Marine

The Marine Environment

The presence of seawater in various forms is the defining characteristic of marine environments. Seawater is an aggressive, corrosive agent and a good electrolyte. These characteristics make it particularly harmful to solar modules.

Why a Marine Module

Applications of solar modules in marine environments are a significant fraction of today's market and represent some of the most cost effective applications for solar power. Solarex pioneered the development of solar navaid systems beginning with the supply of prototype systems to the US Coast Guard in the late '70s. Field tests of these systems led to the development of test procedures capable of duplicating the severe effects of the marine environment and the parallel development of solar modules that would survive in this environment and pass the qualification tests. These tests are designed to simulate (in an accelerated fashion) the conditions encountered on floating buoys, including full immersion in seawater to a depth of 5m. Known as the PIT Test (Pressure, Immersion, Temperature) modules are immersed in a sealed tank of brine, the temperature and pressure of which is varied cyclically. It is important to note that ordinary solar modules will not pass these tests.

Special products were developed to qualify to these standards including the versions of Solarex's MSX-38 MM and MSX-20 MM purchased by the US Coast Guard. The only difference in construction between the commercially available MM series and those bought by the USCG is their label and the number of solar cells. The MM series of modules has a full compliment of either 35 or 36 cells making them suitable for applications in all climates in regulated systems. The USCG modules have 30 or 31 cells and are designed to be "self-regulating". This is a design practice that Solarex do not generally recommend, particularly at higher European latitudes. It is worth noting that most other navigational authorities purchase the standard MM version.

Failure Mechanisms and Solutions

The dissimilar metals used in solar cells and different electrical potentials existing among the cells in a module when exposed to sunlight can result in rapid corrosion of the cell metalization if seawater penetrates into the cell matrix. This results in rapid loss of power and failure of the module. Seawater can penetrate into the cell matrix through mechanical defects in the encapsulant/backsheet (delaminations, punctures, etc.), through diffusion or wicking in from the edges of the laminate, or from wicking along the output wires. Full marine grade modules such as Solarex's MM series have features which specifically address these potential sources of failure:

• Highly impermeable and inert, tempered glass front
• Rigid, marine grade, aluminum backplate fully protecting the rear of the laminate
• Edges of the laminate protected with a compressed silicone rubber gasket
• J- box potted with silicone rubber gel and sealed (cable attached)

Modules incorporating these features have been used for over 11 years by the USCG without failure related to the marine environment. In the USCG, buoys are brought in for replacement or major overhaul approximately every 5 years depending on the environment. The solar modules installed on these buoys are removed, cleaned, and checked for performance which is typically no different to the initial value within the tolerance of the measurement. The modules are reinstalled on new buoys and put out to sea for another 3 to 5 years with no maintenance other than cleaning. The reliability of these modules is born out by the statistics - the USCG has purchased over 13,000 marine modules from Solarex and has never made a warranty claim, customers in the UK have purchased almost 2,000 marine modules from Solarex over the last 9 years and, similarly, have never made a warranty claim.

The term "marine environment" can be used to describe many stressful situations with a wide variation in the severity of seawater exposure. Exposure can vary from occasional salt mists to wave crashes and even total immersion in seawater. The life of a solar module in these environments will thus be a function of the amount of exposure to seawater and the module's resistance to its effects.

What are our recommendations?

Marine grade modules should be chosen for any application within the splash zone. Modules should be mounted with a sufficient tilt angle and proper orientation to allow water to freely flow off the front surface. Buoys located in exposed water should have the modules mounted as high as possible and braced behind to resist deflection from breaking waves. Any bare metal surfaces on wires, terminals etc. should be protected against corrosion by the use of potting compounds or conformal coatings. Wire connections should be sealed to prevent wicking into the module j-box or laminate.

Following these recommendations will result in the high standard of performance experienced by maritime authorities, offshore petroleum producers, and others using Solarex marine modules around the world.

Left: Part of the PV array and lantern tower on a Solar Lightvessel. Right: PV powered buoys Both the lightvessel and the buoys use Solarex MSX-38 Marine Modules