Update pvlib/transformer.py

Author: kandersolar

pvlib/transformer.py

@@ -111,6 +111,8 @@ def simple_efficiency(
     b = 1
     c = no_load_loss - input_power_normalized
 
+    # alternative form of the quadratic equation to avoid
+    # divide-by-zero when a == 0
     disc = (b*b - 4*a*c)**0.5
     output_power_normalized = 2*c / (-b - disc)