# What's the most efficient water-based electricity generator mechanism? Water wheel vs. top-down propeller?

#### humptydumptyaac

Joined Nov 3, 2021
24
Hi,

I want to make an electricity generator based on water, which can produce lots of power (enough for a household), but it doesn't occupy a lot of space.

I've learned that a water-wheel based generator would have to be huge to produce 20 kWh, and I was wondering if instead of a water wheel there was a tube/cylinder through which water falls down onto a propeller/blade - would that be a more efficient way of producing electricity when it comes to size?

I saw a youtube video where a guy had such a cylinder/pipe of about 2 meters long, 20 cm in diameter, had a small-ish generator at the bottom from an electric bike or something, and was getting between 300 to 500 watts (he had different models)

I was wondering if you had a large tube, 1 meter in diameter, and 2 meters in height/length, could hold up to 1.5 tonnes of water, and it had a propeller/generator at the bottom, same size as the tube diameter.

Would that generator then use the entire 1.5 tonnes of water falling down to produce 14.7 kWh theoretical maximum?

If not, what would be a better design in terms of getting lots of power output (10-20 kWh) from a small space/area using water and gravity as the driving forces?

Thank you.

#### Ian0

Joined Aug 7, 2020
10,277
Before you go any further, I suggest that you fully acquaint yourself with the difference between energy and power.
kWh = 3.6MJ = a measure of energy
kW = A measure of power

Then look at Archimedes screw generators.

#### BobTPH

Joined Jun 5, 2013
9,301
To add to what Ian has said, a tiny generator could generate 20 KWh. It just might take a year to do so.

Bob

#### Ya’akov

Joined Jan 27, 2019
9,270
What you want is a Pelton Wheel. It is an impulse generator rather than using just the weight of the water. It is much more efficient and can be very small relative to output. It requires a housing but a lot of people make them so there will be plenty of resources online for DIY.

#### crutschow

Joined Mar 14, 2008
34,855
What water flow rate and water pressure do you have available to power the generator?
That will determine how much power you can generate.

#### SamR

Joined Mar 19, 2019
5,106
Folks in Alaska use rolls of black polyethylene tubing anchored in a creek to a downhill centrifugal pump driving its motor as a generator. Very cheap installation cost. The flow in the piping prevents freezing. The trick is hydraulic head to power the motor. Over and undershot water wheels are far less efficient than the horizontal turbines that replaced them. A lot of the waterwheel sites in New England have been modified to co-gen turbines.

#### bassbindevil

Joined Jan 23, 2014
838
Mother Earth News published the "Handbook of Homemade Power" back in 1974, and there's "Cloudburst : a handbook of rural skills & technology" from 1977; they both have good info on small hydro. You can "borrow" both of those at Archive.org.

#### sparky 1

Joined Nov 3, 2018
787
Hydroelectric generators have reached 90% efficiency. Small hydro have different criteria.
The designs that reached the high efficiency are turbine. Usually not called propellers.

#### boostbuck

Joined Oct 5, 2017
573
Selecting most effective design depends on the nature of the water supply - in basic terms does your water flow have a large drop in height or a small (high or low head). This, and the quantity available, will determine the power you can extract and the best way to extract it.

For a high head, hence high pressure, a Pelton Wheel is often the easiest and for low head one of the many forms of turbine.

#### Ramussons

Joined May 3, 2013
1,418
From an engineering point of view, the type of "water wheel", known as a Turbine depends on the Water Head - the height from which the water f,lows into the turbine.

High Head - Pelton Wheel
Medium Head - Francis Turbine
Low Head - Kaplan Turbine.

In your case, as is with most houses, it will be low head - a few feet - Kaplan or its derivatives.

Have a look here:

#### shortbus

Joined Sep 30, 2009
10,049
A Tesla turbine is another one that would/should work for a low head, low flow situation. No blades involved -
https://en.wikipedia.org/wiki/Tesla_turbine A lot of information out there but it is almost all in PDF form but a Google of Tesla turbine and hydroelectric gets results.

#### sparky 1

Joined Nov 3, 2018
787
If you are studying a site a hydro turbine for a particular site, there are advantages and disadvantages
to consider regarding which type will be most efficient. The size and practicality of the project such as maintenance and repair are
involved construction and planning. There is much more involved in developing an excellent plan.

This video gives a basic overview of the three main types of turbines.

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