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Can electricity be produced from running water by the use of dc motors? For example rainwater collected from from the roof of a very tall house say 15m high is directed through a pipe and at it's exit, makes the wheels of a dc motor turn.

  • "Low" hydro dams usually have a fall of 20m or more, and those are rare because not much power is available. Normal or "high" hydro dams are more likely 100m-1000m of fall. So it would need to be a tall house to even count as "low head" :) And you don't have even a small river running through the downpipes. – Móż Nov 24 '15 at 22:07
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If it's a very simple motor then it may be possible just to run it backwards to generate electricity. If it's got electronic controls, probably not.

But is it worth it? Do a quick calculation of the amount of energy available. How much water are you expecting to fall? (roof area x annual rainfall). One cubic metre of water weights 1000 kg.

Height (metres) x mass (kg) x 10 will give you the energy in joules - the total it would be theoretically possible to harvest if you could achieve 100% efficiency.

There are 3.6 million joules in one kWh (one unit of electricity on your bill).

There's just not going to be that much energy to collect.

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    If you live in a climate that gets a meter of rain per year and you have a 100 m2 house, then the roof will collect about 100 m3 of water per year. That's 100,000 kg. 15 m * 100,000 kg * 10nt/kg = 15 million joules. Not quite half a kilowatt hour. – Sherwood Botsford Dec 2 '15 at 19:57

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