Advanced Wind Turbine Program Next Generation Turbine ... - NREL

Case b is about twice that of Case a. It may not be worth engineering a system to cope with the
large motions of Case b when most of the benefit can be provided with the Case a system. This
view is reinforced when the effect of nodding rotations on tower clearance is considered. The
results show that the Case a configurations are marginal for tower clearance (probably inadequate
for lifetime extreme tip deflections), and that the Case b hinge is unrealistic for an upwind
machine configuration.
Overall, there is some cumulative benefit in having a soft tower, soft blade, and soft tower top
connection but it is much less than simply additive, and it seems necessary to have a soft blade to
prevent increase of blade loading because of tower head flexibility. The benefits from reductions
in tower top tilt and yaw fatigue are questionable, as the only wind system component driven by
these components of fatigue is the bedplate-tower interface, which will increase in cost and complexity
anyway, in order to introduce the compliance. A brief engineering analysis of the mechanical
requirements for implementing the tower top compliance was conducted. The conclusions
show the Case a system added to the baseline 750i turbine featuring a soft-soft tower and a
softer rotor and would cost approximately the same as the yaw drive system, which is the only
clear cost savings implemented from yaw or tilt compliance. There is no benefit to blades, and
unless a substantial benefit to tower costs, nacelle structure, or drive train can be established, it
will be hard to justify the costs.
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