Mini hydro miracle – nonsence!

According to multiple news sources, a Mr Gilmartin from Cumbria has re-invented the water wheel.

Apparently the 60-year-old electrician and inventor, who does not own a television (so what?) and has never lived in a house with electricity (??), has invented a micro hydro power station which can power a house from a stream with only 8 inches of head. This has been reported as some how miraculous and how he has solved a century’s old problem in building a micro hydro (there is nothing new about micro-hydro schemes).

What actually is miraculous is the idea that one can run a house from a stream with only 8 inches of head, it seems he has solved the problem of how to break the laws of physics; this is risible nonsense, by my calculations that is 1.7 cubic meters of water per second for a mere 2kW load (an conservative average UK household load)…….. 1.7 cubic meters of water per second!! That would fill a bath tub twice, every second; quite some stream.

A Danny Miller, in this wiki, comes up with a very similar conclusion:

2000W is 2000 joules/sec. 1 joule is the energy of raising or lowering 0.7376 lbs over 1 ft. So at 100% efficiency, you’d need to move 2212.8 lbs/sec over 8″, 276.6 gal/sec. 16,596 gal/min. Water turbines have had 80%-90% efficiency for over 100 years when used under ideal circumstances. As such it’s notable that while a small, economical, low draw waterwheel may be something new, it cannot possibly produce much more power than turbines have in the past. The 70% specified is a somewhat low performer but operating on such low head may be something new. So let’s take 70% specified in. Then we need 23,709 gpm through the turbine to generate 2KW. That’s a pretty powerful stream @ 8″ of head! This would fill a 50m by 25m by 2m Olympic swimming pool in 27.8 minutes. I have to note that since the speed of water in a natural stream is usually limited to a few feet per sec, the width of the device depicted is perhaps a meter, and the height of the water channel’s cross sectional area must be only a small fraction of the 8″ head then I don’t see how such a volume could flow through a device of the width depicted. I get 89.9 cu meter/min through a 1 meter wide by 2cm high cross section (10% of head) requires 74.8 m/sec flow rate, or 167.3 mph!

So what is going on here, bad science, another Windsave, or just bad reporting?


  1. scruss:

    About a decade ago, the standard UK domestic average demand was 450W. Has it increased to 2kW? It\’s only about 1kW in Canada.

  2. admin:

    I can’t back up my 2kw, it is just an estimate but I’d think it to be about right – are you sure that in Canada is only 1Kw? Still, at 1Kw, or even 1/2 a Kw it is still silly.

  3. Pictsidhe:

    2kW seems high, I use on average 7kWh a day: ~300W, I don’t have a TV either, but do have electric welders… People always seem to overestimate how much power they can get from water, I’ve had several people insist that they can get 5-10x what one of my 15 minute surveys estimates from a stream through their garden, so far, none of them have proven me wrong. Very low head hydro system are tricky to make efficient, if he’s managed 70%, my hat goes off to him, whatever the actual power.

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