Add minus sign in front of dEgdT, sdm.py (#2322)

* Add - in front of dEgdT

Co-Authored-By: Cliff Hansen <5393711+cwhanse@users.noreply.github.com>
Co-Authored-By: Kevin Anderson <57452607+kandersolar@users.noreply.github.com>

* assert np.allclose -> assert_allclose

* test scalar values

* rtol unnecessary

* revert back assert_allclose changes

* document returned value `dEgdT`

* whatsnew

* Revert "document returned value `dEgdT`"

This reverts commit 40451a1.

---------

Co-authored-by: Cliff Hansen <5393711+cwhanse@users.noreply.github.com>
Co-authored-by: Kevin Anderson <57452607+kandersolar@users.noreply.github.com>

Author: 3 people

docs/sphinx/source/whatsnew/v0.11.2.rst

@@ -32,6 +32,8 @@ Bug fixes
 ~~~~~~~~~
 * :py:func:`~pvlib.spa.julian_day_dt` now accounts for the 10 day difference
   between Julian and Gregorian calendars prior to the year 1582. (:issue:`2077`, :pull:`2249`)
+* Corrected sign of temperature coefficient ``dEgdT`` in :py:func:`~pvlib.pvsystem.fit_desoto_sandia`.
+  Results may differ slightly from previous versions. (:issue:`2311`, :pull:`2322`)
 
 Documentation
 ~~~~~~~~~~~~~

pvlib/ivtools/sdm.py

@@ -878,7 +878,7 @@ def fun_rsh(x, rshexp, ee, e0, rsh):
         params['R_sh_exp'] = R_sh_exp
 
     elif model == 'desoto':
-        dEgdT = 0.0002677
+        dEgdT = -0.0002677
         x_for_io = const['q'] / const['k'] * (
             1. / tok - 1. / tck[u] + dEgdT * (tc[u] - const['T0']) / tck[u])
 

pvlib/tests/ivtools/test_sdm.py

@@ -140,6 +140,9 @@ def test_fit_desoto_sandia(cec_params_cansol_cs5p_220p):
     expected = pd.Series(params)
     assert np.allclose(modeled[params.keys()].values,
                        expected[params.keys()].values, rtol=5e-2)
+    assert_allclose(result['dEgdT'], -0.0002677)
+    assert_allclose(result['EgRef'], 1.3112547292120638)
+    assert_allclose(result['cells_in_series'], specs['cells_in_series'])
 
 
 def _read_iv_curves_for_test(datafile, npts):