Allowing spa_c() to use localized time index 0.4.5 (#333)

* Allowing spa_c() to use localized time index

* converting time to 'UTC' if time index is localized

* Updating whatsnew file with changes

* move note from one whatsnew to the other

Author: wholmgren

docs/sphinx/source/whatsnew/v0.4.5.txt

@@ -9,6 +9,7 @@ Bug fixes
 
 * Fix pandas 0.20 incompatibilities in Location.get_clearsky,
   solarposition.ephemeris (:issue:`325`)
+* Fixes timezone issue in solarposition spa_c function (:issue:`237`)
 * Added NREL Bird clear sky model. (:issue:`276`)
 * Added lower accuracy formulas for equation of time, declination, hour angle
   and solar zenith.
@@ -31,5 +32,6 @@ Contributors
 ~~~~~~~~~~~~
 
 * Will Holmgren
+* Marc Anoma
 * Mark Mikofski
 * Birgit Schachler

pvlib/solarposition.py

@@ -182,7 +182,11 @@ def spa_c(time, latitude, longitude, pressure=101325, altitude=0,
 
     pvl_logger.debug('using built-in spa code to calculate solar position')
 
-    time_utc = time
+    # if localized, convert to UTC. otherwise, assume UTC.
+    try:
+        time_utc = time.tz_convert('UTC')
+    except TypeError:
+        time_utc = time
 
     spa_out = []
 
@@ -193,7 +197,7 @@ def spa_c(time, latitude, longitude, pressure=101325, altitude=0,
                                 hour=date.hour,
                                 minute=date.minute,
                                 second=date.second,
-                                timezone=0,  # must input localized or utc time
+                                timezone=0,  # date uses utc time
                                 latitude=latitude,
                                 longitude=longitude,
                                 elevation=altitude,
@@ -202,7 +206,7 @@ def spa_c(time, latitude, longitude, pressure=101325, altitude=0,
                                 delta_t=delta_t
                                 ))
 
-    spa_df = pd.DataFrame(spa_out, index=time_utc)
+    spa_df = pd.DataFrame(spa_out, index=time)
 
     if raw_spa_output:
         return spa_df