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       2.3.2.1.2 Design and Materials of Rotor Blade

      Two types of wind turbine designs are horizontal axis wind turbine and vertical axis wind turbine, and the former type dominates in the wind turbine industry. Nowadays, focussed research is carried out to improve the aerodynamic profile of blades as well as enhancement in the quality of materials so that energy production can be increased along with cost reduction of operation and maintenance. Advances in the manufacturing of composite materials leads to better performances particularly in rough and corrosive environments of sea and deserts (Windtrust 2016). Blades made up of composite materials can spin faster and capture winds even at lower speed.

       2.3.2.1.3 Power Electronics Optimization

      To cut the cost of wind turbine installation and operation, optimized design of the various parts of power electronics has been used by different manufactures via concentrating on the several features such as humidity protection, scalability and decreasing the number of components. These features lead to minimizing the failure of power modules, creation of smart and innovative power modules having power density of nearly 30% more than their predecessor and better performance of power electronics by reducing the number of active elements in power modules (Windtrust 2016).

       2.3.2.1.4 Smart Wind Turbines

      These turbines are equipped with novel technologies which control and monitor the turbine. These turbines possess the advanced mechanism to forecast using big data and artificial intelligence along with the automatic regulations of turbines which results in higher energy output (Windtrust 2016). In addition, these digitized turbines also reduce the maintenance costs (www.woodmac.com). Recently, GE Japan has exemplified the manufacturing of such a smart turbine with the help of artificial intelligence which has higher efficiency, low maintenance costs (20% lesser) and higher output (5% more) (IRENA 2019e).

       2.3.2.1.5 Recycling of Materials

In recent times, recycling of various materials in the wind energy sector has become popular due to reduction in cost for power generation. By increasing the three R's i.e. reduce, reuse and recycle of raw materials, residues, metals and other resources in the wind sector will cut down the overall cost of electricity generation. At present, about 2.5 million tonnes of composite materials are used in the wind energy sector. In the next five years, around 12,000 wind turbines will be out of service in Europe (www.recycling‐magazine.com) which will produce large amounts of materials that need to be recycled. For the recycling of materials, mechanical process i.e. cutting the turbine blades into smaller slices for easy transport or thermal processes such as combustion or pyrolysis provide viable options (WindEurope 2017). For the circular economy along with the production of new blades, reuse of decommissioned blades after some processing should be considered (WindEurope 2017). For example, the Dreamwind project (Designing REcyclable Advanced Materials for WIND energy) is working towards the development of a chemical substance which can separate the glass (expensive component) from the plastic fibres by heating the composite materials at 600 °C. After the separation and cleaning, the glass component produced from the recycling process can be used in making new blades for wind turbines (www.dreamwind.dk).

      2.3.2.2 Offshore Wind Energy Technology

      Offshore wind power generation is an emerging giant technology and has seen more potential owing to advances in technology. Due to limitation of space availability onshore, growth of offshore wind farms is gaining more popularity. In many European countries, offshore wind power projects are in trend. Offshore wind technology is leading in the wind energy sector because it is exploring more resources further offshore. In contrast to onshore wind turbines, installation of offshore wind turbines has many advantages, namely availability of more space, less complaints of noise and visual interference, and winds are stronger and even more regular in the offshore region (IRENA 2019a). In addition to the advantages, offshore wind also comes with some disadvantages i.e. their cost is high as compared with onshore wind turbines and they are difficult to install and maintain due to harsh and changing weather conditions of coastal regions.

      The major offshore wind technologies based on the maximum overall potential are future‐generation turbines; floating foundations; repowering of sites; integrated turbine and foundation installation; high‐voltage direct current (HVDC) infrastructure; direct current (DC) power take‐off and array cables; and site layout optimization (IRENA 2019a). These technologies have beneficial impacts ranging from high, medium and low on five different aspects which are decreasing the cost of energy, increasing grid integration, opening up new markets, reducing environmental effect, and improving health and safety levels.

       2.3.2.2.1 Future‐Generation Turbines Technology

      It is one of the most relevant technologies in the offshore wind energy sector based on the development of turbines. With the important developments in size of blade, drivetrain and control technologies, wind turbines are becoming more reliable and larger along with the increase in capacity ratings. Rotor diameters of offshore wind turbines have increased to 148 m with an average rated capacity of 5.5 MW (in 2018) from 43.73 m with an average rated capacity of 1.6 MW (in 2000) (IRENA 2019a). Thus, in the last two decades, the average size of offshore wind turbines has grown by a factor of 3.4. Size of turbines is expected to grow (rotor diameters >230 m) with turbine ratings between 15 and 20 MW by 2030. Due to the increased size of turbines, there will be a smaller number of turbines in a wind farm for a particular rated capacity so it will reduce the cost, and impact on the environment will also be less along with some other advantages.

       2.3.2.2.2 Floating Foundations

It is another major technology in the offshore wind energy sector. In this technology, turbines are rooted in the seabed by monopile or jacket foundations, and these are restricted to waters which are <60 m deep. The spar‐buoys, spar‐submersible and tension‐leg platforms are three main designs for turbines which are under development and have been tested (IRENA 2019a). Under this technology, turbines are installed in water depths of up to 40 m and these are about 80 km away from the shore. If one looks at the largest potential markets for offshore wind sector i.e. Japan and the United States (US), then they have less shallow water sites, which makes current floating foundations as the limiting technology. On the basis of recent advances which are taking place across various regions, floating wind farms can contribute 5–15% in total offshore wind capacity installed worldwide (~1000 GW) by 2050 (IRENA 2019a). Along with the ease of turbine set‐up, floating foundations also come with environmental benefits such as less invasive activity on the seabed during installations as compared with fixed bottom designs.

       2.3.2.2.3 Repowering of Sites

      In this technique, turbines and their foundation and array cables are replaced by larger units which are spaced at larger distances. This is an alternative technique to continue operation with the same configuration. This technology faces a major challenge due to the rough and corrosive offshore environment. Further, to reduce the cost of repowering wind farms, transmission assets can be retained after some renovation. Retainment of transmission assets lowers the cost of farm by decreasing the energy cost for the repowered phase. This will also reduce the levelized cost of electricity during the entire lifetime of the farm site (IRENA 2016).

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