Effective Efficiency of Busbarless solar cells P. Papet 1, J. Levrat 2, N. Bassi 3, Y. Yao 4, A. Waltinger 5, V. Fakhfouri 3, T. Soderstrom 4, B. Strahm 1 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 pierre.papet@meyerburger.com
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 2
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 3
Evolution of Cell Connection Technology??? Cell with 3 BB Cell with 5 BB Cell with SWCT Towards higher module power output with less silver consumption 4
SmartWire Connection Technology (SWCT) 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 $/kwh Higher module power up to +6% 1) Up to 83% less silver in cell production 1) Higher energy yield up to 15% 2) Fast track certification Better tolerance to micro cracks 5 1) with HJT/SWCT compared to 3BB 2) with HJT/SWCT GG bifacial compared to 3BB
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 6
GRID TOUCH 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 Contacting bars Fingers Fingers Busbars GT wires Substrate BB cell case : schematic cross-section BB0 cell case : schematic cross-section 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 8
Best number of contacting wires 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 With 30 current wires, tested cells show accurate & precise FF valid for Grid Resistance below 20ohm/m In accordance with ISE CalLab standard Measured fill factor as function of the number of wires in the GRID TOUCH configurations. 9 Official way to measure BBless cell performances (GT efficiency)
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 10
Why do we need the effective efficiency Example with only interconnector shading effect Hypothesis: - SWCT: 18 wires/250um - Finger, wire & tabs conductive CTM-L equation : - 3BB: 3tabs/1500um - Encapsulation losses: 2% on Pmax - 3BB/SWCT Shadow: 2.9% ᵑGT : BB0 measured with GT - Cell area: 244 cm 2 CTM L = P max cell P max end ᵑCB : BB measured with Contacting Bars 11 P max cell
Why do we need the effective efficiency Example with only interconnector shading effect Reduced process cost Increased cell efficiency Unfair cell price based on $/Wp for BB cells, Increased CTM losses Necessity to have an intermediate and BB-equivalent efficiency definition Effective efficiency ( eff )
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 13
Effective efficiency First parameter: interconnector shading Hypothesis: - SWCT: 18 wires/250um - 3BB: 3tabs/1500um - 3BB/SWCT Shadow: 2.9% - Cell area: 244 cm 2 - Finger, wire & tabs conductive Interconnector shading Hypothesis: - Encapsulation losses: 2% on Pmax ᵑGT : BB0 measured with GT ᵑCB : BB measured with Contacting Bars ᵑeff : BB/BB0 calculation
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 Busbar cell case BBless cell case L : Distance depends on nb of wires in module 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 16 We define the Grid resistance as : GR= R BBtoBB L BB to BB =R fingers L fingers [Ohm. m 1 ] 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
Effective efficiency second parameter : the grid resistance 17 Interconnector shading Finger resistance effect Hypothesis: - SWCT: 18 wires/250um - Cell area: 244 cm 2 - Back fingers & wires conductive Effective efficiency : Gives the real potential of the cell in the specific module : CTM & $/Wp Efficient parameter for cell sorting and cell process optimizations
Effective efficiency practical calculation BBless efficiency - ᵑGT Grid resistance : GR f & GR b Interconnection number & size : N sw & D sw Equations Effective efficiency - ᵑeff 18
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 19
Effective efficiency : practical validation Special R&D HJT BBless cells : Same front grid shading (Isc) Varia front Grid Resistance GR b = 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 20
Bifacial SWCT HJT Module performances Power distribution 1000 modules (front side illumination only and black backsheet reflector) 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% 1000 modules produced power between 300-320W (with black backsheet) 21
Table of contents Features SWCT GRID TOUCH measurement unit Why the effective efficiency Effective efficiency Validation Summary 22
Conclusions SWCT is mature module technology >200MWp module installed 327Wp with 60 cells record module Certification IEC & UL fast track Busbarless cells measured with GRID TOUCH 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 BB cell BBless cell-gt BBless cell_gteff Losses 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 GT measure + measured at finger ohmics F & B finger ohmics BB position Not included affected no extra losses no extra losses losses included estimation Wires/ribbons shading BB shading close to future ribbon shading included no extra losses Not 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 23 (glass, encapsulant..) Not included CTM Not included CTM Not included CTM
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