Salt mist corrosion testing is a critical environmental qualification procedure that verifies the durability, material integrity, and electrical safety of photovoltaic (PV) modules installed in coastal, offshore, and other chloride-rich environments. Performed in accordance with IEC 61701 and related international standards, the test accelerates the corrosive effects of salt-laden atmospheres and confirms that module frames, coatings, and electrical performance remain within acceptable limits. This article explains the applicable standards, sample requirements, test severities, procedures, and pass criteria used by accredited third-party laboratories.
Technical Overview
Photovoltaic modules deployed in coastal zones, islands, offshore platforms, floating power plants, and saline-alkali deserts are continuously exposed to salt-laden air and moisture. Chloride ions in salt mist attack metallic components such as aluminum frames, cell interconnect ribbons, junction box terminals, and connector contacts, while also degrading anodic coatings, sealants, and polymer encapsulation. The result can be increased series resistance, reduced power output, loss of insulation capability, and ultimately safety hazards or premature module failure.
Salt mist corrosion testing simulates these degradation mechanisms under accelerated laboratory conditions. The governing standard for complete PV modules is IEC 61701 (Photovoltaic (PV) modules – Salt mist corrosion testing), which builds on the cyclic salt mist method of IEC 60068-2-52. Supporting references include ISO 9227 and ASTM B117 for neutral salt spray exposure, GB/T 10125 as the corresponding Chinese method standard, and IEC 61215 / IEC 61730 (or UL 61730 in North America) for the baseline electrical performance and safety criteria applied before and after exposure. Testing is typically carried out by accredited third-party laboratories as a supplemental qualification beyond the standard design and safety certification sequences.
Testing Samples
Complete PV Modules
The primary test objects are fully assembled modules representative of series production, including monocrystalline and polycrystalline silicon modules, PERC, TOPCon, and heterojunction designs, as well as frameless glass-glass laminates. Modules should be fabricated using the same materials, coatings, and processes as commercial products, and are usually tested in an electrically functional configuration with the junction box and cables installed.
Module Components and Materials
Component-level samples are frequently tested to characterize susceptibility to corrosion in isolation. Typical items include anodized or coated aluminum frames, stainless steel and galvanized mounting fasteners, junction boxes, cable assemblies and connectors, backsheets, encapsulant coupons for adhesion assessment, and cell interconnect ribbons.
Sample Preparation and Quantity
Before exposure, samples are visually inspected, cleaned as specified by the standard, and characterized electrically to establish baseline values. IEC 61701 specifies the minimum number of modules to be tested per severity level, commonly two modules, and requires that all samples be marked and documented so that post-test measurements can be compared with initial results. Components may be tested in parallel on fixtures that reproduce realistic orientation and drainage conditions.
Testing Items
The evaluation program combines environmental exposure with electrical and visual assessments. Core testing items typically include:
- Visual inspection for frame corrosion, coating blistering or flaking, sealant degradation, delamination, bubbles, and corrosion of cells, busbars, and interconnects
- Maximum power (Pmax) determination at Standard Test Conditions (STC) before and after exposure to quantify power degradation
- Insulation resistance test and dielectric withstand verification in accordance with IEC 61730-2
- Wet leakage current test to confirm electrical safety under moist conditions
- Electroluminescence (EL) imaging to reveal hidden cracks, corrosion-induced dark areas, and metallization defects
- Component-level assessments such as coating adhesion, mass loss, and red-rust evaluation for frames and fasteners
Testing Methods
Neutral Salt Spray (NSS) Exposure
Neutral salt spray, described in ISO 9227, ASTM B117, and GB/T 10125, is widely used for material and component screening. Samples are exposed to a continuous fog of a 5% sodium chloride solution (50 g/L ± 5 g/L) at 35 °C ± 2 °C. The collected solution must maintain a pH of 6.5 to 7.2, with a collection rate of 1.0 to 2.0 mL per 80 cm² per hour. This method provides a stable and reproducible corrosive environment but does not include drying phases, so it is generally complemented by cyclic methods for whole-module qualification.
Cyclic Salt Mist Testing per IEC 60068-2-52
IEC 61701 adopts the cyclic salt mist procedure of IEC 60068-2-52, which more closely reproduces natural wet-dry coastal exposure. Each cycle consists of a salt mist spray phase of two hours at 35 °C followed by a humidity storage phase of approximately 22 hours at 40 °C and high relative humidity (≥ 85%). The repeated spray-storage cycling drives salt concentration and corrosion processes deep into joints, edges, and crevices of the module.
Severity Levels in IEC 61701
IEC 61701 defines a series of severity levels (Severity 1 through the highest severity) corresponding to progressively greater cumulative cyclic exposure. Lower severities represent moderate coastal atmospheres, intermediate severities represent typical marine shoreline installations, and the highest severities address severe marine, offshore, and floating PV applications. Project specifications and certifiable test programs should select the severity appropriate to the intended installation environment.
Test Sequence and Recovery
The standard sequence comprises initial measurements (visual inspection, power at STC, insulation, and wet leakage), exposure to the specified number of salt mist cycles in a calibrated chamber, a defined recovery period during which samples are gently rinsed and stabilized, and final repetition of all initial measurements. Post-test examination is performed under controlled illumination to identify corrosion products, coating failures, and structural defects.
Pass and Fail Criteria
A module is considered to have passed when it exhibits no major visual defects defined by IEC 61215 criteria, maximum power degradation remains within the permitted limit (typically no more than 5% relative to initial values), insulation resistance and dielectric withstand satisfy IEC 61730-2 requirements, and the wet leakage current test is passed. Any red rust compromising function or safety, severe coating failure, or excessive power loss constitutes grounds for failure.
Applications
Salt mist corrosion testing supports product qualification, market access, and engineering quality assurance wherever chloride exposure is a credible degradation driver. Typical applications include:
- Qualification of modules for coastal ground-mount power plants and island microgrids
- Certification and bankability documentation for floating PV and near-shore or offshore installations
- Validation of corrosion-resistant frame coatings, anodizing processes, and mounting hardware for saline environments
- Research and development screening of encapsulants, backsheets, junction boxes, and connector designs
- Procurement compliance, incoming quality control, and comparative evaluation of competing module suppliers for projects in saline-alkali deserts and coastal industrial zones
FAQ
Which standard is authoritative for PV module salt mist testing?
IEC 61701 is the module-level standard and is the primary reference. It incorporates the cyclic exposure method of IEC 60068-2-52, while ISO 9227, ASTM B117, and GB/T 10125 are used for the underlying spray methods and component-level testing.
Is the salt mist test part of standard IEC 61215 certification?
No. Salt mist corrosion testing is a supplemental environmental test outside the baseline IEC 61215 design qualification and IEC 61730 safety sequences. However, it is routinely required by project developers, financiers, and certification bodies for installations in coastal, offshore, and floating applications.
How long does the test take?
Duration depends on the selected severity level, since each 24-hour cycle combines two hours of spray with approximately 22 hours of humidity storage. Programs range from a few days for lower severities to several weeks for the most severe offshore classifications, plus time for initial and final electrical characterization and recovery.
How is the appropriate severity level chosen?
Severity selection is based on the installation environment: distance from the coastline, airborne salinity, humidity cycling, and whether the modules are land-based, floating, or offshore. Project specifications or certification schemes normally define the required severity, and accredited third-party laboratories can advise on matching the level to site conditions.
What causes modules to fail the test?
Common failure modes include galvanic and crevice corrosion at frame corners and fastener holes, inadequate anodizing or coating thickness, corrosion of junction box terminals and connector contacts, sealant breakdown allowing salt ingress, increased series resistance in cell metallization, and consequent power degradation or wet leakage current failure.
How does ASTM B117 differ from the IEC 61701 approach?
ASTM B117 applies a continuous neutral salt spray that is well suited to ranking materials and coatings, whereas IEC 61701 evaluates complete modules under cyclic spray-humidity conditions and adds functional pass criteria covering visual defects, power output, insulation, and wet leakage. The two methods are complementary rather than interchangeable.