Force required to turn generator turbine

[davidclayton]

Hi all,

Complete newbie here, just doing some very rough research on coming up with ways to save the planet!

Where can I find out what force is required to turn a generator turbine by a liquid? (Hydroelectric generator may be sufficient), and what amount of electricity/power is generated?

I know that all generators require different amounts of force to starting making electricity, but where can I find these statistics? I guess I'm looking for detailed statistics documents on a Hydroelectric generator.

Just to get the research kicked-off, info on one generator (of any size) would do for the moment to get some very rough calculations made up - I don't need a range of generators to compare.

All advice greatly appreciated.

Dave

[feral air]

It's totally variable and there's no simple answer. A dripping facet could power a generator if it was small and efficient enough.

I think you need to work it from the opposite angle. Figure out what you've got to work with first, then find the generator to match. If you've got a pond up on a hill, say, and an oultet pipe some distance down hill...how many gpm comes out and at what pressure?

I'm not a hydro guy and I know just enough about electricty to electrocute myself so..yeah, take that for what it's worth.

[davidclayton]

I get what you are saying about starting the other way around, but in my case I do not have any pond/hill/river in place. I am researching a thoery, so amount of liquid pushing against the turbine in not yet definited.

If I can find out how much force is required, then I can build an equation to see how much liquid is needed and what pressure it needs to be at. I know it seems weird, but it's just the way I'm approaching it at the moment. I don't plan to build the apparatus for the moment, I just want to prove that it could generate electricity.

Does anyone know where can I get the technical details I require on hydro generators?

[feral air]

How much power are you looking to get out of the system? That might give someone something to work with.

If nothing else you could search the hydro section. The few times I've ventured in there it's been interesting reading at least.

[spinningmagnets]

I am a big fan of hydro, but most people don't have water running through their property (I hope to when I retire soon).

The first thing is to have, or make (by building a flume), as much head as possible, then measure the volume of flow. Then the fun begins (be aware I haven't made anything yet, I've just read and recorded other peoples results).

If the head (amount of drop from input to outflow) of your system is only a couple of feet, you can spin a car alternator with a simple Banki turbine to get 12 volts (sadly, low amps)

Or, if you want to make a big water wheel, a Poncelet with curved buckets is a little more efficient than a simple wheel with flat paddles (like a river boat). Having just the bottom of a water wheel in the flow makes it an "undershot". A large diameter will turn slow, a small diameter will turn fast. Also, in order to add adequate torque to a fast spinning small diameter undershot, you may have to make it very wide (depending on the load you put on it).

from two to 10 feet of head, it is popular to have a hipshot/breastshot wheel. This is where the water flow is introduced to the wheel just above the axle. The weight of the water pulling down can be calculated (given adequate flow, of course) to determine how wide the buckets need to be to get enough torque to get the job done.

Above ten feet of head, you have the option of using a high-torque, low RPM "overshot" wheel if you want, but unless you're grinding grain, you may need gears to raise the RPM's if you want to generate electricity.

Water gains about 19 PSI for every 10 feet of head when it is contained in a pipe. From 50 feet to 100 feet, you might be interested in a high RPM "Pelton Wheel". It uses a small volume of water, but a high-pressure jet shoots at "spoons" around its rim that allow the water jet to flow around a curved path to extract as much energy as possible.

As you near 100 feet (or more) you might be able to use a water turbine, which looks like a turbocharger compressor. The flow can be precisely adjusted to give you an exact voltage at a very stable output, for direct use, or for charging a battery pack.

There are sooo many variables...what is your head height, flow rate, and desired work load?

[Capt Slog]

With respect to others who have answered and know a lot more about this than me, I think I understand what he's asking.

I know that all generators require different amounts of force to starting making electricity,  

It doesn't work that way around.  Basically, as the other responders have said, people realise the potential energy they have, and then build/put in a generator to suit.

The potential energy in water is the amount of head (height) you can get the water to drop. Keeping it simple, when it drops it produces kinetic energy and this you can calculate from 1/2 mass x velocity^2 . This will be the most you can get.

But you won't get that due to losses in the system and the generator, and this is where efficiency comes in, and each generator will be different even at different speeds.

  Obviously if you only have a trickle but a big generator you will never overcome the losses and the thing will not turn at all, but in a reasonable flow the amount of power out will be proportional to the power (water flow) in.   Bearing in mind that a generator would be chosen to suit the site, it would be working at its best efficiency.

It would help if you told us more where you are coming from in your research.  I apologise if I'm wrong, but the question sounds like one set in college.  I've no problem with that by the way, it just helps to know.

[davidclayton]

Thanks for the comments all, it is gradually giving me a feel for what info i'll need.

It is not a college project, I just had a sudden ambition to look into this, and have no previous experience, so I'm thought I'd ask some people who are passionate about it!

How about I give an example, so that I can extract some figures?

Let's say the head height is 10 metres and the water flow is 50 litres per second.

Is it possible for me to find out from these figures what the pressure would be at the bottom? (not even sure what to measure it in - PSI, Newtons per square metre, etc).

The above numbers are sufficient for a cross-flow turbine, which will generate 60kw (presumably per hour - it does not say).

Info from here: http://www.irem.it/en/Mhp/MHPset.htm

[Capt Slog]

Where are you getting 60kW from?  If you are looking at the graph with the green and beige segments on it, then you are reading it incorrectly.

Find the point where the 10m and the 15 lps intersect, and then follow the diagonal  up and left to the top scale.  In the case quoted this is around 2.5kW.

Understanding pressure, try this page  

http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html

and follow this route first.... mechanics > fluids > static fluid pressure.

[thefinis]

Try doing a search in the hydro section I tried in a google search under the menu box(upper right hand of page) with this entry " head flow kw " and got enough to give what I think you want if it is for hydro.

If it is just to find what it takes to power a gen then a quick web search of/for conversion tables hp to kw or kw to force should work but the basic one is force/torque x rpms x efficiency x conversion factor = power output. How you want the power to be shown(hp, kw, etc) determines what conversion factor plus if you are working in metric or not.

Multiply the torque by the rpm and divide by 5252 to get Horse Power and multiply HP by 746 to get watts. Remember that these are for a perfect conversion so always add in an efficiency factor

Good luck and keep searching and reading

Finis

[spinningmagnets]

10 meters of head is 32 feet, if the feed pipe is inclined 45 degrees on a hillside, the pipe will be about 44 feet long from the feed pond to the turbine (but still 10M/32' of drop).

The PSI at the bottom will be about 60 psi.

50L/sec is 3,000L/Min, which is about 792 Gallons/min.

Whether you are buying an off-the-shelf generator, or building one because you have an uncommon voltage/RPM desire, the higher RPM's are very desireable. Doubling the RPM's can quadruple the Watts.

The higher the PSI, the smaller the diameter of the turbine can be in order to handle load "X".

792 GPM means you have the option of using a large diameter turbine that can produce a lot of torque for a high load, but at 60 PSI, you will have to specify a lower RPM generator thats wound to give your target volts.

I think the biggest benefit of hydro (for those who are able to have it) is that you can adjust the flow to get a specific RPM (if the turbine is properly sized) and 120/240 volts AC can travel very far without much degradation, and when it reaches your home, you can run it through a transformer and rectifiers to get the low voltage DC neccessary to charge a battery pack, or even to use the 120 VAC directly.

Low force limits you to low volts/low watts. Higher head and higher flow gives you many options.

[spinningmagnets]

I owe everyone an apology! I don't know where I got the 19 PSI per 10 ft from.

I double checked at a diving website and they state 60 PSI @ 100 ft (6 PSI/10 ft)

also 47 psi + atmospheric (normally 14.7 PSI @ sea level), for calculating dives in high altitude mountain lakes.

The next time I feel the urge to post, I'll just drink some red wine (for my heart) until the feeling goes away. (If you listen carefully, you can almost hear the cheering)

"When I was a boy of fourteen, my father was so ignorant I could hardly stand to have the old man around. But when I got to be twenty-one, I was astonished by how much he'd learned in seven years." -Mark Twain