Three Wind Turbines On One Floating Unit, Feasibility, Design And Cost

Abstract

Abstract The paper presents results from the design work and the model tests [1] performed to verify the feasibility of a new offshore floating wind concept with three turbines on one platform. The economics of the concept is also discussed. The platform is a semi-submersible with three columns shaped in a regular triangular supporting three turbines, two turbines in front (up wind) and one turbine in the rear (down wind). This geometry challenges the established state of the art since one of the three turbines is located in the wake of the two other at a distance of one rotor diameter. The platform is anchored through a " turret?? at its geometrical centre. This enables the platform to rotate in to the wind at all times. One major issue is the wake effect produced by the two upwind turbines on the downwind turbine. This aspect has been addressed by CFD analysis and verified by model tests in wind tunnel. Interaction between motions due to wave and wind action has been evaluated based on computer simulation and tested on scaled model in wave basin. Based on the data collected in the model tests, a concept supporting three turbines of 3,6 MW has been sized for a location in the southern part of the North Sea. The cost for fabrication and installation has also been estimated as well as the annual energy production based on specific wind data. The production loss on the rear turbine caused by shadowing effect from the front turbines has been verified to be only 25% of theoretical maximum production. This is a significant finding because the loss is by many industry experts expected to be much higher. The up wind turbines experience no loss due to interference between the turbines. Based on these findings the cost of production per kwh has been estimated. Results will be presented in the paper. Following the verification described in the paper the platform concept will be optimised and subsequently detail engineering, construction and testing of a full scale prototype will be carried out.