Deline › Published

Method

At every timestep the total irradiance of each of the six rear cell rows of the rear model is the front irradiance plus the bifaciality times the row's rear irradiance (1). Their mean absolute difference, relative to their mean, gives the module's mismatch by the second-order fit the authors recommend for every bifacial system, scaled by the module's fill factor over 0.79 (2). The mismatch is converted into a loss of the rear irradiance through the rear side's gain over the front (3, 4). The mismatch has no upper limit, and the loss is held between 0 and the whole rear irradiance.

The math

1. Spread of the cell rows
2. Fitted mismatch
3. Bifacial gain
4. Loss on the rear irradiance

$$G_{cr,j} = G_{front} + b_f\,G_{rear,j},\qquad MAD = \frac{\sum_j \sum_k |G_{cr,j} - G_{cr,k}|}{N_{cr}^2\,\bar G_{cr}}\times 100 \tag{1}$$ $$M_{rm} = (0.142\,MAD + 0.032\,MAD^2)\,\frac{FF_0}{0.79} \tag{2}$$ $$g_{rear} = \frac{b_f\,\bar G_{rear}}{G_{front}}\times 100 \tag{3}$$ $$f_{rm} = \min\!\left(1,\ \frac{M_{rm}\,(1 + 100/g_{rear})}{100}\right) \tag{4}$$

where

Symbol	Meaning	Unit
$G_{cr,j}$	the total irradiance of rear cell row $j$	W/m²
$b_f$	the bifaciality factor of the module: its rear-side efficiency relative to the front	—
$G_{rear,j}$	the rear irradiance of cell row $j$ after the structure shade	W/m²
$N_{cr}$	the number of cell rows, 6	—
$\bar G_{cr}$	the mean of the $G_{cr,j}$	W/m²
$MAD$	the mean absolute difference	%
$M_{rm}$	the mismatch of the module's power	%
$FF_0$	the module fill factor at standard conditions	—
$g_{rear}$	the rear side's gain over the front	%
$f_{rm}$	the rear mismatch loss fraction. Of the timestep	—

References

1. Deline, Ayala Pelaez, MacAlpine & Olalla 2020, Estimating and parameterizing mismatch power loss in bifacial photovoltaic systems, Progress in Photovoltaics 28(7) 691–703

API

bifacial.rear_mismatch_model = deline_2020_published

Symbols follow the symbol registry.