Raise error instead of passing as nominal power must be known in order to do calcs using power coefficient curve

Author: birgits

windpowerlib/wind_turbine.py

@@ -235,9 +235,10 @@ def __init__(self, hub_height, power_curve=False,
                 try:
                     self.nominal_power = get_oedb_turbine_data(
                         self.turbine_type, fetch_data='nominal_power')
-                except KeyError:
-                    pass
-
+                except (KeyError, ValueError):
+                    raise ValueError(
+                        "nominal_power must be provided when using power "
+                        "coefficient curve.")
 
     def __repr__(self):
         info = []