Page 215 - Wind Energy Handbook

ESTIMATION OF ENERGY CAPTURE 189

100

P(U )f(U ) 50
i i

0
0 1 2 3 4 5
U
i
Figure 4.18 Energy Capture Curve for Numerical Integration

reliability. A turbine operating at variable speed (constant tip speed ratio) until
maximum power is reached and thence at constant speed, constant power and pitch
control, see Figure 4.19, would capture the maximum possible amount of energy in
a given time.
The annual energy capture would be

5
E ¼ 4:8138 3 10 kWh
which is a 6 percent increase in energy capture compared with the fixed-speed,
stall-regulated machine. Whether or not the increase in captured energy is econom-
ically worthwhile is a matter for debate.
600

400

P (kW)
200

0
0 5 10 15 20 25
U (m/s)
Figure 4.19 Power Curve for Variable Speed Turbine