In nPro, the wind speed at hub height of the wind turbine is calculated in a first step. For this purpose, the power law according to Hellmann is used: $$w_\mathrm{hub} = w_\mathrm{ref} \left(\frac{h_\mathrm{hub}}{h_\mathrm{ref}}\right)^a$$ Here, $w_\mathrm{hub}$ is the wind speed at hub height, $w_\mathrm{ref}$ the measured wind speed, $h_\mathrm{hub}$ the hub height, $h_\mathrm{ref}$ the reference height at which the wind speed measurement took place, and $a$ the Hellmann coefficient. In a second step, the generation power of the turbine is calculated with power curves from manufacturer data. In Table 1 the power curve of the wind turbine Enercon E141 is illustrated.

The nPro tool calculates for different wind turbine models the power generation profile with hourly resolution.

Figure 1: Annual energy yield of an ENERCON E115-EP3 turbine for the two size classes 4.2 MW and 2.99 MW.

Table 1: Power curve of the wind turbine Enercon E141.

Wind speed at hub height	Power generation
0 m/s	0 kW
1 m/s	0 kW
2 m/s	22 kW
3 m/s	104 kW
4 m/s	260 kW
5 m/s	523 kW
6 m/s	920 kW
7 m/s	1471 kW
8 m/s	2151 kW
9 m/s	2867 kW
10 m/s	3481 kW
11 m/s	3903 kW
12 m/s	4119 kW
13 m/s	4196 kW
14 m/s	4200 kW
...	4200 kW
25 m/s	4200 kW
25.1 m/s	0 kW