Rooftop Structure: Recently we visited a factory in Tamilnadu where a 100kWp system was installed 5 years ago using MS (Mild Steel) rooftop solar structures. The elements had taken their toll on these structures over the past 5 years and they have now started to rust as can be seen below. Another problem is that the structures are installed on the valley of the trapezoidal sheet roof. So when it rains, the structures are directly on the path of flow of water and this accelerates the rusting process.

With Aluminium structures, there is no issue of rust formation and they can easily last 25 years or more. EcoSoch procures mill finished Aluminium mounting structures from reputed manufacturers like Jindal Aluminium, Jurchen, etc. Mill finish is the natural finish that aluminum extrusions have as they emerge from the extruder die and often has lines running along the length of the extrusion.

Mill finish has no surface treatment. It’s basically bare aluminum – the raw state of aluminum as extruded – no surface treatment. Mill finish will oxidize with a light white powder (aluminum oxide) as it is exposed to air and moisture. It can oxidize a lot under very moist or salty conditions.

Metallic aluminium is very reactive with atmospheric oxygen, and a thin passivation layer of aluminium oxide (4 nm thickness) forms on any exposed aluminium surface almost immediately. This layer protects the metal from further oxidation. The thickness and properties of this oxide layer can be enhanced using a process called anodising.

Anodising is a surface treatment and an electrolytic process in which an electric current is passed through the aluminium whilst it is immersed in a sulphuric acid bath. This increases the thickness of the oxide coating on the aluminium improving its resistance to abrasion. This process increases corrosion resistance and wear resistance.

For dry environments like in Bangalore, we go with mill finish. For corrosive environments, we can go with anodized and some manufacturers can supply Anodized (10~15 microns). Anodized rail is pre-oxidized in a controlled environment, which creates a very thin but very hard natural barrier to corrosion. If the anodizing is kept intact, it can resist a fair amount of moisture and even salt in the air – this is why anodized parts are always suggested for corrosive environments.