The technology behind the VertAx wind turbine design is a culmination of contributions from universities and privately funded research carried out by the founders over many years. It includes a combination of older technology re-visited with new design knowledge as well as substantial innovation, incorporating state of the art materials and modern manufacturing techniques. Much of the technology has been taken from other industrial sectors and then improved upon and adapted for the application of an off-shore wind turbine generator. This approach means that there are few aspects pertaining to the individual components that remain unproven, albeit in other industrial applications.
The primary goal driving the technology development was to provide a stepped reduction in the cost of electrical power generation from off-shore wind. By designing a machine that is modular and has few moving parts, VertAx Wind Ltd and its technology partners believe they now have the makings of a design that will enable them to achieve their stated objectives.
The C-Gen machine is a modular, permanent magnet, ring generator, in which the rotors core material is C shaped with magnets mounted on the limbs of the C and the coils of the stator arranged in a disk that passes between the C’s magnets. It has no iron in its windings; this greatly reduces difficulty in assembly (as there is no attractive force between stator and rotor) and enables the use of an increased air-gap size. This leads to overall mass and cost savings when compared to a conventional layout. The machine also provides the following significant performance advantages:
- High reliability
- Minimum part count
- Use of standardised components
- Built-in redundancy and flexibility
- High efficiency across full operating range
- Zero cogging torque
- Reduced weight
- Lower cost manufacture
The machine has been modelled and extensively demonstrated up to 6MW, with a range of prototypes also having been built and thoroughly tested since 2004 in sizes from 15 kW to 1 MW.
Due to their constant gravitational loads, the blades and rotor arms are likely to be of a sectional geodetic design. The use of high strength, low weight and cost effective composite materials will be predominant within R&D in this area being carried out in conjunction with the National Composites Centre in Bristol.
The CFD animations on the right show the movement of air over and around a notional blade profile through a machines 360° of rotation. The vortex shedding from the blade is undesirable, inducing drag and creating turbulence that can interfere with the performance of the other blades and create wake for other down wind turbines.
Through further R & D, we will be able to identify and design a profile that will operate at a tip speed ratio ideally suited to the application, whilst minimising the vortex shedding effects.
The support structure will be of standard sectional steel construction, designed to incorporate the turbine’s two Power Modules. The wind turbine will be suitable for use with a number of differing foundation types, including monopole, gravity base and floating options.
The tower engineering will be completed by Lloyds Register in Bristol and detailed dynamic modelling of the integrated tower and foundation, accounting for both wind and wave loads, will be researched by Cranfield University, Marine Engineering department.
The overall design includes for the option of a permanently installed crane in order to facilitate changing of the blades and rotor arms at any time during the operational life of the wind turbine, including at the expiry of their 25 year design life. This hydraulic arm will be housed in the 'Top-Hat' section of the structure that supports the helipad at the very top of the tower.
This on-board crane will also facilitate the loading and unloading of any equipment being transferred from a sea going supply vessel. The design ensures that this piece of industrial machinery and associated equipment will not interfere with any other aspect of the turbine’s generation and electrical control facilities.
The design allows for the option of a permanent helipad enabling service crew access by a 4-6 seater helicopter thus eliminating the hindrances caused by use of marine vessels during severe sea states. There will also be included a traditional boat landing facility enabling marine access / egress as appropriate and when suitable conditions prevail.