Correct power coefficient function

Author: SabineHaas

windpowerlib/power_output.py

@@ -66,13 +66,18 @@ def power_coefficient_curve(wind_speed, power_coefficient_curve_wind_speeds,
             Wirtschaftlichkeit". 4. Auflage, Springer-Verlag, 2008, p. 542
 
     """
-    power_curve_values = (1 / 8 * 1.225 * rotor_diameter ** 2 * np.pi *
-                          np.power(power_coefficient_curve_wind_speeds,
-                                   3) *
-                          power_coefficient_curve_values)
-    power_output = power_curve_density_correction(
+    power_coefficient_time_series = np.interp(
         wind_speed, power_coefficient_curve_wind_speeds,
-        power_curve_values, density)
+        power_coefficient_curve_values, left=0, right=0)
+    power_output = (1 / 8 * density * rotor_diameter ** 2 * np.pi *
+                    np.power(wind_speed, 3) *
+                    power_coefficient_time_series)
+    # Power_output as pd.Series if wind_speed is pd.Series (else: np.array)
+    if isinstance(wind_speed, pd.Series):
+        power_output = pd.Series(data=power_output, index=wind_speed.index,
+                                 name='feedin_power_plant')
+    else:
+        power_output = np.array(power_output)
     return power_output