windpowerlib.wind_speed.v_wind_hellman¶
-
windpowerlib.wind_speed.
v_wind_hellman
(v_wind, v_wind_height, hub_height, hellman_exp=None, z_0=None)[source]¶ Calculates the wind speed at hub height using the hellman equation.
It is assumed that the wind profile follows a power law. This fuction is carried out when the parameter wind_model of an instance of the
Modelchain
class is ‘hellman’.Parameters: - v_wind (pandas.Series or array) – Wind speed time series.
- v_wind_height (float) – Height for which the parameter v_wind applies.
- hub_height (float) – Hub height of wind turbine.
- hellman_exp (float) – The Hellman exponent, which combines the increase in wind speed due to stability of atmospheric conditions and surface roughness into one constant. Default: 1/7. If roughness length is given hellman_exp = 1 / ln(h_hub/z_0).
- z_0 (float) – Roughness length. Default: None.
Returns: Wind speed at hub height.
Return type: pandas.Series or array
Notes
The following equation is used [1], [2], [3]:
- with:
- v: wind speed, h: height, : Hellman exponent
is the height in which the wind speed is measured and is the hub height of the wind turbine.
For the Hellman exponent many studies use a value of 1/7 for onshore and a value of 1/9 for offshore. The Hellman exponent can also be calulated by the following equation [2], [3]:
- with:
- : roughness length
References
[1] Sharp, E.: “Spatiotemporal disaggregation of GB scenarios depicting increased wind capacity and electrified heat demand in dwellings”. UCL, Energy Institute, 2015, p. 83 [2] (1, 2) Hau, E.: “Windkraftanlagen - Grundlagen, Technik, Einsatz, Wirtschaftlichkeit”. 4. Auflage, Springer-Verlag, 2008, p. 517 [3] (1, 2) Quaschning V.: “Regenerative Energiesysteme”. München, Hanser Verlag, 2011, p. 279