Environmental Engineering Reference
In-Depth Information
retrofits, and other issues can cause extended periods of downtime that reduce the
lifetime average availability. Some observers have also noted a tendency for turbines
to break down under high wind conditions, which increases the energy loss (e.g., 3%
downtime may actually correspond to a 5% energy loss). An average availability loss
of 2-10% is typically encountered in operation.
16.6.3 Electrical Losses
Losses are experienced in all electrical components of the wind project, including the
padmount transformer, electrical collection system, and substation transformer. These
losses are established in the electrical system design. A loss range of 2-3% is typical.
16.6.4 Turbine Performance
This factor includes the effects of suboptimal turbine control settings (e.g., yaw mis-
alignments, control anemometer calibration errors, and blade pitch inaccuracies or
misalignments), high wind control hysteresis (accounting for the fact that a turbine
which has been shut down because of high winds must wait until the speed drops below
a lower speed threshold before restarting), and high turbulence, shear, or inclined flow
departing from the conditions for which the power curve has been defined. These losses
individually tend to be small, but at sites experiencing unusually high winds, high tur-
bulence, or other extreme conditions, they can be as much as 3% in the aggregate.
In addition, there is evidence that turbines often fall short of their advertised power
curves even in IEC-compliant power curve tests (10). This may justify an additional
2-3% loss.
16.6.5 Environmental Losses
This category includes losses due to the accumulation of ice on the blades, blade
soiling and degradation, shutdowns triggered by very high or very low temperatures
or by lightning, and the difficulty of accessing sites in bad weather to carry out repairs.
These losses may be estimated in some cases based on information collected from the
site, such as temperature records and the frequency of icing observed in the wind data
validation, or from regional records such as lightning frequency maps and snowfall
records. Remote sites that are likely to be inaccessible in bad weather, including
offshore sites, often incur greater than normal losses.
16.6.6 Curtailments
If turbines are spaced closer than 3 rotor diameters from each other, the manufacturer
may impose a curtailment strategy to limit wear and tear caused by wake-induced
turbulence. This typically requires that some turbines (such as every other turbine in
a row) be shut down when the wind is from a certain range of directions and above
a certain speed threshold.
In addition, the utility company or grid operator can impose plant-wide curtailment
as a means to help manage the transmission grid. As wind power's penetration on
utility systems has grown, plant-level curtailments have become more common, and
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