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Design and material considerations for solar mounting structures

As India continues to tap into its massive solar potential in order to reduce its carbon emissions, it has become clear that the country needs a lot more than solar panels and modules. In addition to inverters and transmission systems, solar installations need a supporting infrastructure, also known as mounting structures. The market for mounting structures has grown considerably in the past decade. At the same time, there have been concerns that the quality of this crucial component has been neglected.

Solar mounting structures

Solar panels are not directly attached to the ground or rooftops; rather, they need to be mounted on supporting structures that can align them perfectly for optimised energy production. The primary purpose of mounting structures is to position the solar panel at an angle that can maximise the amount of sunlight it receives. These structures also protect the modules from natural calamities and prevent dust, water and other elements from accumulating on their surface. In addition, mounting structures allow for easy maintenance and repairs of solar panels.

Solar modules can be positioned on the ground, on roofs and on poles based on the scale and type of solar capacity. Roof-mounted racks can secure the position of modules either through metal clips (flush mounts) or weights (ballasted mounts). The former is cost-effective, but runs the risk of causing roof leakages, whereas the latter increases the load on the roof. The structural elements of the two technologies can also be combined, though at a significantly higher cost.

Module mounting structures can also be set up on the ground. This, however, exposes the modules to a potential threat of vandalism and the risk of soiling. To avoid this, solar modules can be placed at an elevation, several feet off the ground, mounted on poles.

Solar tracking

To enhance their performance, solar mounting structures, are often equipped with tracking systems that are designed to move manually or automatically depending on the position of the sun. Based on the degree of freedom they offer, manual tracking systems can be of two types – single-axis and dual axis.

Single-axis solar trackers have only one degree of freedom as they can only be rotated from right to left. This design works well in regions closer to the equator, such as southern India, where there are minimal seasonal variations. In regions towards the north India, however, it could be more feasible to implement dual-axis solar trackers. These trackers can help move the panels in two directions, from east to west and from north to south, which can adjust to both the diurnal and seasonal movements of the sun. Dual-axis trackers, though more expensive, have been found to offer an increased efficiency of 15-23 per cent over single-axis trackers.

Manual systems have to be moved with seasonal changes in the sun’s direction and also based on daily variations. To avoid this, automatic trackers have been developed, which use preprogrammed algorithms to achieve maximum output. These systems are optimised to allow a complete collection of available solar resources and minimise energy wastage. A 2017 study on the efficiency of various methods of tracking concluded that automatic systems offer increased efficiency of 30 per cent over manual tracking systems. Although automatic trackers have a higher output than their manual counterparts, they entail a higher investment. Further, they have complex hardware and are prone to more damage, which translates into a higher maintenance cost.

Innovations in materials

Solar parks are being built to last 25 years. Thus, it is important to have robust mounting structures that have a long life. In this regard, the materials used are crucial. The choice of material depends on the climate and location of the proposed project. Conventionally, mounting structures have been made with steel, iron and aluminium. Of late, these compounds are being coated with zinc to prevent rusting and corrosion. Steel is arguably the most widely used material for making mounting structures in the country due to its relatively lower cost and ease of supply. In India, the compound is also coated with molten zinc in a process known as hot-dip galvanisation (HDG). Although this adds to costs, the method protects the mounting structures from corroding. It is believed that galvanised steel will be widely used in the Indian market.

Over the past decade, the Indian steel industry has witnessed considerable innovation. Most significantly, the average weight of tilted steel mounting structures in the country has reduced from 100 tonnes per MW in 2011-12 to about 30 tonnes per MW in 2019. The steel industry has also seen materials like POSMAC, steel coated with an alloy of zinc, magnesium and aluminium, which offers 10 times higher strength than normal HDG steel. Tata Blue Scope has also introduced special steel, ILIOS, for racking, which is coated with cold-rolled zinc or zinc-aluminium blend. It is expected to last four times longer than normal HDG steel.

Aluminium has been widely used to manufacture mounting structures given its versatility, light weight and high strength-to-weight ratio, which protects it from strong winds. Further, it is resistant to corrosion and is fully recyclable. Aluminium can also be galvanised. JSW Steel is the first Indian licensee of the product, which is an alloy of 55 per cent aluminium, 43.5 per cent zinc and 1.5 per cent silicon. In humid regions of the country, aluminium can be a good choice due to its resistance against wind. It can also help prevent rusting.

Aluminium-based structures are easy to install and maintain and hence can be a suitable choice across all small- and large-scale solar producers. The suitability of aluminium for the rooftop and the residential segment can be argued as these structures have limited weight-bearing and are more exposed to strong winds. The challenge, however, is the high upfront cost of these structures.

In addition to aluminium and steel, EPC contractors and manufacturers can look to adopting a hybrid approach for their mounting structures. For example, a representative from Granzor Engineering suggests that fibre-reinforced plastic structures can be used for rafters and purlins and be combined with legs made of HDG steel as a good alternative to aluminium.

Status of the Indian market

Solar mounting structures are estimated to account for 7-10 per cent of the total project cost. However, if they are not chosen appropriately or are of poor quality, it can lead to losses, either in terms of output or recurring maintenance costs. In the utility-scale solar segment, the country has witnessed a huge fall in tariffs, leading experts to question whether developers could cut costs in their BoS components. In 2019, the Rewa Solar Park in Madhya Pradesh faced moderate damage due to cyclones and storms. Hence, there is a need to minimise damages by choosing appropriately designed mounting structures.

A representative of Riddhim Siddhim Steel, a manufacturer of mounting structures, reported that there is a minimal difference between steel and aluminium on the cost end. The large manufacturing steel base in the country combined with regular innovations for improving its performance suggests that steel can be widely adopted for all types of solar mounting structures. Although aluminium does offer its benefits, there is not enough evidence to suggest that it is superior to steel, barring a few applications like tin roofs.

This can be validated by analysing recent tenders for mounting systems in the country. Most recently, in November 2020, Rajasthan Electronics and Instruments Limited invited bids for the supply of 1,500 HDG steel mounting structures for its 75 W modules. In February 2019, Bharat Heavy Electricals Limited floated a similar tender for 129 MW of solar projects for the supply of cold-rolled steel mounting structures.

Installing tracking systems in India is still a trade-off given the problems in procuring land for solar projects. A review of solar tracking systems in India found that module mounting structures with tracking devices required up to 7 acres of land per MW of capacity, whereas fixed-tilt structures only require a maximum of 5 acres per MW of installed capacity. In addition, dual-axis solar trackers, in particular, have seen poor adoption rates owing to their heavy structure and high capital costs.

A pilot project by Asun Trackers and the Indian Institute of Technology, New Delhi, for instance, has demonstrated a dual-axis tracker that optimises structural weight to reduce capital costs significantly. The technology is also reported to offer an incremental efficiency of 5 per cent over standard single-axis trackers. This could give a huge impetus to developers as they can reap the benefits of dual-axis trackers at a cost comparable to single-axis variants.

Future outlook

Despite several innovations in the design and materials of module mounting structures, the Indian solar market faces challenges in making the optimal choice. Although the government has prescribed standards for the galvanisation of steel, there is need for a larger, exhaustive set of guidelines for mounting structures. With solar projects exposed to huge variations in weather, including floods and cyclones, the stability and durability of these vital components must not be compromised.

The government can also play a key role in the promotion and scaling up of tracker-mounted module structures. This will make them cost-competitive for developers. At the same time, future innovations must be structured to offer flexibility to manufacturers. Mounting technologies must be made versatile to cater to varying module sizes. This could significantly drive down costs. Further, efforts must be directed towards dismantlability and refixing, which could make maintenance easier. Above all, prior planning, based on environmental factors such as climate, location and potential risks, must be undertaken to ensure that mounting structures and trackers optimise the performance of India’s ever-growing solar capacity.

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