Variable
blade pitch, which gives the turbine blades the optimum angle
of attack. Allowing the angle of attack to be remotely adjusted
gives greater control, so the turbine collects the maximum
amount of wind energy for the time of day and season.
The
tall tower base allows access to stronger wind in sites with
wind shear. In some wind shear sites, every ten meters up,
the wind speed can increase by 20% and the power output by
34%.
High
efficiency, since the blades always move perpendicularly to
the wind, receiving power through the whole rotation. In contrast,
all vertical axis wind turbines, and most proposed airborne
wind turbine designs, involve various types of reciprocating
actions, requiring airfoil surfaces to backtrack against the
wind for part of the cycle. Backtracking against the wind leads
to inherently lower efficiency.
The
tall towers and blades up to 90 meters long are difficult to
transport. Transportation can reach 20% of equipment costs.
Tall
HAWTs are difficult to install, needing very tall and expensive
cranes and skilled operators.
Massive
tower construction is required to support the heavy blades,
gearbox, and generator.
Reflections
from tall HAWTs may affect side lobes of radar installations
creating signal clutter, although filtering can suppress it.
Their
height makes them obtrusively visible across large areas, disrupting
the appearance of the landscape and sometimes creating local
opposition.
Downwind
variants suffer from fatigue and structural failure caused
by turbulence when a blade passes through the tower's wind
shadow (for this reason, the majority of HAWTs use an upwind
design, with the rotor facing the wind in front of the tower).
HAWTs
require an additional yaw control mechanism to turn the blades
toward the wind.
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