There are a few different designs of vertical axis turbines in use around the world today. At present, all the machines in use are mounted on top of specially designed and built towers.
The current models either have their gearbox and generating plant mounted within the structures of the tower or in a plant room at the base with a drive shaft connection to the rotor arm and blades.
The first generation of modern Vertical Axis Wind Turbine (VAWT) machines (1970-80’s) were relatively expensive to construct, partly due to their one off aeronautical type of manufacture and their overly complex design. They proved extremely problematic, having problems with bearings and torque tubes. They also proved slightly less efficient than their Horizontal Axis Wind Turbine (HAWT) counterparts, largely due to mechanical losses.
Now, extensive research and development by UK-based Eurowind Developments has found that a basic H configuration of blade is an efficient alternative and that cost effective shipbuilding materials and construction techniques can be used to build such a structure.
The design, dubbed the Vertical Axis Wind Turbine Modular Unit, is capable of being mounted on or to an existing industrial chimney, tower or similar structure. And the option of supplying the machine with its own support structure, for use on windfarm’s and offshore applications is also available.
The unit comprises of at least two vertical blades, attached via horizontal arms, to either a single module incorporated in a section of smaller steel structures, or, on larger steel and concrete structures, two or more modules mounted around the structure’s circumference at different levels.
Each module comprises a segmental framework attached around the circumference of the structure. Using the framework as support on concrete structures, especially reinforced concrete ring beams can be cast in situ around the structures outside periphery. This not only strengthens the structure locally, but also provides a solid platform on which to mount the generating plant.
The exterior of the framework is clad to protect the plant from the elements and to create a smooth rounded surface, which offers less wind resistance. Mounted between the top and bottom frames and the concrete ring beams of each module, at the outermost point, is the rotor arm ring. This incorporates rollers that rotate around the outer boundary of the module on tracks fixed to the concrete ring beams.
The blades via the rotor arms are attached to the outside of the ring causing it to rotate. The generator plant then takes its drive from the inside of the ring via a rack-on-pinion or hydraulic power takeoff arrangement. The company is also considering the use of a directly coupled slow speed alternator.
The power output of the turbine unit is dependent on the size and type of the structure. As the design of each structure varies, a detailed survey of the candidate structure is required to determine the power and, to a lesser extent, the weight of the machine. The survey would not only determine the condition of the structure, but it would also take into account such things as original design codes used, changes in usage and changes in fuel used and/or thermal insulation. All of these factors would help establish the reserve strength of a given structure. Using this known reserve strength, the machines would then be tailor made.
For example, on a typical power station chimney built from the 1960s onwards, consisting of a multi-flue chimney with a concrete shell, it is likely that a large machine with two or more modular units (each containing a number of generator and gear box sets) could be mounted, each generator set being capable of developing around 1 MW of power. This would give this type of structure a potential overall output of around 5-6 MW. As the machine is of a modular design, the most cost effective combination of components can be used to construct the most viable (highest output) machine, within the structural and safety constraints of any given structure.
The gearbox drive shafts on such units can be connected via an electro-hydraulic clutch and an electro-hydraulic brake. The clutch will allow the optimum use of plant at different wind speeds. The most efficient combination of generator plant can be maintained by clutching or de-clutching in or out of drive to meet the maximum, or required, output for any prevailing wind speed. It also allows the power plant to be de-clutched individually from drive, for maintenance purposes. The brake is a safety device which, in the unlikely event of a total grid failure, will stop the rotation of the rotor arms, so preventing an over speed situation from arising.
The clutch and brake control are automatic with a manual override. The control system is computerised and gathers information from sensors, such as wind speed and power demand, as well as keeping the right combination of plant in operation.
On smaller structures, the plant and controls can be housed in a plant room at the base of the structure. Here, a drive shaft mounted to the outside of the structure connects the generating plant to the rotor arm ring using a simple bevel gear and universal joint arrangement at each end.
The blades of the machine are aerofoil shaped and react in a similar way to an aircraft wing. The wind (which can be picked up from any direction) blows over the rounded leading edge of the blade and rushes to fill the void down its sloping back. This is known as aerodynamic lift and it is this aerodynamic lift that propels the blades forward. The rotor arms and blades can be manufactured to three standard chord sizes and standard length sections of 10m. Reducers made in all chord sizes enable any size of rotor or blade to be assembled in multiples of 10m. The sections can be manufactured using shipyard techniques and, due to their reduced stresses, will be produced using more cost effective s-type glass fibre materials and a Kevlar leading edge.
On larger machines, the rotor arm to rotor arm ring connecting sections will have extractor fans incorporated. These fans serve two purposes, one to extract hot air (that has been generated by the plant) from the module using the rotor arms and blades as a heat sink and second, to heat the rotor arms and blades to prevent ice build-up in cold weather conditions. The whole design is aimed to be interchangeable and so be adaptable for most tall structures. It is also designed to be easy to construct and erect, so making it economical to produce in a wide range of sizes and power outputs. It could be erected easily on site without the use of cranes if necessary.
In order to give the blades further stability on the larger machines, three or more sets of blades and rotor arms can be used. These can be connected via cables, and so triangulate the blade structure around the central support. On smaller machines, the third blade may not be necessary and extra stability can be gained by using cables held away from the module by a strut on either side. In addition, for reasons of safety, tensioning cables can run along the entire internal lengths of both the rotor arms and blades. This adds to the strength of the blade and rotor arm sections by keeping them in compression.
The technology used in the design is not entirely new. Eurowind has taken the latest wind turbine, shipbuilding, aircraft and construction technology (which is now well proven) and combined it with new innovation.
Designing the modules with a steel cantilever framework together with two concrete ring beams has solved the problem of attaching the machine to an existing structure without over stressing the structure.
The concrete ring beams will have specially designed reinforcement and will absorb all significant additional loads as well as effectively strengthening the existing construction.
Making as much of the machine as possible sectional, interchangeable, and using shipyard construction methods rather than aircraft methods has made the new design cost effective and adaptable. This reduces the production costs and together with the amount saved by not having to build a tower (when using an existing structure), will substantially reduce the overall cost.
Furthermore, most existing structures already have access roads and are located close to existing grid connections, and with a cost of such connections presently at around £250,000 + per kilometre and service roads around £130,000 + per kilometre, this should not be overlooked.
With this design, the mechanical problems experienced by the earlier machines have been removed. There is no torque tube to fail in this machine, and the bearings are small common sized bearings incorporated within the rollers. These bearings can be easily and cheaply replaced during PPM visits, whereas the first generation machines had a large single bearing which required a crane and the total removal of the blades and cross arm to replace. Furthermore, using the newest blade design improves the efficiency/performance of the machine, creating more lift and less drag.
The machine’s design makes it ideally suited for offshore applications. Out of site from land, in areas of higher than average wind speeds, the larger and more rugged the machine the better. The vertical axis wind turbine modular unit is designed to be built larger than its horizontal axis counterparts (5 MW and upwards is quite possible). It is designed to have a life expectancy of 25 – 30 years, and therefore it has to be rugged. With less stress on the blades and the simplistic design of bearings and plant, the vertical axis wind turbine modular unit should require less maintenance than a horizontal axis machine.
The company is keen to hear from any corporate, institutional, private, or syndicate investors that could fund the new company and would be able to support our funding requirements.