Page 188 - Fluid Power Engineering

Advanced W ind Resource Assessment 161

1. Transformer losses
2. Transmission losses from generator to grid
3. Turbine and wind farm internal power consumption
Turbineperformance.Thisisadecreaseinenergyproductionbe-

cause of aerodynamic, mechanical, or electrical performance
of the turbine and high wind hysteresis. The first three are
usually lumped into power curve loss. Subcategories are:
1. Power curve loss due to soiling of blades, deterioration
in performance of gearbox, other mechanical components
and the generator
2. High-wind hysteresis. When the 10-min average wind speed
exceeds the cutoff speed, the turbine will shut down. Sub-
sequently, the turbine controller monitors the wind speed
and does not restart as soon as the wind speed is below
the cutoff wind speed. Instead, the controller waits for
the wind speed to drop by a certain amount below the
cutoff before restarting. This loss in energy is high-wind
hysteresis.
3. Windmodeling.Thisaccountsforsourcesoflossesthatwere
not modeled in wind resource assessment like inflow an-
gle, rough terrain, and others.
Environmental. Several environmental factors can cause lower

energy production. Some of the environmental effects may be
accounted for by the preprocessing of wind data and wind
resource assessment software. If these are accounted for, then
the losses are already included in the annual energy produc-
tion estimate, and the losses should not be double counted.
Examples of environmental factors include:
1. Shut down and performance degradation because of icing
2. Extreme weather conditions that are outside the range al-
lowed by manufacturer for operating a turbine. For ex-
ample, turbine manufacturers specify operational range
of temperatures outside which the turbine is shutdown.
Other weather related events that cause shutdown include
cyclones, hurricanes, and tornadoes.
3. Seasonal activity of migratory birds, bats, and other
species. In order to reduce the impact on wildlife, tur-
bine operators deploy methods (including radar) to de-
tect presence of seasonal migratory birds and bats. When
the conditions are detected, the turbines are slowed or
shut down. Sometimes these are voluntary and other
times it is a condition for obtaining an environmental
permit.