return same object type that was input

Author: williamhobbs

pvlib/pvsystem.py

@@ -2963,18 +2963,27 @@ def pvwatts_dc(effective_irradiance, temp_cell, pdc0, gamma_pdc, temp_ref=25.,
 
     # apply Marion's correction if k is anything but zero
     if k is not None:
+        pdc_marion = pdc
         err_1 = k * (1 - (1 - effective_irradiance / 200)**4)
         err_2 = k * (1000 - effective_irradiance) / (1000 - 200)
 
-        pdc_marion = np.where(effective_irradiance <= 200,
-                              pdc - (pdc0 * err_1),
-                              pdc - (pdc0 * err_2))
+        if hasattr(effective_irradiance, '__len__'):
+            pdc_marion[effective_irradiance <= 200] = pdc - (pdc0 * err_1)
+            pdc_marion[effective_irradiance > 200] = pdc - (pdc0 * err_2)
+        else:
+            if effective_irradiance <= 200:
+                pdc_marion = pdc - (pdc0 * err_1)
+            elif effective_irradiance > 200:
+                pdc_marion = pdc - (pdc0 * err_2)
+
 
         # "cap" Marion's correction at 1000 W/m^2
         if cap_adjustment:
-            pdc_marion = np.where(effective_irradiance >= 1000,
-                                  pdc,
-                                  pdc_marion)
+            if hasattr(effective_irradiance, '__len__'):
+                pdc_marion[effective_irradiance >= 1000] = pdc
+            else:
+                if effective_irradiance >= 1000:
+                    pdc_marion = pdc
 
         # large k values can result in negative power at low irradiance, so
         # set negative power to zero