What thermal cycling in saltwater climates does to solar cell encapsulation over time

By:sealite | August 25, 2026

Solar-powered Aids to Navigation (AtoN) depend on one component above all others to convert sunlight into reliable operational energy: the solar cell. But the cell itself is only as durable as the encapsulant layer that surrounds it. In saltwater climates, that encapsulant faces a relentless combination of temperature extremes, ultraviolet radiation, and humidity that no land-based solar installation encounters at the same intensity. Understanding what happens to solar cell encapsulation under these conditions is not an academic exercise for port safety managers and AtoN engineers. It is the foundation for making informed decisions about which marine solar panels will continue performing at year ten the same way they performed at installation.

This article builds that understanding progressively, starting with the mechanics of thermal cycling itself, moving through the material science of encapsulant degradation, and arriving at practical guidance for evaluating solar panel specifications in the context of AtoN deployment.

What thermal cycling means for solar cells in marine environments

Thermal cycling refers to the repeated process of a material heating up and cooling down over time. In the context of solar cell encapsulation, each day-to-night temperature transition constitutes one cycle, and in marine environments, those cycles are more extreme and more frequent than in most other settings.

A marine solar panel mounted on a navigation buoy or lantern housing experiences direct solar irradiance during the day, which can raise surface temperatures well above ambient air temperature. At night, particularly in open-water environments where there is no thermal mass to retain heat, temperatures drop sharply. In tropical and subtropical saltwater climates, the daily temperature differential across the panel surface can be substantial. In higher-latitude environments, seasonal cycling adds a second layer of stress on top of the daily pattern.

The critical point is that solar cells, encapsulant materials, and the backing layers of a panel all expand and contract at different rates as temperature changes. This difference in thermal expansion coefficients means that each cycle introduces mechanical stress at the interfaces between these materials. A single cycle produces negligible damage. Thousands of cycles, accumulated over years of continuous offshore deployment, produce cumulative micro-stress that eventually compromises the structural integrity of the encapsulant layer.

How repeated temperature swings break down encapsulant materials

The encapsulant in a solar panel is the transparent polymer layer bonded directly to the surface of the solar cells, protecting them from physical damage, moisture, and contamination while transmitting light. The most widely used encapsulant material in solar panel manufacturing is ethylene-vinyl acetate (EVA), though polyolefin-based alternatives have gained ground in demanding applications.

Under thermal cycling stress, EVA encapsulants undergo a progressive sequence of physical changes. Initially, the material experiences micro-cracking at points of highest mechanical stress, typically at cell edges and busbars where the geometry creates stress concentrations. These micro-cracks are invisible to the naked eye and do not immediately affect power output. Over time, however, the cracks propagate and coalesce.

A second mechanism is delamination, where the encapsulant partially separates from the cell surface or from the glass superstrate above it. Encapsulant delamination creates air pockets within the panel structure. These pockets have two damaging consequences: they interrupt the optical path, reducing the light reaching the cell, and they create pathways for moisture ingress. In a land-based installation, delamination progresses slowly. In a saltwater climate, moisture ingress becomes a far more aggressive problem, as the next section explains.

UV degradation in marine environments is a third mechanism operating in parallel. Prolonged ultraviolet exposure causes EVA to undergo photo-oxidation, a chemical process that yellows and embrittles the encapsulant. A yellowed encapsulant transmits less light to the cell, directly reducing power generation. An embrittled encapsulant is also more susceptible to cracking under the mechanical stress of continued thermal cycling, creating a compounding degradation pathway.

Why saltwater humidity turns micro-damage into system failure

Building on the encapsulant damage mechanisms described above, the marine environment introduces a factor that transforms manageable degradation into accelerated system failure: the combination of high humidity and salt-laden air that characterises saltwater climates.

When micro-cracks and delamination voids form in the encapsulant, they create pathways for water vapour to reach the interior of the panel. In a dry inland environment, this moisture ingress would be limited. In a marine environment, the air is continuously saturated with humidity and carries dissolved salts. Once moisture penetrates the encapsulant, it reaches the cell metallisation, the thin metal conductors printed onto the cell surface.

Salt-laden moisture is electrochemically active. It accelerates corrosion of cell metallisation and solder bonds at a rate that dry or fresh-water moisture cannot match. The result is increased electrical resistance at cell contacts, which reduces current output, and in advanced cases, complete open-circuit failure of individual cells or strings. Because marine solar panels on AtoN equipment are typically self-contained systems with no external power backup, a degraded panel does not simply reduce efficiency. It threatens the continuous operation of the navigation light itself.

A useful analogy is to consider the encapsulant as a sealed envelope protecting a letter from rain. Thermal cycling gradually perforates that envelope with microscopic holes. In a freshwater environment, the occasional raindrop that enters causes limited damage. In a saltwater environment, every drop that enters carries a corrosive agent that attacks the contents directly. The rate of damage is not linear with moisture exposure. It is amplified by the chemistry of the marine atmosphere.

Evaluating encapsulant material choices for harsh marine duty

Not all encapsulant materials respond to thermal cycling and saltwater humidity in the same way. Understanding the differences between the principal options allows procurement and engineering teams to evaluate solar panel specifications with greater precision.

EVA remains the most common encapsulant in general solar panel manufacturing due to its low cost and proven performance in standard terrestrial applications. However, EVA has known limitations in high-humidity, high-UV environments. Its tendency to yellow under UV exposure and its relatively modest resistance to hydrolysis make it a less optimal choice for continuous offshore marine deployment compared to alternatives.

Polyolefin elastomer (POE) encapsulants offer improved hydrolysis resistance and lower water vapour transmission rates than standard EVA. This means moisture penetration through an intact POE encapsulant is slower, giving the system greater tolerance for the conditions that follow thermal cycling damage. POE also tends to maintain adhesion more consistently across a wider temperature range, which directly addresses the delamination risk described earlier.

Key material properties to evaluate when assessing encapsulant suitability for marine solar panels include:

Water vapour transmission rate (WVTR): lower values indicate better resistance to moisture ingress
UV stability: resistance to photo-oxidation and yellowing under prolonged solar irradiance
Adhesion retention after thermal cycling: the encapsulant’s ability to maintain bonding to cell and glass surfaces across repeated temperature differentials
Operating temperature range: the material’s mechanical stability at both the high end (peak solar heating) and low end (overnight or seasonal cold) of the deployment environment
Hydrolysis resistance: the material’s chemical stability when exposed to moisture over extended periods

Panel construction choices beyond the encapsulant also matter. UV-stabilised backing materials and robust frame sealing contribute to the overall barrier against saltwater humidity. A high-quality encapsulant inside a poorly sealed frame assembly will still allow moisture pathways to develop over time.

What qualification standards reveal about long-term encapsulation durability

The most reliable way to assess how a solar panel’s encapsulation will perform over years of marine deployment is to examine the qualification standards to which it has been tested. These standards exist precisely because real-world degradation takes years to manifest, and accelerated laboratory testing is designed to simulate that cumulative stress in compressed timeframes.

IEC 61215 is the primary international standard for the design qualification and type approval of terrestrial photovoltaic modules. Its thermal cycling test protocol subjects panels to a defined number of temperature cycles between specified extremes, evaluating whether the encapsulant, cell interconnections, and frame assembly maintain their performance and structural integrity. Panels that pass IEC 61215 thermal cycling testing have demonstrated baseline resilience to temperature-driven stress.

IEC 61701 addresses salt mist corrosion testing specifically, making it the more directly relevant standard for marine solar panel applications. This test exposes panels to concentrated salt fog under controlled conditions, evaluating whether the encapsulant and frame sealing prevent corrosive ingress to cell metallisation and electrical contacts. A panel that has passed IEC 61701 testing provides documented evidence of resistance to the precise failure mode that saltwater humidity creates following thermal cycling damage.

It is worth noting that passing a qualification standard at the time of manufacture does not guarantee performance over the full service life of an AtoN installation. Qualification testing validates the design and materials at a point in time. Ongoing quality assurance under a certified manufacturing system, such as ISO 9001:2015, provides the process discipline that ensures consistent production quality across every unit manufactured, not just the sample submitted for type testing.

Applying encapsulation knowledge to AtoN solar panel selection

With the mechanisms of thermal cycling damage, saltwater humidity amplification, material performance differences, and qualification standards now established, the practical question for port safety managers and AtoN engineers is how to apply this knowledge when evaluating solar marine lanterns and their integrated panel systems.

The first step is to treat stated service life figures as the starting point for a more detailed evaluation, not the conclusion. A claimed service life of 12 or 15 years for a solar marine lantern is meaningful only if the solar panel system supporting it is designed and qualified to sustain power generation across that full period in the specific deployment environment. Ask manufacturers for the encapsulant material specification, the relevant qualification test certifications, and the manufacturing quality standard under which the panels are produced.

The second step is to match the panel specification to the deployment environment. A lantern installed in a tropical port approach, where daily thermal cycling is intense and humidity is consistently high, places greater demands on encapsulation than a lantern installed in a temperate inland waterway. Conversely, a high-latitude offshore installation introduces severe seasonal thermal cycling that may stress encapsulant adhesion differently than daily cycling in warmer climates. The deployment environment should drive the specification requirement.

The third step is to consider the consequences of encapsulation failure in the context of AtoN reliability. For a solar marine lantern deployed on a remote offshore buoy, a degraded solar panel does not trigger an automatic maintenance response. It gradually reduces the energy available to the lantern, potentially compromising flash intensity, operating hours, or continuous operation during extended low-sunlight periods. In a safety-critical AtoN role, that degradation pathway carries direct navigational risk. Specifying panels with demonstrated encapsulation durability is not a premium consideration. It is a core reliability requirement.

Contact Sealite to discuss the solar panel specifications and qualification standards applied to your AtoN deployment requirements, and to identify the right marine lantern configuration for your specific environmental conditions.