Invited Paper
Junction box wiring and connector durability issues in photovoltaic
modules
Juris Kalejs*, American Capital Energy, Lowell MA 01854
ABSTRACT
We report here on Photovoltaic (PV) module durability issues associated with junction boxes which are under study in
Task 10 of the International PV Quality Assurance Task Force (PVQAT). A number of failure modes are being
identified in junction boxes in PV arrays in the field which have less than 5 years outdoor operation. Observed failure
modes include melted contacts and plastic walls in the junction boxes, separated external connectors and broken latches.
Standard IEC and UL tests for modules are designed to expose early mortality failures due to materials selection and
design in the assembled module and their impact on performance and safety. Test standards for individual junction box
components, when not part of a PV module, are still in development. We will give an overview of the reported field
failures associated with junction boxes, and examine standard development as it may impact on testing for durability of
junction box connectors over a 25 year life.
Keywords: photovoltaic, modules, junction box, standards testing, durability, quality assurance, connectors
1. INTRODUCTION
Mechanical robustness and electrical stability of Junction Box (JB) electrical terminations are critical to safe, reliable
and durable functioning of a photovoltaic (PV) module. This functionality is expected to extend over the 25 year
warranty period of a typical PV product. Standards for testing JB components and understanding of factors which affect
lifetime and durability are governed by manufacturing guidelines on wiring, insulation and materials, and by
performance testing, e.g., IEC 61215 and IEC 61646 certification testing for the PV module [1], where the JB is an
embedded component of the completed module. The module certification tests do not specifically stress JB components,
such as the electrical connector joints. Additionally, other standards, e.g., IEC 60352, specify assembly procedures
which are mainly visual and mechanical in nature, and which are oriented toward safety, but do not provide any
understanding of durability limitations or end-of-life failure modes.
The junction box is attached to the back skin of the module with adhesive. We do not address JB adhesive durability
testing in this paper, but only issues related to electrical connections, enabled by connectors of various configurations
which provide current paths to the outside wiring of the module, the as covered by the objectives of the PVQAT Task
10. The next Section 2 gives examples of early (<5 years outdoor exposure) connector failures, followed in Section 3 by
details on JB connector configurations and current standards for test practices. The last two Sections 4 and 5 outline
Task 10 activities.
2. FIELD OBSERVATIONS ON JUNCTION BOX CONNECTORS
Concerns have been raised about JB robustness and durability as a result of failures in the field after less than 5 years of
deployment. Typical failures seen are illustrated in Fig. 1 below. In Fig. 1(a), there is shown a breakdown in an interior
pressure contact on the right side of the JB. This likely starts with some slight defect or dust particle, or misalignment of
pin and sleeve during manufacturing, and then, over time, which in this case is likely over a time span of several years,
leads to sparking and then overheating and melting of the joint. Figure 1(b) shows a failure which initiates at a connector
joint which is penetrating the JB wall.
Various causes spanning all areas of manufacturing and use can be advanced as contributing to observed JB connector
failures: connector manufacturing deficiencies and materials, module manufacturing assembly procedures, stresses
exerted on connector joints in handling of external wiring during installation, and critically, field conditions which
produce environmental stresses exceeding those encountered in IEC standards testing.
* [email protected]; phone: 1-978-221-2023; fax; 978-455-7326
Reliability of Photovoltaic Cells, Modules, Components, and Systems VII, edited by Neelkanth G. Dhere,
John H. Wohlgemuth, Rebecca Jones-Albertus, Proc. of SPIE Vol. 9179, 91790S · © 2014 SPIE
CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2063488
Proc. of SPIE Vol. 9179 91790S-1
(a)
(b)
Figure 1. Typical failures encountered in JB wiring and connectors: (a) interior sparking and melting of right side connector pin; (b)
failure of connector penetrating JB wall and leading to exterior wiring.
Specific mechanisms which can be invoked are:
• Inadequate stress safety factors in design of parts
• Pin misalignments, metal-to-metal pressure contact mechanism failures
• Pin O-ring weathering
• Inadequate manufacturing practices in soldering or welding (flux, temperature control)
• Dirt/dust ingress in connector joint areas during shipping, warehousing and installation; some connector
manufacturers recommend capping of open connector joints such as pins, but industry-wide recommendations
are not available to manufacturers and installers
• Lack of standards in ensuring uniform installation procedures to protect against stress on wiring
• Combining visually compatible connector parts from different manufacturers (statements to ban this practice
are being incorporated in draft standards now)
Proc. of SPIE Vol. 9179 91790S-2
Failure mechanisms which may be caused by faulty installation procedure mechanisms are outside of the scope of Task
10 activities. We concentrate on connector failure mechanisms within the JB of the type shown in Figure 1 which could
be revealed in extended durability testing, such as those resulting from JB design and manufacturing deficiencies, and
from environmental factors, including temperature cycling, humidity and joint contamination.
3. JUNCTION BOX ELECTRICAL CONSTRUCTION AND TEST PARAMETERS
All aspects of JB connector materials, configurations and tests that govern safety requirements set by the IEC
(International Electrotechnical Commission) and UL (in the U.S.A.) are detailed in document PNW 82-707 Ed 1 titled
Connectors for DC-application in photovoltaic systems. Among the specifications which are of relevance to Task 10
activities are descriptions of the following terminations and connection methods to which this standard and additional
IEC standards apply:
a)
b)
crimped connections
insulation displacement connections
c)
insulation displacement connections
d)
e)
f)
press-in connections
insulation piercing connections
screwless-type clamping units
g)
h)
screw-type clamping units
flat, quick-connect terminations
according to IEC 60352-2
according to IEC 60352-3 (accessible IDC) or
IEC 60998-2-3
according to IEC 60352-4 (non-accessible IDC)
or IEC 60998-2-3
according to IEC 60352-5
according to IEC 60352-6 or IEC 60998-2-3
according to IEC 60999-1 or IEC 60999-2
or IEC 60352-7
according to IEC 60999-1 or IEC 60999-2
according to IEC 61210
Table 1. List of connector types excerpted from IEC standard PNW 82-707 Ed 1 [1] and relevant standards.
The PNW document further states that “Soldering and welding connections are also allowed under condition, that the
connection is ensured by an additional means of securement.” Most commercial commoditized PV module JB
constructions utilize press-in connections d), such as shown in Fig. 1, or solder connections. Screw-type and welding has
been introduced by some companies, but is not as common. The additional IEC standards referred to above call out, as
an example for configuration d) above, “visual and dimensional tests on the press-in post and test of the push-out force
as specified in IEC 60352-5.” We will see in Table 4 below that standards for testing JB components and understanding
of factors which affect lifetime and durability are governed and constrained by performance testing, e.g., IEC 61215 and
IEC 61646 for the PV module, where the JB is an embedded component of the completed module. These are for
detecting early morality and are pass/fail tests. These module qualification tests do not specifically stress JB
components, such as the electrical wiring and connector joints, nor will they be predictors of their lifetime or durability.
Task 10 activities are designed to go beyond pass/fail tests. Task 10 objectives are explained in the next sections to
provide a framework for extended lifetime and durability testing of connectors which appears to be lacking in PV
module qualification standards.
4.
TASK 10 ACTIVITIES
Task 10 members were surveyed and voted on top issues they have encountered in connector utilization. Table 2
summarizes their priorities on action items. An initial item of activity which is in progress now is a review of existing JB
standards and testing protocols to evaluate their potential impact in stressing JB connectors.
An activity which will be derived from this initial survey and review of existing JB protocols will be to develop
recommendations for durability tests which go beyond stresses encountered in module qualification/certification, as well
as beyond currently proposed JB standards being drafted, e.g., PNW 82-707, and which would be aimed at revealing
failure mechanisms related to the early field failures as observed above.
Proc. of SPIE Vol. 9179 91790S-3
Task
Objective
Description
Proposed Action Items
10.1
Junction Box
wiring – electrical
and mechanical
stress testing
10.2
Durability
parameters for
Junction Boxes
Review standards for electrical
and mechanical assembly
procedures and strategies for
junction box manufacturing and
propose stress tests to extend them
to expose potential failure
mechanisms.
Review standards and testing for
durability issues for junction
boxes and propose durability tests
to extend them and expose
potential failure mechanisms.
10.3
Junction Box
materials
Review durability testing
methods for component materials
to examine
insulation and corrosion
properties and propose tests for
various JB material constituents.
10.4
Junction Box
Wiring
terminations
Review manufacturing practices
and designs for soldered,
resistance welded and pressure
contacts and propose tests to
uncover end-of-life JB metal
corrosion failure modes
10.5
Junction Box
manufacturing
Establish testing protocols and
verification methods for
manufactured JB component and
assembly durability.
1. Review IEC 62852 ed.1.CVD, 60364-7712, 62548(CD)
2. Review work of Tasks 1-9 for duplication,
overlap
3. Define stress parameters for testing
4. Propose experiments to expose critical
stress factors causing failures
1. Review IEC 62790 ed.1.CVD (JB’s), 62852
ed.1.CVD (connectors), IEC 60998, 60999
(terminals).
2. Review work of Tasks 1-9 for duplication,
overlap
3. Define durability parameters for testing
4. Propose experiments to expose durability
issues
1. Compile information on available
characterization methods or polymer
degradation rates, molded material inprocess produced stresses, flux
corrosiveness, and wiring
2. Define durability parameters for testing
3. Propose experiments to test for durability
failures including melt flow rate analysis,
chemical stress crack analysis and residual
stress.
1. Develop best practices and designs for
soldered, resistance welded and pressure
contact formation.
2. Propose tests to uncover JB metal
corrosion failure modes induced by
pottants, fluxes and humidity.
3. Propose durability tests to reveal end of
life failure modes for JB metal joints.
Develop testing protocols and verification
methods for manufactured JB component
and assembly durability.
Table 2. Summary of Junction Box (JB) Connectors and Wiring durability survey listing top Task 10 objectives.
5. DURABILITY PROGRAM DISCUSSION
IEC and UL PV module pass/fail qualification/certification testing was established to meet industry needs to provide
guidance to PV module manufacturers in design, materials and construction, and to understand module performance
responses to environmental factors such as humidity and temperature excursions, and elements influencing safety.
However, certification soon became perceived by the business community as a standard which could back up warranties,
now extending to 25 to 30 years, without any evidence that passing of these tests would somehow eliminate module
failure mechanisms. Once this misinformation was fully digested in the marketplace, demand by PV system owners for
tests which could reduce investment risk has grown rapidly.
Proc. of SPIE Vol. 9179 91790S-4
Table 3. Exam
mple of durabilityy testing of JB coonnections and wiring
w
proposedd as Task 10 activvities [4].
The PV com
mmunity has reesponded to thee need for mittigating risk reelated to long term
t
operationn and ownershiip of PV
installations by proposing extensions too the qualificaation/certification testing prootocols. Two examples
e
of enhanced
e
programs aree the PV Modu
ule Qualificatioon Plus testing program written by NREL [22], and the Fraaunhofer PV Durability
Initiative PV
VDI) [3]. Theirr programs aree outlined in Table
T
4. Brieffly, they advoccate extended outdoor expossure and
accelerated laboratory testiing beyond thee IEC and UL standards
s
to im
mprove correlaations between field life and chamber
testing. As examples, combinations off some tests are
a advocated and dynamic loading testinng is recommeended in
addition to sttatic loading ussed in the IEC standards.
Task 10 will consider the enhanced
e
Quallification Plus and
a PVDI proggrams as potenntial starting points
p
for JB durability
d
studies, and include temperature cycling (TC), dynamic mechanical load
l
(DML), damp
d
heat (DH
H) and humiditty freeze
(HF), all of thhem with and without
w
bias. We
W also see a need
n
to do relattive testing to failure
f
betweenn pin/sleeve joints (Fig
1a) and solddered/welded jo
oints, the two most prominennt ones used in commercial PV modules. The number of
o cycles
needed for failure
fa
needs to
o be establisheed. Guidance is given by a considerable
c
boody of work carried
c
out in the
t early
days of the PV
P program spo
onsored by DO
OE and adminisstered by the Jeet Propulsion Laboratory
L
(JPL) [5]. Since thhe JB by
itself has muuch smaller mass than when attached
a
to a module,
m
a fasterr cycle rate andd more cycles than
t
for modulle testing
could be carrried out exped
diently on connnector joints in
i the TC, DM
ML, DH and HF
H tests. New tests proposedd for JB
connector tessting would ap
pply bias voltagges to the interrnal and externnal JB connecttor joints whilee the JB underrgoes the
indicated cyccling. Tests on
n 5 or 10 yeaar field-exposeed JB connectoors would alsoo be included once benchm
marks for
connectors are
a established.. This would require removinng the JB from
m the modules which have been outdoors for
f these
periods of tim
me.
6. CONCL
LUDING REM
MARKS
Task 10, Duurability of Ju
unction Box Connectors
C
andd Wiring, of the
t Module Quality
Q
Assurannce (QA) Proogram of
PVQAT wass established to
o study additionnal testing requuired to undersstand junction box connectorr field failure observed
o
after less thaan 5 years of outdoor
o
exposuure, and to devvelop a durabillity program for
fo junction box connector jooints and
wiring. Current activities include
i
review
w of existing PV
V module testting programs. Extended NR
REL Qualificattion Plus
and Fraunhofer PVDI test protocols can be used as staarting points foor stressing eleectrical wiring and connectorrs within
the junction box to reveal end-of-life faiilure mechanissms. Several new tests addinng bias voltagees and tests onn already
weathered JB
B’s recovered from
f
installed modules
m
in thee field are proposed.
Proc. of SPIE Vol. 9179 91790S-5
Area
IEC/UL
Qualification
Plus [Ref 2]
PVDI
[Ref 3]
Material weathering by
UV
UV 15 kWh/m2
Temperature cycling (TC)
Mechanical load
200 cycles
2,400 Pa for 2 h
5,400 Pa for
snow areas
240 encapsulant
320 backsheet
30 JB
(kWh/m2)
500 cycles
1000 cycles at
+/- 1000 Pa
Humidity freeze (HF)
10
Damp heat (DH)
Potential Induced
Degradation (PID*)
** Stress tests at elevated
voltages
** Stress tests on fieldexposed JB connector
joints
Outdoor
1000 h
In draft
Combination
- HF 10 cycles
- UV 200 kWh/m2
- HF 10 cycles
600 cycles
1000 cycles dynamic and
static tests with load
done at - 40 deg C, plus
50 TC, plus 10 HF
20 with UV and 10 with
mechanical load
288 hours with bias
-
-
96 hours with
bias
-
-
-
-
-
6 months
-
Ongoing,
characterization every 6
months
TC– temperature cycling between -40 deg C and 85 deg C. 200 cycles correspond to about 10 years in the field.
HF - Humidity Freeze cycling between – 40 deg C and +85 deg C.
DH – Damp Heat performed at +85 deg C and 85% Relative Humidity (RH)
PID* - new test proposed to IEC for PID susceptibility at up to 1000 V, 60 deg C and 85% RH
** New for JB electrical connector/joints
Table 4. Comparison of some proposed durability tests. More details are given in the specified references.
REFERENCES
[1] Descriptions of standard protocols may be found at www.tuvamerica.com for example.
[2] Kurtz, S., et. al., “Photovoltaic Module Qualification Plus Testing,” Technical Report NREL/TP-5200-60950,
December, [2013].
[3] Meakin, David H., et. al., “Fraunhofer PV Durability Initiative for solar modules, Photovoltaics International, Parts I
and II,” www.pvtech.org [2014]; PVDI program is still evolving as outdoor characterization is compared to accelerated
testing.
[4] Kalejs, J., presenting for Task 10, “Report on activities in QA Task 10: Durability of Junction Box Connectors and
Wiring,” NREL QA Workshop, Golden, CO, February 25-26, [2014].
[5] G. R. Mon, D. M. Moore and R. G. Ross Jr., “Solar-cell Interconnect Design for Terrestrial photovoltaic Modules”,
Journal of Solar Energy Engineering, Vol. 106, pp. 379-386 [1984].
ACKNOWLEDGEMENTS
I wish to acknowledge the advice and guidance of Sarah Kurtz of NREL and the participation of Task 10 members in
formulating and developing the concepts described here.
Proc. of SPIE Vol. 9179 91790S-6