.5/3.122 = 119.2Km (or 74.5 mile) long pipe to have zero net flow. still need 10.8 times deeper ocean than known.

    It is the "c =33" that is killing it as a real possibility, if that deepest point were under floating melting ice and c were only 3 (possible less) it would work in practice.* That also explains why my first "hit" said 50 psi was typical for making drinking water, but not from sea water.
    But again the real point is how does it avoid violation of conservation of energy.

    * No, not true. Yes the required pressure could be 10.8 times less with c much lower but so would the pressure difference between salt and fresh water be less by the same factor.
     
    Last edited by a moderator: Mar 16, 2014
  22. KitemanSA Registered Senior Member

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    Home drinking water systems do not start out with salty water. The salinity gradient is minute and thus so is the pressure differential.
     
  23. KitemanSA Registered Senior Member

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    So 27.8bar * 14.5 psi/bar ≈ 403 psi. Yup, I was wrong alright, I was off by <1%. Oh dear oh dear how horrible... SMH

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