The Renegade

Well it seems Richard has me hooked on blogging. Let's just hope the blogger servers don't die on me!

The physics class has embarked on a windmill project, and I became interested and decided to join in the fun. This is my renegade wind power team blog. The team consists of me, whatever, it's still a team!

Info thus far...

To get power from the wind: Connect some windmill blades to an alternator and point them into the wind. Ok, winner for minimum words right there. In reality, the wind turbine turns the rotor inside the alternator which generates alternating current in the armature of the alternator which is located in the stator (including some terms at the end of this). The AC power generated by the alternator gets piped into a rectifier and then into a battery for storage.

The alternator is the tricky part... It requires coils of magnet wire in the stator, and magnets in the rotor. On many the magnets in the rotor are electromagnets (generally coils of wire that are electrified to produce a magnetic field). Permanent magnets make things much more simple, and also more expensive, whatever.

The magnet wire is assembled in coils that alternate wrap direction (not sure on this) and the magnets on the rotor are assembled with the poles from the center to the outside in a radial manner, except that every other one is turned. So magnet A has the north side facing the armature, and magnet B has the south side, and magnet C has the north side, etc.

I'm going to need to acquire magnet wire (Nick will give me some, hopefully), magnets (preferably neodymium magnets), some sort of axle on which to attach the blades and alternator, the windmill blades themselves, and last but not least a tower. I'm going to need a rectifier too, but those cost like $1 at radio shack... which basically means I have to go to radio shack. Sounds like fun to me!

Some equations I ran across:

*total power in wind*

P = rho * A * V^3
where
rho = air density (kg/m^3)
A = swept area (by the windmill blades) (m^2)
V = wind speed (m/s)

*more practical calculation of power derived from wind*

P = rho * A * V^3 * Cp * Ng * Nb
where (these guys are all efficiency, so percentages are used (decimal))
Cp = coefficient of performance (.59 is the Betz limit, generally .1 to .3)
Ng = generator efficiency (alternator in my case)
Nb = gearing and bearing efficiency

What this all boils down to:
Wind speed doubled = 8x the power
Blade radius doubled = 4x the power

Also
746 Watts = 1HP
mph/2.24 = m/s

Some useful links:

http://otherpower.com/otherpower_wind.html (general info)
http://www.awea.org/faq/windpower.html (calculations)
http://www.reuk.co.uk/Betz-Limit.htm (Betz limit info)
http://www.fieldlines.com/ (a forum for assorted alt-power sources)

Some wiki:

http://en.wikipedia.org/wiki/Rectifier
http://en.wikipedia.org/wiki/Alternator


==Terms==

Alternator - produces AC power from mechanical power.
Rotor - the part of the alternator that rotates.
Stator - the part of the alternator that is static.
Armature - the part of the alternator that generates the power (consisting of coiled magnet wire, generally).
Rectifier - changes AC power into DC power through the use of diodes.
Diode - lets current through in only one direction.