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Re: [LUG] OT PIC examples/lessons

 

Tom Potts wrote:

> As for cheap wind generator:
> A bloke called Ken Upton patented and let the patent drop (nice man) for a 
> thing called a conveyor. Imagine a (==) railway track with vertical sails on 
> it. Self powering sushi bar!
>
> Now imagine same as two rotating columns connected  with wire loops top and 
> bottom and simple plastic sails attached between them.

I reckon this is a VAWT by any other name.  It just has two axes rather
than one.  They're not as efficient as HAWTs, but when your power is
all but free, that may not be a big issue.  The best I've seen suggested
for a VAWT is 30% efficiency.

> Small gearing and car 
> alternator for power in one column, attach to two chimneys on roof of house. 
> Should give you a 1kva for ~£300

As long as it doesn't pull the chimneys off your house :)  Could cause
a fair bit of vibration noise, too.

However, the power of the wind passing through an area at right angles
is:

  P = 0.5 . rho . v^3 . A

where rho is the density of dry air in kg/m^3, say 1.225, v is the wind
velocity (m/s) and A is the area (m^2).  If you could build a 10m^2
collector, that gives a required windspeed of around 5.5m/s for 1kW.
Over a house roof, where there's a lot of turbulence, and when you can't
move your collector to face the wind, I think you're going to have
serious trouble achieving anything close to that.  I'd be pleasantly
surprised if you averaged more than a few hundred watts out from a
collector that size.

Placing the whole thing in a field would probably be more sensible, but
then at ground level the wind speed will be slower and as your power
varies with the cube of the wind speed, you really want to maximise
that.

(FWIW, the average wind speed in the very open field in front of my
house over the last three weeks, measured at 4m above ground, has been
2.81m/s.  Estimated average at 7.5m, which I'd guess is reasonably close
to roof-top height for most people, is a shade over 3m/s.)

James

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