How Much Water?

Regarding my previous post, how much water would a typical home have to pump into its own virtual dam in order to provide energy during a typical night while the water flows back out and through a generator?

Are we talking swimming pool size?

How big a container would you need to store the compressed air for the same purpose? Refrigerator size? Garage size?

I have the smartest readers in the world. Someone can probably answer that question on the back of an envelope.

Comments

[Chris]

Most people live near coasts. My plan is to build whole towns (but perhaps starting with just novelty tourist shops and cafes) on floating pontoons with some sort of hydraulic pistons fixed to both the pontoon and the sea or river bed. As the tide rises and falls (a distance of around two metres where I live) a constant flow of high pressure water would be forced through a turbine to supply power to the buildings on the pontoon.

I believe such things have been tried before and it turns out to be extremely difficult to build sufficiently robust hardware. But still, it should work in theory. I think.

[Jacko]

If we say we have: 50 kW hours / day, 20% of which needs to be stored overnight (more if you are in a cold climate), with a 1/3 efficiency in energy recovery, and a drop of 20m from the storage tank to the generator.
The volume of water needed is 550m^3. If we assume that the house has a footprint of 2000 square feet (185 m^2), then a storage tank under the floor would have to be 3 meters high, with the generator another 20m below the bottom of that.

On the plus side, the 550 tonnes of water under your house will save on heating overnight if you just warm it during the daylight hours.

Better yet, make it double as a giant heated indoor pool (unfortunately, no swimming before dawn).

[phosphorious]

"If this was such a wonderful idea, dont you think water which falls down those huge dams and and generates hydro electricity would have been pumped back up in a perpetual cycle?"

According to wikipedia, this is exactly what's done: hydroelectric plants sometimes use their output to draw water into resevoirs, which act as batteries, storing the energy for later use. You get something like eighty percent of the energy used to fill the resevoir back when you empty it.

Assuming scott is right about the future cheapness and effective ness of solar cells, this might be a useful method for storing energy in a hiusehold situation.

But I have no idea how big such a resevoir would have ot be to be useful.

[Mike]

As a first step, how about just an adobe (or brick) house? The Spanish used these in California and the Southwest because they are suited to the climate. During the day, they tend to be cooler than outside because the heat takes a while to penetrate the material, then at night they are warmer as the walls release the pent up heat. I lived in a brick house in New Mexico and we didn't have air conditioning and did fine. Kept the house closed up during the day, opened it up at night and ran a fan to bring in cool air.

[Arno]

There is a better idea - you already almost mentioned it. When solar power is that cheap, everybody will want to drive an electric car anyway. Electric cars have batteries and if everybody plugs in their car when they are not driving, all this storage capacity can be used to stabilize the net. Your car won't get charged overnight - it will instead put power back into the grid, while it is charged during the day, during work time when you don't use your car anyway.

[Satyam]

this is utopian .... can't be done .... Scott I can't believe you fell for such childish ideas.... the amount of energy required by your motor to pump all the water up into the reservoir would be equal to the amount of potential energy released by the water while falling down .... and factor in the inefficiencies and the fact that you cannot capture all the potential energy released, you end up expending more energy in getting all the water up than you get.
If this was such a wonderful idea, dont you think water which falls down those huge dams and and generates hydro electricity would have been pumped back up in a perpetual cycle?
Thats why if u want to use potential energy for your good then you need to take advantage of some natural phenomenon for the refilling.... maybe collect rain water or sth .....

[I once was a sailor named bob...]

To all of the anti-nuke people...

The US Navy has more than a 40 year safety record with Nukes. AND they have to float and work while being shot at. I think we are at a level of technology were we can do it safely.

Think - Chernobyl was before we even knew what the hell happened in a reactor, and 3 mile island was just a scare. but we know more now.

[Andrew]

Have you considered ice plants instead? They offer a similar energy storage function, except they can also provide direct cooling without an additional conversion step.

Underneath Stanford University is the third largest ice storage facility in the world:
http://facilities.stanford.edu/energy/iceplant/index.html

I toured the inside of the tank before it was filled...it's almost like going into the Grand Canyon.

(Ok, i exaggerate a bit)

[Mr. Wampus]

All we need is for someone to invent a sort of "Gravity Mirror." That would be a device that reflects gravity. The effect would be like when you put 2 magnets together with the magnetic poles reversed so they repel each other. The gravity mirrow would not require an external power source, it would simply reflect existing gravitational pull and therefore push against it. I'm sure it would have to be made of some sort of exotic material that would itself be controversial, like baby kittens. Nothing is entirely free, but we'd learn to live with it.

You could adjust the lifting power by changing the angle of the gravity mirror to the source of gravity. To keep it stable you would probably have an array of smaller gravity mirrors that reflected in different directions. If you pointed them all straight down at the earth, the platform would accelerate at 9.8 M/sec squared away from earth. That would solve a bunch of problems for NASA. Come to think of it, it would solve a bunch of problems for the airline industry too. In fact, gravity would become our chief source of energy. It is abundant and it would be essentially free.

Now all we need to do is figure out exactly what gravity is and how it could be "reflected" and we'd be in business.

OK, I've done the hard part of thinking up the idea. Someone else can thake this and implement it and pay me a small but endless royalty.

[rjf]

What about flushing toilets?

[Mark]

Interesting thought, but too much political hype like ethanol. Instead of feeding corn to livestock or making cornmeal, the US makes hooch out of it, and helps to drive up the price of food.

Instead of ensuring clean water supply for everyone, rich nations hoard water so they can heat/cool their homes while using all the power hungry devices with all the lights on 24/7.

[cvantuss]

You are all wrong. The answer is 42.

[Drew]

Scott, you aren't trying to put together a super army of geniuses, because you know they aren't any good in a combat situation, right? Are you going to get all of your smarter readers into MENSA with you? I always get stuck in the shallow end of the dream pool...

[Stomper]

To all advocates of nuclear power:

It is misleading to refer to nuclear energy as "clean," unless:

1. You have figured out what to do with all the primary and secondary radioactive waste (not in general terms, but in specific terms that account for the NIMBY problem); and

2. You have figured out how to eliminate the kinds of engineering errors, human errors, "deferred maintenance" issues and earthquakes that can lead to Three-Mile Island, Chernobyl, and other disasters (real or potential).

I have yet to see any practical solution to the first, and the second is impossible to solve. Nuclear energy may still be the answer, but let's not delude ourselves about the costs and risks involved.

--Stomper

[AC]

"...but wouldnt' creating that many windmills cause dragon on the earth resulting in higher tides and possibly messing up how fast our days are?"

We have ripped down so many trees all over the planet which has reduced the natural drag. Adding some drag that was eliminated would be a good thing.

[Tibor]

Instead of water you could lift and lower your ENTIRE HOUSE to store energy:
During the day use an electric motor to slowly lift your entire home one store, making the basement become first floor.
Then during the night let your house slowly lower again, making it spin the electric motor backways becoming a generator...
Just remember to use the correct door when going to work on the morning ;-)

[Roger]

Some interesting reading here on perpetual motion / free energy.
http://www.surphzup.com/index.html
http://www.overunity.com/index.php/topic,4540.new.html#new

[Richard]

Scott, what about a global power grid for solar energy. We already have national power grids. Seeing that it is always daylight somewhere in the world, we could just hook all the grids together and have constant solar power, day and night.

[Yes.]

I'd be half crazy too if I learned to draw poses out of a Penthouse magazine. That's not art training, that's some crazy $hit. Hell– I'd feel ripped off if that were my childhood.

[Sillyones]

If I told a plumber that I was hiring an architect to design my new house, I doubt he'd be offended I didn't ask him to do it. LOL!

[henry]

did very deep holes in the ground until you get to the hot bits, pour in water. Job done.

[SkiBumPaul]

On a larger scale, it's been done already. See here:

http://www.nypa.gov/facilities/blengil.htm

[Jaime Bakulic]

...not a lot, not a few.

[Greg]

Why would each house need its own reservoir? In NSW, Australia, excess power generated within in the grid can be used to pump water back up the hydro electricity system. If all houses had the solar panels, excess power during the day could be fed into the grid and do the same. A few large projects would provide economy of scale and probably better efficiency than many small systems.

[WCE]

You forgot to provide an envelope.

OK, really, the right answer is "none of the above".

You want heat at night, you want cool during the hot part of the day, and you have lots of water. Pumping it isn't the right approach, using it as a heat-sink is. Water has one of the highest specific heats of any material (meaning it takes more energy to heat it up than just about anything else). So your swimming pool out back is average temperature of the day, minus a few degrees from evaporation. That's usually cool enough to use to replace your air conditioner with a simple heat exchanger. (Think "big car radiator + fan, plus a pump to circulate the water.) Your A/C bill just dropped to almost zero. At night, you use the same system to pump air through the water you warmed up all day while cooling your house. Your heating bill just dropped to almost zero.

If you don't have a pool and you aren't living where it gets hot during the day, then you buy a septic tank and byry it in the backyard and do the same trick, except you add a heat pump and use the water in the septic tank (not hooked up to your toilets, a separate dedicated heat reservoir with brine to keep it from freezing) to store the heat from the day for the following night to keep you warm. Heat pumps are more energy-efficient than A/C units or furnaces, but do require a fraction of the energy produced to run, and the buried-brine-tank method is the most energy-efficient approach. (On second thought, you'd probably want something other than brine, as it's corrosive to metals. Antifreeze would be bad for the groundwater if it leaks, so maybe somebody with a chemistry background could provide a good alternative.)

You lose energy when you compress air because air gets hot when it compresses, and that's heat that's generally lost by the time you want to use the compressed air for energy. When the compressed air is released, it's cold air at lower pressure than it was in the tank when you compressed it.

Water pumps are not efficient, either to get the water up into the attic or to recover the energy later.

You lose energy whenever you convert it, so the fewer conversions the more efficient the system. Just save the heat from the hot part of the day for night, when you need the heat. Water's cheap and good for storing heat. Underground concrete tanks are already available cheap (septic tanks cost about $500), and you really can use car radiators as viable heat exchangers. The rest is plumbing, and PVC pipe is about as cheap as anything gets.