Photovoltaic (PV) module immersion testing evaluates how well a solar module resists direct water submersion, verifying the integrity of its encapsulation, edge sealing, junction box, and electrical insulation under prolonged wet conditions. This test is particularly critical for floating solar plants, flood-prone ground-mounted systems, and highly humid climates, and it is typically performed by accredited third-party laboratories using frameworks established by IEC, ISO, ASTM, and GB standards. This article explains the technical purpose, sample types, test items, procedures, and typical applications of PV module immersion testing.
Technical Overview
Photovoltaic module immersion testing is an environmental stress test in which a complete PV module, or one of its critical sub-components, is submerged or partially submerged in water for a defined period and then examined for water ingress, electrical degradation, and structural damage. Because water is one of the most aggressive agents for long-term module reliability, this test provides direct evidence of whether the laminate edge sealing, encapsulant, backsheet or glass-glass structure, cable entry points, and junction box can prevent moisture from reaching live electrical parts and cell metallization.
Immersion testing complements the moisture-related tests already embedded in the IEC qualification sequence, such as damp heat (85 °C / 85 % relative humidity) and humidity-freeze cycling described in IEC 61215-2, as well as the insulation and wet leakage current safety tests in IEC 61730-2. While those standards simulate humid air exposure, immersion testing simulates the far more severe condition of liquid water contact or flooding, which is representative of floating PV deployment, seasonal flooding, ponding on low-tilt roofs, and agrivoltaic sites with irrigation.
The core objectives of immersion testing include:
- Verifying that encapsulation and edge-seal systems block liquid water penetration under static submersion pressure
- Confirming that insulation resistance and wet leakage current remain within the safety limits defined in IEC 61730-2 after water exposure
- Detecting delamination, bubbling, corrosion of cell interconnects, and moisture pathways that accelerate potential induced degradation (PID)
- Qualifying modules, junction boxes, and connectors intended for floating solar or flood-exposed installations, often in combination with salt mist testing per IEC 61701
Testing Samples
Crystalline Silicon Modules
Standard glass-backsheet and glass-glass crystalline silicon modules form the largest share of immersion test samples. Full-size production modules are preferred for certification-oriented programs because they include real junction boxes, cables, connectors, and frame sealing. Mini-modules or coupons may be used for research and development provided the construction faithfully reproduces the edge-seal and lamination design of the commercial product.
Thin-Film Modules
CIGS, CdTe, and amorphous silicon modules rely heavily on high-quality edge seals to protect moisture-sensitive absorber layers, making immersion exposure especially informative. Water ingress in thin-film products can rapidly cause electrode corrosion and irreversible power loss, so post-immersion electrical characterization is essential.
Floating PV and Bifacial Modules
Modules designed for floating solar installations are frequently tested in partial immersion configurations that reproduce the waterline condition of a pontoon-mounted array. These modules often feature modified encapsulants, double-glass structures, sealed frames, and IP68-rated electrical components, all of which require dedicated verification.
Components and Materials
Sub-component immersion programs cover junction boxes tested in accordance with IEC 62790, PV connectors tested in accordance with IEC 62852, cables, cable glands, and mounting accessories. At the material level, polymeric films and encapsulants can be evaluated for water absorption and hydrolytic stability using procedures aligned with IEC 62788 measurement methods and ASTM D570 water absorption testing.
Testing Items
A typical immersion test program packages water exposure with a battery of pre-test and post-test characterizations so that any degradation can be quantified:
- Visual inspection before and after immersion, following the defect categories defined in IEC 61215-2
- Wet leakage current testing per IEC 61215-2 and IEC 61730-2, performed while the module surfaces remain wet
- Insulation resistance and dielectric withstand verification to confirm electrical safety margins
- Maximum power measurement at standard test conditions (STC) with power retention compared against the pre-test baseline
- Electroluminescence (EL) imaging to reveal hidden cell cracks, corrosion, and moisture-related shunting that are invisible to the eye
- Delamination, bubble, and moisture ingress inspection of laminates, edge seals, and junction box potting
- Bypass diode functional verification, since flooded junction boxes can compromise diode thermal performance
- Optional combined evaluations, including salt mist corrosion per IEC 61701, PID susceptibility per IEC TS 62804, and extended stress sequences per IEC TS 63209-1 for harsh environments
Testing Methods
Pre-Test Characterization
Samples are first conditioned in a controlled environment, typically at 23 °C and moderate relative humidity, and then fully characterized. This baseline includes visual inspection, EL imaging, STC power measurement, and dry insulation testing. Documenting the initial condition is essential because pass or fail decisions are based on measurable changes, not merely on the visual outcome of the immersion step.
Immersion Procedure
The module or component is immersed in deionized water or a controlled-conductivity test solution held at a stable temperature, commonly 25 °C ± 5 °C. Test depth and duration depend on the engineering specification being applied. Verification aligned with IEC 60529 IPX7 ratings commonly uses submersion at approximately 1 meter for 30 minutes, while IPX8 verification follows the manufacturer's declared depth and duration. Floating PV qualification programs frequently extend exposure to several hours or even 24 hours or more, and may use partial immersion to simulate the waterline. Some specifications also apply thermal cycling after immersion to aggravate any absorbed moisture and reveal latent defects.
Post-Immersion Evaluation
Immediately after removal, and again after a defined drying period, the sample undergoes wet leakage and insulation testing, repeated STC power measurement, EL imaging, and detailed visual examination. Acceptance criteria generally require no visible water ingress into live parts, insulation resistance within the limits of IEC 61730-2, wet leakage results compliant with IEC 61215-2, no new major visual defects, and maximum power retention typically at or above 95 percent of the initial value, depending on the applicable program.
Combined Stress Sequences
For demanding applications such as offshore floating arrays, immersion exposure is often sequenced with damp heat, humidity-freeze, thermal cycling, and salt mist tests to build a realistic picture of long-term performance. Extended stress testing concepts in IEC TS 63209-1 are increasingly referenced when purchasers define supplemental qualification requirements beyond the baseline IEC 61215 sequence.
Applications
Immersion testing supports engineering decisions, procurement specifications, and product development across the entire PV value chain. Key application scenarios include:
- Qualification of modules for floating solar power plants and fishery-solar hybrid projects where components operate at or near the water surface
- Verification of modules for flood-prone ground-mounted plants, wetlands, and sites with high water tables
- Assessment of building-integrated PV and low-slope rooftop systems exposed to ponding water
- Screening of agrivoltaic installations that experience frequent irrigation spray and elevated humidity
- Ranking of encapsulants, edge-seal chemistries, backsheets, and junction box designs during manufacturer research and development
- Technical due diligence for project developers, lenders, and insurers who require documented moisture robustness before financing
- Incoming quality control and supplier benchmarking by module manufacturers and EPC contractors
FAQ
What is the difference between immersion testing and damp heat testing?
Damp heat testing exposes modules to hot, humid air at 85 °C and 85 % relative humidity for 1,000 hours or longer, driving moisture diffusion through polymers. Immersion testing places the sample directly in liquid water, which applies stronger hydrostatic and wetting conditions and is more representative of flooding or floating deployment. The two methods are complementary and are frequently combined in comprehensive qualification programs.
Is immersion testing mandatory for IEC 61215 or IEC 61730 certification?
Baseline immersion of the complete module is not part of the standard IEC 61215 or IEC 61730 test sequence. However, wet leakage current and insulation tests in those standards are moisture-related, and component standards such as IEC 62790 for junction boxes include water exposure requirements. Immersion testing of full modules is typically specified by purchasers, floating PV project requirements, or performed as a supplemental study by accredited third-party laboratories.
What immersion conditions are most commonly used?
Common conditions include full or partial submersion in deionized or controlled-conductivity water at 25 °C ± 5 °C, with durations ranging from 30 minutes for IPX7-type verification to 24 hours or longer for floating PV specifications, at depths up to approximately 1 meter unless a deeper rating is being verified.
What failure modes can immersion testing reveal?
Typical findings include edge-seal or encapsulant delamination, water ingress into junction boxes, corrosion of ribbon interconnects and cell metallization, moisture-driven shunting visible in EL imaging, elevated wet leakage current, degraded insulation resistance, and excessive power loss after re-measurement.
How many samples are required?
For certification-style programs, accredited third-party laboratories commonly test two to six modules depending on the sampling plan agreed with the client. For research and development, smaller coupon or mini-module programs are acceptable when the specimen construction is representative of the full-size product.
Which standards are most relevant to immersion testing programs?
Frequently referenced frameworks include IEC 61215-2, IEC 61730-2, IEC 60529 for IP ratings, IEC 61701 for salt mist, IEC TS 62804 for PID, IEC TS 63209-1 for extended stress testing, IEC 62790 and IEC 62852 for junction boxes and connectors, IEC 62788 for polymeric materials, ASTM D570 for water absorption, and the corresponding GB/T national standards adopted in regional markets.