## 2 Literature Review
### Wind Energy
#### 2.1.1 Offshore Wind Energy vs. Onshore Wind Energy  
The main difference between onshore and offshore wind installations is in their respective production environments. In the following paragraphs a comparison is made between onshore and offshore wind farms, demonstrating some of the clear advantages and disadvantages of both types of wind energy [18; 19; 20; 21; 12; 15]. One of the advantages of offshore wind energy comes from the quality of the wind resource at the sea, as the turbine is placed at an ideal height to use the maximum wind intensity. In addition, winds at sea are typically stronger and more stable, producing more energy per installed unit. This production increases with the distance to the coast, where the wind is more uniform, leading to fewer turbulence effects. Another advantage of offshore wind energy is related to the space available on land for the development of onshore wind energy, which has become increasingly limited. The ocean is the largest portion of the planet and is an area with much to explore, where wind farms can be installed. Moreover, the marine environment allows for a more efficient transport of the resources needed for energy production, as well as the installation of larger wind turbine units, achieving greater production per unit of installation. In general, the environmental impacts associated with technologies for the production of this type of energy are lower for offshore wind farms than for onshore wind farms. With regard to visual and acoustic impacts, offshore wind turbines are less invasive than onshore turbines, as their apparent size and noise can be attenuated by the distance to the coast. Thus, it allows a greater exploitation of resources, with larger equipment and greater rotation speed, making it possible to use more efficient geometries with thinner cables. However, marine biology can be affected by the structures placed in this environment. Although at onshore level there is also this type of impact, especially on birds, the placement of this equipment in the ocean changes a large part of the system, causing a higher impact. Another disadvantage related to offshore wind energy comes from the construction, assembly, and maintenance of structures, as they are more complex activities to be carried out compared with onshore structures. Nevertheless, this disadvantage contributes to the creation of more jobs during installation and exploration, which can be considered a positive factor, even though it causes more costs for developers of offshore wind farms. In addition, this energy has the possibility to take advantage of the infrastructures of other marine resources to produce electric energy, such as wave and tidal energies in mixed installations. The costs of the licensing process are more stringent, and the engineering methods and phases of operation are more expensive than onshore. In offshore wind farms, the cost of wind turbines, towers, and foundations is also much higher, which can be explained, mainly, due to the high costs of maritime operations. In addition, fixed or submersible platforms are required for the marine environment, as well as the construction of longer electrical networks, considering that, generally, there are no marine electrical infrastructures that connect the higher areas of wind resources to consumer centers, also leading to greater costs. There is a need for more developed offshore wind farm technology. This is essential for wind turbine generators, which are subjected to high loads and must adapt to the marine environment, where there is a faster degradation of this equipment and, therefore, they must be prepared for corrosion conditions. However, the use of the various equipment and the associated costs, will largely depend on the weather conditions, the waves, the depth of the water, and the distance to the coast. Another disadvantage refers to the accessibility restrictions and the difficulties existing in foundations, in maritime operations, and in the construction and operation phases.