Hydroelectricity

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Cyril333
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Hydroelectricity




by Cyril333 » 23/03/19, 23:34

Hello,
I am looking for a house with a little land, I dream of energy autonomy, and I have trouble knowing if a river can help me, hence the following questions, to which my research on the web could not give clear answers:
Let's say I have a stream of 10 l / s debit;
- according to the formula P = pressure x flow I can have at turbine output a theoretical power P = 1 x 0.01 = 0.01 kW = 10 W; That's right ?
- if I channel this flow in an inclined pipe let's say at 30% over 10 m of difference in level, according to the formula P = gxhx flow I can have at the turbine outlet a theoretical power P = 9.8 x 10 x 0.01 = 0.98 kW = 980 W; That's right ? (the pressure drops will be such that it would be much less in reality but whatever, I would first like to understand "how it works")
- according to the law of conservation of the flow, if my pipe of 100 mm of diameter is reduced on the last meter with 25 mm, I always have the same flow but a pressure and a speed greater; it's just ??
If you can enlighten me a little ... :-)
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Re: hydro-electricity




by thibr » 24/03/19, 09:41

did you watch the videos

ou

There are others
there are some achievements and pitfalls / mistakes to avoid
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Re: hydro-electricity




by Cyril333 » 24/03/19, 13:08

Thank you thibr.
Interesting videos, but they do not answer my questions ...
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Re: hydro-electricity




by Bardal » 24/03/19, 13:41

Your reasoning is not completely exact, but chance makes you fall back on your feet; with the only flow, it is impossible to calculate a power, it is necessary to take into account either the speed of the water (and you will have a kinetic energy) or the uneven one, and you will have a potential energy.

With 10 m, the recoverable power is 10x9,81x10, which is actually 980 W, from which you can expect to recover 50% if the installation is well done (which is not so simple).

On the second problem, introducing a throat on a pipe carrying water is to increase the pressure losses, so to reduce the flow; in a pipe of 100 mm, a flow rate of 10 L / s leads to a speed close to 1 m / s, which would lead to a speed 16 times greater in a pipe of 25 mm, ie approximately 15 m / s, which is impossible with a pressure of 1 bar. The flow would be reduced, in important proportions. The pressure it can not increase, it remains 10mhe, 1 bar, at the entrance of the pipe of 25, and would decrease at the exit of pipe. This assembly is totally unsuitable if you want to install a turbine.
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Re: hydro-electricity




by thibr » 24/03/19, 13:45

https://www.connaissancedesenergies.org ... lectricite
a performance factor is missing in your calculation
The power of a hydraulic power plant can be calculated by the following formula (9):

P = Q.ρ.Hgr
with:
P: power (expressed in W);
Q: average flow measured in cubic meters per second;
ρ: density of water, ie 1 000 kg / m3;
H: height of fall in meters;
g: gravity constant, which is close to 9,8 (m / s2);
r: plant efficiency (between 0,6 and 0,9)
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Re: hydro-electricity




by izentrop » 24/03/19, 15:44

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Cyril333
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Re: hydro-electricity




by Cyril333 » 24/03/19, 17:08

Thank you for the link izentrop, but I know this site, it is excellent and full of information but it did not allow me to answer all my questions.

Thank you very much, bardal, I'm starting to see more clearly!
To see it even more clearly, let's say now that I have a tank at the bottom of which is drilled a 100 mm hole from which comes out a pipe of the same diameter which drives a turbine 10 m lower. By neglecting the pressure drops and the height of the tank, my pressure at the bottom should be 2 bars, with a high flow rate. If instead of a 100 pipe I put a 25 mm diameter pipe, the flow rate will be much less. If I keep 100 mm over almost the entire difference in level and gradually reduce the diameter to 25 just before the turbine, thanks to the weight of the "column" of water I will have a greater flow rate than if the entire length of the pipe is in 25 mm, right?
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Re: hydro-electricity




by sicetaitsimple » 24/03/19, 18:05

Cyril333 wrote:To see it even more clearly, let's say now that I have a tank at the bottom of which is drilled a 100 mm hole from which comes out a pipe of the same diameter which drives a turbine 10 m lower. By neglecting the pressure drops and the height of the tank, my pressure at the bottom should be 2 bars, with a high flow rate. If instead of a 100 pipe I put a 25 mm diameter pipe, the flow rate will be much less. If I keep 100 mm over almost the entire difference in level and gradually reduce the diameter to 25 just before the turbine, thanks to the weight of the "column" of water I will have a greater flow rate than if the entire length of the pipe is in 25 mm, right?


Hello,

first of all a small remark, in hydraulics one generally speaks in relative bar, that is to say in bar above atmospheric pressure. In your example, your "pressure at the bottom", at zero flow (turbine inlet valve closed), will therefore be around 1 bar, and not 2, in both cases (100 or 25mm).

If now you open the valve, you will create in both cases a flow and therefore losses, but these will be less important in the case of the pipe of 100mm than in that of the pipe of 25 and therefore your flow will be more important in an 100 pipe.

If you choose a hybrid solution (100m on one part and 25 on the other), you will be in between, but we cannot say that it will be thanks to "the weight of the water column", but rather to "reduced" pressure losses in the part of your pipe in 100mm.
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Re: hydro-electricity




by Bardal » 24/03/19, 18:10

With an altitude difference of 10 m, you will not be able to exceed a pressure of 1 bar (10 m of water level), whatever the solution you choose. It's physically impossible.

In terms of turbine performance, for such small drops, it is very difficult to exceed a yield of 0,5, perhaps 0,6; no need to refer to yields from industrial plants, which involve falls and / or flows much larger than the one you are targeting.
The types of turbines to be used are rather to choose in Kaplan, or Archimedes screw turbines or more recent models (VLH, much more cumbersome and more expensive); but do not deceive yourself, small turbines always have a rather low yield.

If this project materializes, do not skimp on the diameter of the downspout (it's cheap and it works well) and does not put any shrinkage that is not mandatory; very low-pressure turbines work at low pressure, but require the best possible flow; such devices are found on the net ( https://www.made-in-china.com/products- ... rator.html it's Chinese of course).
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Re: hydro-electricity




by Cyril333 » 24/03/19, 19:06

Thanks to all 2!
one more question: is there a system to regulate the flow at the outlet of the pipe, on demand? can a solenoid valve open more or less automatically depending on the electricity demand?
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