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).
2.3.2.2.4 Integrated Turbine and Foundation Installation
Using this technique, wind turbines are assembled and pre‐commissioned in nearby place and after that a complete and integrated turbine which includes a rotor, tower and foundation is installed in a single offshore operation (IRENA 2016). Thus, using this technique most of the offshore installation operations can be put to an end. With the help of customized vessels or tugboats, the combined turbine foundation is taken to the wind farm site. Use of this technology in the floating foundation technique will further make the usage of the latter more promising. As far as fixed foundations are concerned, use of gravity‐based foundations that can be floated out and sunk at the site is more useful. Installation cost as well as the exposure to health and safety risks decreases by these innovative techniques. Projected commercialization of this technique is by 2025 with more advances in technology to fulfil the requirement of large turbines.
2.3.2.2.5 HVDC Infrastructure
This technique is based on the electrical interconnections. For the offshore wind farms which are located between 80 and 150 km, HVDC transmission is preferred over HVAC (high‐voltage alternating current). At present, this is an expensive technique; however, with the help of invention in the offshore installations and component techniques, its cost can be reduced in future. This technique comes with an advantage i.e. installation of a wind farm in a further offshore region which has rich wind resources. In future, this technique can lead to higher annual production of energy with less planning. Further this technology opens new doors for the regions where near‐shore developments are not possible (IRENA 2016). With the invention of direct current nodes in upcoming time, a multi‐nodal network can be built which is required for integration of this technique. With point‐to‐point grid connections used on few projects in European waters, commercialization of this technique is ongoing.
2.3.2.2.6 DC Power Take‐off and Array Cables
Same as HVDC infrastructure, this technique is also based on the electrical interconnections. It is in its infancy; however, using this technique, the industry can get rid of the other half of the conventional turbine power conversion system which converts back to grid‐frequency alternating current (AC). This technique saves the capital cost and enhances reliability. By shifting towards DC collection, the array of cable cores decreases to two from three and the amount of material also reduces by 20–30% (IRENA 2016). Progression of this technique is happening at a slower rate due to non‐acceptance of higher‐voltage AC array cables by the industry.
2.3.2.2.7 Site Layout Optimization
For energy production from wind farms, different options of site layout are analysed with the help of software tools commonly described as wind farm design tools. One of the tools is WAsP model which calculates wind flow of the site (IRENA 2019a). With the help of these tools, various predictions are done by calculations, namely variation in wind speed with height, variation in wind speed over the site area and the wake interaction between wind turbines. In this technology, usage of software tools enables more informed and complete layout of wind farm which enhances the characterization of wind resources, aerodynamic wake effects, meteorology oceanic climate and seabed conditions (IRENA 2016). If installation process methods and foundation technique are further combined with layout, then energy production from the wind farm will be more effective.