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IEA INTERNATIONAL ENERGY AGENCY

PHOTOVOLTAIC POWER SYSTEMS PROGRAMME

[email protected] IEA PVPS Task13 Meeting & WS 2016-04-08 1

Potential Induced Degradation of PV modules & systems

IEA Task 13 Meeting & WorkshopEURAC, Bolzano 2016-04-08

Karl A. Berger

AIT Austrian Institute of TechnologyEnergy Department

Giefinggasse 2A-1210 Vienna, Austria

+43 664 825 [email protected]




Outline

Intro: PID - Potential induced degradation effects

PID – Module IV and effects at STC and LIC

Influencing parameters

PID-Testing

PID-Test description IEC TS 62804-1

Temperature & humidity

Regeneration

Module material investigations

PID detection methods

IEA-PVPS T13-01 Module failure review report




PID - Potential induced degradation effects

• Potential differences between in a string connected PV-cells and the ground potential cause a leakage current

• As early as 1978 and in the nineties leakage-current driven electro-chemical corrosion and polarization effects of crystalline and thin-film cells in modules were reported, and a minimum required insulation resistivity under wet conditions was established as a short term test (wet leakage current test)

• In applications the voltage stress was very limited, PV-modules were used to load batteries and the systems were small …

• 2005: High efficiency n-type cells evolved potential induced power degradation at positive polarity from cells to ground. Several different module types with (standard) p-type cells degraded in negative polarity too.




PID – Ion accumulation at stacking faults

Different effects summarized under PID

• In p-type cells Na+ ions from the front glass accumulate at stacking faults on the cell surface resulting in a – more or less –reversible polarization

• These Sodium enriched areas can cause a massive reduction of the cell’s shunt resistance

• The power loss of the affected modules depends on duration and voltage stress level, bill of materials and various ambient conditions, and is able to re-duce the module power to values below 30% within a few month in the field under unfavorable conditions.




Electric circuit schema

• How the potential of the d.c. side of the inverter is relative to the ground is essential

• Reduced VOC and Vmp of PID-faulty modules “pulls” then further modules on the bad side of the string …




Module failures – bathtub upside down

Typical failure scenarios for wafer-based crystalline PV modules• PID is not detectable on site during capacity measurements in

the commissioning phase, but degradation may start soon after

IEA-PVPS T13-01: 2014




PID – Module IV at STC and LIC

IV-curve measurement results, before and after PIDa) Massive reduction in FF, and reduced VOC & ISC

b) Massive VOC and FF reduction (7 month outdoor in IT), stable Isc

Because the shunt resistance is drastically reduced, the low light behavior (here LIC down to 200 W/m²) is even worse




PID – irreversible corrosion effects

Different effects summarized under PID• Beside reversible PID-effects, electro-corrosion can occur• Also crystalline module types may show visible degradation

(e.g. of the SiNx anti-reflective coating at the cells• In TF PID mechanisms some with, and without the availability

of water(vapour) in the module are known• Often PID affected modules look perfect, without visible failures• Detecting PID in OD performance data is hindered by

measurement UC at LIC





Different effects summarized under PID• Beside reversible PID-effects, electro-corrosion can occur




PID – Influencing parameters

Lots of influencing factors from cells, module bill of materials, mounting and electric operation, as well as from climatic operating conditions - temperature, humidity, soiling, etc.

IEA-PVPS T13-01: 2014




PID – Test standard

PID effect not covered in module design and safety qualification

• Discussion for years in IEC TC82 WG2 -PV module group howa meaningful PID-test should look like

• Accelerate by humidity and temperature (a), or

• Enhance surface con-ductivity by applying a conductive foil

• IEC TS 62804-1 for x-Siwithout PASS/FAIL




PID – Accelerating & influencing factors

(a) Desert climate: dew over night, dries during daytime

All: Fair Arrhenius-like change in leakage current as f(temperature)

Climaticchamber85% rH





(a) Desert climate: dew over night, dries during daytime(b) Climate with frequent rainfallAll: Fair Arrhenius-like change in leakage current as f(temperature)


Aluminumfoil, dry

Outdoorrain





(a) Desert climate: dew over night, dries during daytime(b) Climate with frequent rainfall, and or soiling, salt mistAll: Fair Arrhenius-like change in leakage current as f(temperature)


Outdoorsoiled

Aluminumfoil, dry




PID – Affected system locations

PID affected systems (2014): most of them hot and/or coastal sitesBut: continental& rainy too




PID – Regeneration

Two competing processes: PID degradation vs. thermal and/or potential induced recovery processes

• Thermal diffusion extracts ions from stacking faults

• Diffusion rate strongly dependent on temperature: Arrhenius





• Reverse ele. potential speeds up the ion removal, S-shaped

• Leakage current, respective transferred charge matter for regeneration, one master curve for all temperatures

Peter Lechner, Bad Staffelstein 2016






• Outdoor regeneration with voltage applied quite fast when hot

Slow TR

time [h]

time [h]

Ther

mal

rege

nera

tion

TR

0.1 1 10 100 1 000 10 000 100 000







• Outdoor regeneration with voltage applied quite fast when hot

Slow TR

time [h]

time [h]

time [h]

Ther

mal

rege

nera

tion

TR

0.1 1 10 100 1 000 10 000 100 000

0.1 1 10 100 1 000


Fast PIR

Pote

ntia

l ind

uced

rege

nera

tion

PIR

time [h]




PID – accelerated aging IEC 62804-1

PC controlled HV-operation & measurementAutomatic periodic switch to dark IV-measmt.

Dark IV

-1000 V ON10kΩ

1Ω

RpPID = 1/8000 Rp0




Purchased modules: accelerated aging IEC 62804-1

• Method (a) – climate chamber test @ 85% r.H., 60oC, -1000V• Leakage current 2µA … 100µA – not correlated with Power loss

NO Power




Purchased modules: accelerated aging IEC 62804-1• Degradation phase: Best Modules -1%, worst 95% loss• Recovery phase: low PID degradation – good recovery

high degradation – poor recovery




Purchased modules: accelerated aging IEC 62804-1• Degradation phase: Module #12: -95%

Pmpp = 220W Pmpp = 12W

EL

PID

EL




Purchased modules: accelerated aging IEC 62804-1• Degradation phase: Module #12: -95%• Recovery phase: 50% only

Pmpp = 220W Pmpp = 12W

Pmpp = 110W Dark IR Pmpp = 110W

EL

PID

EL

EL




Components varied: accelerated aging IEC 62804-13×2 cell mini-modules• 8 encapsulants

a) Variations of encapsulant Module No. stress 1 stress 2EVA 1 1 PID 24hEVA 1* 2 PID 24h recover 24hEVA 2 3 PID 24h recover 24hEVA 3 4 PID 24h recover 24hEVA 4 5 PID 24h

Silicon 6 PID 24hPolyolefin 1 7 PID 24hPolyolefin 2 8 PID 24h

PVB 9 PID 24h




Components varied: accelerated aging IEC 62804-13×2 cell mini-modules• 8 encapsulants• 3 back sheets

a) Variations of encapsulant Module No. stress 1 stress 2EVA 1 1 PID 24hEVA 1* 2 PID 24h recover 24hEVA 2 3 PID 24h recover 24hEVA 3 4 PID 24h recover 24hEVA 4 5 PID 24h

Silicon 6 PID 24hPolyolefin 1 7 PID 24hPolyolefin 2 8 PID 24h

PVB 9 PID 24h

b) Variations of back sheetsBS 1 10 PID 24h recover 24hBS 2 11 PID 24hBS 3 12 PID 24h




Components varied: accelerated aging IEC 62804-1Parameter Degradation (100% = initial value)

The encapsulant influences V, I , Pmpp and FF different !




Components varied: accelerated aging IEC 62804-1IV-curves, encapsulant varied

The encapsulant influences V, I , Pmpp and FF different !




Components varied: accelerated aging IEC 62804-1IV-curves, encapsulant varied

IV-curves, back sheet varied

The backsheet influences PID!The encapsulant influences V, I , Pmpp and FF different !




PID – Can affect small to utility scale systems

• Check combinations of intended materials – even when cells are claimed “PID-free” with the PID-test procedure(s) IEC 62804-1 for xSi modules. (A part 2 for TF modules is under consideration)

• Take care selecting the right inverter model

• Check operating sys-tems, e.g. by detailledmonitoring analysis, infrared and/or electro-luminescence imaging …

because PID is a major reason for underperforming systems!




PID detection methodsElectroluminescence imaging (EL):Near IR-emission by rekombinationstimulated from forward bias current

The IEA-PVPS T13-01 report, Review of Failures of PV Modules

is, together with many others freely available at the IEA-PVPS

website http://iea-pvps.org/index.php?id=275

IV-curve measurement under illumination, or dark-IV curve msmt.

Dark IR imaging

Abbreviations for Safety & Power loss categories: PID

Outdoor infrared image of a PV module string with PID

B. Weinreich, 2013




http://www.pv-reliability.com/

Announcement: Coming Soon …




Thank You for Your Attention!

The Austrian contribution within the IEA-PVPS Task 13 is (partly) funded by KLIEN

and the Austrian Federal Ministry for Transport, Innovation and Technology

Karl A. [email protected]://www.ait.ac.at/research-services/research-services-energy/?L=1

IECEE CB-Schemehttp://www.iecee.org/cbscheme/Certificate_of_Acceptance/tl001.pdf

/

http://www.ait.ac.at/research-services/research-services-energy/photovoltaik/

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