Waterwheels Generating Power.

[Jack]

Gidday

Wellthere you go Muddy. You got me there a beauty Eh!. I missed out an h

I meant 18kw/h and most domestic houses run on between 12 and 15 if you are reasonably careful. Deep cycle batteries are normally rated on kw/h, well down here anyway. A turbine is only any good if you have a higher head and can be run on a lower flow.

My calculations were based on approx 750 w per hp.

That figure of mine is what the shaft of the wheel will produce from water running through a 4 inch pipe that is full.

[paddy]

Well obviously none of you went to the " Aternative Technology Centre " in Wales.

They had a water wheel say about 8 feet in diameter being fed from the top with a half inch hose pipe which was set at UK mains pressure which i think is 2 gallon per minute.

This wheel was spinning like billio it had to be seen to be believed.
I have no idea how much electric it could produce.

What Jack says with a four inch pipe i think would be a super powered thing but in the summer months my stream can become a trickle so for say 4 months of the year it would be maybe not very efficient.

The reason for my question was there is a river with a steady flow so i was thinking if it was possible to erect a wheel on the bank.

The river would in no way be flowing fast enough to turn a wheel as a top supply does so i was just seeing if it is a viable idea or a waste of time and looking for info.

Saying that in many European countries in the old days they used river bottom powered wheels to mill flour from wheat all day long so you never know.

I dont think pumping water to your roof would be a good idea because surely you would use more energy to pump than you could produce but i stand to be corrected.

[Wombat]

G'Day Paddy,

Here's a few links you might find of interest, if you haven't already seen them.

http://www.homepower.com/files/hp65-36.pdf

http://www.stewardwood.org/resources/DIYhydro.htm

http://www.motherearthnews.com/Alternat ... Plant.aspx

http://www.ecoinnovation.co.nz/pdf/energywise_mag.pdf

Nev

[Muddypause]

I missed out an h

I figured that might be the case after I'd posted. Do you have a useful equation for working out the output of a waterwheel, or are you just basing it on the height the water falls through?

This wheel was spinning like billio it had to be seen to be believed.
I have no idea how much electric it could produce.

Unfortunately, high speed of the wheel does not necessarily translate into a high energy output. Even if the wheel is 100% efficient, it's still only 2 gallons a minute, falling through a hight of 8'. Jack can check my calculations, but I reckon that can't possibly produce more than 3.6W, which is enough for a sizeable torch bulb. After conversion into electricity, the reality would probably be less than a small torch bulb.

I dont think pumping water to your roof would be a good idea because surely you would use more energy to pump than you could produce but i stand to be corrected.

Yes, you are quite right in absolute terms, but I think this might be a more efficient way to store energy. Electricity stored in batteries is pretty inefficient and expensive, and the batteries have a limited life. Storing the energy as water in a high tank, before it is converted into electricity, may be more efficient, overall - you could end up being able to make more use of the energy in the same amount of wind.

[paddy]

This wheel was spinning like billio it had to be seen to be believed.
I have no idea how much electric it could produce.

Unfortunately, high speed of the wheel does not necessarily translate into a high energy output. Even if the wheel is 100% efficient, it's still only 2 gallons a minute, falling through a hight of 8'. Jack can check my calculations, but I reckon that can't possibly produce more than 3.6W, which is enough for a sizeable torch bulb. After conversion into electricity, the reality would probably be less than a small torch bulb.

You seem to know a bit about it Stew could you please explain this part.

[Jack]

Gidday

Sorry but I think I have lost all my charts with all the technical stuff on them and was just going by my old memory.

But 3.6w although being bugger all can charge a battery because that would be constant over 24 hours.

And for your river undershot wheel you would really need to take your water out of the river into a canal of some sort then put your wheel in that otherwise the water will just go around it. It wouldn't have to have much head as long as you have a good flow. But to do this sorta thing down here would take thousands of bucks and years of piddling around with resource consents.


But good onya mate for checking out things like this. Keep it up.

[Muddypause]

You seem to know a bit about it Stew could you please explain this part.

Now, there's an invitiation. I can try to explain a bit about my understanding of it. But you may find yourself with the irresistable urge to drift away before you get to the end. I know very little about waterwheels (and, some may point out, not a great deal about physics), so have made a few assumptions:

There is an immutable rule in physics that says you cannot get more energy out of a system than you put into it[1]. I like to think of this as a form of economics; energy is an actual thing, even though we can't see it in literal terms. But we can store it and use it. And like in any other type of economics, you can only expend it if you actually have it to spend. You cannot put 10 biscuits into a tin, and then get 20 out of it. Similarly, you cannot put 10 units of energy into a system and get 20 units out of it - if you put 10 units in, that is all there is to get out again.

Energy can be made to do work which can be expressed in lots of different forms - not only in electricity in wires and batteries, but in water flowing through a hosepipe, and in the turning of a waterwheel. But the amount of work that the waterwheel can do is dependent upon the amount of work that the water can do in turning the wheel in the first place - if there is not much work being done by the water in turning the wheel, then the wheel will, in turn, not be able to do much work. In effect, all we are doing is converting that energy from one form to another. We are not adding to it.

So, OK, we have a big wheel which is turning very fast. Ideally, it will be a well balanced wheel, on bearings that are pretty low friction. This means that it will turn easily. Because it is well balanced, it will start to turn even when a small amount of water is in one of the buckets. The low friction bearings will offer little resistance to this turning, and if we apply no more water, it will still keep turning for a long while. But if we go on adding more and more water, it will go on getting faster, because there is very little to stop it. In terms of physics, this is covered by the rule that says a body will keep on accellerating for as long as we apply a force to it (Newton's second law of dynamics). The only thing that can stop it getting faster and faster is the friction in the bearings, and the resistance of the air around it. The effect of these two resistances will increase as the wheel gets faster, and eventually it will get fast enough for them to exactly oppose the input effort of the water. Given enough time, even a fairly heavy wheel may get up to quite a fast speed.

But if we were to connect a dynamo to it, and generate some electricity, we are adding some more resistance to it, so the wheel must start to slow down, and the resistance of the three opposing forces (friction, air resistance, and the dynamo) must equal the effort that the water is putting in to the wheel. What is interesting to learn about any sort of generator, is that the more work you ask it to do, the harder work it is to turn it. And remember, that the wheel cannot do more work than the water applies to the wheel in the first place.

In reality, a waterwheel is more complicated than this, in energy conservation terms. Not all the water will be able to turn the wheel efficiently; some of it will be spilled, some of it will be tipped out of the bucket before it has travelled from top to bottom. There are other ways that energy is lost beside friction and air resistance. All of this lost energy can only come from the input source (the hosepipe), leaving less than 100% for the dynamo to convert into electricity. And the dynamo itself will not be 100% efficient either (nothing is).

But what we can say, with absolute certainty, is that the output of the wheel cannot exceed the amount of work we apply to it. Since this input is only coming from a single hosepipe, and we know the rate of flow of the water (2 gallons a minute), and we know the height that water is falling as it turns the wheel (8' diameter), we can use some basic formulae to work out a maximum figure that the output cannot exceed. The speed of the free wheel (without the load of the dynamo applied to it) may be impressive to watch, but it doesn't represent the amount of work that we can get out of that wheel.

In this case, 2 gallons a minute is falling through about 8'. It's not doing anything else. 2 gallons weighs 20 lbs, so, as a rate of work, this is equivalent to about 5 ozs falling 8' per second (in metric measure, this multiplies out to a rate of work - power - of about 3.6 W). There is no other effort being applied to the wheel, so we will not be able to get any more work than this out of it.

But enough of the physics. I reckon there is an interesting project in your waterwheel idea. The only real way you are going to see if you can make something viable is to do a bit of experimentation. Maybe make a small version of the wheel, and see how it goes in different parts of the river.

[1] Periodically, someone will claim to have invented a way round this, and that they are getting more energy out of a system than they put in. I've looked at many of them with increasing disgust. They are never able to say where this additional energy is coming from. This is the basis of the perpetual motion machine (there are one or two example of this in some old posts on this forum). They will defend their invention stoutly, some will offer to demonstrate it, and yet, for some reason, we never see any of them in proper applications. Often, the inventor asks for people to 'invest' in the development of their invention, and people always lose their money. I am, of course, an unrepentant Newtonian in my (limited) understanding of physics. Others may choose to put their faith elsewhere.

[Jack]

Gidday

Hey that's an excellent post there Muddy. Interesting you being a fan of old Issac, Newton that is. Me, I'm a fan of old Bert Einstein.

But when I read through how you worked out the 3.6w I figure that may even be an over estimation because the bucket only hold the water till they have decended to the half way point then it starts to spill, even on the best designed wheels.

But Paddy has said he has a river he has access to and if he can get water into a canal he only has the get a few feet fall to run an undershot wheel. With an undershot wheel it uses the total volumn of the water in the canal rather than just the amount that the buckets of an overshot wheel can hold.

[Thomzo]

Hi
This might be of some interest.

http://www.millatsonning.com/

This is a watermill that has been converted into a theatre. They now use their wheel to generate all their electricity. From the sound of it, though, they have a lot more flow than your river, Paddy.

Muddy - thank you so much for your comments on my mini scheme. I know that you can't have a perpetual motion machine but I just wanted to know how efficient it could be. That was a great help.

Cheers
Zoe

[Cheezy]

[quote="Muddypause]
[/quote]I would suggest a separate system for reclaiming the heat from a chimney - the heat exchanger running its own underfloor heating, for example, or its own radiators. But maybe the most efficient thing to do is to redesign the chimney, so that the hot flue gasses are diverted around the areas where the heat is most needed.
[/quote]

Now there's an idea redesigning the chimney. I've had an idea on this, now it seems familiar, so it might have been thought of before..see what you think.

What about building your house on piles, say made out of clay tiles. The walls have hollow channels running all the way up, these could be made also out of say hollow clay tubes.
these effectively make a flue all around the house, so all the walls get warm .. when you set a fire going under the floor the heat is drawn under the floor and up the walls, there can be one escape point which is the final "chimney", at least you've made the most of the hot air and gases.
Obviously the point nearest the fire is going to be the hottest so you could put a large volume of water over it to heat this could be a pre heat of your hot water in a boiler, or even say... a swimming pool hey you call that room for want of a better word a caldarium.

Does seem remarkably familiar, just can't put my finger on it.

[Jack]

Gidday

Now here's a new idea.

Dig a basement and put the fire in it then flue the heat through the floors and up the inside walls.


But nothing under the sun is really new Eh! The romans were doing thast a couple of thousand years ago.

[Wombat]

Gidday

Now here's a new idea.

Dig a basement and put the fire in it then flue the heat through the floors and up the inside walls.


But nothing under the sun is really new Eh! The romans were doing thast a couple of thousand years ago.

You just beat me to it Jack.

Muddy! I must take you to task for your disparagement of the concept of not being able to get more energy out of a system than you get in. Newton did his work long before quantum physics was discovered whcih explains all of this. The reason you never see them being used in real applications is due to the work of one or another of the global conspiracies - masons, CIA, catholic church, petrochemical companies - I am not sure it makes a difference so just pick one.

The above paragraph is the simplified text of a conversation I had with one of the owners (sorry ex-owners) of the company I work for. A very creative individual in some ways - in others a complete nutter!

Nev

[Muddypause]

Muddy! I must take you to task for your disparagement of the concept of not being able to get more energy out of a system than you get in. Newton did his work long before quantum physics was discovered whcih explains all of this. The reason you never see them being used in real applications is due to the work of one or another of the global conspiracies - masons, CIA, catholic church, petrochemical companies - I am not sure it makes a difference so just pick one.

Quite right, Nev. In fact there are a worrying number of black helicopters flying around outside as I write this. Maybe I'd better keep quiet about the dilithium crystal mine I just found.