Impact of soiling on PV module performance for various climates

1. Impact of Soiling on PV Module
Performance for Various Climates
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany
Dr Werner Herrmann
TÜV Rheinland Energie und Umwelt GmbH
51101 Cologne, Germany
werner.herrmann@de.tuv.com
http://www.tuv.com/solarpower

2. Outline
 Introduction
 PV-KLIMA test locations
 Experimental approach
 Results:
 Angular impact on soiling loss
 Soiling patterns for different climates
 Impact of periodical cleaning
 Summary
26.10.20152 4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

3. Introduction – PV power loss due to soiling
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 Dust deposition on the PV module surface is a complex phenomenon, which is
mainly influenced by the environmental/weather conditions, mounting principle
and glazing characteristics.
 Performance losses are site-specific and can strongly depend on O&M work.
Photo:TÜVRheinlandShanghai
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany
Installation conditions
Non-uniform soiling,
glazing characteristics
Surrounding environment
Climatic impacts

4. PV-KLIMA Project
Comparative energy yield testing of PV modules
Location Country Operation since Köppen-Geiger climate classification
Ancona Italy 01 Nov 2013 Cfa (mediterranean)
Tempe Arizona/USA 15 Dec 2013 Bwh (hot dessert)
Chennai India 01 Feb 2014 Aw (tropical savanna, hot-humid/dry)
Cologne Germany 01 Mar 2014 Cfb (temperate)
Thuwal Saudi-Arabia 11 Mar 2015 Bwh (hot desert, sandstorm impact)
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ChennaiAnconaCologneTempe
Saudi
Arabia
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

5. PV-KLIMA Test Locations
:
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Tempe / Arizona Chennai / Southeast India
2)
http://www.chennai.climatemp
s.com/
Location TUV Rheinland PTL, LLC
Tempe, AZ 85282
TUV Rheinland (India) Pvt. Ltd.
Chennai 602117, India
Geographical position: 33.4°N / 111.9°W
358 m above sea level
13°N / 80°E
35 m above sea level
Inclination angle 33.5° 15°
Annual in-plane global
solar irradiation
2360 kWh/m² 1860 kWh/m²
Average annual rainfall 219 mm 1597 mm
Surrounding
environment
industrial area,
no vegetation
Rural environment,
Farm land
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

6. PV-KLIMA Test Locations
:
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Cologne / Germany Ancona / Italy
Location TUV Rheinland Group
51101 Cologne, Germany
Loccioni
60030 Angeli di Rosora, Italy
Geographical position: 50.6°N / 7.0°E
53 m above sea level
13°N / 80°E
35 m above sea level
Inclination angle 35° 35°
Annual in-plane global
solar irradiation
1195 kWh/m² 1556 kWh/m²
Average annual rainfall 774 mm 757 mm
Surrounding
environment
Urban environment,
Flat roof of 5 storey building
Hilly landscape with grassland
and forest, agricultural use
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

7. :
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Thuwal / Saudi-Arabia
Location KAUST, NEO
Thuwal, Saudi-Arabia
Geographical position: 22.3°N / 39.1°O
3 m above sea level
Inclination angle 25°
Annual in-plane global
solar irradiation
23861) kWh/m² 1) Extrapolation from 204 days
Average annual rainfall 70 mm
Surrounding
environment
University ground, coastal
environment
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany
PV-KLIMA Test Locations

8. Experimental Approach
Measurement of soiling rate
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 Side-by-side irradiance measurement with two mini-modules:
 Standard PV glazing, center cell operated in short circuit (reference cell)
 Data recording interval: 30 seconds
 Soiling loss = Transmission loss  Lower effective irradiance reaching the cells
 Soiling loss factor (SLF) = Ratio of irradiances from “clean” and “dirty” cell
“Clean” mini-module “Dirty” mini-module
𝐺 𝐸𝐹𝐹 = 𝐼𝑆𝐶,𝑀𝐸𝐴𝑆/𝐼𝑆𝐶,𝑆𝑇𝐶 × 1 +  × (𝑇 𝑀𝑂𝐷 − 25°𝐶) × 1000 𝑊/𝑚²
𝑆𝐿𝐹 =
𝐺 𝐸𝐹𝐹,𝐷𝑖𝑟𝑡𝑦
𝐺 𝐸𝐹𝐹,𝐶𝑙𝑒𝑎𝑛
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

9. Results
Angular impacts on soiling loss
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 Dust accumulation on the glass surface changes its angular response
 Soiling loss depends on the angle of incidence (AoI) of direct sunlight
 Soiling loss due to AoI effects can be significant
 Tempe: -0.8% annual soiling loss is caused by angular transmission losses
in the range AoI >30°
W. Herrmann, M. Schweiger: Soiling and self-cleaning of PV modules under the weather conditions of two locations in
Arizona and South-East India, IEEE-PVSC42, New Orleans, USA, 2015
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

10. Results
Soiling pattern for Tempe/Arizona: Dec 2013 – Sep 2015
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Average daily
SLF decrease in
dry periods:
-0.08% to -0.22%
Annual soiling loss
(year 1):
-3.7% total loss
-0.8% angular loss
Annual soiling loss
(year 2*):
-1.4% total loss
 Single rainfall events  Effective cleaning: SLF recovery >99% observed
 Significant differences in soiling patterns for 1st and 2nd year  frequency of
rainfall, dust accumulation rate
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

11. Results
Soiling pattern for Chennai/India: Feb 2014 – Sep 2015
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Average daily
SLF decrease in
dry periods:
-0.12% to -0.39%
Annual soiling loss
(year 1):
-2.2% total loss
 3-months dry season  25% soiling loss observed
 Recovery in rainy season: SLF >99% in first year, SLF >98% in second year
 Significant differences in soiling patterns for 1st and 2nd year
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

12. Results
Soiling pattern for Ancona/Italy: Nov 2013 – Sep 2015
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Daily SLF decrease:
Not applicable
Annual soiling loss:
0,04% (Year 1)
0,02% (Year 2)
 High cleaning effectiveness due to rainfall during the whole year
 Comparable soiling patterns for 1st and 2nd year  ±1% SLF variation
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

13. Results
Soiling pattern for Cologne/Germany: Mar 2014 – Sep 2015
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Daily SLF decrease:
Not applicable
Annual soiling loss:
-0,16% (Year 1)
+0.17% (Year 2*)
 High cleaning effectiveness due to rainfall during the whole year
 Comparable soiling patterns for 1st and 2nd year  ±2% SLF variation
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

14. Results
Soiling pattern for Thuwal/Saudi-Arabia: Mar 2015 – Sep 2015
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 Corresponding wet cleaning of “dirty” mini-module  Reset SLF = 1
Experimental approach
for Thuwal test site:
Periodical mechanical
cleaning of the PV module
surface with rotating
brushes (Type NOMADD)
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany
 PV installations in desert climate (i.e. MENA region) require periodical
cleaning of PV module glass surface to optimize the energy yield

15. Results
Soiling pattern for Thuwal/Saudi-Arabia: Mar 2015 – Sep 2015
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 High ambient dust concentration  Average daily percent decrease of SLF = -0.5%
 Dust storm  Max. SLF change per day = -7.7%
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

16. Summary 1/3
Measuring results
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Average
annual
rainfall1)
Annual transmission
loss due to soiling
(Year 1)
Average SLF
decrease
between rainfall
events
Max. daily
SLF
decrease
Tempe /
Arizona
219 mm Year 1: -3.7%
Year 2: -1.4% 2)
-0,15% per day -1.8%
Chennai /
India
1597 mm Year 1: -2.1%
Year 2: -7.5% 2)
-0,2% per day -2.2%
Ancona /
Italy
757 mm negligible N/A -0.4%
Cologne /
Germany
774 mm negligible N/A -1.1%
Thuwal /
Saudi-Arabia
70 mm N/A
Periodical cleaning
-0.5% per day -7.7%
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany
1) http://de.climate-data.org
2) Measuring data of year incomplete

17. Summary 2/3
Principle effects
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 Self-cleaning effect:
Rainfall leads to nearly full recovery of PV module performance.
Permanent soiling can occur if humidity condensate sticks dust to the surface
or can be caused by algae growth.
 Soiling pattern:
Great variation in daily percent decrease of soiling loss factor (SLF) makes
soiling loss prediction difficult in tropical and arid climates
 Broader data basis required
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

18. Summary 3/3
Impact of soiling for various climates
18 26.10.2015
 Hot-dry climate:
Tempe: Moderate dust settlement between periodic rainfall events leads to
annual performance loss <4%
Thuwal: Considerable dust settlement and missing rainfall lead to substantial
annual performance loss >50%, which requires periodical cleaning for
economic operation of a PV power plant.
 Hot-humid/dry climate:
Chennai: Considerable dust settlement during 3-months dry season can lead to
substantial soling loss. Cleaning during dry season must be considered to
improve the performance of a PV power plant.
 Temperate and Mediterranean climate:
Ancona, Cologne: No measureable performance loss due to frequent rainfall.
4th PV Performance Modelling and Monitoring Workshop
22/23 October 2015, Cologne, Germany

19. Thank you for your attention!
werner.herrmann@de.tuv.com
http://www.tuv.com/solarpower
Work was partially funded by the German Federal Ministry for Economic
Affairs and Energy (BMWi) under contract No. 0325517B.