In recent years, numerous projects for floating PV systems have been developed. These plants of various sizes have mainly been installed on enclosed lakes or basins characterised by the absence of external forcing related to waves and currents. However, offshore installation would allow the development of such plants in areas where land is not available, such as islands. This paper analyses the state of the art of floating PV, describes the design of a floating PV platform and the development of a numerical model to evaluate the system performance in an offshore environment. The case study of the island of Lampedusa is then analyzed: starting from a single floating foundation with its mooring system, a floating PV system is designed to meet the island’s electricity needs. In order to provide the competitiveness of the system, a techno-economic analysis is carried out, evaluating the main cost items of Capex, Opex and LCOE. Although the LCOE obtained is significantly higher than a traditional solar plant installed on land, this technology is competitive compared to other offshore marine technologies such as offshore wind and wave energy.

Compared to onshore wind power, floating offshore wind power is a promising renewable energy source due to higher wind speeds and larger suitable available areas. However, costs are still too high compared to onshore wind power. In general, the economic viability of offshore wind technology decreases with greater water depth and distance from shore. Floating wind platforms are more competitive compared to fixed offshore structures above a certain water depth, but there is still great variety and no clear design convergence. Therefore, optimisation of the floating support structure in the preliminary phase of the design process is still of great importance, often up to personal experience and sensibility. It is fundamental that a suitable optimisation approach is chosen to obtain meaningful results at early development stages. This review provides a comparative overview of the methods, numerical tools and optimisation approaches that can be used with respect to the conceptual design of the support structure for Floating offshore wind turbines (FOWT) attempting to detail the limitations preventing the convergence to an optimal floating support structure. This work is intended to be as a reference for any researcher and developer that would like to optimise the support platform for FOWT.

In the past few years, advanced technologies such as floating offshore wind turbines (FOWT) and wave energy converters (WECs) have been developed. As demonstrated by the innovative hybrid platform Poseidon, the feasibility of combining floating wind turbines and wave energy converters has already been explored. Furthermore, diversification of offshore renewable energy technologies reduces power fluctuations and lowers investment costs. This paper focuses on the development of an integrated wind and wave platform and the creation of a numerical model to evaluate the system performance for the Belmullet site. The novel concept consists of the semi-submersible Nautilus platform, integrated with four-point absorbers. A hydro-servo-aero time-domain model, combining WEC-Sim with an in-house wind turbine model, simulated the device motion and estimated the power generated. The performance of the Wave Energy Converters (WECs) was optimised based on their Power Take Off (PTO) damping. Finally, the hybrid concept was compared with the simple FOWT concerning the energy produced, Levelized Cost of Energy (LCOE) and hydrodynamic stability. The hybrid configuration proved to be a promising solution with 10% lower LCOE and improved hydrodynamic stability evaluated in terms of nacelle acceleration and platform pitch motion. These results show that wind and wave could be one of the best solutions for the future of the marine energy sector and the energy transition.