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10.4 Adaptation to a Wind Regime
The following wind speeds may be determined.
• Cut-in speed. This is the wind speed under which the wind turbine is not operated, because the energy yield is too low to justify wearing the system. The value
typically amounts to 4–5 m/s. The example takes 5 m/s.
• Rated speed. The power is limited to the value corresponding to this wind speed.
From this speed onwards, the generator produces at its maximum power, called
rated power, and the wind energy flux is not completely used. The rated speed is
determined by balancing the yield against the cost. In Fig. 10.14, this velocity is
13 m/s. A dashed line indicates the energy captured above the rated wind speed.
• Cut-out speed. This is the wind speed above which the turbine is stopped in order
to avoid damage. Together with wind speed, wind unsteadiness increases. In the
example, the cut-out speed is 25/s. The available energy above this speed is very
small.
Figure 10.15 shows the variation of the power coefficient and the power of a 4.5 MW
turbine as an example. Cut-in speed is 3 m/s and rated wind speed is 13 m/s. Within
the 3–6 m/s wind speed range, the turbine turns at the minimum generator speed
(− 30 %). Pitch changes with wind velocity. The speed ratio is optimal within the
6 –10.5 m/s velocity range. From 10.5 m/s onwards, the generator turns at maximum speed (+ 30 %) and the C P value decreases with increasing wind velocity.
From 13 m/s wind speed onwards, power is limited to 4500 kW.
The wind speed histogram (Fig. 10.14) demonstrates that the wind turbine is
stopped during about 30 % of time; it turns below rated wind speed during 60 % of
time and above rated wind speed during 10 % of time. The yearly yield corresponds
to about 30 % of the yield of a wind turbine producing at rated power during the
whole year. This ratio is called capacity factor. It can also be expressed in hours.
A capacity factor around 3000 h is typical, somewhat less at inland locations and
Fig. 10.15 Power coefficient and power of E112 (Enercon)
10.4 Adaptation to a Wind Regime
The following wind speeds may be determined.
• Cut-in speed. This is the wind speed under which the wind turbine is not operated, because the energy yield is too low to justify wearing the system. The value
typically amounts to 4–5 m/s. The example takes 5 m/s.
• Rated speed. The power is limited to the value corresponding to this wind speed.
From this speed onwards, the generator produces at its maximum power, called
rated power, and the wind energy flux is not completely used. The rated speed is
determined by balancing the yield against the cost. In Fig. 10.14, this velocity is
13 m/s. A dashed line indicates the energy captured above the rated wind speed.
• Cut-out speed. This is the wind speed above which the turbine is stopped in order
to avoid damage. Together with wind speed, wind unsteadiness increases. In the
example, the cut-out speed is 25/s. The available energy above this speed is very
small.
Figure 10.15 shows the variation of the power coefficient and the power of a 4.5 MW
turbine as an example. Cut-in speed is 3 m/s and rated wind speed is 13 m/s. Within
the 3–6 m/s wind speed range, the turbine turns at the minimum generator speed
(− 30 %). Pitch changes with wind velocity. The speed ratio is optimal within the
6 –10.5 m/s velocity range. From 10.5 m/s onwards, the generator turns at maximum speed (+ 30 %) and the C P value decreases with increasing wind velocity.
From 13 m/s wind speed onwards, power is limited to 4500 kW.
The wind speed histogram (Fig. 10.14) demonstrates that the wind turbine is
stopped during about 30 % of time; it turns below rated wind speed during 60 % of
time and above rated wind speed during 10 % of time. The yearly yield corresponds
to about 30 % of the yield of a wind turbine producing at rated power during the
whole year. This ratio is called capacity factor. It can also be expressed in hours.
A capacity factor around 3000 h is typical, somewhat less at inland locations and
Fig. 10.15 Power coefficient and power of E112 (Enercon)