Design Wind Power Turbine - Hybrid Anisotropic Materials for Wind Power Turbine Blades - page 30

Z

Wind

Yaw axis

Hub

X

Rotor axis

Yaw system

Y

Blade

Tower

Wind turbine nacelle rotation by yaw system

FIGURE 2.8
Wind.turbine.nacelle.rotation.by.the.yaw.system.

into.the.wind.as.the.wind.direction.changes..This.only.applies.for.wind.tur-
bines. with. a. horizontal. axis. rotor.. The. wind. turbine. is. said. to. have. a. yaw.
error.if.the.rotor.is.not.aligned.to.the.wind..A.yaw.error.implies.that.a.lower.
share.of.the.energy.in.the.wind.will.be.running.through.the.rotor.area..(The.
generated. energy. will. be. proportional. to. the. cosine. of. the. yaw. error). (see.
Figure 2.8). 10

2.7.1 History

When.the.windmills.of.the.eighteenth.century.included.the.feature.of.rotor.
orientation. via. the. rotation. of. the. nacelle,. an. actuation. mechanism. able. to.
provide. that. turning. moment. was. necessary.. Initially,. the. windmills. used.
ropes.or.chains.extending.from.the.nacelle.to.the.ground.in.order.to.allow.
the.rotation.of.the.nacelle.by.means.of.human.or.animal.power.
Another.historical.innovation.was.the.fantail..This.device.was.actually.
an. auxiliary. rotor. equipped. with. plurality. of. blades. and. located. down-
wind. of. the. main. rotor,. behind. the. nacelle. in. a. 90°. (approximately). ori-
entation. to. the. main. rotor. sweep. plane.. In. the. event. of. change. in. wind.
direction,.the.fantail.would.rotate,.thus.transmitting.its.mechanical.power.
through.a.gearbox.(and.via.a.gear-rim-to-pinion.mesh).to.the.tower.of.the.
windmill..The.effect.of.the.aforementioned.transmission.was.the.rotation.
of. the. nacelle. toward. the. direction. of. the. wind,. where. the. fantail. would.
not.face.the.wind,.thus.stop.turning.(i.e.,.the.nacelle.would.stop.at.its.new.
position). 11,12