Apply suggestions from code review

Co-authored-by: Cliff Hansen <cwhanse@sandia.gov>

Author: kandersolar

pvlib/ivtools/sdm/desoto.py

@@ -407,7 +407,7 @@ def fit_desoto_batzelis(isc0, voc0, imp0, vmp0, alpha_sc, beta_voc):
     Determine De Soto single-diode model parameters from datasheet values
     using Batzelis's method.
 
-    This method is described in Section II.C of [1]_.
+    This method is described in Section II.C of [1]_ and fully documented in [2]_.
 
     Parameters
     ----------
@@ -441,6 +441,10 @@ def fit_desoto_batzelis(isc0, voc0, imp0, vmp0, alpha_sc, beta_voc):
     .. [1] E. I. Batzelis, "Simple PV Performance Equations Theoretically Well
        Founded on the Single-Diode Model," Journal of Photovoltaics vol. 7,
        no. 5, pp. 1400-1409, Sep 2017, :doi:`10.1109/JPHOTOV.2017.2711431`
+    .. [2] E. I. Batzelis and S. A. Papathanassiou, "A method for the analytical
+       extraction of the single-diode PV model parameters, IEEE Trans.
+       Sustain. Energy, vol. 7, no. 2, pp. 504-512, Apr 2016.
+       :doi:`10.1109/TSTE.2015.2503435`
     """
     t0 = 298.15  # K
     del0 = (1 - beta_voc * t0) / (50.1 - alpha_sc * t0)  # Eq 9