With the steep fall in solar tariffs, there is an increasing pressure on the solar industry to continuously optimise the cost of various plant components. The past few years have seen a significant decline in module prices and the attention has now shifted to balance of system (BoS) components. In this respect, mounting structures have seen a major decline in costs. As per the Central Electricity Regulatory Commission’s benchmark capital cost for solar projects, the benchmark cost for mounting structures reduced from Rs 10.5 million per MW in 2013-14 to Rs 3.5 million per MW in 2016-17. Competitive bidding in state and central government programmes is pushing developers to employ technology solutions that can ensure higher generation and boost returns. In this respect, there is a major focus on utilising mounting structures with solar trackers, which can result in higher generation than that from the same installed capacity of photovoltaic (PV) modules.
Mounting structures, mostly made of stainless steel, either hot dipped galvanised (HDG) or pre-galvanised cold rolled, are used to mount the panels at an appropriate angle and provide structural support. These are of three types – fixed tilt, seasonal tilt and structures with trackers. As against fixed-tilt mounting structures in which solar panels are mounted facing the south, in seasonal-tilt mounting structures, the solar panels are mounted facing the south and the angle is adjusted seasonally. The steel used for these two types of structures is HDG, pre-galvanised or galvalume. In mounting structures with trackers, the solar panels are mounted facing the east-west direction and the tracker follows the path of the sun to maximise the generation gain. The material used for this type of technology is HDG. At present, the majority of the installations in India have fixed-tilt and seasonal-tilt structures. However, with the steep fall in solar tariffs in 2016, there is a shift in demand from fixed-and seasonal-tilt structures to solar tracker-based structures.
Moving with the sun
A solar tracker is a system that aligns the solar panels with the sun. It changes their orientation throughout the day to follow the sun’s path, thus maximising the energy capture. There are two types of trackers currently available in the market. These are array trackers and row trackers. In an array tracker, a single shaft is built across multiple rows and it continuously tilts all the rows using a single high power motor. In a row tracker, a tracker system is installed for each row. Both types have different advantages and disadvantages. An array tracker is cheaper as there are only three to four motors per MW against 40-50 motors per MW in a row tracker. Additionally, there are fewer electronic components to be maintained. However, as each row in a row tracking system has a separate tracker, it takes care of the undulation of the land, ensures better land utilisation as well as easy maintenance as the cleaning carts can drive through the rows as against an array tracker. Also, depending on the geographical location and other costs associated with the site, a combination of array and row trackers can be deployed.
Another important concept pertaining to trackers is how they are powered – alternating current (AC) or direct current (DC). In an AC-powered tracker, the tracker motors are connected directly to the mains and do not include any battery. In a DC-powered tracker, there is a localised battery installed near the tracker motor. These are also called self-powered trackers. While the battery in the latter is an additional electrical component and would need replacement every six to seven years, these are strongly recommended in Indian markets. This is because in high wind conditions when there is a high possibility of grid failure, trackers’ inability to move may cause excessive generation loss. In developed countries, where the grids are very stable, developers shy away from including batteries to avoid operations and maintenance (O&M) costs.
Tracker technology is a well-proven one. Most of the trackers installed today have more than 99 per cent uptime and provide a significant energy gain. Single-axis trackers are common all over the world, especially in the US where 80 per cent of the projects are on single-axis trackers. In India, the trend is catching on. It is important to note that with the installation of the tracker system, the land requirement increases, as higher row-to-row spacing is required. Hence, with respect to India, the deployment of trackers is dependent on land costs, the economics between the rates of power purchase agreements, and the energy gain with tracker installation.
Despite the comparatively lower cost of fixed-tilt systems, many developers are now shifting to a tracker system. This is mainly on account of the gain in energy generation by using trackers. This energy gain varies, depending on the location of the site. For instance, an increase of over 21 per cent has been observed in Tamil Nadu and Andhra Pradesh. However, states farther away from the equator such as Rajasthan and Madhya Pradesh have shown an energy gain of 15.5 per cent and 17 per cent respectively. Additionally, trackers give a flatter generation output vis-à-vis the fixed-tilt system, hence providing better load matching. According to various industry stakeholders, in comparison to fixed-tilt structures, mounting structures with solar trackers can increase energy output by 18-25 per cent with a 9-12 per cent increase in capital expenditure.
Along with the uptake of tracker technology, other technologies around tracker systems such as drone mapping and analysis have been developed. The utilisation of a drone provides high resolution land maps, which can give the user an estimate of the cutting and filling that is needed at the site for the tracker structure installation. This can help the customer in reaching a more accurate cost estimate of the tracker before placing the bid.
Developers today have reservations regarding the operational reliability and high O&M costs of trackers. However, it is important to note that trackers are a well-proven technology and the operational challenges can be easily addressed, almost all suppliers offer a minimum 10-year warranty on the structure and a five-year warranty on the electrical components. Additionally, internationally published research shows that the O&M costs of the projects actually reduce by including trackers. This is because the module cleaning and replacement expense calculated in the 25-year model goes down by installing trackers and reducing the number of panels, to reach the same level of energy generation.
Trackers, no doubt, require more land as compared to fixed-tilt systems. However, this challenge can be addressed utilising a combination of array and row-tracking systems. Also, with the utilisation of different technologies, trackers can easily manage land undulation of almost 1 metre over a 65 metre tracker row.
A shift towards tracker-based projects is already visible across the country. As the solar market matures, a significant share of installations will be based on tracker structures. With a clear increase in energy generation, there is a strong case for the utilisation of trackers. Going forward, the global installed tracker capacity is likely to grow at a compound annual growth rate of 18 per cent to reach an installed base of 20 GW by 2020, with a major contribution from India. n
Based on presentations by Monika Rathi, Head, Product Business Development, Mahindra Susten; Shailesh Vaidya, Chief Executive Officer, Scorpius Trackers; and Rajan Sharma, Manager, Business Development, Archtech Solar