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.
The blades and rotor arms are likely to be of a sectional geodetic design. They will take the form of a space framed skeletal structure, clad with sheet material to the desired profiled shape. The use of high strength, low weight and cost effective composite materials will be predominant with R&D in this area being carried out by the Northwest Composites Centre at the University of Manchester.
It is the intention that the 110 metre blades will be manufactured in sections of approximately 11 metres each in order to facilitate ease of logistics from the point of manufacture to the construction site. The design life of the blades and supporting rotor arms will be 20 years.
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.
Research and CFD by Engenuity Ltd on behalf of Vertical Wind Energy Ltd.
The overall structure from sea-bed to the electrical hub will be of marine concrete material with a design life of 50 years. Three different sea-bed interfaces (foundations) are being developed in order to accommodate varying geological conditions at different offshore sites. These include a gravity type base, a concrete mono-pile and a unique tri-pile base where severe scouring could be an issue.
It is the intention to deploy the entire structure, less the sea-bed interface, as one completely assembled unit inclusive of generators and rotor. In order to eliminate any unwanted wind loading on the blades during this operation the blades are collapsed into their nesting position close to the tower structure. The rotor blades are then extended into their operational position once the structure is firmly affixed to the sea-bed.
The overall design includes 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 20 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 includes for 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.