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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 201224 April 2012
� Motivation
� Characterization of bifacial solar cells
� Structure of bifacial module simulations
Outline
� Analysis of various sorting approaches
� Conclusion
� Motivation
� Characterization of bifacial solar cells
� Structure of bifacial module simulations
Outline
� Analysis of various sorting approaches
� Conclusion
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
A: Minimize current mismatches and hence to improve the module performance
Voltage [V] Voltage [V]
Cu
rren
t [A
]
Cu
rren
t [A
]Cell #1Cell #2
Cell #1Cell #2Cell #1 & #1Cell #1 & #2
� Motivation
� Characterization of bifacial solar cells
� Structure of bifacial module simulations
Outline
� Analysis of various sorting approaches
� Conclusion
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
� 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
� Motivation
� Characterization of bifacial solar cells
� Structure of bifacial module simulations
Outline
� Analysis of various sorting approaches
� Conclusion
Structure of bifacial module simulations
Dark IV &Illuminated IV( 50-100-250-500-1000 W/m2 )
Two Diode Model Fits
Measurements
Determination ofJphoto, Jdiff, Jrec, Rser, Rshunt
Configuration of modules Number of cells per module, illumination intensity, temperature, packing density
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
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
Cell # Isc Voc Impp Vmpp Pmpp η
1 17,81
2 17,69
3 17,65
4
... ...
Structure of bifacial module simulations
23 16,66
24 16,65
25 16,57
26 16,56
27 16,52
... ...
Simulated module number: 1234
� Motivation
� Characterization of bifacial solar cells
� Structure of bifacial module simulations
Outline
� Analysis of various sorting approaches
� Conclusion
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 I
SC [A]
10 Measured I
MPP [A]
Data obtained from front side illumination with black chuck
0 200 400 600 800 100015,0
15,5
16,0
16,5
17,0
17,5
Illumination intensity [W/m2]0 200 400 600 800 1000
0
2
4
6
8
10
Illumination intensity [W/m2]0 200 400 600 800 1000
0
2
4
6
8
10
Illumination intensity [W/m2]
Can this behavior be exploited to achieve higher module performance?
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]
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
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 enhancedmodule performance
P [W] P [W] P [W]
cells sorted by ISC cells sorted by IMPP cells sorted by η
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
<
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
Mea
sure
d ef
ficie
ncy
[%]
Measurement at front side with black chuck Measurement at rear side with balck chuck
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 35Cell Number
0 5 10 15 20 25 30 355,5
6,0
6,5
7,0
7,5
8,0
8,5
9,0
I SC [A
]
Cell Number
Illumination at front with black chuck Illumination at back with black chuck
0 5 10 15 20 25 30 355,0
5,5
6,0
6,5
7,0
7,5
8,0
8,5
I MP
P [A
]
Cell Number
Illumination at front with black chuck Illumination at back with black chuck
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/m2250 W/m2500 W/m2
Front
Back
>
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.
>
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) illuminationintensity 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
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.
>
Conclusion
� Various sorting parameters have been analyzed with respect to the bifacialmodule performance.
� Highest module performance is observed if the cells are sorted by efficiencyvalues at the front side.
� Sorting by IMPP and ISC led to lower module performances since fill factor effectsare not taken into consideration by these sorting approaches.
� Comparison of the sorting approaches were compared regarding the modulepower.
� Even if rear side illumination is larger than front side illumination sorting by frontparameters enabled higher module performance.
Thank you for your attention!
Thanks to the colleagues at ISC Konstanz for the measurements.
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.
