Effective Efficiency of Busbarless solar cells P. Papet1, J. Levrat2, N. Bassi3, Y. Yao4, A. Waltinger5, V. Fakhfouri3, T. Soderstrom4, B. Strahm1
1 Meyer Burger Research, Hauterive, Switzerland.
2 CSEM PV-Center, Neuchâtel, Switzerland.
3 Meyer Burger (PASAN), Neuchâtel, Switzerland
4 Meyer Burger AG, GWATT, Switzerland
5 Meyer Burger (Germany), Hohenstein, Germany
Table of contents
2
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
Table of contents
3
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
Evolution of Cell Connection Technology
4
Towards higher module power output
with less silver consumption
? ? ?
Cell with 3 BB Cell with 5 BB Cell with SWCT
SmartWire Connection Technology (SWCT)
5
Innovative and patented Foil-
Wire Electrode Concept
Multiple wires are used instead
of conventional cell connectors
(tab ribbons)
Compatible with HJT, PERC,
PERT, thin wafer and bifacial
cells
Higher module power
up to +6%1)
Higher energy yield up to 15%2)
Up to 83% less silver
in cell production1)
1) with HJT/SWCT compared to 3BB
2) with HJT/SWCT GG bifacial compared to 3BB
Better tolerance to
micro cracks
$/kWh
Fast track certification
Table of contents
6
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
GRIDTOUCH measurement unit (GT)
7
Electrical Contacts
• Front Side : 30 current wires and 5 voltage wires
• Back Side :
• Grid Touch : up to 30 current wires and 5 voltage wires
• PCB Touch : PCB with up to 30 current track and 5 voltage tracks
Optics :
• no alteration of the light spectrum & intensity
• Different back reflectance available with PCB Touch version
Temperature :
• IR sensor
System & procedures approved and used at ISE CalLab
Compensation of the contacting unit shading
8
• By definition, shading of the contacting units is
not included in the solar cell performances
• Accredited method : measure with different
number of front wires and extrapolate the real Isc
of solar cell without wires.
• Practically : use a BBless reference cell for
calibration
Current measured on BBless cell is typically
higher than for a BB cell when same cell
technology used
BB cell case : schematic cross-section
Fingers Busbars
Substrate
Contacting bars
Fingers GT wires
BB0 cell case : schematic cross-section
Best number of contacting wires
9
Contact interface for BB cell is the Busbar and for a BBless cell the fingers.
The number of probes should be sufficient to satisfy accuracy and precision
Usually we desire no ohmic losses from the contact interface
Large number of pogo pins to avoid ohmic losses along BB for BB cell measure
Measured fill factor as function of the number of wires in the
GRIDTOUCH configurations.
• With 30 current wires, tested cells show
accurate & precise FF
• valid for Grid Resistance below 20ohm/m
• In accordance with ISE CalLab standard
Official way to measure BBless cell performances (GT efficiency)
Table of contents
10
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
Why do we need the effective efficiency
11
Hypothesis:
- SWCT: 18 wires/250um
- 3BB: 3tabs/1500um
- 3BB/SWCT Shadow: 2.9%
- Cell area: 244 cm2 𝐂𝐓𝐌 − 𝐋 =𝐏𝐦𝐚𝐱−𝐜𝐞𝐥𝐥 − 𝐏𝐦𝐚𝐱−𝐞𝐧𝐝
𝐏𝐦𝐚𝐱−𝐜𝐞𝐥𝐥
Example with only interconnector shading effect
CTM-L equation : - Finger, wire & tabs ∞ conductive
- Encapsulation losses: 2% on Pmax
ᵑGT : BB0 measured with GT
ᵑCB : BB measured with Contacting Bars
Why do we need the effective efficiency
Example with only interconnector shading effect
Reduced process cost
Increased cell efficiency
Necessity to have an intermediate and “BB-equivalent” efficiency definition
Effective efficiency (eff)
Unfair cell price based on $/Wp for BB
cells, Increased CTM losses
Table of contents
13
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
Effective efficiency First parameter: interconnector shading
Hypothesis:
- SWCT: 18 wires/250um
- 3BB: 3tabs/1500um
- 3BB/SWCT Shadow: 2.9%
- Cell area: 244 cm2
- Finger, wire & tabs ∞ conductive
Hypothesis:
- Encapsulation losses: 2% on Pmax
ᵑGT : BB0 measured with GT
ᵑCB : BB measured with Contacting Bars
ᵑeff : BB/BB0 calculation
Interconnector
shading
Effective efficiency First parameter: interconnector shading
Reduced process cost
Same Efficiency Same cell efficiency
Same CTM losses
Close value between BBless effective efficiency and BB cell efficiency (contacting bar)
Positive for both manufacturers
Effective efficiency second parameter : the grid resistance
16
Busbar cell case BBless cell case
Busbar to Busbar resistance parameter is widely
used to characterize cells.
• Average finger resistance
• Evaluate the finger ohmic losses
For BB cell, fingers resistance influence cell
performances at LIV and in module
BBless measure is by definition not influenced by finger
resistance.
• True for the GT up to 20Ohm/m
However, in the module, finger resistance depend of number
of interconnectors used (12/15/18/36…)
Implement the finger ohmic losses based on the future
module interconnection design
• Grid resistance on front & back side are the key
values
• As for BB cell performances, finger ohmic losses
are inherent in the BBless effective efficiency
We define the Grid resistance as :
GR=𝑹𝑩𝑩𝒕𝒐𝑩𝑩
𝑳𝑩𝑩 𝒕𝒐 𝑩𝑩 =
𝑅𝑓𝑖𝑛𝑔𝑒𝑟𝑠
𝐿𝑓𝑖𝑛𝑔𝑒𝑟𝑠 [𝑂ℎ𝑚. 𝑚−1]
L : Distance
depends on nb of
wires in module
17
Effective efficiency second parameter : the grid resistance
Hypothesis:
- SWCT: 18 wires/250um
- Cell area: 244 cm2
- Back fingers & wires ∞ conductive Interconnector
shading Finger resistance
effect
Effective efficiency :
• Gives the real potential of the cell in the specific module : CTM & $/Wp
• Efficient parameter for cell sorting and cell process optimizations
18
Effective efficiency practical calculation
BBless efficiency - ᵑGT
Grid resistance : GRf & GRb
Interconnection number &
size : Nsw & Dsw
Equations Effective efficiency - ᵑeff
Table of contents
19
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
20
Effective efficiency : practical validation
Special R&D HJT BBless cells :
• Same front grid shading (Isc)
• Varia front Grid Resistance
• GRb = cte =2Ohm/m
Module integration :
• SWCT 18W200
• 16 cells module
CTM-L based on Effective efficiency
is independent of finger resistance
CTM-L is closer than typical value
with BB cells
Bifacial SWCT HJT Module performances
21
1000 modules produced power between 300-320W (with black backsheet)
Pmax
[W]
Voc
[V]
Isc
[A]
FF
[%]
White Backsheet 330 44.5 9.5 78.5%
Black Backsheet 320 44.4 9.1 79.5%
Power distribution
1000 modules (front side
illumination only and black
backsheet reflector)
Table of contents
22
Features SWCT
GRIDTOUCH measurement unit
Summary
Effective efficiency
Why the effective efficiency
Validation
SWCT is mature module technology
>200MWp module installed
327Wp with 60 cells record module
Certification IEC & UL fast track
Busbarless cells measured with GRIDTOUCH contacting unit
System & method approved and available at ISE CalLab for independent validation
Effective efficiency : practical method to evaluate BBless cell performances based on module design
Efficient way for cell and module maker to improve their products
Feature available on Meyer Burger cell sorter
Conclusions
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Pogo pins CTM Ribbon GT CTM SWCT GT_effective CTM SWCT
Fingers shading incl. on air effective shading incl. on air effective shading incl. on air effective shading
F & B finger ohmics
measured at
BB position
includedno extra losses
Not included affected
GT measure +
finger ohmics
losses
estimation
no extra losses
Wires/ribbons shading
BB shading
close to future
ribbon shading
included
no extra lossesNot included
wires cover cell
extra shading /
GT
GT measures +
SWCT wire
shading effect
estimation
no extra losses
Ribbons/wires ohmics Not included CTM Not included CTM Not included CTM
Optics (glass, encapsulant..) Not included CTM Not included CTM Not included CTM
BB cell BBless cell-GT BBless cell_GTeffLosses
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