Global incident rear side

What this step does

The row adds to the array energy the energy from the light on the rear side of bifacial modules. The rear irradiance is converted at the rated efficiency and scaled by the bifaciality factor. The Model tab's Rear side and front ground reflection step computes the rear irradiance.

The math

1. Running total
2. Gain at a timestep

$$E_{after} = E_{before} + E_{row},\qquad E_{row} = \frac{\Delta t}{1000\,P_{DC}}\sum_i L_i \tag{1}$$ $$L_i = N\,P_{nom}\,b_f\,\frac{G_{rear,i}}{G_{ref}} \tag{2}$$

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, a gain	kWh/kWp
$\Delta t$	the length of one timestep	hours
$P_{DC}$	the DC nameplate of the system	kWp
$L_i$	the power gained at timestep $i$ over the whole system	W
$N$	the number of modules in the system	—
$P_{nom}$	the module nameplate power at standard test conditions	W
$b_f$	the bifaciality factor of the module	—
$G_{rear,i}$	the irradiance on the rear side at timestep $i$	W/m²
$G_{ref}$	the reference irradiance of the standard test conditions (1,000 W/m²)	W/m²

Reading the number

A gain, positive: typically 3 to 10 % of the nominal energy on a bifacial utility plant. A bright ground, modules mounted high, a low ground cover ratio and a high bifaciality factor raise it. Monofacial modules and rooftop systems show zero.

References

1. Marion et al. 2017, A practical irradiance model for bifacial PV modules, NREL/CP-5J00-67847

API

loss.rear_incident

Symbols follow the symbol registry.