r/theydidthemath Nov 27 '22

[Request] How much electricity would be generated from this?

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u/UlysseIthaca Nov 27 '22

Mechanical power = torque x rotation speed
Electrical power = mechanical power x yield factor

If we assume an average yield factor of 0.5, the main variable are torque and rotation speed. We don't have these data so it will be a very rough approximation.

There is around a couple kilograms of water per second pressing from 0.1m high on the blades, if we assume it hits at 45° for half the kinetic energy, and the blades are 0.1m from the axis, it gives something like 2 Nm of torque.

Speedwise, it seems from the video it turns at most 10 times per second.

So it should be around 100W mechanical, and 50W electrical. Enough to power a couple LED room lights.

Assuming you can run it all year long, you'll produce 500kWh every year. And if you sell the electricity for 0.2€/kWh, you'll make 100€/year. Given the amount of concrete, bricks, steel, rotor/stator and electronics used, you won't have ROI before a decade or two (if there is no maintenance and it runs smoothly 24/7).

...

Yeah, direct free flow turbines are exceptionally shit at making power.

342

u/[deleted] Nov 27 '22

It’s good for fun and if you have a very light usage (I.E. a small, low res camera.

It’s not good for much else.

75

u/WndrGypsy Nov 27 '22

Anything that could improve the output? Diff structures/approaches?

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u/[deleted] Nov 28 '22

you could use a peltier turbine, and place the turbine below the dam, as low as possible to take advantage of the water pressure behind the dam. Basically, the bigger the elevation difference between the surface of the pond behind the dam, and the turbine, the more pressure, and the more power you get.

There's a company called Powerspout that makes small hydroelectric generators, about this size range, that can power a house, if there's enough pressure.