Wet Leakage Current Testing for Solar Modules
Author: Steve Fairless
Originally Published: 20th February 2024 · Updated: 2nd September 2026
Wet leakage testing is a laboratory qualification and reliability test used to assess whether a photovoltaic module maintains adequate electrical insulation when its surfaces and edges are exposed to a wet environment. It matters because a module spends decades outdoors, where rain, condensation, fog, snowmelt and humidity can challenge encapsulation, edges, backsheets, glass interfaces and junction-box assemblies.
At Sustainable Energy Engineering, we are installers rather than a module-certification laboratory. Our interest in wet leakage testing is practical: the test is one part of the evidence that helps us understand how a module design has been qualified, and it provides context when investigating insulation faults on an operating PV system.
Wet Leakage Testing: The Short Answer
- It checks electrical insulation under wet conditions. The objective is to identify pathways that could allow unwanted current between live parts and accessible/external surfaces.
- It is a laboratory test, not a homeowner maintenance task. Certified test facilities follow controlled methods and safety procedures.
- IEC 61215-2 covers PV design-qualification test procedures. IEC 61730-2 covers PV module safety-qualification test requirements.
- A failure can point toward an insulation weakness. Potential contributors include damaged encapsulation, backsheets, edges, junction boxes, connectors or cracks.
- Passing one test does not prove a module can never fail in the field. Reliability depends on the bill of materials, manufacturing quality, installation, environment and ageing.
Why Moisture Matters to a High-Voltage DC Product
A solar module is designed to keep its electrical circuit isolated from the environment. That insulation system is more than one layer: glass, encapsulant, backsheet or rear glass, edge regions, junction-box bonding, cable exits and connectors all contribute.
Moisture itself does not mean a module is faulty. Outdoor PV is expected to get wet. The test asks whether wetting creates an unacceptable conductive path or exposes a weakness that dry conditions might not reveal.
IEC 61215 and IEC 61730 Do Different Jobs
The official IEC page for IEC 61215-2:2021 describes design qualification and type-approval test procedures intended to show that terrestrial PV modules can withstand prolonged outdoor exposure within the limits of the test sequence. The current official page for IEC 61730-2:2023 describes the safety-qualification test requirements intended to detect breakdowns that could lead to hazards such as electric shock or fire.
Qualification Is Evidence, Not a Lifetime Guarantee
Standards testing is essential, but it is a defined laboratory qualification process. A module can pass qualification and later encounter field stresses, manufacturing variations or installation damage that were not reproduced exactly in a type test. That is why reliability evidence and site inspection remain important.
What the Test Is Looking For
In principle, the module is exposed to controlled wet conditions while its insulation behaviour is assessed under a specified electrical test. We are deliberately not reproducing the proprietary standard procedure or pass criteria here. The correct method belongs to the current applicable standard, laboratory equipment and trained personnel.
The engineering question is simpler: does the module still behave as an electrically insulated outdoor product when it is wet?
Where Wet Leakage Problems Can Develop
Material and Manufacturing Routes
- backsheet cracking, chalking or loss of barrier properties;
- encapsulant voids, delamination or contamination;
- edge-seal or lamination defects;
- junction-box bonding or sealing problems;
- connector/cable assembly defects;
- cell or interconnect damage associated with a broader module failure.
Field and Installation Routes
- mechanical damage during handling or mounting;
- cables or connectors exposed to water where they should not be;
- module glass or rear-layer damage;
- long-term UV, thermal and humidity ageing;
- repeated mechanical stress or severe weather;
- incorrect diagnosis where the actual insulation fault is elsewhere in the DC circuit.
Why We Do Not Diagnose a Whole Array From One Test Name
An operating system’s insulation fault can arise from modules, connectors, damaged DC cable, junction boxes, isolators, inverter inputs or moisture at other components. A laboratory wet-leakage failure mechanism is relevant context, but it does not justify replacing panels without electrical fault-finding.
Our solar electric servicing work therefore treats insulation warnings as a circuit-level diagnostic problem. We isolate sections safely, inspect the physical installation, review fault history and narrow the cause before attributing it to a module construction.
What Kiwa PVEL Reliability Testing Adds
Kiwa PVEL’s current PV Module Reliability Scorecard methodology includes wet leakage within its broader Product Qualification Program. Its published failure material explains that wet leakage testing evaluates module insulation and that bills of materials failing applicable minimum requirements are treated as safety failures in the Scorecard framework.
That does not mean a “Top Performer” list is a universal buying ranking. It does show why the exact bill of materials and extended reliability evidence can add useful context beyond a brochure efficiency percentage.
How Wet Leakage Relates to Backsheet Degradation
Published field research by Buerhop and co-authors examined water ingress, backsheet construction and falling insulation/ground-impedance behaviour in a large operating PV plant. The study found different moisture-related behaviours for different backsheet groups and linked worsening insulation conditions with inverter shutdown risk.
We discuss that research separately because it is field evidence, not our own laboratory study. It is useful precisely because it shows how a material issue can develop over years rather than appearing as an immediate manufacturing fault.
Why Module Construction Is Changing
Modern products include glass-backsheet and glass-glass architectures, different encapsulants, new cell technologies and evolving interconnection methods. Each change can alter the route by which moisture, stress and electrical insulation interact. That is one reason we read the current product datasheets and warranty documents for the exact module rather than assuming all panels share the same construction.
What a Homeowner Should Do With an Insulation Fault
Safe Practical Response
- Do not open DC connectors or dismantle modules to investigate the fault yourself.
- Record inverter error codes and the weather conditions when the warning appears.
- Check whether the problem is intermittent and rain/humidity-related, without repeatedly forcing resets.
- Arrange competent PV fault diagnosis.
- Keep serial numbers, installation records and warranty documents available.
- If a module is confirmed defective, follow the manufacturer/installer warranty route using the diagnostic evidence.
What We Look For When Selecting Modules
Module choice is broader than a certification logo. We consider electrical characteristics, construction, manufacturer support, reliability evidence, mechanical loading, degradation/warranty terms and how the module fits the actual system. Certification is a baseline requirement; it is not the entire product assessment.
The same principle applies to solar PV installation: the module has to be installed without introducing cable, connector or mechanical damage that undermines the product’s tested construction.
Our View: Wet Leakage Testing Is a Small Test With a Big Safety Purpose
The test is technical and mostly invisible to the end user, but the underlying question is fundamental: can the module remain electrically insulated in the wet environment it was designed to live in? Understanding that helps customers see why module reliability is about more than headline watts and efficiency.
Why a Dry Electrical Check Can Miss a Moisture-Dependent Weakness
An insulation path can behave differently as humidity or surface wetting changes. A module or cable may appear normal in a dry workshop or on a sunny afternoon and then produce an insulation warning after prolonged rain. Controlled wet testing exists because the real operating environment includes moisture.
For field service, that means weather history is evidence. If a customer reports that the same fault appears after rain and clears after a dry period, we record that pattern rather than dismissing an intermittent alarm.
Insulation Is a System Property as Well as a Module Property
A PV string contains many interfaces: module laminates, junction boxes, leads, plug connectors, extension cables, DC isolators and inverter inputs. The inverter sees the electrical condition of the connected circuit, not a label saying which component caused the problem.
| Possible fault area | Moisture-related clue | Diagnostic caution |
|---|---|---|
| Module laminate/backsheet | Fault follows a particular module/string and worsens in wet weather | Needs isolation/testing; appearance alone may not prove electrical failure. |
| Connector | Water ingress, damaged seal or poor mating | Do not disconnect live DC connectors to inspect casually. |
| DC cable | Abrasion, crush damage or water pathway | Fault may be hidden beneath modules or in containment. |
| Junction box/lead | Local damage or sealing problem | Can mimic a broader module insulation issue. |
Certification and Extended Reliability Testing Answer Different Questions
IEC qualification establishes whether a module design meets defined test requirements. Extended programmes such as Kiwa PVEL’s PQP expose specific bills of materials to additional sequences intended to compare reliability performance. Both are useful, but they should not be confused.
For a buyer, certification is a baseline. Extended reliability evidence can help differentiate products that all carry the expected certification marks.
Field Damage Can Undermine a Qualified Product
A module can leave the factory compliant and later be damaged by poor handling, an inappropriate clamp position, impact, cable abrasion or other installation stress. Qualification therefore does not replace careful transport, mounting and commissioning.
Do Not “Test” a Suspected Module by Spraying Water on Live Equipment
Reproducing a wet fault deliberately on an energised array is not a homeowner diagnostic method. Insulation investigation involves hazardous DC voltages and should be carried out with the correct isolation, test equipment and competence.
Why the Test Matters Even When the Customer Never Sees It
Many of the most important product-quality controls happen before installation. A customer may never read IEC 61215 or a reliability Scorecard, but those frameworks are part of the evidence chain behind choosing equipment expected to operate safely outdoors for decades.
Concerned About Insulation or Leakage Faults on a Solar System?
We can inspect and electrically diagnose PV systems rather than guessing which component is responsible.
