© Fraunhofer ISE

The impact of half cells on module power and costs

FRAUNHOFER INSTITUTEFOR SOLAR ENERGY SYSTEMS ISE

Max Mittag

Fraunhofer Institutefor Solar Energy Systems ISE

Webinar PV-magazine

Freiburg, 30.10.2018

www.ise.fraunhofer.de

© Fraunhofer ISE

2

Cell-to-Module AnalysisMotivation

◼ Power loss = financial loss (€/Wp)

◼ Module materials (BoM) and module design influence power

◼ Power cells > power module

→ cell-to-module loss (CTM)

→ Analysis of losses allows techno-economic optimization of PV modules

© Fraunhofer ISE

3

Cell-to-Module AnalysisMotivation

◼ CTM-optimization increases revenue

◼ Solar cells are bought at €/Wp

◼ PV modules are sold at €/Wp

→ Goal: Increase module power without using solar cells with higher power

→ Are half cell modules a promising approach?

PV-Module with 5.6% cell-to-module gain, manufactured at Fraunhofer ISE Module-TEC (2016)

© Fraunhofer ISE

4

Cell-to-Module AnalysisGain and Loss Factors

◼ Geometry: inactive areas near the frame and cell spacing

◼ Optics: reflection, absorption, transmission, internal shading, “light management”

◼ Electrics: Resistances, Mismatch

→ Scientific models allow analysis and prediction

Optical gains and losses in PV modules

Haedrich, I. et al, “Unified methodology for determining CTM ratios: Systematic prediction of module power”, SiliconPV, 2014

© Fraunhofer ISE

5

Cell-to-Module Analysis

M. Mittag et al., “Systematic PV module optimization with the cell-to-module (CTM) analysis software,” Photovoltaics International, no. 36

SmartCalc.CTMwww.cell-to-module.com

free demo-version

Geometrie Optik Elektrik

CTM

Graphical User Interface ofSmartCalc.CTM

© Fraunhofer ISE

6

Module Design for Half and Full Cell Modules

◼ Necessary adaptions for modules with half cells

◼ Cell spacing

◼ Number of cells

◼ Module size

◼ Cell spacing → Backsheet reflection gains, electrical losses

◼ Number of solar cells →Module power, costs

◼ Module size → costs

Mechanism of backsheet reflection, gains depending on cell spacing

full cellhalf cell

encapsulant

front glass

solar cell

backsheet

Full and half cell module with identical size and cell spacing but withdifferent active area

M. Mittag et al., “Analysis of Backsheet and Rear Cover Coupling Gains for Bifacial Solar Cells”, 33rd EU PVSEC, 2017

© Fraunhofer ISE

7

Cell-to-Module AnalysisHalf and Full Cells

→ Assumptions necessary to compare concepts, modules and materials

◼ Module design for comparative CTM-Analysis

◼ Same module size

◼ Identical active area

→ Different cell distances

◼ Chosen designs are exemplary

SmartCalc.CTMwww.cell-to-module.com

free demo-version

Full cell

Same module area, same active area, different cellspacing

Half cell

© Fraunhofer ISE

8

Cell-to-Module AnalysisInput parameters

◼ Solar cells and other materials are identical in both modules

Full Cell Half Cell

Solar cells 60 120

Length [mm] 1670 1670

Width [mm] 998 998

Cell distance [mm] 5.3 2.5

String distance [mm] 2.5 2.5

Module area [m²] 1.677 1.677

Active area share 87.9% 87.9%

© Fraunhofer ISE

9

Cell-to-Module AnalysisFull Cell Module

SmartCalc.CTMwww.cell-to-module.com

free demo-version

! !

© Fraunhofer ISE

10

Cell-to-Module AnalysisConcept Comparison

SmartCalc.CTMwww.cell-to-module.com

Full cell module

Half cell module◼ Reduced electrical losses

◼ Larger number of cell spacings

◼ Reduced cell distances

→ Only minor additional gains from internal reflection

+7 Wp

Full Cell Half Cell

Power [Wp] 305 313

CTMpower [%] 98.1 100.7

Efficiency [%] 18.25 18.73

+0.4 Wp

© Fraunhofer ISE

11

Cell-to-Module AnalysisConcept Comparison

◼ Initial cell power identical in both modules

◼ Higher module power with half cells through improved CTM

◼ Module area unchanged (→ identical BoM)

◼ Results change for other module designs → detailed analysis necessary

→ Economical analysis possible after calculating the module power

Full Cell Half Cell

Power [Wp] 305 313 +8 Wp

CTMpower [%] 98.1 100.7 +2.6%abs

Efficiency [%] 18.25 18.73 +0.5%abs

© Fraunhofer ISE

12

Techno-Economic Analysis

◼ CTM-analysis shows advantages of half cells regarding module power

◼ Exact module setup necessary to quantify advantages

→ Module power

◼ Cost Calculation

◼ Material costs

◼ Processes

→ Cost of Ownership

€

Wp

J. Shahid et al., “A Multidimensional Optimization Approach To Improve Module Efficiency, Power And Costs”, 35th EU PVSEC, 2018

© Fraunhofer ISE

13

Cost of Ownership AnalysisScenario A: Low Additional Costs for Half Cells

◼ No additional Stringer

◼ No increased cell breakage

◼ No extra costs for cell handling

◼ No power losses through cell splitting

◼ No change in BoM (same module size)

◼ Increased power for half cell module (+8 Wp)

◼ Additional cell splitting machine

◼ Max. 6000 pcs/h, 300 k€ Invest

Material Cost Assumptions for the Cost of Ownership (CoO) Calculation

Glass 4 €/m²

EVA 0.9 €/m²

Solar cells 12 €ct/Wp

Ribbons 3.5 €ct/m

Backsheet 2 €/m

Junction Box 3 €/pcs

Frame 1.10 €/m

© Fraunhofer ISE

14

Cost of Ownership AnalysisScenario A: Low Additional Costs for Half Cells

◼ Full cell module

◼ 75.8 €/Module

◼ 25.0 €ct/Wp

◼ Half cell module

◼ 76.3 €/Module

◼ 24.4 €ct/Wp

◼ Results Scenario A:

→ Half cell module with higher absolute costs

→ CTM-power gains reduce specific costs (€/Wp) for half cell modules

Example production, only manufacturing costs

© Fraunhofer ISE

15

Cost of Ownership AnalysisScenario B: Additional Costs for Half Cells

◼ Additional Stringer: +1

◼ Increased breakage rates: 0.1% (+100% breakage at cell splitting)

◼ Additional costs for cell handling: +1% on total invest

◼ Power loss through cell splitting: -1%

◼ No change in BoM (same module size)

◼ Increased power for half cell module (+8 Wp)

◼ Additional cell splitting machine

◼ Max. 6000 pcs/h, 300 k€ Invest

Material Cost Assumptions for the Cost of Ownership (CoO) Calculation

Glass 4 €/m²

EVA 0.9 €/m²

Solar cells 12 €ct/Wp

Ribbons 3.5 €ct/m

Backsheet 2 €/m

Junction Box 3 €/pcs

Frame 1.10 €/m

© Fraunhofer ISE

16

Cost of Ownership AnalysisScenario B: Additional Costs for Half Cells

◼ Full cell module

◼ 75.8 €/Modul

◼ 25.0 €ct/Wp

◼ Half cell module

◼ 77.3 €/Modul

◼ 25.0 €ct/Wp

◼ Results Scenario B:

→ Additional costs through processes and technological risks may compensate power gains

→ Detailed analysis necessary

◼ Consideration of additional aspects (System + LCoE)

Example production, only manufacturing costs

© Fraunhofer ISE

17

Summary

◼ Half cells increase module power (~ 2-3%)

◼ Full cell modules with lower absolute costs (€)

◼ Advantage (€/Wp) of half cell modules depends on

◼ Manufacturing equipment and processes

◼ Impact of cell splitting on breakage rates and power losses

→ Results of techno-economic analysis depend on specific inputs (production environment, module design)

◼ Change of module design and topology necessary for half cells (serial and parallel connection of strings)

◼ Change of BoM may be necessary (change in module size)

© Fraunhofer ISE

18

Compatibility to future trends

◼ Half cells compatible to most new approaches in module design

◼ Glass-glass, round wire interconnection,…

◼ Larger solar cells (156 → 161 mm)

→ Larger currents and electrical losses (~ +10%)

→ BoM–change likely (module size)

◼ Bifaciality

→ Larger currents and electrical losses(up to +30% depending on albedo)

→ Detailed analysis of every setup necessary

© Fraunhofer ISE

19

Thank you for your attention!

Fraunhofer Institute for Solar Energy Systems ISE

www.cell-to-module.com

www.ise.fraunhofer.de

ctm@ise.fraunhofer.de

© Fraunhofer ISE

20

Preview

◼ SmartCalc.CTM features in development (coming soon)

◼ Non-STC modelling

◼ Inhomogeneous module operation

◼ Bifaciality

◼ …

◼ Free access to software updates for SmartCalc.CTM users

SmartCalc.CTMwww.cell-to-module.com

A. Pfreundt et al., “Rapid Calculation Of The Backsheet Couping Gain Using Ray Groups”J. Shahid et al., “A Multidimensional Optimization Approach To Improve Module Efficiency, Power And Costs”M. Mittag et al. “Approach for a Holistic Optimization from Wafer to PV System”

© Fraunhofer ISE

21

Non-STC Modelling

◼ Current increases with irradiance

◼ Electrical losses in full cell module especially high for high irradiance (STC)

Ploss, interconnection ~ I² x R

→ Relative disadvantage of full cell module decreases for low irradiances

→ STC measurements and STC-modelling may overestimate half-cell gains

→ Non-STC modelling and extended characterization necessary for concept evaluation

→ advantage of half cells is smaller at low irradiances (but still there)

Non-STC modelling results created withSmartCalc.CTM

SmartCalc.CTMwww.cell-to-module.com