Wind-wave hybrid energy system: An innovative marine energy technology for sustainable development

Offshore wind energy and wave energy are of great interest due to their huge reserves and potential for providing reliable sources of renewable power. As a primary means of decarbonization, offshore floating wind turbines (FOWTs) are advancing towards larger structural sizes to extract more energy, and wave energy converters (WECs) are seeking economies of scale by increasing the number of installations. However, this trend means that more seabed area will be taken up by the development of these devices into large array commercial projects. Considering the strong space-time correlation between wind and wave resources, the combination of FOWT and WEC, i.e., the wind-wave hybrid energy system, would be a beneficial way to optimize the seabed area required for energy extraction, while minimizing the impact on the marine environment.

The main advantages of integrating FOWT and WEC are as follows: (i) The wind turbine and WEC array share the floating platform foundation, mooring system and electrical equipment, significantly reducing the construction costs; (ii) The WEC array mounted on the platform could not only convert the wave loads acting on the platform into power outputs, but enhance the platform stability via control strategies to further improve the overall energy extraction efficiency; (iii) The synergistic harvesting of wind and wave energy offsets the intermittent nature of a single energy source and decreases the hours of zero production compared with a stand-alone FOWT.

For such a complex multi-physics, multi-body system, the key challenge is its survivability in extreme sea conditions, where the platform stability is highly dependent on the collaborative control of the WECs. To this end, this study focuses mainly on the control strategy of the WEC array, as well as its contribution to the system stability and overall power performance. The analysis object is a typical FOWT-WEC hybrid system, consisting of an IEA-15-MW reference wind turbine (RWT), a UMaine-VolturnUS-S semi-submersible platform, and three toroidal, heaving-type WECs installed on the side columns of the platform. Based on an aero-hydro-elastic-servo-mooring coupling numerical framework, multiple WEC-based survival strategies are proposed to enhance the wind and wave resistance of the integrated system. Moreover, a multi-objective, multi-parameter optimization model is introduced to identify the optimal system configuration using global-local-combination intelligent algorithms. This study discusses in detail the key technologies for enhancing the survivability of wind-wave hybrid systems, and the findings are of great significance in achieving net-zero goals.