Small turbine dam - Vertical drop vs. large dam

Conundrum
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Small turbine dam - Vertical drop vs. large dam

Postby Conundrum » Sun Jun 14, 2009 10:16 pm

I was recently asked a question that needed to be answered here. The question was, if I have a small dam in a stream, is it more important to have a large quantity of water as a 'head' or is it more important to have the water drop a greater distance to a turbine?

The best way to answer is a little bit of both. It is important to have a quantity of water available as a head to maintain adequate flow, the drop is the most important component.

If a dam has a water height of 10 feet, and a horizontal dimension of 10' x 10', it has the water pressure as a dam that is 1' x 1' and 10' deep. Pressure is derived from the vertical force exerted by the weight that is directly above it.

For a more in-depth explanation of why, try this link:
http://scubageek.com/articles/wwwparad.html

I hope that clears things up. When designing your dam, think about what is required in terms of how far you can cause the water to move vertically. That way, you may not need much of a dam at all.



Hapts
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Re: Small turbine dam - Vertical drop vs. large dam

Postby Hapts » Sun Apr 18, 2010 1:55 pm

In most small pico-hydro dams, you do not dam the river. What you do is simply run a pipe in brook as far back as you need to get the proper head you need. Then with a simple reducer install a weir on the end of the pipe. I don't think the govn't would be real happy with damming the river.

Conundrum
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Re: Small turbine dam - Vertical drop vs. large dam

Postby Conundrum » Mon Apr 19, 2010 10:00 am

By definition a weir is also known as a lowhead dam. Actually there are a few reasons to dam a stream. Obviously not a river, or it wouldn't be micro or pico hydro, that is why I specified a stream. First would be sediment. if you can provide a place for any heavy particles to gather, it is better than allowing them to flow through your turbine and possibly clog the jet(s). Second (depending on the season) would be to regulate flow. Thats more into dam design, and really not where I was headed with this conversation.

As for running a pipe 'back' to get more head, by definition head is the vertical drop, not the horizontal travel. Without a vertical component, the gain from horizontal travel is negligible.

Hapts
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Re: Small turbine dam - Vertical drop vs. large dam

Postby Hapts » Sun Apr 25, 2010 8:18 am

Yes, horizontal distance does not help, it is more of a problem with friction in which you lose power. I've seen where they run the pipe back the stream to get as much head as possible. You physically do not need water falling, the elevation of the pipe back the stream to where you generator is placed in the stream is now your head. When they place the weir it is not on the bottom of the brook, and they have protection from debris, but this might not stop sediment. the reason for also laying the pipe in the stream is that it hides the pipe. But from reading you need a fairly good size of pipe to reduce friction.
Have you ever seen this HEB wheel, i guess they are still producing these wheels, i think it is a pretty clever wheel! I tried to buy one but i think i will make my own.

http://www.hydro-electric-barrel.com/

Conundrum
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Re: Small turbine dam - Vertical drop vs. large dam

Postby Conundrum » Sun Apr 25, 2010 3:26 pm

Cool ideal. I have seen one done with an exposed chain to turn a generator. I would prefer to use a plastic detergent barrel. If I had some running water I would probably play with that idea.

Beardo McShorts
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Re: Small turbine dam - Vertical drop vs. large dam

Postby Beardo McShorts » Thu May 17, 2012 7:39 pm

An exposed chain seems like a bad thing... Especially when it comes to running water....
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