1

PID – ANALYSIS AND MITIGATION

In the past few years, Potential Induced

Degradation (PID) has been recognized as a

failure mechanism that can cause substan-

tial power loss in different PV module types

and decrease the power plant performance

ratio. In some cases, corrosive PID also

becomes visible in module appearance.

Fraunhofer ISE offers comprehensive

services to module manufacturers, EPCs

(Engineering, Procurement, Construction)

and operators of PV power plants in order to:

n develop modules with low sensitivity

to PID

n avoid PID in advance

n determine if a plant is already affected

n identify the initiating factors and

predictfieldPIDbehaviorofmodules

n allocate procedures to reverse

degradation effects on module and

system level.

PID Diagnostics in PV Power Plants

Prediction and early detection of PID at the

system level are of particular interest for

owners and operators of PV power plants.

A PV power plant’s susceptibility to PID can

be determined within our comprehensive test

program either before plant commissioning

orduringoperation.Deficienciescanbe

identifiedevenbeforeperformancedegrada-

tion is observed.

At the system level, the PID investigation

startswithastreamlinedfieldexamination,

which includes IR (thermographic) inspection

and voltage or I-V curve measurements to

identify modules with affected cells. The

plant topology, in particular ground poten-

tial, inverter type and electrical layout, is

evaluated on-site. Local environmental risk

factors are assessed as well. Optionally, re-

presentative affected modules are selected

for laboratory tests. In most cases, it is

reasonable to follow up with laboratory

tests of selected modules to understand the

specificeffectandtoanalyzetherecovery

characteristics of the module types in use.

1 Module string of a PV power plant.

The electroluminescence and thermo-

graphic images are taken of the module

with the highest negative potential.

Fraunhofer Institute for

Solar Energy Systems ISE

Heidenhofstr. 2

79110 Freiburg, Germany

Phone +49 761 4588-0

Fax+497614588-9000

TestLab PV Modules

Daniel Philipp

Phone +49 761 4588-5414

tlpv@ise.fraunhofer.de

ServiceLab PV Power Plants

Boris Farnung

Phone +49 761 4588-5471

service.pvpowerplants@ise.fraunhofer.de

www.ise.fraunhofer.de

06-924-16

F R A U N H O F E R I N S T I T U T E F O R S O L A R E N E R G Y S Y S T E M S I S E

Beyond accelerated laboratory testing,

the PID behavior of modules can also be

examinedunderrealoperatingconditions.

We perform comprehensive outdoor PID

monitoring at our test sites worldwide or

at customer sites. A fundamental require-

ment for sound degradation analysis

is highly precise module characterization.

Our accredited CalLab PV Modules pro-

vides worldwide leading measurement

accuracy with an uncertainty down to

1.6 %.

Recovery from PID Degradation

Power degradation caused by PID may be

partly or fully reversible. By initiating suita-

ble measures, it is possible to regain a large

part of the original power. The recovery

rates of modules vary depending on the

level of degradation. At Fraunhofer ISE, we

examinetherecoverabilityinadedicated

recovery test.

Furthermore, we offer recovery services for

modulesinfieldoperation,providingcon-

sultancy in system design adjustment and

recovery strategies, as well as independent

monitoring and reports on the success of

the initiated changes.

The level of power, which can be regained

due to recovery measures, strongly depends

on the level of power loss due to PID. It

isrecommendedtoexecuteadequate

measures as early as possible.

2 Installed equipment for field recovery.

3 Outdoor PID monitoring at Gran Canaria, Spain.

2 3

PID at Module Level

Potential Induced Degradation may become

manifest in wafer-based modules through

corrosion of metallic components like cell

metallization and connectors, as well as

throughTCOcorrosioninthinfilmmodu-

les, accompanied by more or less reversible

module power loss due to a reduction of

shunt resistance Rsh.

The accredited TestLab PV Modules at

Fraunhofer ISE offers profound investigati-

on via measurements and tests to analyze

the sensitivity of PV modules. The test

program, which includes a PID test1 accor-

dingtotheTechnicalSpecificationIECTS

62804, is a well-established procedure for

testing the susceptibility of PV modules to

PID. More profound procedures also respect

the short-term (thermal) recovery. These

testsallowanassessmentofexpectable

PIDlossesoffieldinstalledmodules.For

EPCs, it has been proven to be helpful to

benchmark different module types with re-

spect to PID sensitivity. Comprehensive and

precise analytical procedures help to gain

a deep understanding of PID mechanisms,

and provide important information for PID

prevention activities.

Module manufacturers can take advantage

of our testing and material analysis capa-

bilities to understand the PID electro-

chemistry in their products and to improve

their module designs.

95.391.1

82.8

66.8

95.1 95.5 95.791

M04 M05 M03 M060 %

20 %

40 %

60 %

80 %

95 %100 %

% o

f no

min

al P

max

% of nominal Pmax before recovery % of nominal Pmax after recovery

4 Percentage of nominal PMAX before and after a

PID recovery experiment.

5 Declining PR of a PV power plant because of PID

and recovery of PR after installation of a recovery

box in 2013.

0

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30

40

50

60

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100

2008 2009 2010 2011 2012 2013 2014 2015

Performance Ratio [%]

1Note: PID strongly depends on the material composition

of a PV module. The PID test applies to the specific bill of

materials (BOM) which was tested.