xxxxx
Hazard to Others
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Registered: 21-5-2004
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windpower on the cheap
i was thinking about how much it might cost to weld some fins on a bicycle wheel and turn a car alternator with a bicycle chain and sprocket to
produce 12 volts to charge a lead acid battery which would be connected to a power inverter to produce 110 or 220 volts and how much power could be
produced if the fins were 26 inches with a band welded around them for strength
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chief
National Hazard
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Any wind-generator cannot produce more elctricity than the wind contains kinetic energy:
E == m/2 * v*v ; mass is 1.5 kg/m^3 ;
So for example a column of air, 1 m^2 of ground-surface, when moving with 5 m/s, will only have some lousy 1.5/2 * 5^2 == 0.75 * 25 == 18.75 Watt (at
100 % efficiency) ; as soon as the windmill gets much bigger you will need a special construction, and maybe legal allowance etc., because of the
dangers of mechanical failure ...
A windmill with 4 or 5 blades, 5 m lenght each, therby covering a circle of 5 m radius, 5^2 * pi == 78.53 m^2 surface, will have 78.52/2 kg * v^2 Watt
of power (to be corrected by the efficiency-factor), so at
==> 10 m/s windspeed it will have 7.8 kW,
==> 15 m/s 17.67 kW etc.
Wind energy is unworthy for the hobbyist ; much easier are other sources, like gasifying biomass and burning the gas in a car-engine, driving a
generator ...
On the other hand: For a big company, having a windmill with 25 m blades, at 15 m/s windspeed it gives already 441.773 kW ! ; thats how it scales ...
Of course all the calculated powers to be corrected for the efficiency of such a windmill ; does anyone know ballpark figures for that ?
[Edited on 7-2-2009 by chief]
[Edited on 7-2-2009 by chief]
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not_important
International Hazard
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Beyond the total energy in the wind, Betz's Law limits the maximum extractable energy to 59% of that total energy.
After that you need to consider that the quality of wind goes down sharply the closer you are to the ground, and as the terrain becomes rougher from
trees, buildings, and so on.
Simple fins aren't very good blades, anymore than they would be as blades on an airplane propeller.
A lot of information at http://www.windpower.org/
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