Mounting structures, contrary to popular opinion, are not just support structures for solar panels. They serve a much more important purpose, of ensuring that the optimum solar radiation reaches the solar panels in solar power projects. Forming the backbone of solar projects, the height, tilt, design and construction of mounting structures determines the efficiency of and actual generation from these projects. Thus, even though the best quality modules and inverters are used in a project, if the height, spacing and tilt are not proper, the energy generation will be much lower than estimated. Fixed tilt mounting structures are installed at a fixed angle based on the latitude of the site, while seasonal tilt structures are adjusted seasonally, according to the earth’s movement around the sun in order to capture optimum sunlight. Moreover, tracker solutions are deployed to change the orientation of solar panels as per the season and time of day to ensure more effective results. Thus, mounting structures provide a strong base for not only modules but also trackers in such projects.
With the increasing pace of solar power installations worldwide, the focus is on developing cost-effective components. As far as mounting structures are concerned, technology advancements are centred around material, structure and design to improve quality and reduce costs. These developments are not only limited to product costs but also logistics, installation and maintenance-related expenses. For instance, a lighter mounting structure will be easier to handle, saving on transport and labour cost, while a corrosion-resistant product will be easier to maintain.
Material and design to use
Aluminium racking systems dominate the pitched or sloping rooftop solar market. A variety of mounting structure designs and configurations are available for flat rooftop solar projects. Some structures are preassembled at particular tilt angles, others can be directly attached to the roof, while many are ballasted with concrete blocks to keep racks and modules in place. Various materials including aluminium, steel and composites are used to develop these structures. However, aluminium is the most preferred material for rooftop systems as it is lightweight, durable and easy to assemble. For ground-mounted solar projects, the design and material of module mounting structures depends on the geographical location, soil conditions and the climate. In many projects, the mounting structures are attached to concrete foundations with front and back supporting legs, while in others, galvanised steel beams are pile driven into the soil. For ground-mounted systems, stainless steel is the material of choice as aluminium posts cannot withstand the forces associated with pile driving.
Projects in certain locations in India undergo immense environmental stress due to a high concentration of salt, heat, rain and strong winds. Thus, module mounting structures need to be designed taking into account these factors. Corrosion is an especially common problem for these metal-based mounting structures, and therefore, hot-dip galvanisation and cold-formed steel are used to mitigate this risk. Similarly, galvalume, an alloy of 55 per cent aluminium, 43.5 per cent zinc and 1.5 per cent silicon, is also gaining popularity due to its cost-effectiveness and low maintenance requirement. JSW Steel is the first licensee of the technology in India. In 2019, Clenergy launched a new ground-mounting system, PV-ezRackSolarTerraceMAC. Its main components are made of PosMAC, a POSCO magnesium aluminium alloy coating product. PosMAC is a ternary alloy coated steel with high corrosion resistance developed by a South Korea-based company, POSCO. The company claims that the product has a self-healing performance and eliminates the need for regular maintenance.
Mounting practices in India
In 2018, PI Photovoltaik-Institut Berlin AG, on behalf of Physikalisch-TechnischeBundesanstalt, carried out the “Pilot Study on Quality Aspects of PV Power Plants in India” to analyse the present status of operational solar photovoltaic plants installed in the country. The results obtained from the study highlight serious faults in the development, execution and operation of solar projects in the Indian market. Commonly found defects in mounting structures include rust, weak anchorage and foundation. Similarly, at a workshop organised by Renewable Watch on “Solar Plant Performance” in 2019, various industry leaders and experts discussed common issues and challenges found in mounting practices in India. These include dissimilar metals that are not isolated from one another, leading to material incompatibility issues in the form of galvanic corrosion, deformation of the mounting structure during piling, and out-of-position installation of piles leading to a misalignment of piles and steel sections. Other design faults highlighted were inadequate quantity of steel, poor quality of galvanisation, insufficient clamps, incorrect positioning of modules resulting in reduced load-bearing capacity, and modified or wrong type of clamps used as a result of inadequate spacing between the modules.
Mounting structures need to be strong enough to handle the load as well as high winds. They need to be designed and installed as per site conditions, which often is not the case. Moreover, according to a report by PV Diagnostics, a project at a salt lake basin in Rajasthan used hollow columns despite a highly corrosive soil texture. Thus, water can collect inside these columns, rapidly corroding the structures from inside. This can be prevented by epoxy zinc coating as well as by reducing the frequency of water-based module cleaning. In addition, low power air blasts can be used to clean salt and soil deposits and drain holes can be drilled at the bottom of the structures to remove water.
While most of the solar projects are prepared for extreme weather conditions, there are many that do not stand a chance against the natural elements. For instance, in July 2019, a section of the Rewa Solar Park in Madhya Pradesh was damaged due to severe rainfall and high speed winds. According to media reports, damages were reported in modules, inverters, cable tray as well as mounting structures. The sudden rise in water levels due to heavy rains caused a flash flood situation, which overflowed the drainage points with debris collecting there, and damaging mounting structures, and thereby, the modules on them. More recently, in June 2020, there were reports of solar panels getting damaged after a dust storm and rain, at the Delhi-Meerut Expressway in New Delhi. Thus, sturdier materials and structures need to be used in solar projects with better protection measures to sustain these plants for 25 years even in the face of extreme weather conditions.
Developments in tracking solutions
While trackers definitely increase the energy yields from a solar project, they are more complex than fixed racking systems. They require more site preparation, including additional trenching and grading, which adds to the total cost of a project. Thus, in a price-sensitive market like India, trackers have been traditionally used in projects where the efficiency gains are high so as to offset the greater costs. However, with bifacial modules set to gain prominence, the tracker market might further offer new opportunities for manufacturers. Trackers ensure optimal absorption on the front side and enable higher view factor gains for greater albedo values from the rear side. The higher energy gains will lead to better rate of returns, and experts believe that due to this reason, bifacial modules along with trackers may see a greater uptake. Industry forecasts by IHS Markit show that though Asia is projected to be the largest market for solar installations going forward, demand for trackers will be weak due to land constraints and greater popularity of fixed-tilt systems. At the same time, in Asia, China and India are set to be among the top 10 largest markets for trackers from 2019-23.
The way forward
Going forward, steel-based structures are expected to dominate the mounting structure market along with small volumes of cost-competitive polymer-based materials. According to industry data, 40-60 tonnes of steel is required for producing mounting structures for 1 MW of solar power capacity. With India planning to add about 65 GW of new solar capacity to achieve the 100 GW target over the next few years, a significant quantity of steel is required. This creates a huge opportunity for steel giants as well. However, steel prices, along with the cost of aluminium and other components, are subject to market variations. Thus, there is a need to invest in the development of more cost-efficient products.
Summing up, the proper quality of mounting structures is of great importance to ensure the longevity and performance of solar projects. Thus, developers and project installers should pay attention to optimising the design and not compromise the project returns by using substandard materials, designs and practices.
By Khushboo Goyal