Getting Bigger

Innovations in wind turbine rotors and blades

Wind energy technology has undergone a sea change over the years. Turbine capacities have shifted from kW to MW with improved efficiency parameters. The technology is constantly evolving towards improved reliability, inc­reased capacity factors, and re­duced as­sociated fixed and variable costs. Modern wind turbines incorporate longer and li­gh­ter rotor blades, taller turbine towers, more reliable drivetrains and performance optimising control systems. The amount of wi­nd power generated is largely influenced by factors such as wind speed and technology of the generating systems.

Despite ambitious targets set by the government of India for increasing the capacities for wind power generation by 2022, new installations have fallen dramatically. As per the Central Electricity Authority, the aggregate wind power generated in India as of June 2022 was 40,788 MW vis-à-vis 39,487 MW in June 2021. This indicates that there has been a meagre growth, of just 3 per cent, in the span of one year.  Many projects are held up or have been cancelled owing to issues related to land availability and delays in signing power purchase agreements. Moreover, the grid augmentation gestation period of 36 to 48 months is double the wind project gestation period of 18 to 24 months and this often leads to delays. Much of the slowdown has also been on account of supply chain disruptions and restrictions impo­­s­ed due to Covid-19.

However, wind power is a mature industry in India and significant growth is expected in this space owing to the high available potential, intent of both the government and industry as well as technology ad­va­ncements. Wind turbine generators have advanced over the years with locally produced state-of-the-art technologies now available in the country. According to the Ministry of New and Renewable Energy, many international players have entered the Indian wind segment. Over 31 different wind turbine models are produced in India by about 15 different companies. The production takes place either through joint ventures under licensed production, fore­i­gn company subsidiaries, or with the as­sis­tance of available domestic technologies.

Technology trends

According to the Indian Wind Atlas, published by the Centre for Wind Energy Te­ch­nology (C-WET), Chennai, and Riso DTU National Laboratory, the very first pro­­­jections for constructing a wind turbine were made in 2010 and began with a hei­ght of 50 metres above ground level. With the passage of time and technological ad­vancements, these projections ha­ve grown to hub heights of more than 120 me­tres, with plans to increase them up to 150 metres. With the increase in height, the power generation capacity by wind tur­bines has increased from 250 kW to around 2.5 MW currently.

Most turbines have three blades that vary in size and material composition. As re­po­r­ted in a research paper titled “Materials for Wi­nd Turbine Blades: An Overview”, different types of materials such as  glass and carbon fibres, aramid and basalt fib­res, hybrid composites and natural fibres are used to manufacture the wind turbine blades. The blades and hub together form the turbine’s rotor. When wind blows across the blade, the air pressure on one side falls. Lift and drag are created by the difference in air pressure between the two sides of the blade. When the lift force is greater than the drag force, it causes the rotor to spin. A wind turbine converts wind energy into electricity by using the aerodynamic force of the rotor blades. The rotor is connected to the generator either directly or through a shaft and a series of ge­ars, which speed up the rotation and it allows for a physically smaller generator. The aerodynamic force that leads to ge­nerator rotation results in the generation of electricity.

Wind turbine generators must be robust, cost effective, fault tolerant and must re­quire minimal maintenance. These chara­cteristics are required for wind applications because the deployed structures and machines are frequently placed in ho­s­tile environments at remote locations far from immediate technical assistance. Th­us, technology advancements are a must to constantly improve the quality of components and their reliability.

Innovations in rotors and blades

The increase in the size of wind turbines is a major trend in the segment. The weight of the rotor blades increases with size, so, gravitational loads become design drivers. The UK-based company ACT Blade is working on making technological chan­ges to address this issue of blade weight. It is developing blades with lower weight which allows for building longer blades with lower mass. These blades can produce more energy with minimal change in turbine loads. As reported by the comp­any, a 10 per cent longer blade can pro­du­ce 9.3 per cent more energy and re­d­u­ce the cost of energy by 6.7 per cent. Un­like conventional fibreglass blades, the ones designed by ACT Blade are partly re­cyclable. This would help in reducing land­fill waste and contribute towards res­ponsible energy production.

Sustainability and recycling are important factors especially considering the massive volume of wind turbines already installed and also being deployed around the globe Significant amount of waste is expected from these installations at the end of project lives. As per a recent report by rese­a­rchers at the Institute for Manu­facturing, University of Cambridge, wind turbine blade waste could amount to 43.4 million metric tonnes by 2050. With such forecasts, more wind turbine manufacturers are looking at ways to recycle their products when they are no longer operational.

In April 2022, researchers from the DLR Institutes of Aeroelasticity, and Composite Structures and Adaptive Systems assisted in the manufacturing of six rotor blades for two wind turbines at a research farm. This was done in collaboration with ForWind: Centre for Wind Energy Research at Lei­bniz University Hannover. The team equi­pp­ed the rotor blades with approximately 1,500 sensors in the Portuguese factory of industrial partner Enercon, enabling state-of-the-art measurement technology from the blade tip to the blade root. This is the first time that a wind turbine’s vibration and load behaviour as well as its aerodynamics and statics have been thoroughly investigated on a full-scale device and during actual operation. Rotor blades twist as well as bend under load. This is also recorded by sensors inside the blades. This data can help in the creation of novel strategies for controlling wind turbines in order to operate them more efficiently and for a longer period of time.

Blade maintenance and logistics

Large blades, which are designed to spin at high speeds and produce more power, are essential to every wind turbine. How­ever, these blades are prone to failure that can be due to weather conditions, insufficient blade material strength, fatigue loads or any other manufacturing process defect. According to a research paper titled, “Failure Mechanisms of Wind Tur­b­ine Blades in India: Climatic, Regional, and Seasonal Variability”, there are a bunch of reasons that lead to failure of wi­nd turbine blades. These factors are da­­­­mage mechanisms commonly observ­ed in blades such as skin or adhesive de-bonding, adhesive joint failure, sandwich de-bonding, delamination, splitting along fibres, gelcoat cracks, etc. As per a white paper published by the National Institute of Wind Energy, advanced blades should be made of materials such as carbon fibre and smart materials that are cost effective, lighter and stiffer.

In comparison to their onshore equivalents, offshore wind energy components are larger and have longer support structures and blades. In India, moving these parts over land is a significant challenge. By situating the necessary manufacturing facilities, supply networks and infrastructure close to ports, this can be avoided. Additionally, the ports must be big enough and have the right kind of vessels available. Furthermore, with the increasing nu­m­ber of outdated wind turbines, it is expected that demand for new rotors and blades will increase over the years.

Outlook

In order to accelerate wind energy generation in the country, technical specifications for increased unit size, higher hub height and larger motor diameter are required. Since materials can account for a major share in the price of a turbine bla­de, developing novel cost-effective ma­te­rials can result in significant cost savings. Opera­tions and maintenance (O&M) of wind turbines is an important factor influencing the wind energy price. Thus, considerations wh­ile manufacturing components should en­sure lower O&M-related costs.

Many wind turbines in India are very old and have capacities of less than 1 MW. Older turbines can be replaced with larger wind turbines with bigger rotors and longer blades to capture more wind energy. Thus, there is huge scope for repowering wind power plants in India to ensure more en­ergy generation and optimum utilisation of the country’s wind power potential.

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