The drivetrain is often called the “powerhouse” of a wind turbine as it contains a generator and a gearbox. These appliances convert the torque generated from the rotation of the wind turbine blades into electricity. The role of the gearbox is to increase the speed of the rotation of the turbine blades to generate electricity. Gearbox-based wind turbine technology is widely used, but it has some issues. One, it has a lot of moving parts, and thus requires frequent and substantial maintenance. Two, it is a very heavy component and its installation is a cumbersome task. Three, wind turbulence often causes technical stress on the wheels and bearings inside the gearbox, thereby causing degradation of the turbine components.
Direct drive-based wind turbine technology has been developed in a bid to resolve these challenges. Electricity can be generated at much lower speeds using this new technology, thus eliminating the need for gearboxes. However, direct drive technology has its own pros and cons. The positive is that this technology uses fewer moving parts, thus reducing operations and maintenance (O&M) costs. This is important as according to Wood Mackenzie, the 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 negative is that this technology uses magnets that are made from expensive rare earth materials such as neodymium and dysprosium. Research is currently under way to develop direct drive technologies that do not use permanent magnets or rare earth materials. In addition, these materials are heavy. Accordingly, wind turbines that use direct drives require heavier generators for a given turbine capacity.
The US Department of Energy (DOE) has already selected projects to develop next-generation wind turbine drivetrain technologies for both onshore and offshore wind turbines. These projects will develop more efficient, smaller and lighter-weight generators, thereby lowering costs and making wind energy more affordable. The funding for such technologies is significant. Each of the selected projects has received $500,000 to design a wind turbine generator that can be scaled up to at least 10 MW. This is in line with the industry trend of installing larger wind turbines, particularly for offshore projects.
Among these, one project (WEG Energy Corporation of Duluth) developed a direct drive permanent magnet generator design that is smaller, lighter, less expensive, more reliable, more efficient and uses less rare earth materials than conventional gearbox designs. Two projects (American Superconductor Corporation of Ayer and General Electric Research of Niskayuna) have developed superconducting generators, which make a much stronger magnetic field using superconducting windings. This significantly reduces the need for sourcing rare earth materials from foreign countries and also results in a significant size and mass reduction over conventional generators.
In January 2021, the DOE selected GE Research to receive up to $20.3 million to build and test a scaled prototype of its generator on a wind turbine. According to the DOE, this will result in a design that is up to 50 per cent lighter while reducing the cost of wind generation by up to 10 per cent.
Direct drive market
As per the Global Direct Drive Wind Turbine Market (2017-2022) report published by Market Research Future, the global direct drive market will expand at a compound annual growth rate (CAGR) of 11.5 per cent during the forecast period 2017-22. A higher torque with fewer rotations per minute, improved efficiency and reduced noise will be the key factors that will shape the growth of the market. The other key factors that will give a fillip to the direct drive wind turbine market are the depletion of fossil fuel reserves, favourable government policies, growing awareness on renewable energy sources and rising demand for energy.
Europe is the largest market for direct drive technologies and is expected to retain this position till 2022, as per the report. This is so because key market players are already operating in European countries. Favourable government regulations for the wind power segment in the European countries are another key factor contributing to the market growth. Countries like France, Ireland, Spain and the UK are expected to take the lead in the European market.
The Asia-Pacific region is expected to be the second largest market for direct drives after Europe. In this region, China and India will be the key markets. High capacity addition plans, availability of experienced industry players and increased awareness of renewable energy usage will help in the promotion of the technology and contribute to market growth in these countries. Another key reason for the greater interest in direct drive technology is efficient O&M of wind turbines, which will increase electricity generation and reduce overall maintenance costs. The other important markets for direct drives in Asia Pacific include Japan and South Korea.
The market for direct drives is strong in North America due to the presence of established industries in the region. The key players in the global direct drive wind turbine market include the American Superconductor Corporation (the US), Emergya Wind Technologies B.V. (the Netherlands), ENERCON GmbH (Germany), GE Renewable Energy (the US), Goldwind Science & Technology (China), Leitwind AG (Italy), Siemens AG (Germany), VENSYS Energy AG (Germany), Windtronics LLC (the US) and the Xiangtan Electric Manufacturing Group (China).
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. According to the report, geared wind turbine systems continue to be the preferred turbine technology based on market size. In 2018, the conventional high speed geared systems and medium speed turbines occupied market shares of 69.7 per cent and 3.7 per cent respectively. Meanwhile, the market share of direct drive turbine technologies was 26.6 per cent in 2018 (2 per cent less than that in 2017). This was due to the reduction in wind turbine installations by Germany-based Enercon.
According to the report, the turbine sizes have increased rapidly in recent decades, and such technological improvements are expected to continue beyond 2022. According to IRENA, the MingYang Smart Energy Group’s MySE11-203 wind turbine 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. To reduce loads to the drivetrain, the turbine is composed of less fragile components. Its medium speed gearbox is similar in structure to aero-engine gearboxes with high reliability. The prototype of this turbine is planned to be erected in 2021, but it will be commercially available only in 2022. Thus, drivetrains in the future will need to be made lighter and more compact in order to reduce O&M costs.
The way forward
Going forward, with the use of advanced manufacturing techniques, more efficient, reliable and affordable drivetrains will be produced. The technological developments in this space include the use of new single-stage gearboxes, permanent magnet generators, high efficiency power electronics, direct drive systems and hybrid systems. In particular, advancements in blades, drivetrains and control technologies will enable further development of larger, more reliable turbines with higher capacity ratings. The capital cost per MW of installed capacity is also likely to increase as the turbines get bigger. Meanwhile, the cost of energy will reduce with higher energy production, and lower costs of foundations and installations. The operating expenditure will also reduce with greater reliability and less need for maintenance.
Gearbox turbines still enjoy greater popularity in the wind energy market due to the relatively high cost of direct drive technology. To use the new direct drive technology, developers will not suddenly decommission the operational gearbox-based turbines. Wind turbine manufacturers are looking to improve the efficiency and reliability of gearbox technology. Still, direct drive technology will see significant uptake in the future with manufacturers already investing substantially in research and development to increase its competitiveness over gearbox-based wind turbines.
Over the years, this research has shown positive results. Overall, the design of direct drive technology has improved, making it less complex. Moreover, direct drive-based wind turbines have become lighter and more affordable with improvements in magnets and generator arrangements. The price of the magnets used in these turbines has also been dropping continuously. Thus, the uptake of this technology is set to increase.
Considering the market opportunity of the two mainstream technologies, it is expected that both will create a dent in the market going forward. They will have a significant share in the wind turbine market as both onshore and offshore wind installations are expected to increase in the future.