# Wind Turbine Technology Trends
## 3 Discussion
### Offshore Wind Turbine Development
The study is based on the reference floating wind turbines NREL 5 MW and IEA 15 MW. Vibration control of a floating wind turbine becomes increasingly important as the size of the wind turbine increases. Therefore, a new three-branch mooring system for Spar-type floating wind turbines is proposed in the work of [PERSON] et al. [55]. The sway, pitch and yaw motions of the wind turbine in regular and irregular waves are calculated to quantify the performance of the mooring system. In the work of [PERSON] et al. [56], the main issues related to the structural dynamics of offshore wind turbines were analyzed, including modal alignment, aeroelasticity, hydroelasticity, bottom interaction, mooring cable-float interaction, drivetrain vibration, and others. Offshore wind turbines can be sized larger because their transportation is not as problematic as onshore wind turbines. Vestas plans to develop a 15 MW wind turbine, with a prototype expected to enter service in 2022. With a rotor diameter of 236 m, this wind turbine will have a larger wind-swept area than any other turbine in operation. Series production is planned for 2024 [53]. Floating wind farms are a major breakthrough in ocean energy technology. Floating foundations offer two important opportunities:  
* they provide access to sites with water depths greater than 60 m, and
* they facilitate turbine installation even in intermediate water depths (30-50 m) and could ultimately provide a lower-cost alternative to fixed foundations. In general, floating foundations have environmental benefits compared to fixed foundations because less seabed intervention is required during installation. Floating wind turbines can be installed far offshore and in deep waters. The shift to offshore will increase the use of offshore wind farms. There are plans to install more floating wind turbines in Southeast Asia, Oceania, and Northern Europe (Figure 6). The most common foundation type for offshore wind turbines (OWT) is the monopie: a single pile six to eight meters in diameter and 20 to 30 m long below the seabed. It accounts for about 80% of the installed OWT foundations. Figure 7 shows the technology of offshore wind substructure for future projects. The use of jacket foundations will be more than quadruple in future projects. In addition, the share of monopiles will decrease to 51.6% of the market. This change is due to the fact that projects are planned for deeper waters and increasing manufacturing capabilities for jackets. The share of floating foundations is also increasing. However, the industry's ability to adapt monopiles to deeper waters while maintaining low costs could result in monopiles remaining the dominant foundation type for some time. Based on information  
Figure 6: Global floating offshore wind energy projects by depth, country, and project size [53]. about planned projects, gravity foundations will increase their market share because they are better suited to rocky soils where it can be difficult to drive monopiles. Most floating wind farm projects provide for a semi-submersible substructure. The advantage of this type of substructure is a relatively shallow draft and hydrodynamic stability during operation of the wind turbine. This allows for dockside installation and towing to the site without the use of heavy lift vessels. Figure 8 shows the steady increase in global offshore wind turbine capacity. This continuous growth in rated capacity is one of the factors that has led to a reduction in the cost of offshore wind farms [57]. The significant growth of large offshore wind farms in Europe is also due to improvements in wind turbines and basic structures [58]. Figure 9 shows the cumulative deployment of floating offshore wind turbines. Of the 3,688 MW floating offshore wind turbines that will be installed by 2026, most will be located in South Korea (2300 MW), Saudi Arabia (500 MW), Spain (365 MW), and France (132 MW). Other wind farms will be evenly distributed in Europe, some of which are still in the planning phase [53].