simple_efficiency raises ZeroDivisionError when load_loss=0 #2645
Description
Describe the bug
pvlib.transformer.simple_efficiency raises a ZeroDivisionError when
load_loss = 0.
A zero load_loss is a physically valid case (e.g., an ideal transformer
with only no-load losses), but the current implementation always solves
a quadratic equation and divides by 2 * load_loss, which leads to a
division by zero.
To Reproduce
from pvlib.transformer import simple_efficiency
simple_efficiency(
input_power=1000,
no_load_loss=0.01,
load_loss=0,
transformer_rating=1000,
)
Expected behavior
When load_loss = 0, the loss model becomes linear rather than quadratic.
The output power should be computed as:
P_out = P_in - L_no_load * P_nom
and the function should return a finite value instead of raising an
exception.
Proposed solution
Handle the special case where load_loss == 0 explicitly before solving
the quadratic equation.
When load_loss = 0, the loss model reduces to a linear relationship:
P_out = P_in - L_no_load * P_nom
A conditional check can be added at the beginning of the function to
return the linear solution and avoid division by zero, for example:
if load_loss == 0:
return input_power - no_load_loss * transformer_rating
This preserves existing behavior for load_loss > 0 while correctly
handling a physically valid edge case.