Getting Bigger

Wind industry moves towards higher rated turbines

As per the latest figures of the National Institute of Wind Energy (NIWE), India’s wind energy potential at a 100 metre hub height is about 302 GW. The fresh estimates are almost six times the wind energy potential determined at 50 metre hub height, and three times that estimated at a hub height of 80 metres. And, according to studies conducted by The Energy and Resources Institute, the Lawrence Berkeley National Laboratory and the World Wind Energy Association, the potential is even higher. Clearly, there is considerable scope and opportunity for wind power development in India.

In order to tap this potential, there is a need to encourage technology advancements and innovations on the turbine front. One of the most prominent trends in the Indian wind power space in recent times has been the increasing size of turbines. This trend is driven by the need to derive benefits from higher capacity installations, achieve better space utilisation and reduce overhead costs per MW, among others. At present, the highest rated wind turbine approved by NIWE is  of 3 MW as compared to the earlier wind turbines that were of 55/110/225 kW rating. One of the key notable trends is the installation of taller towers for supporting longer rotor blades. This has led to an increase in the capacity rating of turbines.

To capitalise on these opportunities, several large-scale players are introducing new technologies in the Indian market and are rapidly expanding their production base. For instance, Spanish wind turbine manufacturer Gamesa recently introduced a 2.5 MW turbine at the China Wind Power 2015 trade fair. The turbine has a rotor diameter of 126 metres and will be available at hub heights of 84 metres, 102 metres, and 129 metres. The company will sell the turbine in the Indian market as well. Recently, Senvion forayed into the Indian wind energy market with the aim of providing high quality wind energy solutions. The company has established a research and development centre in Bengaluru, which supports Senvion’s global TechCenter in Osterrönfeld, Germany. Inox Wind, which offers 2 MW of wind turbines in the country, commissioned a new production facility in November 2015 in Madhya Pradesh. The facility will have a production capacity of 800 MW of wind energy equipment and will increase the company’s overall production capacity to 1.6 GW annually. The company is also planning to launch a wind turbine generator (WTG) with a 113 metre rotor diameter and hub heights of 92 metres, 100 metres and 120 metres. Meanwhile, ReGen Powertech has installed a 2.8 MW wind turbine at Vagarai near Coimbatore.

Various technological innovations are also taking place in the drives and motors segment to improve the overall wind energy conversion efficiency. Meanwhile, the storage solutions segment is witnessing a shift from conventional lead batteries to lithium-ion batteries as the viability of the latter improves.

Going forward, technological developments can also be expected in the Indian offshore wind energy space. The government has announced the National Offshore Wind Energy Policy, 2015. However, the domestic wind manufacturing industry lacks experience on this front. Suzlon Energy is the only Indian manufacturer with some experience in offshore wind turbines. The government is also making efforts to attract foreign players to set up and expand manufacturing facilities. It recently exempted wind turbine equipment from central excise duty, which is paid for the manufacture and sale of products. The equipment exempted from excise duty includes towers, nacelles, rotors, blades and wind turbine controllers.

Technology trends

A wind turbine comprises various components such as rotors, blades, towers, generators, gear boxes, nacelles and yaw drives. The rotor blades account for 15-18 per cent of the total investment in an onshore wind turbine. The most direct way to exert any decisive influence on the cost of wind energy is by increasing the rotor performance and thus, the annual energy production (AEP) of the wind turbine. It is estimated that an increase of 4-5 per cent in the AEP over the normal lifespan of the wind turbine (25 years) covers three times the cost of a blade set.

Today, many large-sized wind turbines have both rotor diameter and hub height of more than 100 metres. This helps the manufacturers utilise higher energy from low-wind sites, which are the primarily available sites in India. This practice of modifying turbines only by increasing their hub height and rotor diameter while keeping the rated capacity the same has been adopted mainly because the previous WTG model has already been installed and is being operated successfully. Thus, the same design with a higher hub height will be able to capture more wind energy at greater heights as compared to lower heights. Meanwhile, the increase in the rotor diameter improves the power curve characteristics of a wind turbine, implying that a higher power output can be achieved in similar wind conditions as compared to a turbine with a smaller rotor diameter.

However, as the towers get taller, their transportation becomes a major challenge. A possible solution to this is the use of modular towers of either concrete or steel or a hybrid of steel and concrete. Some domestic tower manufacturers are adopting this approach while others are exploring the option of on-site manufacturing of concrete towers. However, on-site manufacturing poses challenges relating to the availability of skilled labour, longer production schedules as compared to steel towers, and exposure to weather vagaries.

Two distinct designs are commercially available at present – full concrete designs developed by companies such as Enercon, a German turbine manufacturer and systems integrator, and Inneo, a Spanish tower manufacturer; and hybrid systems, which combine a steel tower with a concrete pedestal, developed by companies such as ATS, a Dutch tower manufacturer and Tindall, a US manufacturer of precast concrete products.

Various innovations are also taking place such as the use of alternative transmission systems like those based on magnets instead of mechanical gearboxes. Magnetic gears eliminate the need for a number of moving parts and the resultant friction that creates greater wear and tear in mechanical gearboxes. There is no physical contact between the two magnetic gear rotors and their movement is based on the flux generated by the magnets present in them. Magnetic gears tend to be lighter as well. However, the technology is not commercially developed and there are performance and cost issues that need to be resolved.

Fundamentally, there are three types of magnetic gears – axial, radial and trans-rotary. The axial design consists of two discs or rotors with positive and negative magnets, separated by a modular disc. According to researchers, axial designs are tough to analyse and implement as there is a huge axial load on the bearings, which creates reliability issues. Thus, a complete three-dimensional model is needed for analysis, which is very time consuming.

Radial magnetic gears have a low-speed outer rotor with a concentric high-speed inner rotor, which are separated by a stator that modulates the flux between the permanent magnets on the two rotors. Trans-rotary designs, on the other hand, incorporate superior gearing through a ball and shaft design. According to various studies, a large-scale trans-rotary design is much better than hydraulics for transmission purposes.

Gyroscopic variable transmission and hydrostatic transmission technologies are currently being developed. The former is being developed by New Zealand-based Gyro Technologies, which has undertaken prototype demonstration of several small kilowatt-level projects. Meanwhile, more research related to hydrostatic transmission technology is being undertaken in European markets such as Germany.

Techno-commercial aspects

Increase in the rotor blade length and tower height increases the cost of a wind turbine, which, in turn, increases the cost of the project. This not only includes the difference due to hardware costs but also the additional cost of transportation and handling, on-site erection, proportionate increases in loan processing charges, and the interest accrued during construction. As per preliminary data, an increase of 10-15 metres in rotor diameter or 20-30 metres in hub height without any change in the generator rating increases the cost of a wind turbine by Rs 2.5 million-Rs 5 million per MW. It is also estimated that power generation from such large wind turbines will be 10-20 per cent higher than wind turbines with smaller rotor diameters and hub heights, depending on a site’s wind conditions. Thus, investors need to choose a model in line with their objectives.

Challenges

The adoption of these giant wind turbines is not easy. From design and manufacturing to installation and operations, they entail multiple evaluations and tests, due diligence, quality control, etc. The logistical requirements include transportation, storage, construction of wider roads, permissions, and safety. Any modification in wind turbine designs has to go through a complete process of design approval, type test certification, prototype installation and test certification. Manufacturers need to adopt a strong quality control mechanism to meet the standards and produce reliable turbines that can survive the desired economic life of at least 20 years. The process of getting clearances for the widening of roads and transportation of such large components can also be a hindrance.

Conclusion

Wind power will remain one of the main renewable energy sources in India. In order to achieve the ambitious installation targets in the segment, it is important to adopt technologies that can capture greater energy even at low-wind-potential sites. This has led manufacturers to move towards giant wind turbines. While these come with their own challenges relating to transportation, storage, approvals and safety, the industry is looking at these developments with interest.

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