The X-Rotor Offshore Wind Turbine Concept

Abstract

The following paper provides an overview of a novel wind turbine concept known as the X-Rotor Offshore Wind Turbine. The X-Rotor is a new wind turbine concept that aims to reduce the cost of energy from offshore wind. Cost reductions are achieved through reduced capital costs and reduced maintenance costs. The following paper includes results from an early feasibility study completed on the concept. In the feasibility study exemplary designs were created and structural analyses were carried out. Turbine capital costs and maintenance cost of the X-Rotor concept were then roughly estimated. X-Rotor turbine costs and O&M costs were compared to four existing wind turbine types to investigate potential cost savings from the X-Rotor concept. Results show that the X-Rotor has potential to reduce O&M costs by up to 55% and capital costs by up to 32%. The combination of the capital cost and O&M cost savings show potential to reduce the CoE by up to 26%.

Top-level rotor optimisations based on actuator disc theory

“…Secondary rotors have not been used on an operational wind turbine although a design is now being developed (Leithead et al, 2019). The main aim in using secondary rotors is to have a drivetrain with much reduced design torque compared to the usual transmission system based on power takeoff from a central shaft.…”

“…The preliminary evaluation of the X-rotor VAWT design (Leithead et al, 2019) suggests that use of secondary rotors will lead to more competitive VAWT designs. Another innovative VAWT design, the DeepWind VAWT of Paulsen et al (2015), has major savings through integration of the rotor blade shaft and support structure into a single element.…”

“…This is a huge increase in steady operational loading compared to conventional design. Also the steady and turbulent components of the ambient wind speed will introduce cyclic and random disturbances to secondary-rotor inflow, which may increase available power (Leithead et al, 2019) but will inevitably introduce fatigue loading. Now it is vital for the secondary rotors to minimise parasitic drag in the hub region as torque from this will absorb power from the primary rotor that cannot be recovered.…”

“…Jamieson (2011) highlighted it as a possible solution to the design challenge faced by large vertical-axis wind turbines (VAWTs), where a very low optimum speed leads to high drivetrain torque, weight and cost if the power is extracted in the most usual way from the central shaft. Leithead et al (2019) employed secondary rotors for power take-off in an innovative X-rotor VAWT design.…”

Top Level Rotor Optimisations based on Actuator Disc Theory

“…Jamieson (2011) mentioned it as a possible solution to the design challenge faced by large VAWTs where a very low optimum speed leads to high drive train torque, weight and cost if the power is extracted in the most usual way from the 10 central shaft. Leithead (2019) employs secondary rotors for power take-off in an innovative X-rotor VAWT design. The design tip speed of a large offshore HAWT may be 2 or 3 times greater than the 40 -45 m/s typical of a VAWT.…”