Post on 10-Jan-2017
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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CONFIDENTIAL
Coal Mining
DSM – understands change
Commodity
Chemicals
Life Sciences
& Materials
Sciences
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Specialty
Chemicals
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CONFIDENTIAL
1. IntroductionAlice Springs, Australia
Pune, India
Dunhuang, China
Ground Module
Module
Module
3
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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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