Fix major error in singlediode p_mp calculation for array/Series input (#222)

* fix issue with singlediode p_mp, i_mp, v_mp calculation for arrays

* edit whatsnew

Author: wholmgren

docs/sphinx/source/whatsnew/v0.4.0.txt

@@ -51,6 +51,12 @@ Enhancements
 Bug fixes
 ~~~~~~~~~
 
+* Fixed an error in pvsystem.singlediode's i_mp, v_mp, and p_mp
+  calculations when using array or Series input. The function wrongly
+  returned solutions when any single point is within the error tolerance,
+  rather than requiring that the solution for all points be within the
+  error tolerance. Results in test scenarios changed by 1-10%.
+  (:issue:`221`)
 * dirint function yielded the wrong results for non-sea-level pressures.
   Fixed. (:issue:`212`)
 * Fixed a bug in the day angle calculation used by the 'spencer' and 'asce'

pvlib/pvsystem.py

@@ -1734,7 +1734,7 @@ def _golden_sect_DataFrame(params, VL, VH, func):
 
         err = df['V1'] - df['V2']
         try:
-            errflag = (abs(err) > .01).all()
+            errflag = (abs(err) > .01).any()
         except ValueError:
             errflag = (abs(err) > .01)
 

pvlib/test/test_pvsystem.py

@@ -393,6 +393,26 @@ def test_singlediode_series(sam_data):
     assert isinstance(out, pd.DataFrame)
 
 
+@requires_scipy
+def test_singlediode_array():
+    # github issue 221
+    photocurrent = np.linspace(0, 10, 11)
+    resistance_shunt = 16
+    resistance_series = 0.094
+    nNsVth = 0.473
+    saturation_current = 1.943e-09
+
+    sd = pvsystem.singlediode(photocurrent, saturation_current,
+                              resistance_series, resistance_shunt, nNsVth)
+
+    expected = np.array([
+        0.        ,  0.54538398,  1.43273966,  2.36328163,  3.29255606,
+        4.23101358,  5.16177031,  6.09368251,  7.02197553,  7.96846051,
+        8.88220557])
+
+    assert_allclose(sd['i_mp'], expected, atol=0.01)
+
+
 @requires_scipy
 def test_singlediode_floats(sam_data):
     module = 'Example_Module'