Revert removal of parameter in docstring (new issue)

Author: uvchik

windpowerlib/wind_farm.py

@@ -307,6 +307,10 @@ def assign_power_curve(self, wake_losses_model='wind_farm_efficiency',
             Turbulence intensity at hub height of the wind farm for power curve
             smoothing with 'turbulence_intensity' method. Can be calculated
             from `roughness_length` instead. Default: None.
+        roughness_length : float (optional)
+            Roughness length. If `standard_deviation_method` is
+            'turbulence_intensity' and `turbulence_intensity` is not given
+            the turbulence intensity is calculated via the roughness length.
 
         Returns
         -------

windpowerlib/wind_turbine_cluster.py

@@ -178,6 +178,10 @@ def assign_power_curve(self, wake_losses_model='wind_farm_efficiency',
             wind turbine cluster for power curve smoothing with
             'turbulence_intensity' method. Can be calculated from
             `roughness_length` instead. Default: None.
+        roughness_length : float (optional)
+            Roughness length. If `standard_deviation_method` is
+            'turbulence_intensity' and `turbulence_intensity` is not given
+            the turbulence intensity is calculated via the roughness length.
 
         Returns
         -------