Hail Impact on PV Module Reliability - IEA PVPSiea-pvps.org/fileadmin/dam/public/report/technical/03_Intersolar... · IEA INTERNATIONAL ENERGY AGENCY PHOTOVOLTAIC POWER SYSTEMS PROGRAMME

IEA INTERNATIONAL ENERGY AGENCY

PHOTOVOLTAIC POWER SYSTEMS PROGRAMME

Hail Impact on PV Module ReliabilityGerhard Mathiak, TÜV Rheinland, Cologne09 June 2015, Munich, Intersolar, IEA PVPS Task 13J. Sommer, F. Reil, J. Althaus (TÜV Rheinland, Colo gne)M. Köntges (ISFH, Hamelin) – M. Nüsperling (Cologne)



Motivation• Frequency of severe hail storms

increased in the last years

• Insurers / installers ask for more severe

test requirements for the installation in

critical places

• TÜV Rheinland � first German test

center approved by Swiss VKF

Insurability can be demonstrated by test certificates!

Hail Risk



Agenda

1. Hail Damage in the Field

2. Hail Impact Test

3. Hail Damage in the Lab




� Glass breakage is easy to detect� Number of modules with severe

cell cracks may be much higher (after hail event)

� Electroluminescence analysis may be used for crack detection

� Hail-typical cell damages are STAR CRACKS

� Power of cracked cells is mostly unchanged



1. Hail Damage in the FieldField Examples by ISFH and Nüsperling (all modules were investigated)� Roof with 84 modules (6cm)

� 42% glass breakage� Roof with 156 modules (4cm)

� 90% star cracks � No simple relation between

glass breakage and star cracks� Modules without glass breakage

have no power loss directly after the hail event

No Crack

Other Cracks

Star cracks

Glass breakage



1. Hail Damage in the FieldSpatial Distribution of Cell Cracks� The impact of hail stones is randomly distributed� Patterns of cracked cells can be found� Distribution of cracked cells close to the frame and in the center

39 Modules: Cracks 39 Modules: Star cracks



All cracks (991:1006) and hail cracks (238:204) are nearly equallydistributed (close to the frame : in the center) !

System 1 System 2Nr. 1 2 3 4 5 6 7Manufact. A B B B B B CCell type mono multi mono multi mono multi multiCells 6x12 6x8 6x10 6x10 6x10 6x10 6x10

Fr C Fr C Fr C Fr C Fr C Fr C Fr CCells 32 40 24 24 28 32 28 32 28 32 28 32 28 32(in %) 44 50 47 47 47 47 47All Cracks 191 154 275 311 112 75 63 95 40 38 222 153 88 180(in %) 55 47 60 40 51 59 33Hail cracks 34 50 36 33 30 14 21 39 1 3 116 65 0 0(in %) 40 52 68 35 25 64 --


But Nr. 4 and Nr. 6 are identical module types?



Multi

6x10All cracks Star cracks

Frame Center Frame Center

Analysis

(4, 2013)

63

40%

95

60%

7

37%

12

63%

Analysis

(6, 2014)

222

59%

153

41%

52

61%

32

39%

Influencing Parameters� Hail event

� Hail stone size� Intensity, wind � Temperature (EVA stiffness)

� Module � Glass/Glass – Glass/Foil� Glass thickness� Frame thickness� Cracks by transport or snow

� Mounting � Strength of clamps� Mounting angle (30°roof, 0°tracker in strong wind position)




1. Hail Damage in the FieldFollow up Failures� Power and safety in future

operation?

� Environmental simulation� Ageing in environmental

chamber (after 200 thermal cycles nearly no change in performance)

� Mechanical load test



2.Hail Impact Test

Natural Hailstones

• Mainly during summer

• Growth layer by layer (onion)

• Circulation in thunderstorm

Ice Balls for Testing

• Highly reproducible

• Exact diameter, mass

• No visible voids, cracks

• Best method: Cut out of a clear block and melted to final form



2.Hail Impact TestExperimental Setup

• Pneumatic cannon

• 20 l, 10 bar vessel

• Photoelectric speed meter

• Interchangeable barrels with various diameters



Standard IEC 61215 (PV) (normally Ø=25mm ice balls)

VKF test requirement Nr. 00a (mainly HW3, HW4, HW5)

• Storage temperature (-4°C, IEC and -18°C, VKF)

• 11 impact locations

• Fail Criteria: Visual effects (Glass breakage) & >5% power loss

• VKF: Electroluminescence: cell cracks (requirem. are being defined)

2.Hail Impact Test

HW3 HW4 HW5Ø [mm] 30 40 50Mass [g] 12.30 29.15 56.94Speed [m/s] 23.85 27.54 30.79Energy [J] 3.50 11.05 26.99Max. Force [kN] 2.13 4.23 6.98



2.Hail Impact TestForce Measurement for VKF

• Force plate – piezoelectric sensor

• F(x) = -C x1.5 [Elastic theory by H. Hertz]

• Fmax ≈ R2 V1.2; Energy ≈ R3 V2



• Glass damage close to the frame• Hardened glass breaks quickly • Cell cracks detectable with

electroluminescence

High Speed Camera (2500fps)

Time = 0.0 ms (1)

3. Hail damage in the Lab



Time = 2.4 ms (7)




Time = 6.4 ms (17)




Time = 7.6 ms (20)




Time = 16.8 ms (43)




Time = 17.2 ms (44) Distance Step = 12 mm, Step = 0.4 ms




Quick Glass Breakage

Time = 17.6 ms (45)




Time = 18.0 ms (46)




Time = 18.4 ms (47)




Time = 18.8 ms (48)




Time = 19.2 ms (49)




Time = 19.6 ms (50)




Field star crack Lab star crack (Ø 35 mm)




Glass-glass-modules (3.2 mm & 3.0 mm) show no cell cracks!

Module type Module damage

CellsGlassthick

Framethick

Glassbreakage

Cell cracks

[mm] [mm] 50 mm 35 mm 40 mm 50 mm6x10 multi 3.2 50 Frame Branch Branch Star6x10 multi 3.2 42 Frame Single Star Star6x10 multi 3.2 40 no Star Star Star6x10 mono 4.0 42 no no Single Branch6x10 mono 4.0 35 no no Branch Branch6x10 multi 3.2&3.0 51 no no no no

3.2 mm glasses can be destroyed by 50 mm ice balls!4.0 mm glasses reduce cell cracks!




4. SummaryHail Impact Test

• Same failures in field and lab

• IEC and Swiss VKF (more severe)

Quality and Reliability

• Thin glasses (< 3.2 mm) can be broken by hail stones (Ø 40mm)

• Thick frames are good for mechanical load, but for hail?

• Certificates of higher severities demonstrate quality

Outlook for further Investigations

• Development of star cracks (follow up failures)

• Effect of maximum force / energy on glass breakage / cell cracks



Thank you for your attention

Project FidelitasFKZ: 0325735A

Project IEA Task 13FKZ: 0325786A

Documents

Hail Impact on PV Module Reliability - IEA PVPSiea-pvps.org/fileadmin/dam/public/report/technical/03_Intersolar... · IEA INTERNATIONAL ENERGY AGENCY PHOTOVOLTAIC POWER SYSTEMS PROGRAMME