The sun, an infinite source of energy, helps fuel our transition to a sustainable future. Photovoltaic (PV) panel farms, sprawling across landscapes, particularly in South Africa, are the physical manifestation of this shift. As these installations grow in size and number, so does the need to ensure their long term viability. While the PV panels themselves are a marvel of modern technology, a critical and often overlooked aspect is the structural integrity of the metal alloy framework that supports them. This framework, constantly exposed to the elements, is highly susceptible to corrosion. The choice of materials for this framework is paramount, and a two-pronged approach utilizing Magnelis® coated steel for the above ground structure and Duplex coated hot dip galvanized subsoil steel anchors offer a robust solution to combat both atmospheric and subsoil corrosion.

Corrosion protection: A two front war

Corrosion is an electrochemical process that degrades metal alloys, when they interact with their environment. For PV farms, this battle is fought on two fronts: above ground and below.

Atmospheric Corrosion: The above ground PV framework is continuously exposed to a range of atmospheric aggressors. These include moisture from rain/mist, condensation, and local humidity; airborne pollutants such as sulfur dioxide (SO2​), windborne sea sand, industrial pollutants and chlorides especially in coastal environments. This exposure creates a corrosive film on the metal surface, leading to corrosion and a gradual loss of structural strength. Over time, this can compromise the stability of the entire array, leading to costly repairs, replacements, and even catastrophic structural failure.

Sub-soil Corrosion: The subsoil anchors, which provide crucial support for the entire array, face an equally aggressive and variable environment. Soil composition, pH, moisture content, soil conductivity and the presence of microorganisms can all contribute to a highly corrosive soil environment. Unlike the visible signs of atmospheric corrosion, subsoil corrosion is insidious, silently weakening the foundation until it's too late. The failure of just a few anchors can compromise the stability of a large section of the array, leading to significant financial losses and operational downtime.

Magnelis®: A shield against atmospheric corrosion

For the above ground framework, a light weight and cost effective metal alloy is required yet must offer sufficient strength to support thousands of PV panels and resist the force of the wind. While galvanized steel works well, other metallic coatings offer superior corrosion protection and longevity to thin steel sections. Magnelis® is a zinc-aluminum-magnesium coating that provides exceptional corrosion resistance to this steel sheeting formed into purlins and rafters used to construct a PV farm.

The key to Magnelis's effectiveness lies in its unique composition. The addition of magnesium, typically around 3%, creates a stable and highly durable surface layer. When this coating is exposed to moisture, it forms a dense, self-healing protective film of magnesium carbonate and zinc hydroxycarbonate. This film is significantly more stable and resistant to corrosive agents than the protective layer formed on traditional continuously galvanized steel sheet. The self healing property is particularly valuable; if the coating is scratched or damaged, the surrounding magnesium ions migrate to the affected area, forming a new protective layer and preventing corrosion from spreading. This is a critical advantage in the construction environment where mechanical damage is common. Furthermore, Magnelis® exhibits a lower zinc run-off rate, making it a more environmentally friendly option. Its superior performance allows for the use of thinner coatings, leading to material and cost savings without compromising on protection.

Duplex Coating: Defence for Sub-Soil Anchors

While Magnelis® is an excellent choice for the above-ground structure, the harsh and variable nature of the sub-soil environment demands a different approach. This is where a duplex coating system offers the ultimate defence. A duplex coating is a synergistic combination of two different corrosion protection systems: a galvanized layer overcoated by a good barrier organic coating.

The galvanized Layer: The first layer is hot dip galvanized, where steel is immersed in a bath of molten zinc. This creates a metallurgical bond, forming durable iron-zinc alloy layers and a pure zinc outer layer. This layer provides cathodic protection, where the zinc sacrifices itself to protect the underlying steel, even if the coating is scratched. This is the first line of defence against the corrosive soil environment.

The subsoil barrier coating: For the second layer, a tough bituminous or surface tolerant epoxy coating is applied over the galvanized surface. These coatings act as a robust barrier, physically isolating the galvanized layer from the corrosive soil environment. The organic coating also stops differential corrosion at the soil-to-air interface where the structure is located in the soil. The choice between a bituminous or epoxy coating depends on the specific site conditions. Bituminous coatings are well known for their excellent water resistance and flexibility. They are an economical and effective solution for providing a tough, waterproof membrane. Epoxy coatings, on the other hand, offer superior adhesion, chemical resistance, and abrasion resistance. They form a much tougher, more durable film, making them an ideal choice for particularly aggressive soil environments. The combination of the two provides a level of protection that neither system could achieve on its own. The barrier coating seals the galvanized layer from the corrosive soil environment, significantly extending its lifespan, while the galvanizing provides a robust second layer of protection, particularly at areas of potential damage e.g. scratches. The result is a coating system that is highly resistant to abrasion and corrosion, ensuring the long term stability and safety of the PV array’s foundation.

The economic & environmental case for Corrosion Protection

Investing in high quality corrosion protection is not just a technical necessity but also a sound economic decision. While materials like Magnelis® and duplex coatings may have a higher initial cost than standard galvanized steel, this investment is dwarfed by the longer term savings. The cost of replacing corroded components, repairing structural damage, and the loss of revenue from operational downtime far exceeds the initial material cost difference. A well-protected PV framework can have a service life of approximately 30 years, matching the lifespan of the PV panels themselves, ensuring that the entire system operates efficiently and safely for its designed duration.

Furthermore, the enhanced durability reduces the need for frequent maintenance and repair, minimizing the use of resources and the generation of waste.

In conclusion, the success of the transition to solar energy hinges not only on the efficiency of the panels but also on the resilience of the structures that support them. By adopting a comprehensive corrosion protection strategy that leverages the strengths of Magnelis for the atmospheric environment and Duplex coated hot dip galvanized anchors with a bituminous or epoxy barrier for the subsoil, we can ensure that these vital installations stand strong against the test of time, fulfilling their purpose as a cornerstone of our sustainable future.

IZA