PV Module efficiency analysis and optimization

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PV Module efficiency analysis and optimization

Ingrid Haedrich1, Harry Wirth1, Michael Storz2, Gerhard Klingebiel2

1 Fraunhofer Institute for Solar Energy Systems ISE, 2 Schmid Technology Systems

How to rate Solar Energy Efficiency to maximize returns? Webinar, 18th September 2012

www.ise.fraunhofer.de

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Outline

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Introduction

Determination of series resistance

Analysis of optical properties

Modeling of module power

Sensitivity analysis

Conclusions

Module Technology Center, interior view

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Photovoltaic Modules, Systems and Reliability

Module technology

.

Durability analysis and environmental

simulation

Quality Assurance Modules and Power

Plants. Reliability Testing

Material analysis

Testlab PV Modules

Yield certificates

Power plant inspec-tion and testing

Monitoring

CalLab PV Modules

Interconnection technology

Module efficiency and new concepts

Module Technology Center (MTC)

Fields of activity

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Photovoltaic Modules, Systems and Reliability

Efficiency and electric yield improvement

Enabling of advanced cell technologies

Material cost reduction

Production yield improvement

Estimated cost structure for poly-Si PV module

Module technology responsible for:

35-40% of product cost, 15% of product efficiency, 95% of prod. reliability

Objectives

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Work areas and topics

product development

process development

material proving

paste/adhesive

front glass

vac. carrier vac. carrier

PC backsheet

encapsulant (1) cells encapsulant (2)PC backsheet

flip

1 2 3 5

4

One-Layup process for back-contact module production

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Work areas and topics

Interconnection processes

qualification of new cell metallization

lead free/flux free soldering

Al contacting

Cell interconnector design

back contact technology

stress reduction

electrical/optical efficiency

Module efficiency

optical, electrical improvements

inactive area reduction

Bi-metal effect, unilateral soldered, 160 µm cell

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efficiency losses from solar cell to complete module: typ. 10-15 percent

especially for high efficiency cells it is important to understand how to keep the efficiency inside a module

approach

establish procedure for predicting module efficiency from material and geometry data

investigate effects on efficiency change for specific module built-up

analyse sensitivity of module power with respect to material and design improvements

Introduction cell to module losses

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Basic effects:

1. electrical losses generated by string formation and cables

2. optical losses and gains generated by the various interactions between cell, encapsulant, glass and backsheet

3. module format including inactive areas

Introduction

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Introduction

module format

Optical gains and losses

electrical losses

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Series resistance losses

cable,losssc,lossgap,lossemitter,lossbase,lossmod,loss PPPPPP

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Series resistance losses

cable,losssc,lossgap,lossemitter,lossbase,lossmod,loss PPPPPP

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Series resistance losses

cable,losssc,lossgap,lossemitter,lossbase,lossmod,loss PPPPPP

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Series resistance losses

cable,losssc,lossgap,lossemitter,lossbase,lossmod,loss PPPPPP

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Series resistance losses

cable,losssc,lossgap,lossemitter,lossbase,lossmod,loss PPPPPP

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Series resistance losses

IBB current per busbar

l length of the cell

Rb,eff effective resistivity (ribbon, metallization)

eff,b2

BBbase,loss R3

lIP

Assumption: continuous soldering joint over cell length

cable,losssc,lossgap,lossemitter,lossbase,lossmod,loss PPPPPP

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Resistivity of emitter and base busbar

Series resistance losses

TLM measurement results for a commercial mc cell

2 mOhm/cm effective for base busbar (including aluminium screen print)

11 mOhm/cm for emitter busbar

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polycrystalline full square 6” cell

STC power from cell flasher: 4,54 W

short circuit current: 8,35 A

total power loss due to stringing electrical resistivity: 0,156 W/cell

power loss 60-cell module with 3 mm cell distance: 9,9 W

Series resistance losses

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Effective reflection and absorption losses of glass and encapsulation material

Analysis of optical properties

Direct coupling gain due to encapsulation

Optical gains due to an increasing cell space

air

EVA

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measured sheet transmissivity

measured sheet reflectivity

Txy transmissivity from

medium x (air) to medium y

Rxy reflectivity at the surface

from medium x (air) to medium y

t bulk transmissivity

nx refractive index of medium x

Analysis of optical properties

2201

201

tR1

tT

2201

212

201

01tR1

tRTR

21

21

1210011

1

n

nRRR

Effective transmission-, reflection and absorption coefficient

From sheet to material properties

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Effective transmission-, reflection and absorption coefficient

Analysis of optical properties

400 600 800 1000 12000,00

0,05

0,10

0,15

0,20

air glass reflectivity relative spectral response bulk absorptivity glass AM 1.5 spectrum standardized bulk absorptivity EVA

Wavelength

Abs

orpt

ion

/ R

efle

ctio

n

0,0

0,2

0,4

0,6

0,8

1,0

Relative spectral response / A

M 1.5

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Analysis of optical properties

bulk transmission

reflectivity air/medium

bulk absorptivity

glass 99,2% 4,1% 0,3%

encapsulant 97,9% 3,2% 2,1%

Determined optical properties for glass and encapsulation

Effective transmission-, reflection and absorption coefficient

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Coupling effects due to encapsulation

Analysis of optical properties

cellair

encapsulantcell

air

Isc,air

Isc,EVA

Change of Isc

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Analysis of optical properties

The measured change of Isc results from several optical effects:

Coupling effects due to encapsulation

reflection at air/EVA surface

effective bulk absorption of EVA material

direct coupling gain, due to increased refraction index at cell interface

indirect coupling gain, due to multiple reflection between cell surface and encapsulant/air interface

coupling effects

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-6%

-4%

-2%

0%

2%

4%

6%

8%

10%

Poly (Typ A) Mono (Typ B) Mono (Typ C) Mono (Typ D)(Isc,

enca

psul

ated

-Isc,

air)

/Isc,

air

[%] coupling gain

measured total current gains/losses

Analysis of optical propertiesCoupling effects due to encapsulation

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Analysis of optical properties

y = 0,0046x - 0,0174

-3,0%

-2,0%

-1,0%

0,0%

1,0%

2,0%

0 1 2 3 4 5 6

cell distance [mm]

(Isc

,enc

-Isc

,air

)/Is

c,ai

r [%

] Isc change

Linear (Isc change)

Optical gains due to cell spacing with white backsheet

Measurement on 8 samples with increasing cell distances

average Isc gain: 0.5 %/mm spacing

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Modeling of module power

The predicted module power was found to be within the range of module flasher measurement uncertainty = +/- 3%

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Sensitivity of module efficiency of four different parameters

Sensitivity analysis

0,0%

0,5%

1,0%

1,5%

2,0%

2,5%

3,0%

0% 10% 20% 30%

parameter increase [%]

D m

odul

e effi

cien

cy

cross section area cell connector ribbonreduction width module borderreduction width cell distancereduction resistivity emitter busbar

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Major effects and sensitivities have been shown

Efficiency analysis tool has been set up

Module efficiency depends strongly on cell/module interaction

New cell technologies will require adapted module materials

Outlook: additional evaluation of electric yield

this work has been performed in cooperation with:

Schmid Technology Systems

Conclusion

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Thank You Very Much for Your Attention!

Ingrid Haedrich

[email protected]

Fraunhofer Institute for Solar Energy Systems ISE