the Lux Wind Turbine
The Lux Wind Turbine is a six bladed turbine that revolves around a vertical axis. Several cables are connected between each blade in a cross pattern, which supports each blade along its entire length. This rotor is a rigid structure never seen before in the wind industry. Due to this cross cabling, the central structure/tower can be removed, which is the main reason why the turbine can be built using less materials.
+ Comparing Vertical & Horizontal Axis Wind Turbines
Several decades ago, scientists were in disagreement as to which type of turbine would be beneficial to the industry. After extensive research on both types of turbines, the HAWT won the battle, not because it was a great turbine but because scientists at that time were unable to solve the major problems associated with the VAWT and they were also fixated on efficiency.
The Coefficient of Power (Cp) measures the efficiency of the turbine and is the amount of energy extracted divided by the total amount of energy in the wind. Even though the Cp of a HAWT is higher than the Cp of a VAWT (about 50% versus 45%) this should not be a factor when evaluating the two types of wind turbines. The only evaluation tool should be the Levelized Cost of Electricity (LCOE), which is the sum of all the costs over a lifetime/sum of all electricity produced over a lifetime. The Lux Wind Turbine is expected to have ½ the LCOE as a HAWT. There are many reasons for this expectation but the main ones are discussed in the following paragraphs.
Consider a few basic engineering principles to compare the two types of wind turbines. HAWT use cantilevered blades and a cantilevered tower, which means, each of the blades and tower are supported only at one end. This is similar to sweeping a floor with one hand at the end of the broom stick. Engineers avoid using cantilevers wherever possible because cantilevers require more material at the support end to hold the item in place. Structures that require the least amount of material are supported in many places. This basic principle can be seen in truss bridges, buildings and most all other structures built by mankind.
In contrast, the multiple (six or more) Lux Wind Turbine blades are supported at each end and cables are attached at various positions along the blades entire length. This fully supported system is in direct contrast to the cantilevered blades and tower of the HAWT. The cables cross each other and when looking from the top down, each cable forms a hexagon, which is close to a circular shape. This shape ensures that the aerodynamic drag from the rotating cables is kept to a minimum. The cross cables and blades create a rigid structure similar to the shape of a football. This type of structure is also similar to the geodesic dome, which uses the slogan “doing more with less”. The rotor can be built to almost any size, using fewer materials than the HAWT blade and tower system.
There is one other major point that I want to make. The rotor and nacelle, which contains the mechanical and electrical components, of a 5 MW NREL reference turbine, has a weight of 350,000 kg (770,000 pounds). The position of the nacelle is more than 100 meters (328 feet) above the ground mounted on top of a tower. Building a tower and foundation to keep the rotor and nacelle in this position is an unnecessary cost, especially when comparing it to the Lux Wind Turbine, which has all the mechanical and electric components at ground level. In addition to this, the entire 350,000 kg must be turned into the wind every time the wind changes direction. The Lux Wind Turbine does not need to be turned into the wind because it will accept wind from all directions, even the up and down drafts. Companies today are putting 6-8 MW HAWT wind turbines offshore in water up to 60 meters (200 feet) deep and on floating platforms! Again, our turbine, with a low center of gravity, is better suited for these locations.
• The blade and cross cable system eliminates or reduces all problems associated with previous Vertical Axis Wind turbines including reduced vibrations, torque ripple and premature blade failure. The power output is improved, especially in low winds, by using an advanced blade profile and by building a rotor with a larger swept area. This is practical because the blade and cable system is light in weight and therefore relatively inexpensive. The ½ cost analysis includes this larger swept area.
• The tower at the bottom of the rotor is short but the equator of the rotor, on megawatt machines, is as high or higher than the hubs of conventional turbines, therefore, taking advantage of higher wind speeds that occur at higher elevations.
• All of the mechanical and electrical components are at ground level. This makes it easier to erect and also reduces maintenance costs.
• A yaw system is not required because this turbine accepts wind from all directions.
• The blades do not need to be pitched, which eliminates the need for the large diameter slewing bearings, retainers and hydraulic components. The blade speed and power output is controlled by aerodynamic stall.
• According to Dr. John Dabiri at California Institute of Technology, counter rotating Vertical Axis Wind Turbines can be spaced closer together than conventional Horizontal Axis Wind Turbines https://arxiv.org/pdf/1010.3656.pdf. This is advantageous because most high wind speed sites are already occupied by widely spaced conventional wind turbines. • The blades on the prototypes are made from aluminum, which are extruded at relatively low costs. However, since the blades experience only small deflections, they could be made from a wide range of materials or a combination of materials. Conventional wind turbine blades have large deflections, therefore, their material selection is limited.
• The blade profile is constant from one end to the other. Manufacturing this blade is much easier than manufacturing the conventional wind turbine blade, which has a profile that changes in width and curvature along its entire length.
• The blades can be made in sections and assembled like tent poles. This is possible because the blades are always in compression, unlike all other wind turbine blades that change from tension to compression through each cycle. The blade sections are easy to transport and assemble.
The Institute of Aerospace Research, a branch of the National Research Council (NRC), in Ottawa, Canada developed computer models of the Lux turbine and tested these models for aerodynamic and structural performance. The first model they analyzed was 40 meters in diameter and had a power output of 1MW. The results of the analysis showed the Lux Wind Turbine performed well and the blades had a life expectancy well in excess of 25 years. NRC then scaled the computer models to a diameter of 160 meters with a power output of 16MW. The positive results observed in the 1MW turbine analysis were repeated with the larger turbine.
IOPARA, a Vertical Axis Wind Turbine consulting company, in Montreal, used their CARDAAV software, which is well respected around the world, to predict the power output of several Lux Turbine models with and without cross cables. The power curves created from this software were confirmed with data collected from the prototypes. The power loss from the cross cables was low, as expected.
+ Product Development
Work to date on the Lux Wind Turbine has been personally carried out and funded by Mr. Glen Lux B.E. Development of the Lux Wind Turbine began in 2004 with several turbine designs being tested, culminating in the current design.
The first generation of the 40KW Lux Wind Turbine was operational for 1½ years. It was then lowered and 7 other models were assembled and tested for various periods of time. Variations of blade curvature, blade offset angles, solidity ratios, blade profiles, drivelines and air brakes, were applied to these models, with the goal of optimizing turbine performance.
There are two options to hold the rotor in place.
+ Guy Cable Supported Rotor
The least expensive option uses 3 guy cables that go from the top of the rotor to an anchor on the ground. This turbine does not need a central structure/tower or a robust foundation to keep the rotor upright. The guy cable and anchor system is only a fraction of the cost of the traditional robust cement foundation and tower system. This turbine can be used in most rural areas and could reduce the cost of the support structures in offshore locations as well.
+ Lattice Supported Rotor
In locations where it isn’t feasible to use guy cables, the rotor is supported by a lattice structure positioned along the vertical axis that rotates with the blades. The cross cable pattern is still utilized so the blades have very little movement even in hurricane wind conditions. This system requires a robust foundation but the blade, lattice tower and cross cable system is expected to have a cost that is significantly lower than the conventional wind turbines.