Cost Analysis and Design Optimization for Floating Offshore Wind Platforms

In recent years, in Europe, there has been a great development of renewable energies, in order to reduce the emission of pollutants, increase the transition to cleaner energy sources and the decarbonization process. Of all the most promising renewable energy sources, wind energy is one of the most widespread (about 20% of total electricity generation) and the related electricity production is growing steadily. While onshore wind is already well developed and the major potential sites are already occupied by pre-existing power plants, the same cannot be said for offshore wind. The potential of the offshore wind resource, characterized by winds with higher productivity and availability than onshore ones, would make it possible to cover enormous energy needs by limiting further land use. Currently, the largest offshore wind farms are located in the North Sea and the Baltic Sea and exist in fixed structures that exploit sites with shallow waters. To take advantage of deeper water sites such as the Mediterranean Sea and the Atlantic Ocean, floating structures have been introduced by some and have become the focus of offshore wind technology development. These systems consist of a floating platform that supports the wind turbine and is tied to the seabed through a system of moorings and anchors. Furthermore, these plants require an electrical system, consisting of electrical substations and array marine cables, to transfer the electrical energy to the mainland. However, the considerable size of these structures which require large quantities of steel and concrete, the difficulty in construction, the need to employ large ships and the lack of standardized structures imply very high investment and maintenance costs and have slightly slowed down the development of such technologies. Today, the LCOE is much higher than for fossil fuels or other energy sources, although cost reductions are expected in the coming years due to the development of new technologies and industrial innovations. The purpose of this thesis is to present the current floating structures, such as spar-buoy, semisubmersible and tension leg platform, to describe their most relevant characteristics, advantages and disadvantages. A small focus will be on tension leg platforms, which today are the structures on which less investments and research have been made, but which still have interesting characteristics. Subsequently, a hydostatic tool, which allows to analyze the main hydrostatic parameters for four structure concepts (a spar-buoy, a semisubmersible and two TLPs), will be illustrated. This tool, implemented through the genetic algorithm of Matlab, allows to carry out an optimization of the main dimensional parameters of the structure, in order to minimize the economic parameters relating to the cost of the materials used to build the platform, respecting the stability and buoyancy constraints imposed by Standards. Finally, once the optimization through the genetic code was finished, the structure with the most interesting outcome was analyzed using a hydrodynamic tool. Consequently, the platform's RAO was analyzed to analyze the behavior in a state of dynamic perturbation due to sea waves.