Page 185 - Fluid Power Engineering

158 Chapter Eight

and average annual energy production and wake losses for each tur-
bine. Wake loss of 10 to 12% is acceptable; turbines with higher wake
losses are progressively removed from the layout and the layout is
then reoptimized. For instance, consider a first pass wind farm op-
timization of a 120-MW wind farm with 60 turbines (each turbine is
2 MW). Suppose this layout has 10 turbines with wake losses of more
than 10%. In order to reduce the wake losses, the above layout will be
re-optimized by removing the five lowest energy-producing turbines
and setting a constraint of 110 MW. If required, additional reoptimiza-
tions may be performed in order to achieve acceptable wake loss.
As with most real-life modeling problems, at the start of the opti-
mal layout process, not all constraints are available. Even for available
constraints, not all information is available with specificity. The opti-
mal layout is, therefore, executed dozens of times. Optimality of en-
ergy production is important because even small increases (about 1%)
in energy output may lead to additional annual revenue per turbine
of $50,000 to $100,000. 6

Wind Turbine Class Selection
An integral part of wind resources assessment is to determine the
wind turbine class (Table 8-3) that is suitable for the site. This step
involves verifying that the actual site conditions are less severe than
5
the design conditions for the class of turbine. IEC 61400-1 provides
the design conditions. For convenience, the design conditions are split
into two broad categories:

Wind conditions: Extreme wind speed, turbulence, and wake

effects
Other conditions like terrain, soil conditions, and seismic

Wind turbine class must be chosen such that the following condi-
tions are satisfied: 4,5

WTG Class I II III
V ref (m/s) 50 42.5 37.5
A I ref 0.16
B I ref 0.14
C I ref 0.12

Source: From Wind Turbine, Part 1 Design Requirements. International
Electrotechnical Commission, Geneva, 2005. IEC 61400-1 Edition 3.
TABLE 8-3 Wind Turbine Class Definition