Ian Bennett

DSM Advanced Surfaces

October 25th, 2016

CONFIDENTIAL

Internal soiling test method development

6th PV Performance Modeling and Monitoring Workshop

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CONFIDENTIAL

Contents

1. General introduction

2. Taber oscillating test

3. Dust settling test

4. Transmission measurements

5. Conclusions

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Paris- Roubaix

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Coal Mining

DSM – understands change

Commodity

Chemicals

Life Sciences

& Materials

Sciences

2

Specialty

Chemicals

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1. IntroductionAlice Springs, Australia

Pune, India

Dunhuang, China

Ground Module

Module

Module

3

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4

Dunhuang, China

1. Introduction

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1. Introduction

• No standard test equipment or norm for soiling is available in the

market, each company/institute has their own method and believe

that is the right one

• Potential test equipment has to be checked for soiling suitability

or has to be specially built for this purpose

• Soiling and evaluation methods still needed to be developed

• Started the test method development based on availability and

chance of success

• Support development of industry standard

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2. Taber oscillating testDescribed in ASTM F735:

• Used to measure the resistance of a

material to surface abrasion and

scratching

• Primary application for transparent

materials and coatings in lenses and

windows

Key features and parameters:

• Easy and fast screening tool

• Sample is at horizontal position

• Strong interactions of sand with surface by

oscillations

• Oscillation distance, speed and cycles

• Type of soil6

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2. Taber oscillating test

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Method can distinguish soiling performance different coatings

2. Taber oscillating testBlank glass

Soil coverage: 20.8% Soil coverage: 11.1% Soil coverage: 2.3%

AR coating AS coating

Soiling parameters:

- 19 °C and 45 %RH

- 300 cycles, 100 cycles/min

- Arizona coarse sand

- 2 plates per sample

0.0

1.0

2.0

3.0

4.0

5.0

6.0

7.0

Blank glass AR coating AS coating

Tran

smis

sio

n lo

ss %

Samples

80

85

90

95

100

400 500 600 700 800 900 1000 1100

Tan

smis

sio

n %

Wavelength (nm)

Blank glass - Before

Blank glass- After

AR coating - Before

AR coating - After

AS coating - Before

AS coating - After

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3. Dust settling testDescribed in IEC-68-2-68 (Lb):

• Used to test specimen in a low density dust atmosphere

which is freely settled by gravity

• Primary application for checking if electrical instruments

keep functioning in a dusty environment and if their housing

is dust tight

Key features and parameters:

• Gentle blow and free settling of soil, settling speed:

< 0.2m/s

• Sample can be placed at various positions and angles

• Injection time and cycles

• Type of soil

• Temperature

A lot of possible parameters and interactions!

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3. Dust settling test

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Before soiling During soiling After soiling After exposure to air flow

-1.2-1.3

-1.4-1.1AS

coatingBlank

glass

AR

coating -1.2

-1.3

-1.4-1.1AS

coatingBlank

glassAR

coating

0%

10%

20%

30%

40%

50%

60%

70%

blank glass AR coating AS coating

Tran

smis

sio

n lo

ss

Samples

before exposure to air flow after exposure to air flow

AS coating shows lower transmission loss after sequential testing

with China medium sand and exposure to air flow.

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4. Measurement soiling on glass

Field measurement

• Mostly complete panels

• Specific measuring equipment

• Can be expensive

Lab measurement

• Not field applicable

• No universal method

• Measuring area can be limited

Optosol Transpec VIS-NIR spectrometer

Measurement set-up with reference cel

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4. Measurement soiling on glass

In-field transmission measurement

for soiling on glass

• Practical, easy to use

• Accurate

Pyranometer - Li-Cor LI-200R

• Handheld size

• Easy to use

• Spectrum limited to 400–1100 nm

• Response curve equal to a c-Si

solar cell

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4. Measurement soiling on glass

OsramHalospot 11112 V; 50 W; 6°

650 W/m2

10° angle of incidence on lamp to emulate Optosol

Stable power supply

Adjustable height

Shade and sample holder

Lab evaluation

• Comparison transmission measurements Optosol with

pyranometer

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4. Measurement soiling on glass

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.08 0.09 0.1 0.11 0.12 0.13 0.14 0.15 0.16

Frac

tio

nal

loss

mea

sure

d w

ith

pyr

ano

met

er

Fractional loss measure on Optosol

Distance glass

Distance glass to pyranometer7 cm

Distance glass to pyranometer0.7 cm

Distance glass to pyranometer0 cm

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• Able to reproduce measurements Optosol with

pyranometer lab set-up also for soiled glass

samples

• Best correlation between Optosol and

pyranometer at short distance between glass

and sensor

• Distance to light has little effect, same is true

for angle of light

• With pyranometer against glass, more noise in

measurement and correlation is lost

• Next step; validation in the field and other

methods

4. Measurement soiling on glass

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Conclusions

• Developing 2 lab test methods including humidity and

particle size distribution

• Correlations between lab test results and real

outdoor performances still need to be further

verified - extensive outdoor test programme

• Developing method to follow soiling on glass using a

pyranometer or other method

• Additional surface analysis using AFM

• Looking for new concepts/methods/equipment for

testing soiling performances in the lab

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