Technology Priority

Direct drives set to compete with gearbox-based turbines

The drivetrain is one of the most important components of a wind turbine. It is often called the “powerhouse” of a wind turbine – an apt name as it contains a generator and a gearbox, which convert the torque 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’s blades from around 5-15 rotations per minute to the higher speeds of 1,000-1,800 rotations per minute that are needed to generate electricity. Gearbox-based wind turbine technology has been widely used, but it is not without its problems. A gearbox has a lot of moving parts and thus requires regular and high maintenance. It is also one of the heaviest components of a wind turbine and its installation is, therefore, a tedious task. Moreover, wind turbulence often causes technical stress on the wheels and bearings inside the gearbox, leading to degradation of the turbine components, and eventually stopping the entire turbine. The intensity and speed of gearbox damage increase in regions that have faster wind speeds.

In a bid to resolve these challenges, a new direct drive-based wind turbine technology has been developed. This technology can enable electricity to be generated at much lower speeds, thus eliminating the need for gearboxes. However, like any new technology, it has its own set of costs and benefits.

A key benefit of direct drive technology is that it involves fewer moving parts, which reduces the costs incurred on operations and maintenance (O&M). However, this technology uses magnets, which are made from expensive rare earth materials such as neodymium and dysprosium. As these materials are heavy, wind turbines that use direct drives require heavier generators for a given turbine capacity. Also, many experts point out that the mining of these rare earth materials is environmentally unsustainable, thus defeating the entire purpose of investing in clean sources of energy. In an attempt to resolve this issue, research is currently under way to develop direct drive technologies that do not use permanent magnets or rare earth materials.

Direct drive wind turbine market

According to 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. The report mentions that, going forward, the key factors shaping this growth will be higher torque with fewer rotations per minute, improved efficiency and reduced noise. The depletion of fossil fuel reserves, favourable government policies, growing awareness of renewable energy sources and rising demand for energy will be the other key factors that will give a fillip to the direct drive wind turbine market.

According to the report, Europe is the largest market for direct drive technologies and is expected to retain this position till 2022. A major reason for this is that key market players are already operating in European countries. Other factors contributing to the market growth include the favourable government regulations for the wind power segment in the European countries. Within Europe, countries such as France, Ireland, Spain and the UK are expected to take the lead in this market.

After Europe, the Asia-Pacific region is expected to be the second largest market for direct drives, with the adoption of this technology expected to increase in China and India. In these countries, high capacity addition plans and the availability of experienced industry players, along with increased awareness of renewable energy usage, will help in the promotion of the technology and contribute to market growth. The emphasis on efficient O&M of wind turbines to increase electricity generation and reduce overall maintenance costs is another key reason why developers have started to focus more on direct drive technology. Apart from China and India, other important markets for direct drives in Asia Pacific include Japan and South Korea.

The market for direct drives is strong in North America as well due to the presence of established industries. Overall, the key players in the global direct drive wind turbine market include American Superconductor Corporation (USA), Emergya Wind Technologies B.V. (the Netherlands), ENERCON GmbH (Germany), GE Renewable Energy (USA), Goldwind Science & Technology (China), Leitwind AG (Italy), Siemens AG (Germany), VENSYS Energy AG (Germany), Windtronics LLC (USA), and Xiangtan Electric Manufacturing Group (China).

Common challenges

In general, the commissioning of wind turbines using either direct drive or gearbox technology is a cumbersome task. This is because both technologies are large and heavy, and have to be placed on top of the wind turbine tower. Consequently, the weight and cost of the tower and the foundation of the turbine also have to be increased to accommodate these technologies. Moreover, the transportation of these components is an arduous task. Additionally, large and expensive cranes are needed for installation atop the wind turbines. Installation has become even more difficult now with wind turbine tower heights reaching over 100 metres (almost 150 metres in some cases). As wind turbine capacities keep increasing, larger and heavier direct drives and gearboxes will be required, further complicating the commissioning process.

All of these complications get compounded when this technology has to be deployed in offshore wind turbines. And with floating offshore wind technology expected to grow further, discussions are taking place on the need to make floating foundations larger to support heavier direct drives and gearboxes.

The way forward

The relatively high cost of direct drive technology has so far prevented it from overtaking the popularity that gearbox turbines enjoy in the wind energy market. Moreover, developers have already installed a large number of gearbox-based turbines across the world and will not suddenly decommission these turbines to use the new direct drive technology. In fact, wind turbine manufacturers are striving to improve gearbox technology in a bid to improve its reliability. That said, direct drive technology too holds promise for the future. Considering its potential, manufacturers are investing substantially in research and development (R&D) to increase its competitiveness over gearbox-based wind turbines. R&D has shown positive results over the years. The design of the direct drive technology has improved, making it less complex. Moreover, improvements in magnets and generator arrangements have made direct drive-based wind turbines lighter and more affordable. As such, the uptake of this technology is set to increase going forward with the price of the magnets used in these turbines dropping continuously.

Looking at the overall market trends, experts have placed their bets on both of these technologies. Many believe that the pie is big enough for the two technologies to each have a significant share in the wind turbine market.

No doubt, eventually, direct drive technology will carve its space in the wind turbine market. This is because the costs for the support structures of offshore wind turbines will reduce by using the comparatively lighter direct drive turbines. Also, experts believe that gearbox wind turbines have reached their optimal efficiency while direct drive turbines have more scope for improvement. Moreover, power losses from gearboxes will become a key issue once the power ratings and capacities of wind turbines increase further.

Therefore, for gearbox technology to survive, manufacturers need to work harder to reduce the rotating parts and increase its efficiency. This should be their priority as the costs of direct drive technology are continuously falling, making it more financially viable. According to technology experts, there is also a possibility, going forward, of a hybrid wind turbine design that combines the elements of gearbox and direct drive technologies. Either way, the competition between direct drive and gearbox technologies will be one of the most interesting trends to keep track of in the global wind energy market.

By Sarthak Takyar

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