With wind energy gaining traction in the power sector, several wind turbine components are undergoing technology advancements with the aim of improving efficiency and increasing the output of generated electricity. A wind turbine may appear simple in appearance, but it comprises several complex components that cumulatively build and support its overall functioning. These components offer vast potential for technology advancements. These components, including drivetrains and gearboxes, are witnessing radical changes in their technology, as highlighted in this article…
Drivetrains
A drivetrain is an essential component of the wind turbine as it facilitates the conversion of rotational energy from the turbine’s blades into electrical energy. A drivetrain consists of a gearbox and a generator, wherein the drivetrain connects the turbine rotor’s low-speed shaft to the generator’s high-speed shaft, effectively transmitting mechanical power and increasing rotational speed to efficiently generate energy.
A range of wind turbine drivetrains with various costs, technologies, physical features, efficiencies, degrees of reliability and materials are currently available in the market. However, with wind turbines constantly undergoing technological upgrades to meet the growing demands of the global clean energy transition, there is an increasing emphasis on innovating drivetrains. Furthermore, the global wind energy market is experiencing a shift towards offshore wind, opening up further opportunities for the adaptation and enhancement of drivetrains. Offshore wind projects differ from land-based projects not only in their geography but also in their capacity to deploy larger and more powerful wind turbines. Thus, the development of robust drivetrains can support a considerable increase in project capacity.
According to a research paper titled “Wind Turbine Drivetrains: State-of-the-art Technologies and Future Development Trends” published in 2021, the technological drivers of a drivetrain differ from other components of wind turbines. For towers, site-specific solutions are dependent on factors such as wind conditions or other site features, which can significantly affect the cost. However, for the drivetrain, the cost is primarily influenced by the number and size of components, rather than site- or region-specific features.
Drivetrain designs have been constantly upgraded to achieve greater efficiencies in cost as well as performance. Due to its complexity and a significant number of moving parts, the drivetrain is prone to breakdowns and faults. Thus, much of the advancements in drivetrains are focused on reducing the number of moving parts and achieving weight reduction to create more compact, lighter and simpler systems.
Digitalisation of drivetrains is also emerging as a key focus area due to the importance of real-time data management in supporting wind turbine functioning and efficiency. This digitalisation primarily involves the use of sensors and actuators installed on drivetrains, but it may also be extended to other turbine systems to create a more robust control and monitoring system. Digitalisation has also been cited as an enabler for the adoption of digital twin models in wind turbines, which utilise real-time data alongside cloud computing for decision-making.
Gearboxes and direct drives
A gearbox in the wind turbine connects the low-speed shaft, which is connected to the turbine blades, to the high-speed shaft connected to the generator. It translates the spinning motion of the outer blades through a succession of gears of with varied diameters. Its primary function is to increase the rotational speed of the low-speed shaft coming from the wind turbine rotor to a higher speed suitable for the generator, which is connected to the high-speed shaft. This increase in speed allows the generator to produce electricity efficiently. Wind turbines have three kinds of gearboxes, namely, planetary, parallel-shaft, and helical. They are differentiated by the types of gears utilised, and their operational configuration.
A gearbox operates on the principle of gear ratios, using a set of gears with varying sizes to achieve the desired speed increase. The low-speed shaft, connected to the wind turbine rotor, typically rotates at a relatively slow speed due to the large size of the rotor and the need for low wind speeds to effectively capture energy. The high-speed shaft connected to the generator has to rotate at much higher speeds to produce electricity. By incorporating the gearbox, the low-speed but high-torque rotation of the wind turbine rotor can be converted into high-speed rotation with lower torque. This mechanical transformation is important because most electricity grids operate at a fixed frequency. Additionally, the rotational speed of the wind turbine rotor varies depending on wind speed.
According to research, the majority of wind turbine failures may be attributed to failures within the gearbox, which adds to their costly repairs and downtimes. It is crucial to note that not all wind turbines use gearboxes. In recent years, there has been an emerging trend towards direct-drive turbines, which do not require gearboxes. Direct-drive turbines connect the rotor’s low-speed shaft directly to the generator, eliminating the complexity and upkeep of gears. These turbines are preferred over gear-driven turbines due to their lower maintenance costs and better reliability, despite having slightly higher upfront expenditures compared to their counterparts.
When it comes to gearbox wind turbines, wind turbulence can exert immense stress on the wheels and bearings. This can lead to faults within the turbine components and eventually lead to its breakdown. In light of these factors, the technologies for critical components utilised in turbine development are evolving to address challenges and enhance power production.
Over time, the number of possible drivetrain configurations has increased, influenced by factors such as loading and costs. The most significant difference that has emerged over the years is whether a wind turbine has a gearbox or not. Thus, two primary categories of turbines dominate the market. The first category relies on a mechanical transmission system to amplify the rotational speed of the turbine rotor shaft so as to drive a generator. In the second category, the generator directly harnesses the high torque to generate power without the use of any mechanical transmission to increase speeds.
In the case of geared wind turbines, the speed conversion ratios are higher, resulting in higher operations and maintenance (O&M) requirements due to the presence of various gearbox components. On the contrary, slow, rotating electric generators are larger and heavier. Thus, in recent times, manufacturers prefer hybrid drivetrains, incorporating a gearbox to transfer the slow rotational speed of the shaft to a medium- or high-speed generator, coupled with a full converter. Whether a drivetrain is geared, non-geared or hybrid depends on financial factors and other considerations such as weight, reliability and the expertise of the manufacturer. Moreover, there is no consensus regarding the most suitable type of drivetrain for all project sites across various geographies.
Future outlook
Advancements in drivetrains are expected to emerge in tandem with the overall growth of the wind turbine sector. New developments may include single-stage gearboxes, direct drive systems and permanent magnet generators.
The advancements in direct-drive magnets and generator designs for wind turbines have resulted in the development of low-cost and lighter wind turbines. Additionally, the reduced cost of permanent magnets used in direct-drive turbines has further enhanced the prospects for direct-drive turbine adoption.
Further, considering a long-term view of the entire project life cycle, it is essential to design wind turbines and their critical components, such as drivetrains, in a manner that optimises O&M costs. Thus, wind turbine manufacturers are striving to reduce the complexity of conventional drivetrains, especially as they often manage the O&M of wind plants. These factors are driving rapid innovations in the drivetrain space as the race to design the most optimal, efficient and lighter drivetrain continues.
While the digitisation of drivetrain technology is still at a nascent stage, it is crucial to explore its potential for addressing challenges in drivetrain systems. Additionally, it is necessary to address typical faults with gearboxes to enhance their efficiency. Furthermore, the implementation of advanced O&M techniques with data analytics and artificial intelligence-enabled tools can improve the cost efficiency of wind energy plants.
Going forward, land constraints are expected to be exacerbated, especially in countries such as India that are, undergoing rapid urbanisation. Therefore, enhancing turbine efficiency to generate greater energy per turbine would reduce the number of turbines required at a particular site. This can significantly reduce the cost of turbine transportation and installation, while also reducing the overall O&M costs throughout the project’s lifetime. India is actively exploring the offshore wind segment, which would enable the development of larger turbines with greater capacities, thereby increasing the scope for enhancing drivetrain efficiency.
By Nikita Choubey
