International Journal of Energy Research, Vol.45, No.5, 6727-6744, 2021
Open center tidal turbine: How a new mooring system concept affects the performances
The huge manufacturing and installations costs, together with the adverse impact of the mooring systems and structures on the environment, flora and fauna have become one of the major constraints for the application of many marine technologies. An innovative mooring system coupled to an open centre turbine has been developed, adopting a full floating concept, which allows a kite like connection between the turbine and the coast. Replacing the huge underwater mooring structures with such kite flying system dramatically reduces the environmental impact and effects, meanwhile the lightweight open centre turbine coupled to this mooring system, assures a self-adaptive optimal orientation, achieving a new equilibrium arrangement at given depth and distance to the coast, following only the fluid dynamics rules. In addition, the synergy between the two machine components makes also suitable the adoption of low aspect ratio blades, characterized by lower specific loads, and leads to a reduction of the manufacturing cost. To optimize the kite concept, the connecting rope has been replaced with heavy and light nodes connected by tubular elements, where the light ones accommodate the deflectors to increase the lateral force responsible of the machine positioning, facilitating the machine transients, and manoeuvring and leading to improve the output reliability, reducing also the mooring line length. A case study shows that a 12 m diameter open centre turbine with the new mooring line produces, at Messina Strait site (Italy), an output of 362 MWh/year, 17.5% higher than, at same operating conditions, a classic 3 blades turbine moored on the seabed. It confirms the high suitability of this solution for marine purposes.