Fix dtypes in get_pvgis_tmy when outputformat='epw'

pvlib/iotools/pvgis.py

@@ -410,6 +410,8 @@
         np.roll(tmy_data, tz, axis=0),
         columns=tmy_data.columns,
         index=new_index)
+    new_tmy_data = \  # GH 2399
+        new_tmy_data.astype(dtype=dict(zip(tmy_data.columns, tmy_data.dtypes)))
     return new_tmy_data