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Personal dam

 A water tower for residential use that powers home
  (+7, -1)
(+7, -1) 		  [vote for,
against]

A small water tower/tank in your yard, with a second tank for collection and re-use. You set up the high tank and then put an energy generating water turbine at the downspout, so as water drains from it to the lower collection tank, the wheel spins and creates a constant source of power for your home. Sort of like a big battery! The advantage is steady power, something lacking in solar and wind technologies. Using this idea instead would also negate the use of expensive batteries, assuming you could keep water flowing constantly.

The obvious problem here is getting water up into the high tank. This could be done with an old-school farm windmill that pumps water up into it whenever the wind blows. You could also have a hand or other manual pumping system as an optional add-on. It would essentially be a closed loop system, water is pumped up from lower collection tank into high tank, then drained back down past turbine.

Okay, I realize this is not feasible for suburbia, but if you have enough property, and no running water for a microhydro setup, wouldn't this work well? It's fairly low-tech, and would be quite cheap compared to solar or wind.

—Burloncan, Apr 27 2007

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       Welcome to the halfbakery, even if I don't exactly understand your idea...a man-made waterfall waterwheel?
—xandram, Apr 27 2007
   

       What's not to understand? Water falls through a turbine to create electricity and is heaved back up by a windmill powered belt mechnanoism.   

       The only thing is, I'm not sure how much water you would need to place sufficient downward pressure on to the turbine to create a charge of any use. I'm close to bunning it for it's simplicity but unsure if it would work.
—theleopard, Apr 27 2007
   

       Thanks for the welcome, long term reader, first tme poster!   

       Picture a big tank with a narrowed bottom, which ends in a spout. From that point, it's basically a microhydro setup, with the generator hooked up to an inverter. After passing the turbine, the water goes into the collection tank for re-pumping back to the top tank whenever the wind happens to blow.   

       theleopard makes a good point about required flow to generate sufficient power. I will try and do some research on that and post back. Obviously, this isn't going to power a normal home, but I'm thinking one that is set up similar to how you would if you had a solar or wind powered house, super efficient, DC appliances, etc.
—Burloncan, Apr 27 2007
   

       A bun. This would definitely work, but to store any useful amount of energy you'd either need an awfully big tank at the top, or a very high tower. Okay if you own a patch of land on the side of a mountain, preferably with a steep sided hanging valley at the top that you can dam.   

       Even then the round trip efficiency would be difficult to get reasonably high - you'd put a lot more energy into lifting the water than you'd get back. Even on an industrial scale (as at Dinorwig, in North Wales) they only get about 40% back, if I remember correctly.
—Cosh i Pi, Apr 27 2007
   

       Not sure how big or high the tank/tower would need to be, if the required power is only 300kwh/month or so.   

       I agree that it would take lots of energy to get the water into the tank, but it's free energy when the wind blows. A water pumping windmill is much cheaper than a high-tech wind turbine, and with no battery bank required, the main advantage here over straight wind power is cost.
—Burloncan, Apr 27 2007
   

       Hmm, you'd be better off using your windmill to generate your electricity directly, rather than using it to pump water up to an elevation, and then releasing it down again in order to recover your power. However, it is easier to store your power in the form of a tankfull of water, than it might be to keep a bunch of batteries charged up.   

       There are some pumps that have been designed to run using only the temperature changes between day and night, you might be able to use these (and perhaps a big rain catcher) to collect a lot of water at a height that you could then convert into electricity.
—zen_tom, Apr 27 2007
   

       I believe the water pressure necessary to make this work requires 100' or more of head (difference in elevation between source and turbine). It might be easier to build a pond on the surface and tunnel your houswe 100' into the earth.
—nuclear hobo, Apr 27 2007
   

       Energy(potential) = m g h
mass of water: 1000 kg / m ^ 3
gravity potential: 9.81 N / kg m		   

       I'm going to convert to daily numbers: 300 kwh/mo = 10kwh / day = 36 x 10^6 joules / day   

       So you need something like:
9810 * (cu meters of water) * (head in meters) = 36 * 10^6
or:
(cu meters of water) * (head in meters) * (efficiency) = 3700 <yeilds 10 kwh / day>		   

       So with a 30,000 gallon tank 100 feet up (to the *bottom*, mind) you're in the ballpark.
—lurch, Apr 27 2007
   

       Thanks for trying to explain. It seemed like a nice idea when I first read it, but can't exactly get the workings of it. I'm giving a bun. +
—xandram, Apr 27 2007
   

       I was expecting something more, well, dental.
—Noexit, Apr 27 2007
   

       Why not just put a series of sluices and turbines at the base of a glacier? Just wait for global warming to power your house. Probably be good for a couple of decades, really.   

       Barring that, this is a decent approximation. [+]
—shapu, Apr 27 2007
   

       Let's assume that your tank is 100' above the turbine, that the turbine discharge is completely free, and that everything is 100% efficient. How big a tank would be required?   

       Power is pressure change accross the turbine times the volumetric flow rate. Let's do the tricky bits in SI units because imperial units are nutty.   

       P(W) = V'(m3/s) * density(kg/m3) * g(N/kg) * h(m)   

       P = 416.7W (average rate based on 10kWh/day)   

       416.7 = V' * 998 * 9.81 * (100*0.305)   

       V' = 1.395e-3 m3/s or 1.395L/s   

       In a day you would need to circulate 120.6m3 or 120600L (about 30000 US gallons like [lurch] said).   

       If the wind didn't blow for say 2 days - the tank then functioning as a battery as suggested - it's capacity would have to be 241.1m3. That's 63700 US gallons. Consider the feasibility of a 240.6tonne (over half a million pounds) tank perched high above your house. Consider whether such a feat of structural engineering would be worthwhile in the pursuit of a meagre 10kWh/day.   

       Also the flowrates required of the windmill when the wind is blowing are a bit of a stretch.   

       All this is in a world of 100% system efficiency.   

       Good thought, [Burloncan], and welcome. I don't think that the system described is feasible, though.
—Texticle, Apr 28 2007
   


 

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