1) Precise sorting of bifacial solar cells is important to minimize current mismatches and improve module performance. 2) Simulations were conducted to analyze different sorting approaches using characterization data from 35 bifacial solar cells. 3) Sorting cells by efficiency measured under 1000 W/m2 front-side illumination provided the highest maximum module power compared to sorting by short-circuit current, maximum power point, or efficiency at other illumination levels.

1. Importance of precise sorting of bifacial solar cells for
optimal bifacial module performance
U. A. Yusufoglu1, T. M. Pletzer1, B. Min1, H. Kurz1
1Institute of Semiconductor Electronics, RWTH Aachen University
A. Halm2, L. Joseph2, C. Comparotto2, R. Kopecek2
2International Solar Energy Research Center (ISC), Konstanz
bifiPV Workshop 2012
24 April 2012

2. Motivation
Characterization of bifacial solar cells
Structure of bifacial module simulations
Outline
yusufoglu@iht.rwth-aachen.de
Analysis of various sorting approaches
Conclusion

3. Motivation
Characterization of bifacial solar cells
Structure of bifacial module simulations
Outline
yusufoglu@iht.rwth-aachen.de
Analysis of various sorting approaches
Conclusion

4. Motivation
Class I Class II Class III
Q: Why do we need to sort the solar cells?
A: Minimize current mismatches and hence to improve the module performance
Batch of solar cells
yusufoglu@iht.rwth-aachen.de
A: Minimize current mismatches and hence to improve the module performance
Voltage [V] Voltage [V]
Current[A]
Current[A]
Cell #1
Cell #2
Cell #1
Cell #2
Cell #1 & #1
Cell #1 & #2

5. Motivation
Characterization of bifacial solar cells
Structure of bifacial module simulations
Outline
yusufoglu@iht.rwth-aachen.de
Analysis of various sorting approaches
Conclusion

6. Characterization of bifacial solar cells
n-type bifacial solar cells
4 different setups for characterization
p+
n
n+
F
B
n+
n
p+
B
F
Different illumination
intensities :
1000 W/m2
500 W/m2
250 W/m2
100 W/m2
Front illumination Rear illumination
yusufoglu@iht.rwth-aachen.de
These characterization data of cells are used for the module simulations
n+B p+F
p+
n
n+
F
B
n+
n
p+
B
F
Black chuck
Brass chuck
100 W/m2
50 W/m2

7. Motivation
Characterization of bifacial solar cells
Structure of bifacial module simulations
Outline
yusufoglu@iht.rwth-aachen.de
Analysis of various sorting approaches
Conclusion

8. Structure of bifacial module simulations
Dark IV &
Illuminated IV( 50-100-250-500-1000 W/m2 )
Two Diode Model Fits
Measurements
Determination of
Jphoto, Jdiff, Jrec, Rser, Rshunt
Configuration of modules Number of cells per module, illumination
intensity, temperature, packing density
yusufoglu@iht.rwth-aachen.de
intensity, temperature, packing density
Sorting parameters
Module simulations
Evaluation
η, Isc, Impp and combination of
front and rear parameters
Simulation of the modules with LTSPICE using
the chosen configurations
Analysis of the chosen sorting approach
considering the module performance

9. Structure of bifacial module simulations
• Characterization data of 35 cells are available.
• All simulated modules consist of 24 in series connected cells.
• Need for an approach to analyze different sorting parameters
yusufoglu@iht.rwth-aachen.de

10. Cell # Isc Voc Impp Vmpp Pmpp η
1 17,81
2 17,69
3 17,65
4
... ...
Structure of bifacial module simulations
yusufoglu@iht.rwth-aachen.de
23 16,66
24 16,65
25 16,57
26 16,56
27 16,52
... ...
Simulated module number: 1234

11. Motivation
Characterization of bifacial solar cells
Structure of bifacial module simulations
Outline
yusufoglu@iht.rwth-aachen.de
Analysis of various sorting approaches
Conclusion

12. Typical parameters used for the sorting of monofacial solar cells are
• Efficiency (Pmpp) & ISC & IMPP
• Which parameter is most suitable for optimized bifacial operation?
Analysis of different sorting approaches
17,5
18,0
Measured efficiency [%]
10
Measured ISC
[A]
10
Measured IMPP
[A]
Data obtained from front side illumination with black chuck
yusufoglu@iht.rwth-aachen.de
0 200 400 600 800 1000
15,0
15,5
16,0
16,5
17,0
17,5
Illumination intensity [W/m
2
]
0 200 400 600 800 1000
0
2
4
6
8
10
Illumination intensity [W/m
2
]
0 200 400 600 800 1000
0
2
4
6
8
10
Illumination intensity [W/m
2
]
Can this behavior be exploited to achieve higher module performance?

13. Analysis of different sorting approaches
European module efficiency:
ηEUR = 0.03 η50 + 0.06 η100 + 0.13 η200 + 0.10 η300 + 0.48 η500 + 0.2 η1000
Sort cells by efficiency at 1000 W/m2 vs. 500 W/m2 and compare overall performance
Pmax [W] Pmin [W]
cells sorted by
efficiency at 1000 W/m2
cells sorted by
efficiency at 500 W/m2
Pmax [W] Pmin [W]
yusufoglu@iht.rwth-aachen.de
The maximum module performance can be achieved
by sorting the cells by η at 1000 W/m2.
1000 W/m2 95.25 92.76
500 W/m2 49.52 48.66
250 W/m2 24.77 24.46
100 W/m2 9.50 9.46
50 W/m2 4.4 4.39
PEUR 49.22 48.23
95.08 92.74
49.55 48.62
24.83 24.42
9.52 9.38
4.44 4.38
49.21 48.20

14. Analysis of different sorting approaches
IMPP and ISC as sorting parameters
• They can be used to reduce current mismatches
• However, sorting by these parameters does not necessarily lead to enhanced
module performance
P [W] P [W] P [W]
cells sorted by ISC
cells sorted by IMPP cells sorted by η
<
yusufoglu@iht.rwth-aachen.de
Pmax [W] Pmax [W] Pmax [W]
1000 W/m2 94.5 94.68 95.25
500 W/m2 49.24 49.26 49.52
250 W/m2 24.64 24.7 24.77
Ignoring fill factor influences leads to slightly reduced module performance
Sorting the cells by efficiency (power) provides highest module performance
<

15. Analysis of different sorting approaches
Analysis of various illumination intensities on both sides
p+
n
n+
Front
Back
1 0.5 0.25
0.50
0.25 0.25
0.10 0.10 0.10
0.05 0.05 0.05 0 5 10 15 20 25 30 35
10
12
14
16
18
Measuredefficiency[%]
Measurement at front side with black chuck
Measurement at rear side with balck chuck
yusufoglu@iht.rwth-aachen.de
Back side
provides
appox. 20 %
less current
and less
efficiency than
front side
0.05 0.05 0.05 0 5 10 15 20 25 30 35
Cell Number
0 5 10 15 20 25 30 35
5,5
6,0
6,5
7,0
7,5
8,0
8,5
9,0
ISC
[A]
Cell Number
Illumination at front with black chuck
Illumination at back with black chuck
0 5 10 15 20 25 30 35
5,0
5,5
6,0
6,5
7,0
7,5
8,0
8,5
IMPP
[A]
Cell Number
Illumination at front with black chuck
Illumination at back with black chuck

16. Analysis of different sorting approaches
Comparison of the three sorting parameters IMPP and η
Maximum achieved power with these sorting parameters: Pmax [W]
η IMPP η IMPP η IMPP η IMPP
100 W/m2 50 W/m2
250 W/m2500 W/m2
Front
Back
>
yusufoglu@iht.rwth-aachen.de
1000
W/m2
133.5 132.3 114.9 114 103.3 102.5 99.3 98.62
500
W/m2
70.87 70.45 58.22 57.88 53.93 53.61
250
W/m2
33.72 33.56 29.31 29.17
Sorting cells by their efficiencies leads to most efficient bifacial operation as well.
>

17. Analysis of different sorting approaches
Upto now illumination intensity at front was higher than at rear.
Under diffuse light or specific module orientation (East-West) illumination
intensity at rear may be larger than at front.
For these cases, is it sensible to sort the cells by rear parameters?
Achieved power by sorting the cells by front or rear efficieny at 500 W/m2 at rear
yusufoglu@iht.rwth-aachen.de
Illumination at front Sort by η front Sort by η rear
500 W/m2 91.25 88.28
250 W/m2 68.04 64.7
100 W/m2 53.26 50
50 W/m2 47.8 45
Sorting the cells by front efficiencies leads to higher achievable module
performance even if the back illumination is higher.
>

18. Conclusion
Various sorting parameters have been analyzed with respect to the bifacial
module performance.
Highest module performance is observed if the cells are sorted by efficiency
values at the front side.
Sorting by IMPP and ISC led to lower module performances since fill factor effects
are not taken into consideration by these sorting approaches.
yusufoglu@iht.rwth-aachen.de
Comparison of the sorting approaches were compared regarding the module
power.
Even if rear side illumination is larger than front side illumination sorting by front
parameters enabled higher module performance.

19. Thank you for your attention!
Thanks to the colleagues at ISC Konstanz for
the measurements.
yusufoglu@iht.rwth-aachen.de
Thank you for your attention!
This work is part of the project “Kompetenzzentrum für innovative Photovoltaik-Modultechnik NRW” and has been
supported by the European Union – European Regional Development Fund and by the Ministry of Economic Affairs
and Energy of the State of North Rhine-Westphalia, Germany.