Mismatch loss for back irradiance

What this step does

The row measures the mismatch loss on the rear-side share of the array power, taken from the array energy. The rear side of a row of modules is lit unevenly, so the rear contribution carries its own mismatch, applied after the front mismatch and before the wiring loss.

The math

1. Running total
2. Loss at a timestep

$$E_{after} = E_{before} - E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = f_{rm}\,\frac{b_f\,G_{rear,i}}{G_{eff,i} + b_f\,G_{rear,i}}\,P_{sys,i} \tag{2}$$

where

Symbol	Meaning	Unit
$E_{before}$	the running total of the loss diagram before this row	kWh/kWp
$E_{after}$	the running total after this row	kWh/kWp
$E_{row}$	the row taken as a loss	kWh/kWp
$\Delta t$	the length of one timestep	hours
$P_{DC}$	the DC nameplate of the system	kWp
$L_i$	the power lost at timestep $i$ over the whole system	W
$f_{rm}$	the rear mismatch loss input, a fraction	—
$b_f$	the bifaciality factor of the module	—
$G_{rear,i}$	the irradiance on the rear side at timestep $i$	W/m²
$G_{eff,i}$	the effective irradiance on the front at timestep $i$	W/m²
$P_{sys,i}$	the array power of the whole system before this row at timestep $i$	W

Reading the number

A loss, negative: the rear mismatch fraction times the rear share of the array energy, about 0.3 to 1 % for a bifacial plant with the default 10 %. Monofacial modules and rooftop systems show zero.

API

loss.rear_mismatch

Symbols follow the symbol registry.