Getting More Efficient

Technology trends in the renewable energy segment

The past few years in the energy domain have been characterised by a changing energy mix and the emergence of new and efficient technologies. A key factor driving these trends has been the expanding renewable energy footprint. Renewable energy generation in the country has increased nearly 25 per cent, from 81,548 million units (MUs) in 2016-17 to 101,839 MUs in 2017-18. This has been accompanied by a host of technological developments and advancements in the renewable energy sector. A look at the key technology trends in the sector…

Solar energy

Solar energy has a growing share in the country’s total installed renewable capacity and has been at the forefront of the government’s clean energy policies. There has been significant activity in the segment, particularly on the technology front. Although the cost of modules has declined significantly in recent times, the balance of system (BoS) cost has not shown the same rate of decline. Several technological developments are, therefore, under way in the BoS space, particularly in inverters, mounting systems and tracking systems, aimed at reducing their costs and enhancing solar plant efficiency. A key technological development in the segment has been the launch of module level power electronics (MLPE) solutions for solar inverters. MLPE technology is a combination of direct current (DC) power optimisers and microinverters. It is rapidly gaining market share in the solar industry. The key benefits of the technology are increased energy yield, shade tolerance, module reliability and design flexibility.

Smart hybrid inverters are also being developed to ensure greater flexibility and automate the management of energy supply from different sources such as solar photovoltaic (PV), grid and batteries. These inverters work both on-grid and off-grid to ensure a negligible loss of energy. They store the energy in batteries when solar energy production exceeds consumption. These inverters also provide flexibility to choose when to store the energy in batteries and when to transfer it to the grid.

Mounting structures have also witnessed technological developments in recent years. While the initial focus was on developing viable support structures, improved and simplified designs based on better materials and customised solutions have now gained priority. The weight of mounting structures has reduced at a fast pace in recent years, which, in turn, has led to a cost reduction. Another noticeable trend has been the increasing adoption of solar tracking technologies. The installation of trackers in a solar PV plant can increase the energy generation. As per industry experts, while the installation of solar trackers increases the project’s capex by 9-12 per cent, it leads to an additional energy output of 18-25 per cent. With advancements in solar tracker technologies bringing down tracker costs, about 50 per cent of the upcoming solar power capacity is expected to be set up with trackers.

The development of smart modules is another recent trend in the segment. Smart modules are integrated with power optimisers at the time of manufacturing and offer enhanced functionalities such as panel-level maximum power point tracking, remote monitoring and improved safety. Technological developments in the residential segment have largely been around solar inverters. Meanwhile, the industrial segment has witnessed increased uptake of concentrated solar thermal (CST) technology. CST solutions generate solar power by using mirrors or lenses to concentrate sunlight on to a small area. NTPC Dadri is amongst the few plants in the country to have deployed CST technology. Several industrial plants in the country are also beginning to adopt this technology. The Navkar Textiles plant in Jodhpur is a case in point. The textile firm has installed solar dish concentrators for generating steam at the plant.  Integrated solar modules, which can be used in utility-scale, ground-mounted PV systems as well as floating solar panels, have also gained traction in recent years. In this solution, solar modules are combined with a solar tracker system and an inverter, both in terms of hardware and software.

Energy Storage Solutions

The increase in solar power capacity has also given a push to the energy storage segment. Energy storage solutions balance the variable load injected into the grid, and smooth out the imbalances in the consumption and production of power. They enable a quick response to the varying grid requirements, thereby improving grid integration, system stability and the quality of power supply.

A typical solar energy storage system comprises a hybrid inverter, a battery management system (BMS), and batteries. A hybrid inverter can isolate the system from the grid in case of grid failure so that systems are able to supply power to critical loads, without feeding it into the grid. The BMS enables utilities to control parameters such as battery temperature, depth of discharge and the state of charge, which ensure that the battery is not over or undercharged, since inadequate levels of charging can adversely affect battery life. A BMS is particularly important for lithium-ion batteries since there is a higher risk involved in the case of its chemistry. The last and probably the most crucial component of the energy storage system is the battery. Although at present lithium-ion batteries dominate the market, other batteries such as lead acid batteries and smart batteries are also emerging. Smart batteries are equipped with automation technology and can be used to mitigate peaks in grid demand, while utilising the spare generation capacity during low-demand hours.  The heat energy storage system is also gaining ground. These systems are usually deployed in concentrated solar plants where concentrated sunlight is used to raise the temperature of a substance with a high heat-holding capacity, such as molten salt. Hydrogen fuel cells are another energy storage alternative. The process involves using electrolysis to separate hydrogen and oxygen. The hydrogen is stored and subsequently, used to power a fuel cell, which finally supplies electricity.

In January 2017, the first step to put in place a regulatory framework for energy storage systems (ESS) was taken by the Central Electricity Regulatory Commission (CERC) by issuing a staff paper, “Introduction of Electricity Storage System in India”. Meanwhile, the government is planning to launch the National Energy Storage Mission in 2018-19, which will enable the setting up of a regulatory framework and kick-start battery manufacturing. The Central Electricity Authority is also reportedly considering regulation to make storage mandatory for large-scale solar projects ranging between 100 MW and 200 MW. Estimates of the India Energy Storage alliance indicate that the energy storage market is likely to grow to 150-200 GWh by 2022. This implies that energy storage technologies are also likely to evolve and mature, particularly in India, where these solutions are still at a nascent stage.

Wind energy

The technological developments in the wind energy segment are focused on increasing efficiency and reducing costs. Several principal components of wind turbines have undergone changes in recent years. These include drivetrains, generators, rotor blades and hubs.

Overall, the size of wind turbines is increasing due to the increase in rotor diameter and hub heights to enhance energy generation at low wind sites. The additional weight is managed using advanced control technologies. Also, lightweight materials such as thermoplastic foams and plastics are being used to reduce the weight of blades. In terms of the number of blades deployed, three-blade turbines have become the norm as opposed to two-blade turbines, though a few manufacturers still offer the latter. Further, since wind speed is stronger at higher atmospheric levels, taller turbines are able to generate a higher amount of energy. Therefore, manufacturers are increasingly focusing on increasing the hub heights of wind turbines.

In the drives and generators segment, permanent magnet synchronous generators (PMSGs) have attracted a lot of attention. PMSGs use a permanent magnet instead of a coil, thus reducing the number of moving parts and maintenance requirements. PMSGs also have a high energy density and deliver lighter and more compact units. They are also more efficient than traditional doubly-fed induction generators and electrically excited synchronous generators, particularly while operating on partial loads.

A recent development on this front has been the development of a ferrite-based low-cost direct-drive PMSG. Since ferrite is abundant and relatively cheaper than other elements, it is expected to drive down capital expenditure, making it a viable choice for large turbines. Another promising technological solution is the superconductor-based generator. Superconducting generators have the potential to provide a compact and lightweight drivetrain at high torques and slow rotational speeds, resulting in lower losses and improved stability.

In terms of ratings, the average specific rating of wind turbines is gradually decreasing. The lower the rating of a wind turbine, the higher is its capacity utilisation factor. Currently, leading manufacturers are offering wind turbines of ratings 237-398 W per square metre as against 393 and 482 W per square metre in 1999-2000.

Other developments

The small-hydro segment in the country has seen limited activity on the technology front though globally several advancements are taking place. In India, variable speed generators have been developed, which take into account the changes in the hydraulic head and flux. Further, research and development is under way for enhancing the efficiency of automated systems used for monitoring and controlling equipment such as generators, watermills, transformers and protection relays.

Apart from the conventional segments, waste-to-energy (WtE) has emerged as a new source of renewable generation. While the scale of development is limited at present, the segment is likely to witness considerable activity in the near future. Currently, most biogas plants are producing electricity by deploying the biomethanation process, while several new technologies have emerged for industrial waste plants that are producing steam. One such technology is advanced gasification, which has the potential to convert varied waste sources such as wet municipal solid waste, tyres, plastic, paper and medical waste into energy. It is available in the form of modular, transportable or stationary systems. This technology is installed at the industrial WtE plant of Mahavir Synthesis Private Limited in Surat, Gujarat. The industry is also adopting polycrack technology, a heterogeneous catalytic process that converts all types of mixed waste into resources such as gas, water, carbon and power. Unlike other technologies, polycrack technology does not require waste segregation and releases lower emissions.

Conclusion

The installed renewable energy capacity in the country is growing at an unprecedented rate. With further advancements in the sector, a host of new technologies are also expected to emerge, rendering the majority of current technologies redundant. Manufacturers need to constantly innovate and improvise to keep pace with the technological developments in the sector.

Anjali Parashar

 

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