The balance of system (BoS) plays a key role in the efficient operation of a solar power project. Mounting structures and trackers are the main components of BoS, responsible for the overall functioning of a solar project. These technologies have various types, and each has its advantages and disadvantages. Owing to the fall in solar tariffs, the focus has shifted to innovative mounting structures and trackers in a bid to increase efficiency.
While the use of these applications has indeed led to efficiency gains, the challenges of higher operations and maintenance (O&M) costs and greater use of land have emerged. With the roll-out of bifacial modules and promotion of distributed market segments such as rooftop solar and solar water pumps, innovations in mounting structures and tracking solutions have become necessary.
Renewable Watch presents an overview of the two technologies and innovations in the solar space…
Mounting structures are used to mount panels at an appropriate angle and provide them with structural support. These structures are usually made of stainless steel, either hot dipped galvanised or pre-galvanised cold rolled. Broadly, there are three types of mounting structures – fixed tilt, seasonal tilt and structures with trackers. In fixed-tilt mounting structures, solar panels are mounted facing the south. In seasonal-tilt mounting structures, too, solar panels are mounted facing the south, but the angle of the mounting structures is seasonally adjusted. Meanwhile, in mounting structures with trackers, the solar panels are mounted facing the east-west direction, where the tracker follows the sun’s path to maximise the electricity generation. Currently, the majority of the installations in India have fixed-tilt and seasonal-tilt structures. However, of late, the demand has shifted from fixed- and seasonal-tilt structures to solar tracker-based structures as solar tariffs have fallen gradually.
In order to adapt to the environmental conditions at the plant site, module mounting structures require customisation. Mounting structures have evolved over the years in terms of weight, material, adaptability and cost. These structures cater to various plants including rooftop and ground-mounted solar plants, and carports. Roof-mounted racks can be installed with a solar tracker. Ground-mounted racks are also adjustable, and allow panels to tilt up and down for maximum solar absorption to increase generation. Different varieties of pole-mounted racks are also available in the market. These innovative racks allow the solar panel to sit either on top of the pole or elevate it from the ground. Moreover, tracking system-mounted racks are available for solar water pumps.
Types of tracking solutions
There are mainly two types of trackers widely used in the industry – 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. Meanwhile, in a row tracker, a tracker system is installed in each row. Both types of trackers have pros and cons.
An array tracker is less expensive as there are only three to four motors per MW, whereas 40-50 motors per MW are required for a row tracker. Fewer electronic components for maintenance make array trackers cheaper for the entire product life. The use of row trackers ensures better land utilisation, and such trackers are easier to maintain. Despite the pros and cons of the two technologies, they can be used together in a solar plant, depending on the site location and the budget of the developer.
Trackers are also differentiated based on alternating current (AC) and direct current (DC) types. In an AC-powered tracker, the tracker motors are connected directly to the mains and do not include any battery, whereas in a DC-powered tracker (also called self-powered trackers), there is a localised battery installed near the tracker motor.
Self-powered trackers are typically recommended in India even though batteries are an addition to the BoS and need replacement every six to seven years on an average. This is because batteries prove to be useful when there is grid failure and battery-less trackers are unable to operate, leading to generation losses. However, in countries where grid failures are rare, developers prefer to install battery-less trackers to avoid O&M costs.
Trackers are widely used across countries as the technology has matured over the years. Therefore, such technologies have more than 99 per cent uptime and provide significant energy gains. The uptake of single-axis trackers is more in other countries, especially in the US, where 80 per cent of the projects have installed such trackers. However, in India, the uptake of single-axis trackers is comparatively low. With industry awareness and increasing demand, the trend is catching on. While the technology has matured, many developments and innovations are under way to further increase its efficiency.
Developments in tracking solutions and mounting structures
Tracker solutions are more complex than fixed racking systems as they require more site preparation, including additional trenching and grading. Such complications in the installation increase the total cost of a project. Therefore, trackers are typically used in projects where the efficiency gains are high enough to offset the costs. Such analysis matters much more in a price-sensitive market like India. Currently, technologies related to drone mapping and analysis have been developed in a bid to drive the uptake and use of tracker-based solutions. A drone provides high resolution land maps, which can give the users an estimate of the cutting and filling that is needed at the site to install the tracker structure. This helps them reach a more accurate cost estimate of the tracker before placing the bid.
The tracker industry is in an interesting phase, with the greater uptake of bifacial modules. Such a shift in technology preference will create new opportunities for manufacturers of tracker-based solutions. The innovations will focus on ensuring that trackers optimally absorb irradiance on the front side and enable higher view factor gains for greater albedo values from the rear side. The innovations will lead to higher energy gains and better rate of returns from the solar projects. The future of tracker-based solutions also lies in its combined uptake with bifacial modules.
In the mounting structure space, the use of polymer-based materials for mounting structures is expected to increase as they are cost competitive. At present, steel-based structures dominate the market and will continue to do so in the near future. That said, industry stakeholders are looking to work on products that are less expensive and more durable.
Key challenges and future outlook
A key challenge is the increased land requirement for the installation of tracker systems. The deployment of such solutions also depends on the cost of the land. In India, land procurement is a cumbersome process.
A key concern related to module mounting structures is that they have a major share in the total cost of a solar project. Furthermore, unlike other BoS components, mounting structures are not bought from suppliers. The design of mounting structures is undertaken by engineering, procurement and construction companies, which face challenges in both installation and O&M. Often, faulty practices lead to shadowing on other panels and difference in the radiation received across panels. This could not result in generation losses, and degradation due to angle mismatch and different temperatures in the affected panels. As a result of these faulty designs, mounting structures may become unstable, making them prone to damage from high wind speeds. Apart from this, industry stakeholders in India work on thin margins, and there are always concerns regarding cost-benefit analysis.
Going forward, more innovations are needed in mounting structures and tracking solutions to address these challenges and concerns. Gradually, the industry has started to incur extra initial costs on technology to not only increase generation from plants, but also to decrease O&M costs in the long run. In line with this trend, the uptake of innovative mounting structures and tracking solutions is also expected to increase. New products are planned to be introduced in the residential rooftop solar and solar pump segments in particular to address specific consumer concerns. Overall, the market for mounting structures and tracking solutions is expected to evolve with the other sub-segments in the solar power space.
By Sarthak Takyar