Mounting structures are more than just racks for panels. They form the backbone of solar power plants. They adjust the tilt of the panels to ensure maximum irradiation per unit area. The tilt determines the efficiency of a solar power plant and allows for maximum generation. Fixed tilt structures are used for panels facing south, while seasonal tilt structures are flexible and can be adjusted according to the seasonal variation of the sun.
Mounting structures play a bigger role in tracker-based plants providing a strong base for trackers to work effectively. Earlier used only for ground-mounted solar power plants, today mounting structures are deployed on rooftops, carports and other surfaces as well. Mounting structure materials have also evolved over the years to improve the quality of installations.
Types of materials
Stainless steel, aluminium and galvalume are the primary materials used in solar mounting structures in India. While steel and aluminium have been in use for a long time, galvalume is a more recent addition. The type of material used for mounting structures is dependent on the location and the life cycle of the plant. Earlier, wood and polymer were used as mounting structure materials. However, they have been replaced with more durable materials and are no longer actively used.
Durability and stability are the inherent properties of stainless steel, which makes it ideal for manufacturing mounting structures. This helps hold solar panels in place in harsh weather conditions. Most Indian projects use stainless steel for mounting structures.
For components that are exposed directly to damaging weather conditions, hot-dip galvanisation (HDG) is done to prevent corrosion and improve the life of the structure. Typically, a 70 micron coating thickness is sufficient for parts that are not subject to mechanical wear and tear such as mounting structures. However, HDG has its own limitations in terms of quality control as it is largely a semi-automated process. Meanwhile, pre-galvanised steel is used for solar mounting structures. It is typically used for parts that are not highly exposed to corrosive elements and water.
Cold formed steel (CFS) or light gauge steel has been found to be highly suitable for solar mounting structures. It is light and customisable for all types of terrain, including remote areas and unique roof designs. While CFS has been traditionally used in buildings construction, the versatility of the material and process enable it to be used for smaller, modular structures as well, extending its application to solar mounting structures.
CFS has high tensile strength despite being lightweight. This allows the framing of mounting structures to be done on-site as well. The frames can be manufactured and assembled in a factory, or can be assembled at the plant location so as to allow minor adjustments to ensure a well-fitting mounting structure. The material is highly flexible in terms of thickness, design and length. Moreover, it is cost-effective, and can be manufactured and installed with greater precision. CFS is also resistant to corrosion and can withstand high winds and rust with the help of HDG core and a layer of zinc, as used by many manufacturers.
Aluminium extrusions have been widely used as solar mounting structures in India. The extrusion process provides flexibility to the design, and gives it the optimum rigidity and strength. The material is lightweight, has low density and can be easily transported to far-flung areas. Moreover, aluminium so used is highly durable, almost maintenance-free and recyclable.
Some of the key properties of aluminium used in solar mounting structures are high strength, formability, electrical and thermal conduction, resistance to corrosion, and high heat and light reflection. Moreover, it is easy to fabricate and recycle. Aluminium mounting structures are also ideal for rooftop solar plants given the rooftop weight restrictions. It is suitable for the installation of solar panels on carports and other platforms.
Aluminium extrusions can be customised on-site, and require less installation time. They do not entail high labour costs. The low weight of aluminium eases its transportation. It also keeps the transport costs low. Aluminium is naturally resistant to oxidation and other environmentally corrosive effects. These parts can be designed for quick snap-together installation with tight joints.
Galvalume has also gained some popularity in the past few years. It is an alloy of 55 per cent aluminium, 43.5 per cent zinc and 1.5 per cent silicon. JSW Steel is the first licensee of the technology in India. It is typically a more cost-effective and low-maintenance solution for mounting structures.
Renewable Watch Research analysed the module mounting structure of NTPC’s 50 MW solar power plant at Mandsaur, Madhya Pradesh. The material used for this project is primarily stainless steel as is the case with most Indian solar installations. According to the tender, the frame, post, cap plate and assembly of mounting structures must conform to the Indian standard IS 2062 for hot rolled medium and high tensile structural steel and IS 811 for cold formed light gauge structural steel sections. The cold formed sections must have a minimum yield stress of 350 megapascals (MPa) and hot rolled sections must have 250 MPa of minimum yield stress. The steel so used in all materials must undergo HDG with a minimum coating thickness of 85 micron.
The specifications provided by this tender indicate the widespread use of stainless steel in solar installations in India. Some developers have started using galvalume and aluminium as well. However, it will take some time for these technologies to acquire a greater share of the market.
Experts are of the opinion that the use of steel or aluminium depends primarily on the solar power project and its location. In India, stainless steel is the material that is traditionally used, while aluminium has been put to use only in recent years. A comparative study by IBIS Associates of the total cost of ownership of steel- and aluminium-based mounting structures suggests that aluminium is a more cost-effective material globally.
Challenges and outlook
With growth in solar capacity addition, the focus on the quality of material used has also increased. As new players emerge to cater to the growing demand, low quality products are bound to permeate the market. To this end, all critical components, including solar cells and panels, connectors, wires, junction boxes, inverters and mounting structures, need to be subjected to strict quality control.
Solar power tariffs have witnessed a steep decline whereas steel and aluminium have declined gradually. As a result, developers and manufacturers are pressed for margins. They resort to cutting corners in order to inflate profits, leading to poor quality of mounting structures. This puts project safety at risk, which may result in losses. Keeping a strict check on the manufacturing process of mounting structures and their materials will help prevent such losses and provide a sturdy project that may last well past its lifetime of 25 years.
Tenders of over 25 GW were announced in March, 2019. Over the next four years, projects aggregating 25 GW will come online, driving the demand for steel and aluminium for mounting structures. The mounting structures market in India is likely to be largely dominated by stainless steel-based structures with some increase in the share of other technologies as well.
By Ashay Abbhi