Drivetrains are an essential part of a wind turbine set-up. They convert the kinetic energy from wind to electrical energy. These drives comprise smaller components such as bedding, gearboxes, brakes and generators. Gearboxes and generators are the two main subcomponents of the drivetrain assembly, and are among the most expensive. As the wind power market evolves and technology advances, the types of components used and their cost effectiveness change in tandem.
According to the International Renewable Energy Agency’s (IRENA) report, “Future of Wind, 2019”, Denmark’s Vestas and China’s Mingyang and Goldwind were the top suppliers of high speed geared drive, medium speed geared drive and direct drive turbine technologies respectively. Geared wind turbine systems continue to be the preferred turbine technology based on market size (see figure). Conventional high speed geared systems and medium speed turbines occupied market shares of 69.7 per cent and 3.7 per cent respectively in 2018. The market share of direct drive turbine technologies was 26.6 per cent in 2018, which was 2 per cent less than that in 2017, due mainly to the reduction in wind turbine installations by Germany’s Enercon.
Turbine sizes have increased rapidly in recent decades, and such technological improvements are expected to continue beyond 2022. The largest turbine yet is being developed by GE. This turbine for offshore applications, called the 12 MW Haliade-X, has 107 metre long blades, with blade diameters of over 200 metres. According to IRENA, turbines of up to 20 MW for offshore applications can be expected by 2030. Another recently introduced large turbine is the MingYang Smart Energy Group’s MySE11-203 wind turbine, which claims high reliability and a lower levellised cost of energy for offshore wind farms. According to the company, MySE11-203, with a rated power capacity of 11 MW, is the world’s biggest hybrid drive wind turbine. It features a rotor diameter of 203 metres, with 99 metre long carbon-glass hybrid blades. The turbine is composed of less fragile components so that the short and strong structure can reduce loads to the drivetrain. Its medium-speed gearbox is similar in structure to aero-engine gearboxes with high reliability. The prototype of this offshore machine is planned to be erected in 2021, but it will be commercially available only in 2022. As the size and weight of these turbines increase year on year, drivetrains will need to be made lighter and more compact in order to reduce operations and maintenance (O&M) costs.
Currently, most wind turbine drivetrains use generators that are connected to gearboxes. These connections speed up the rotations, from about 5 to 15 rotations per minute to 1,000 to 1,800 rotations per minute. The higher speeds generate electricity using a high speed induction generator. Due to the many moving parts involved in the process, the gearbox set-up requires high maintenance. An alternative to this is a direct drive generator. Although this set-up has fewer moving parts and generates electricity at lower speeds, it uses permanent magnets and heavy generators, which makes it more expensive. Some of the major challenges facing drivetrain technology are deterioration of the gear and gearboxes, loss of lubrication, breakage of gear teeth, fatigue-induced damage of the gearbox and generator components, spoiled braking system, damaged yaw bearings and drives, and worn-out wiring systems. Sustained operation of the wind turbine can also lead to fatigue cracks in shafts over a period of time.
The moving parts of a drivetrain are subject to a significant amount of wear and tear, and any deterioration in its components can have a significant impact on the performance of the wind turbine. Developers thus spend a substantial amount on the O&M of a wind power plant. According to Wood Mackenzie, global onshore wind O&M costs reached nearly $15 billion in 2019. Of this, $8.5 billion was spent on unplanned repairs and corrective maintenance necessitated by component failures. The market is constantly moving towards options that make O&M easier, as more efficient technologies slowly become affordable.
Advanced manufacturing techniques are expected to produce more efficient, reliable and affordable drivetrains. These developments include new single-stage gearboxes, permanent magnet generators, high efficiency power electronics, direct drive systems and hybrid systems. Advancements in blades, drivetrains and control technologies, in particular, will further enable the development of larger, more reliable turbines with higher capacity ratings. As the turbines get bigger, the capital costs per MW of installed capacity are also likely to increase. However, higher energy production and lower costs for foundations and installations will lead to a reduction in the cost of energy. Further, greater reliability and less need for maintenance would also decrease the operating expenditure.
The incorporation of smart technologies in wind power generation has been increasing over time. This has made it easier to monitor and control a huge cache of data that assists operators in running the plant smoothly and efficiently. A digitalised wind power plant allows operators to leverage data and transform it into analytics through specified software platforms. Digitalisation allows power generation to be customised to suit the various assets – plants, farms and fleet – and gain a micro-to-macro perspective of their functioning. The data thus gathered is moved to an analytics platform that uses real-time algorithms to develop actionable insights. The analytics, in turn, are used to run diagnostics on turbines, drivetrains and other parts of the power plant. The insights provided by digitalised operations help reduce the downtime of the plant and its critical components.
In July 2020, renewable power generator Greenko and analytics and engineering firm ONYX Insight signed an agreement to modernise 500 wind turbines in India. ONYX Insight’s technology will enhance the quality of data retrieved from the turbines to improve analysis. It will install sensing equipment in phases as part of a retrofit project across direct drive and geared turbines. The data generated on the platform will be used to identify issues in developing machinery. This will allow a time frame of six months to a year to plan repairs. This project is supposed to make O&M more efficient and improve the reliability of turbines.
India’s wind power industry is quite mature, with the majority of the critical components being manufactured locally. Thus, there is a huge opportunity to scale up domestic manufacturing. This is a particularly good time for expanding domestic capabilities, considering the push from the government to promote reliance on the domestic industry as well as the impetus given to the expansion of the renewable energy segment. Wind energy could follow in the footsteps of the solar segment and set up more domestic manufacturing capacity to meet the growing demand. Domestically produced components such as drivetrains and motors, which can gradually achieve economies of scale and do not have to face import barriers, can thus be utilised at lower costs for future wind plant installations.
Since the wind power segment moved to auctions, lower tariffs have emerged. These lower tariffs, in turn, call for larger capacity turbines to be developed at lower prices. Innovations in the development of wind turbine components are thus improving their efficiency, with fewer moving parts and affordable pricing. At present, the industry is focusing on improving the reliability and affordability of permanent magnet generators, direct drive generators and their combinations. This trend is likely to continue going forward, with an emphasis on fewer and lighter moving parts integrated with advanced digital technologies.
By Meghaa Gangahar