Water Energy Question

Questions of this kind do not necessarily require a "math whiz" to handle them. They often yield to simple arithmetic and knowledge of basic formulas involving density, pressure, head (vertical elevation), etc.

A 20m x 30m "house" is extraordinarily large (=McMansion²). A 3000m³ pool on the roof weighs 3000 metric tonnes--just the water! You don't even want to imagine the seismic bracing this might entail.

You'd need a really tall house.

Pumped-storage hydroelectricity - Wikipedia, the free encyclopedia

I guess moving your thermos elsewhere to the hills, and making a dam with a watermill is a cheaper approach. You still can collect some heat for hot water with panels.

Or tapping in into an existing reservoir? Or a water supply tower?

These situations have or high level differences, or massive volumes of water (weight) to sacrifice.

Although water is not a bad accumulator for temperature. Plenty of high buildings use water to freeze to use it as chillers during day time for AC.

Of course you can use the water also as standby for different purposes, fire extinguisher system, and more.

But if the price of the structure will be compensated by the benefits is a different matter, depending on where you are and what you build.

Maybe a good project for the Middle East?

There are always some money wasting projects. Your 3000m3 will be gone before you know.

You want a constant all year temperature? Become a troglodyte.
Del

Well I know that that might be a bit too much water, but the thing is the way they build in Hong Kong (I lived there for 2 years) Is one HUGE concrete structure. Now It would very much not surprise me that those structures already can support quite a lot of weight. Its nothing like your wooden houses you build in the states. Keep that in mind. ( I also mentioned before to let that fact slide atm. IF you are not however able to get that from your mind. Lets say you live on the bottom of a hill, and you put a huge pool at the top of the hill) Now a second question:

Lets assume that instead of making one big pool at the top. You create a small one but you build your house very tall instead. So instead of using more water, you just increase the height. so say you have a house of 6 stories ( or 25 meters high). That was the height of our house in hong kong. Or maybe even talk about an apartment complex. And again you create a pool at the top, but you also create one huge collum going down the house say 2 meters in diameter. Pumping up the water will cost more energy, but would that not compensate for the weight? The thing you all answered was not the question I asked btw.

I know it was not very efficient and so forth. But what I really want to know is how much electricity or watts you could get (in reality) for a certain amount of water with the technology available today. Because if you think about it:

If you have a huge appartment complex, and you allow the water to drop, hit a turbine, pass through the turbine, allow it to hit its max velocity once more, hit another turbine... and continue this all the way down to the ground.... would this not cause you to get very close to almost no energy loss? Say 80% Because remember this is not really about how much energy you can get from it... its more about the concept of being a decent battery. So the real question I am asking is:

How much energy would it cost to pump up Xliters of water, And how much energy could you get back from thix Xliters of water if one makes it go through turbines?

Also Hong Kong has a lot of rainfall. When it rains, you can sometimes get a few feet of rain.

MJB, great answer (GA). I go all weak at the knees when I see answers like this.

A clearly set out problem, a bit of basic physics and some simple calculations to arrive a clean solution. If only everyone approached problems this way.

All is fine except that the [Litre^3] is not acceptable notation. Litre is already a volume convention where 1 litre = 1 dm³ = 0.001 m³

Also, liter should be litre.

Just for keeping the nomenclatures correct.

Good catch, my mistake. It should just be [litre] or [dm^3] but not [liter^3].

Litre (Liter for us odd folk here in US) is already a volume and your equivalence is the correct one. Thanks for noting. Only wish I would have caught the error before posting.

It might be, when you choose the right location, right investor, and organise some extra activities, that a big water basin on top of the high buildings becomes profitable. These try to get some money to pay for the electric bills by entrance fees from customers:

Thanks everyone... That's the kind of information that I needed. The thing is, Like I mentioned before. I am just a student, and have no interest in becoming some kind of architect. This was more or less something I was thinking about whether or not it was possible.

I have no interest in trying to sell this idea to anyone. However I do think that in certain situations this could be useful. Imagine the following scenario:

A big complex building for example. Instead of pumping the water up to the top of the structure... what about going down? Lots of big buildings have huge parking lots in the basements, often a few stories deep. In this kind of a situation there would be 0 cost to the structural changes of the building. Also it might look quite nice. From outside it would look like a big pool type of thing, If you got a nice architect one might be able to make it look quite nice.

Imagine you have quite a big area where the terrain is very steep. I have seen quite a few houses like this. Where half of the house is actually against a hillside, In these type of situations this might become possible.

One more thing: the simple equations you did there I could have done myself. What I was really wondering and know absolutely nothing about is the loss of a turbine / water pump.

however I think it will actually never be cost effective to do this for the following reason:

In most places you can actually sell your electricity back to the framework. Sure you don't get as much money for it as you pay for electricity, but I am def sure that the cost of the turbines, and pumps. as well as the maintenance will be way too expensive and in no way possible to get your investment costs back out of it.

maybe in the future it would be possible to use the electricity to create hydrogen, which you can then use to drive your car. But again you are talking about massive energy losses, and probably would be better off buying the hydrogen instead of making it yourself.

thanks for the conversation, I have enjoyed discussing it

Chiyo

Maybe there are some negative comments in the replies here. Pooh to them.

Let me just say Consumers Power in the State of Michigan did a very similar project on Lake Michigan. I believe it is near Ludington. I think they call it it pumped storage.

They did just the opposite of what you proposed. They pump water to the top of the bluff into an impoundment during periods of low electricity use (i.e. usually night time). During periods of high electricity use, the water is released from the impoundment and flows through turbines to create additional electricity.

I say you are onto to a concept that maybe needs refining, but there are possibilities. Keep thinking and keep saying what if!!!! That is key to being a great engineer.

What if we were to combine say ten houses on a similar system and use a water tower to create something similar? What if instead of water we used solid such as earth that was on a gear system similar to a grandfather clock so the weight unwound a spring in a controlled motion? What if steam was somehow created during the heat of day that condensed at a higher elevation and dripped back down during night?

Like I said, keep thinking!!!!

When the additional costs for the ten houses (both in dollars and environmental costs) far outweigh the benefits?

Numerous utilities use pumped storage where they have the possibility - they are a business and trying to make money - not let the water go downstream wasted.

The amount of water that has to be pumped is only viable on lake sized projects.

Post from russ123 is correct, economy of SCALE is critical for pump storage hydro-electric. With current costs it only makes sense when it can be done on a large scale (lake/reservoir).

Size is only the first requirement. You must also find the right geographic location AND make it through all the environmental impact studies/restrictions and NIMBY requirements. While large scale pump storage hydro-electric works very well, it will only be a small part of the energy solution.

You probably forgot the link that Lynlinch provided. (post #2)

What needs to be understood that somewhere must be a useful benefit. In this case pumping the water back up in low energy consumption time ( overproduction of power) to save it for the peak power demand.

Other than that there is no profit in it. Only losses. Some element has to be added for free, (like a river that feeds the reservoir, or rain with ditto dances at the right time) or an other model of energy that is cheaper than the losses.

Otherwise, the complete idea is just another perpetuum mobile mishap. Why water towers do not supply through turbines? Worth a thought.

Hydro is always on a river is it not? Be kind of dumb to put one on a lake with no outflow.

By definition hydro is placed in front of a self replenishing body of water

"Be kind of dumb to put one on a lake with no outflow"

Really didn't think about that - did you.

It seems the previous post had not.

I had a different version of the idea in a different situation it is kind of complex, let me try to explain it:

this is possible in places where drinking water is scare but where there is a lot of sunlight and around 1km from the sea. (the closer the better)

You create a sort of tower really close to the ocean so that you can pump lots of sea water to it. this water goes through a few basic filters, up halfway on the tower. There it is sent around the outside of the tower. Either the water is in a metal container, or if possible in glass. Now you create a lot of mirrors to focus in a big radius around the tower. These mirrors focus the sunlight to the water halfway up the tower. There the water turns to steam, and rotates turbines as it rises to the top of the tower (this process can and should be refined). When the steam gets to the top of the tower, it condenses and drips down (like a huge coffeemaker). The salt flows down and gets collected.

- lots of drinking water can be produced, which is very useful in these dry places. Deserts could be turned into workable land, and very beautiful communities could be made. Most of the time these parts are very cheap.
- you generate electricity from the steam. If the the mirrors are very wide and almost all of the sun is focused on just one point, a lot of heat is released. The mirrors should be on posts and able to move so that its optimum for most of the day. This electricity can then be used to cool the top of the tower where the water condenses, allowing the whole process to go even faster. Depending on how much electricity is produced during this whole process, and the community it supplies electricity and water to is, The excess energy can then also be used to create hydrogen. This then can in turn can be sold alongside the salt. I don't know if it is possible to also split the salt into chlorine and sodium, but if so, those could be sold as well.

Any thoughts? would this be possible in theory? or not generate enough energy to make this possible? would be a nice idea. Could even create an airport considering its a desert it should be quite cheap. Australia seems like an ideal place for this.

Daan

I am afraid that if you apply some actual arithmetic to these vague concepts, the results will be quite discouraging.

This is visionary in the same sense that an LSD trip is visionary.

There is no mention anywhere in this of the pressures and temperatures involved, of how the pressures will be contained within the given geometry, of how much power might be collected, thermodynamic efficiency,..., anything!

Not to mention that the tent desalinizer concept works and would be far less expensive.

What year of engineering are you in? University or trade school?