Posters

Abstract

An innovative multi rotor system (MRS) is presented comprising 96 vertical axis wind turbines (VAWTs) mounted on a single floating structure. Each VAWT is of 500 kW rated power comprising a total system of 48 MW. The overall aim is to develop the concept to a detailed level and evaluate its potential for cost of energy reduction. In this initial phase the outline design is developed with a high level evaluation of all the main characteristics. Disadvantages in power performance, in high rated torque and drive train cost that commonly affect a single VAWT in comparison to horizonal axis turbines (HAWTs) are resolved in the new design. A single floating VAWT imposes a very high torque reaction on its moorings, avoided in the VAWT MRS by having adjacent columns of turbines counter- rotating. Many simplifications include avoiding mechanical arrangements on the platform or a turret with swivel bearing for yawing in the sea and instead yawing by downwind drift on catenary moorings. More efficient packing of total swept area, compared to an MRS based on HAWTs, in a rectangular structure well suited to access and component handling, simpler components, reduced numbers of components and elimination of pitch and yaw systems are favorable for operation and maintenance (O&M) cost. In a comparison with a windfarm based on IEA 15 MW turbines, the total generator torque sum (indicative of drive train weight and cost) is reduced by a factor exceeding 6. The power coefficient of the VAWT is enhanced by having a high aspect ratio (blade length to diameter ratio of 5) and the effect is related to relative upwind and downwind loading of the VAWT. Further enhancement arises from the array blockage effect. Results to date sustain the VAWT MRS as a promising concept for reduction of cost of energy.