Wind Turbine Generators (WTG)

WTG datasets contain power curves and operating characteristics for wind turbine generators.

Data Structure

WTG objects are xarray.Dataset with the following schema:

Dimensions:  (mode, wind_speed)
Variables:
    power_output                   (mode, wind_speed)  - power curve (W)
    thrust_coefficient             (mode, wind_speed)  - CT curve
    air_density                    (mode)              - reference density (kg/m³)
    stationary_thrust_coefficient  (mode)              - stationary CT
    wind_speed_cutin               (mode)              - cut-in speed (m/s)
    wind_speed_cutout              (mode)              - cut-out speed (m/s)
    rated_power                    (mode)              - rated power (W)
    name                                               - turbine name (string)
    rotor_diameter                                     - rotor diameter (m)
    hub_height                                         - hub height (m)
    regulation_type                                    - 1=stall, 2=pitch

Operating Modes

The mode dimension supports multiple operating conditions:

• Different air density conditions (sea level vs high altitude)

• Noise-reduced operation modes

• De-rated operation

Each mode has its own air density, cut-in/cut-out speeds, and rated power.

I/O

Reading:

windkit.read_wtg() reads WTG files:

Format	Read	Description
.wtg	yes	WAsP Wind Turbine Generator format

# Get tutorial data path
tutorial_path = wk.get_tutorial_data("serra_santa_luzia")

wtg = wk.read_wtg(tutorial_path / "Bonus1MW.wtg")
wtg

<xarray.Dataset> Size: 704B
Dimensions:                        (mode: 1, wind_speed: 22)
Coordinates:
  * mode                           (mode) int64 8B 0
  * wind_speed                     (wind_speed) float64 176B 4.0 5.0 ... 25.0
Data variables:
    power_output                   (mode, wind_speed) float64 176B 2.41e+04 ....
    thrust_coefficient             (mode, wind_speed) float64 176B 0.915 ... ...
    air_density                    (mode) float64 8B 1.225
    stationary_thrust_coefficient  (mode) float64 8B 0.161
    wind_speed_cutin               (mode) float64 8B 4.0
    wind_speed_cutout              (mode) float64 8B 25.0
    rated_power                    (mode) float64 8B 1e+06
    name                           <U10 40B 'Bonus 1 MW'
    manufacturer                   <U16 64B 'Bonus Energy A/S'
    rotor_diameter                 float64 8B 54.2
    hub_height                     float64 8B 50.0
    regulation_type                int64 8B 2
Attributes:
    Conventions:      CF-1.8
    Package name:     windkit
    Package version:  2.0.1
    Creation date:    2026-01-29T09:30:28+00:00
    author:           Default User
    author_email:     default_email@example.com
    institution:      Default Institution

xarray.Dataset

• Dimensions:
  • mode: 1
  • wind_speed: 22
• Coordinates: (2)
  • mode
    (mode)
    int64
    0

    array([0])

  • wind_speed
    (wind_speed)
    float64
    4.0 5.0 6.0 7.0 ... 23.0 24.0 25.0

    description :

    Speed is the magnitude of velocity. Wind is defined as a two-dimensional (horizontal) air velocity vector, with no vertical component. (Vertical motion in the atmosphere has the standard name upward_air_velocity.) The wind speed is the magnitude of the wind velocity.

    long_name :

    Horizontal Wind Speed

    standard_name :

    wind_speed

    units :

    m s-1

    array([ 4.,  5.,  6.,  7.,  8.,  9., 10., 11., 12., 13., 14., 15., 16., 17.,
           18., 19., 20., 21., 22., 23., 24., 25.])

• Data variables: (12)
  • power_output
    (mode, wind_speed)
    float64
    2.41e+04 6.93e+04 ... 1e+06 1e+06

    description :

    Electrical energy produced by the wind turbine

    long_name :

    Power Output

    standard_name :

    power_output

    units :

    W

    array([[  24100.,   69300.,  130000.,  219100.,  333500.,  463100.,
             598100.,  730000.,  846500.,  928800.,  972600.,  990800.,
             997200.,  999200.,  999800.,  999900., 1000000., 1000000.,
            1000000., 1000000., 1000000., 1000000.]])

  • thrust_coefficient
    (mode, wind_speed)
    float64
    0.915 0.915 0.836 ... 0.169 0.161

    description :

    The thrust coefficient is a non-dimensional number that describes the force exerted by the turbine in the axial direction to the incoming momentum of the flow

    long_name :

    Thrust Coefficient

    standard_name :

    thrust_coefficient

    units :

    `1`

    array([[0.915, 0.915, 0.836, 0.956, 0.864, 0.817, 0.703, 0.637, 0.532,
            0.467, 0.427, 0.372, 0.325, 0.289, 0.262, 0.239, 0.22 , 0.204,
            0.191, 0.179, 0.169, 0.161]])

  • air_density
    (mode)
    float64
    1.225

    description :

    The density of air or atmospheric density, is the mass per unit volume of Earth's atmosphere.

    long_name :

    Air Density

    standard_name :

    air_density

    units :

    kg m-3

    array([1.225])

  • stationary_thrust_coefficient
    (mode)
    float64
    0.161

    description :

    The wind turbine thrust coefficient with the rotor at rest

    long_name :

    Stationary Thrust Cofficient

    standard_name :

    stationary_thrust_coefficient

    units :

    `1`

    array([0.161])

  • wind_speed_cutin
    (mode)
    float64
    4.0

    description :

    The cut-in speed is when the blades start rotating and generating power

    long_name :

    Wind Speed Cut-in

    standard_name :

    wind_speed_cutin

    units :

    m s-1

    array([4.])

  • wind_speed_cutout
    (mode)
    float64
    25.0

    description :

    The wind speed cut-out speed is the maximum wind speed that a wind turbine can handle before it shuts down to prevent damage

    long_name :

    Wind Speed Cut-out

    standard_name :

    wind_speed_cutout

    units :

    m s-1

    array([25.])

  • rated_power
    (mode)
    float64
    1e+06

    description :

    Maximum amount of power by which the wind turbine can produce

    long_name :

    Rated Power

    standard_name :

    rated_power

    units :

    W

    array([1000000.])

  • name
    ()
    <U10
    'Bonus 1 MW'

    array('Bonus 1 MW', dtype='<U10')

  • manufacturer
    ()
    <U16
    'Bonus Energy A/S'

    array('Bonus Energy A/S', dtype='<U16')

  • rotor_diameter
    ()
    float64
    54.2

    description :

    Diameter spanned by the wind turbine rotor blades

    long_name :

    Rotor Diameter

    standard_name :

    rotor_diameter

    units :

    m

    array(54.2)

  • hub_height
    ()
    float64
    50.0

    description :

    Distance from the ground to the middle of the wind turbine's rotor

    long_name :

    Hub Height

    standard_name :

    hub_height

    units :

    m

    array(50.)

  • regulation_type
    ()
    int64
    2

    description :

    Regulation type used by the wind turbine.

    long_name :

    Regulation Type stall=1; pitch=2;

    units :

    array(2)

• Attributes: (7)

  Conventions :

  CF-1.8

  Package name :

  windkit

  Package version :

  2.0.1

  Creation date :

  2026-01-29T09:30:28+00:00

  author :

  Default User

  author_email :

  default_email@example.com

  institution :

  Default Institution

Creating Manually

WTG datasets can be created programmatically:

power_output = np.array([[0, 25, 82, 150, 250, 400, 600, 800, 950, 1000, 1000, 1000]])
thrust_coefficient = np.array([[0.9, 0.9, 0.85, 0.8, 0.75, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, 0.15]])

wtg_manual = xr.Dataset(
    data_vars=dict(
        power_output=(["mode", "wind_speed"], power_output * 1000),  # kW to W
        thrust_coefficient=(["mode", "wind_speed"], thrust_coefficient),
        air_density=(["mode"], [1.225]),
        stationary_thrust_coefficient=(["mode"], [0.161]),
        wind_speed_cutin=(["mode"], [4.0]),
        wind_speed_cutout=(["mode"], [25.0]),
        rated_power=(["mode"], [1e6]),
        name="My 1MW Turbine",
        rotor_diameter=54.0,
        hub_height=50.0,
        regulation_type=2,  # pitch
    ),
    coords=dict(
        wind_speed=np.linspace(4.0, 25.0, 12),
        mode=[0],
    ),
)
wtg_manual

<xarray.Dataset> Size: 416B
Dimensions:                        (mode: 1, wind_speed: 12)
Coordinates:
  * mode                           (mode) int64 8B 0
  * wind_speed                     (wind_speed) float64 96B 4.0 5.909 ... 25.0
Data variables:
    power_output                   (mode, wind_speed) int64 96B 0 ... 1000000
    thrust_coefficient             (mode, wind_speed) float64 96B 0.9 ... 0.15
    air_density                    (mode) float64 8B 1.225
    stationary_thrust_coefficient  (mode) float64 8B 0.161
    wind_speed_cutin               (mode) float64 8B 4.0
    wind_speed_cutout              (mode) float64 8B 25.0
    rated_power                    (mode) float64 8B 1e+06
    name                           <U14 56B 'My 1MW Turbine'
    rotor_diameter                 float64 8B 54.0
    hub_height                     float64 8B 50.0
    regulation_type                int64 8B 2

xarray.Dataset

• Dimensions:
  • mode: 1
  • wind_speed: 12
• Coordinates: (2)
  • mode
    (mode)
    int64
    0

    array([0])

  • wind_speed
    (wind_speed)
    float64
    4.0 5.909 7.818 ... 23.09 25.0

    array([ 4.      ,  5.909091,  7.818182,  9.727273, 11.636364, 13.545455,
           15.454545, 17.363636, 19.272727, 21.181818, 23.090909, 25.      ])

• Data variables: (11)
  • power_output
    (mode, wind_speed)
    int64
    0 25000 82000 ... 1000000 1000000

    array([[      0,   25000,   82000,  150000,  250000,  400000,  600000,
             800000,  950000, 1000000, 1000000, 1000000]])

  • thrust_coefficient
    (mode, wind_speed)
    float64
    0.9 0.9 0.85 0.8 ... 0.3 0.2 0.15

    array([[0.9 , 0.9 , 0.85, 0.8 , 0.75, 0.7 , 0.6 , 0.5 , 0.4 , 0.3 , 0.2 ,
            0.15]])

  • air_density
    (mode)
    float64
    1.225

    array([1.225])

  • stationary_thrust_coefficient
    (mode)
    float64
    0.161

    array([0.161])

  • wind_speed_cutin
    (mode)
    float64
    4.0

    array([4.])

  • wind_speed_cutout
    (mode)
    float64
    25.0

    array([25.])

  • rated_power
    (mode)
    float64
    1e+06

    array([1000000.])

  • name
    ()
    <U14
    'My 1MW Turbine'

    array('My 1MW Turbine', dtype='<U14')

  • rotor_diameter
    ()
    float64
    54.0

    array(54.)

  • hub_height
    ()
    float64
    50.0

    array(50.)

  • regulation_type
    ()
    int64
    2

    array(2)

WTG Functions

Power and coefficients:

• windkit.wtg_power() - Calculate power for given wind speeds

• windkit.wtg_cp() - Calculate power coefficient

• windkit.wtg_ct() - Calculate thrust coefficient

# Calculate power at specific wind speeds
wind_speeds = np.array([6.0, 8.0, 10.0, 12.0])
power = wk.wtg_power(wtg, wind_speeds)
print(f"Power at {wind_speeds} m/s: {power.values / 1000} kW")

Power at [ 6.  8. 10. 12.] m/s: [[130.  333.5 598.1 846.5]] kW

Regulation type:

• windkit.RegulationType - Enum: 1=stall, 2=pitch

• windkit.estimate_regulation_type() - Estimate from power curve

reg_type = wtg.regulation_type.values
print(f"Regulation type: {reg_type} ({'pitch' if reg_type == 2 else 'stall'})")

Regulation type: 2 (pitch)

Validation

• windkit.validate_wtg() - Validate WTG dataset structure

• windkit.is_wtg() - Check if dataset is valid WTG

is_valid = wk.is_wtg(wtg)
print(f"Is valid WTG dataset: {is_valid}")

Is valid WTG dataset: True

Usage with Wind Turbines

WTG datasets are mapped to turbine positions via the wtg_key:

# Load WTG from tutorial data
wtg1 = wk.read_wtg(tutorial_path / "Bonus1MW.wtg")

# Create turbines with wtg_keys
turbines = wk.create_wind_turbines_from_arrays(
    west_east=[0, 500, 1000],
    south_north=[0, 0, 0],
    height=[50, 50, 50],
    crs="EPSG:32632",
    wtg_keys=["bonus", "bonus", "bonus"],
)

# WTG dictionary for AEP calculation
wtgs = {"bonus": wtg1}
print(f"WTG dictionary keys: {list(wtgs.keys())}")

# Verify all turbine wtg_keys exist in dictionary
wk.check_wtg_keys(turbines, wtgs)
print("All WTG keys validated successfully!")

WTG dictionary keys: ['bonus']
All WTG keys validated successfully!