Deep Cycle Batteries - which to choose??

Discussion in 'Designing, building, making and powering your life' started by Shack Living, Nov 15, 2006.

  1. dgriffith

    dgriffith Junior Member

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    I don't think you'll get any practical benefit with pumping/micro-hydro on stored water. Except for the fact that you've now got a convenient source of water at a height for household use.

    Gel lead-acid batteries are currently the most efficient and accessible form of electrical energy storage on the market. If you've excess power, you're probably better off either getting more batteries, using it to heat water in your hot water system or as you've suggested , just to pump it up higher for later household use, to save having to run a pressure pump later when you turn on a tap.

    Or just start turning on a few more appliances :D

    (Long technical babble follows to explain why. If you just want to trust me on this, stop reading now.)

    Joules is a unit of energy, like the amount of water sitting in a tank. Watts is how many Joules you use in one second to do work, like water flowing from a tap. Watts and Joules are very handy to use in situations like this.

    For instance, potential (stored) energy of something raised up above the ground is

    Energy (Joules) = Mass in kilograms X G (gravity) X height in metres.

    So I say I've got a energy surplus equivalent to a 50 watt panel running 6 hours a day. That's 50 watts x 6 hours x 3600 seconds per hour = 1,080,000 joules. Seems like a lot!

    You have 10000 litre tank, 5 metres off the ground, full of water that you want to set up as a micro-hydro system. Water weighs 1 kg per litre, so stored energy in that tank is 10000kg x 9.81 x 5 = 490,000 Joules.

    Now, we have a pump that is 50% efficient at getting water up there.
    From the amount of stored energy, we can work out that it would take 980,000 Joules of energy to pump all that water up there, to get the 490,000 Joules of energy stored in that tank. The other 50% is wasted as heat and a little bit of noise and vibration from the pump. So pretty much all that 1,080,000 Joules is used up getting the water up into the tank.

    Now, for getting power out of the tank with a hydro setup :

    We have a hydro setup that is 50% efficient at turning moving water into electricity. The rest isn't captured (the water's still moving when it exits the turbine, some gets lost in the generator, etc). So now we have 245 kilojoules of usable energy up there.

    If I could dump that 10,000 litres through that turbine in 1 second, it would put out 245 kilowatts. For 1 second, then the water would run out.

    If I did it over 60 minutes (3600 seconds), it would put out 245000/3600 or 68 watts steadily for an hour. That's if the hydro system is 50% efficient, which is a pretty bold claim to make with mechanical systems.

    Note that the 68 watts for one hour is a pretty poor amount left at the end of all this, considering I had a surplus equal to a 50 watt panel running for 6 hours at the start of all this.

    Now, if I used that surplus energy to heat water in my hot water heater, the results are as follows:

    To heat 1 kilo of water 1 degree, you need 4186 joules.
    We have 1,080,000 Joules, and for an example, we have a 50 litre tank of water at 20 degrees. It's pretty small for a good reason, which you'll see in a minute.

    So when we add 1,080,000 Joules of energy to 50 litres of water, it gets warmer by 1,080,000/ (4186 x 50) or a spectacular 5.1 degrees. So now you've got water at 25 degrees instead of 20. You don't get any losses converting electrical energy into heat in this case - it's pretty much 100% efficient. Of course, your water heater insulation isn't however, so you lose a bit there.

    If you've got 250 watts surplus for 6 hours, such as with a wind generator overnight or something, then your water gets an extra 25 degrees warmer, making it 45 degrees , which isn't too bad for a 3 minute shower in the middle of winter.

    (end or rather long technical babble)
     
  2. Richard on Maui

    Richard on Maui Junior Member

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    That was great dg!
     
  3. Cornonthecob

    Cornonthecob Junior Member

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    I need to go and borrow some books.....I can't get my brain around any of this.
     
  4. ho-hum

    ho-hum New Member

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    dg... GREAT STUFF...


    [pssssst someone ask him another question quick so we can keep him here!!!!]


    cheers,

    floot
     
  5. jamessteward

    jamessteward Guest

    How about a slight change of direction....

    Are there any solar water heaters that use a parabolic dish to concentrate the suns heat energy to a point? The dish doesn't have to be circular, a rectangular shape will do provided the curve is parabolic. This is akin to using a magnifying glass to burn paper - something many folk marvelled at as kids.

    I believe the available solar energy lies between 125 and 375 W/m²?

    This given, and that solar panels are only about 15% efficient, it would seem far better to heat water by direct focus of the suns energy than double conversion of solar to electrical and electrical to heat, wouldn't it? (even though the electrical to heat conversion is 100% efficient...)

    Now if the water gets nice and hot, and you could do with some electricity, why not invest in a stirling cycle motor/generator set to make use of the excess heat? See https://en.wikipedia.org/wiki/Stirling_cycle

    Cheers.
     
  6. Tezza

    Tezza Junior Member

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    This is all above my head but its interesting never the less.....


    Just wish someone would hury and invent a hoshold set up that we all can use..

    If we wait for money makers to make the hard desicions well be waiting for ever

    Tezza
     
  7. 9anda1f

    9anda1f Administrator Staff Member

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  8. jamessteward

    jamessteward Guest

    The solar ice maker is a good one. It also shows an example of the parabolic dish I describe. The ammonia absorbtion method for refrigeration is quite old and is the basis of portable camping refrigerators (excepting thermo electric peltier coolers that are horribly inefficient).

    This crowd produce a stirling engine device that both heats the home and generates electricity from gas.

    https://www.whispergen.com/

    In the US and other countries there are already arrays of solar reflectors that drive stirling engines that produce usable electricity.

    Stirling cycle engines have for a long time been used on boats to generate electricity as the abundant water makes for a good cold source.
     
  9. Jez

    Jez Junior Member

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    Welcome James.

    The evacuated tube (Click) style hot water heaters they're building a lot of in China use direct sun to heat...haven't heard of a different method.

    Apparently the evacuated tubes are much cheaper to build than (as you say) the rather inefficient panel style which is common here in Australia.

    Yep, if you had a whole roof full of them you'd have plenty of potential energy! 8)

    Bit more info on them (Click) - becoming hugely popular in China...and probably would be elsewhere if their distribution became more widespread. One huge advantage (beside the cost) is that they work well on cloudy days and even in freezing temps.
     
  10. dgriffith

    dgriffith Junior Member

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    I've got a link here somewhere to a mob that makes/assembles evacuated tube systems here in Australia .... they were the only ones out of quite a few solar hot water people that actually replied to my email, so they've got a head start in my book. I'll look it up and post it after I get home from work. Maybe after I have a bit of a nap - night shift kind of slows me down a little :? . They were quite flexible about it , you can buy single evac tubes and the manifold that the tube goes into pretty cheap. ($40 a tube? Can't quite remember) - edit: the company in question is "endless solar" at https://www.endless-solar.com

    Looking at getting an evac tube system for my new place - a fair bit of the northern roof area is going to be taken up by panels, so a relatively small, efficient, evac tube system will probably be the go on the westward side of the roof. I'm also getting a lister 6/1 genset, so there'll be a heat exchanger linked to the hot water system for the cloudy days. Seeing as when it's cloudy, I'll probably need to top up the batteries , it's a good idea to use some of that excess heat to top up the hot water system as well.

    I should probably post all the info I've got here somewhere - I've been researching a lot of stuff for my new place for a fair while now. Seeing as it's literally a stone's throw from world-heritage-listed rainforest and it's off-grid, it'd probably be useful for people here.
     
  11. jamessteward

    jamessteward Guest

    Thank you for the welcome.

    I have seen these tubes before. They work on the same principle as the vacuum flask for keeping cold drinks cold or hot drinks hot. That is the part that gets heated by the sunlight is insulated via vacuum from the outside world, hence almost completely eliminating the reconvection of absorbed energy. I wonder how they stand up to large hail stones ;-)

    What I was barking at was to use a parabolic dish - like the one in the ammonia absobtion ice maker - to concentrate or focus the sunlight energy to a point (or to a long thin strip ;-).

    I think the temperatures attained can be much higher at the focal point. Although if these tubes are perfect insulators and cover the same surface area...hmmm maybe they would achieve similar temperatures, that requires some pondering.

    Now - a parbolic dish - like the one in the ammonia absobtion ice maker - is pretty easy to manufacture oneself. I made one a while ago from chipboard formers at each end and nicely polished stainless steel for the reflector. It worked very well and heated water to boiling point in a copper tube.

    Don't you think one dish and only 1-2 vacuum tubes would be cheaper than a whole array of vacuum tubes?
     
  12. dgriffith

    dgriffith Junior Member

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    It would be, but I don't know how well the working fluid inside the tubes would stand up to that kind of heat. Specs for the hot water system state that temps at the tube ends (where they go into the manifold) with no coolant circulation are as high as 220-250 degrees C. If you can keep the operating temp below that (eg, with a pretty good thermosiphon setup) you'd be ok.
     
  13. blackandwhite

    blackandwhite New Member

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    Hi,

    Im interested in your NIFE setup. Did you get any data together on how well its been performing the last 5 years?

    Would be very interesting to see how you went with it
     
  14. Benjy136

    Benjy136 Junior Member

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    There is a site at www.noonco.com/edison where much may be found concerning the making if your NiFe batteries. You can make your own with KOH, nickel and Iron and a container if you'd like to monkey with it..

    Now I have a question.
    I have a dish receiver with a diameter of 10 ft. with a depth of 2 ft. It's basic construction is fine metal grid. The receiver is positioned approx. 4 ft. out from the center of the dish. I am anticipating converting it to a solar heater for water or elec. My thoughts are to seal the mesh with epoxy and coat it with silver paint, replace the receiver with coiled stainless tubing (Our well water here has a PH of 5.3 ) and face it south, changing the inclination with the seasons and using stainless flexible connections to a steam engine for elec. or an insulated tank for heat. I am open to any input from you wizards out there.

    Thank you in advance,

    Benjy
     
  15. gardenlen

    gardenlen Group for banned users

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    if we could ever afford a few panels or windy and ancillary equipment we would be buying tested second hand forklift batteries lots cheaper than new.

    len
     
  16. permasculptor

    permasculptor Junior Member

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    I have been thinking of similar idea where you have a evacuated tube with a parabolic trough as a pre heat then a paraboloid (round) dish at the top.I would expect you would get much better eficiency and longevity if you yoused a stainless steel or mirror like finish like the ones found here- https://greenpowerscience.com/SHOPHOME.html
     
  17. blackandwhite

    blackandwhite New Member

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  18. BananaBender

    BananaBender Junior Member

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    Buying second hand deep cycle batteries is pointless. All deep cycles have a limited # of cycles and once you start discharging them below 80% of total there life span halves. Making them useless. Second hand batterys == big problems. I dont want to sound like a asshole len but I speak from personal experience and lots of it.

    I have lived offgrid for 10 years now and have 32 panels, 24v inverter, automation driving a TR1 lister genset that runs on biodiesel and 5 wind turbines. In the 10 years i have gone through 2 battery banks. The first lot i would discharge completly before recharge and i got 3 years out of them. These where exides and set me back about $18000.
    The second lot i have never discharged below 80% and they havnt missed a beat going on 7 years now without any scale build up on plates etc. Both hold charge and discharge like the day i bought them. Water usage is minimal only increasing slightly in 40 degree days of summer. These set me back about the same for 1200aH capacity.

    The nickel irons look great on paper, I havnt met anyone who has ever used them nor vouch for them. The only manufacturer seems to be in china and some of the claims seem dubious. I plan on purchasing some next battery bank to see how they perform.

    Alot of people think they are experts in solar, especially the idiots who install them but i can tell you now real world usage and performance is nothing like they make it out to be.
    The biggest laugh i get is from people thinking they are enviro friendly. A tonne of lead and sulfuric acid isnt friendly to the enviroment at all. Ive got a tonne of "garden gnomes" for any one wanting to argue that with me.
     
  19. blackandwhite

    blackandwhite New Member

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    $18,000 sounds expensive.

    Under $18,000 can get you 20 x 1.2 NiFe (Nickel Iron) batteries from Victoria: https://www.ironcorebatteries.com.au/page3.php even cheaper (~$13,000) if you import them yourself.

    Completely recyclable and environmentally friendly with no sulfuric acid or lead! Higher energy density the lead acid, high rate performance, the one in Edisons car is still running.

    I have some friends installing them for off grid solar home in QLD, will be interesting to see how they go in real life test.
     
  20. gardenlen

    gardenlen Group for banned users

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    have you used second hand batteries bananabender?

    the people who use them would not agree with you and under the permie' banner of as eco' friendly as can be their charter is re-use/re-cycle, this cuts down on manufacture of new which under the carbon fallacy has a big carbon foot print.

    i put my idea you put your idea that is freedom of speech, so if you actually have experience of the personal kind then what you say is pure critical only. those who recycle these batteries set them up in a frame, and deliver them right to where you want them.

    so with the price of new batteries there is no way many of us will ever afford this expensive technology it remains with the rich and infamous the plastic benders.

    len
     

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