+ 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 Horizontal Axis Wind Turbines (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 Vertical Axis Wind Turbines (VAWT) and they were also fixated on efficiency.

How Wind Turbines Work
Wind turbines are categorized as either lift or drag turbines. The blades on lift type turbines travel faster than the speed of the wind and the airfoil shaped blades receive lift and drag similar to the wings of an airplane. Lift is the component that provides the power to the turbine. Drag wind turbines travel slower than the wind speed, have a much lower efficiency, and require more material to produce the same power as a lift type turbine. Drag machines are never used in commercial applications.

Lift wind turbines can rotate around a horizontal axis (HAWT) or around a vertical axis (VAWT). The most popular machine today is the HAWT, but we believe our vertical wind turbine can be built with less material while extracting the same or more power as the HAWT.

The Lux Wind Turbine
Our turbine is a 5 bladed VAWT. 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 producing a lower LCOE.

Lux Wind Power is a Vertical Axis Wind Turbine Manufacturer, but at this time, our turbine is for research purposes only. We do not claim to build the most efficient turbine, but we do believe we can build a turbine that will produce energy at a lower cost than other turbines of equal size. That is, the Levelized Cost of Energy (LCOE), which is the lifetime costs divided by the lifetime energy production, on our turbine is expected to be lower than on the HAWT.

Are Vertical Axis Wind Turbines better than Horizontal Axis Wind Turbines?
The answer is, only if the LCOE is lower. The LCOE is not dependent on efficiency or extracting power from winds high above the earth. It is simply the cost of producing energy. The LCOE of a VAWT can be lower for the following reasons:

• The turbine requires less material to manufacture
• Does not have to be turned into the wind
• Major mechanical and electrical components are at ground level
• Lower transportation and erection costs if components are modular
• Pairs of counter rotating turbines can be spaced closer together than HAWT in a wind farm

We believe our wind turbine has a lower LCOE for all the above reasons.

+ Advantages

• 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 and also makes it a more practical vertical axis wind turbine for residential areas.

• 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 Stanford University, 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.

+ Validation

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

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.

+ Why will the Lux wind turbine produce more power at a lower cost?

The rotor of the Lux turbine is bigger so it extracts more power, especially at wind speeds between 4 and 10 m/s (9 and 22 mph). This is significant because the majority of power production happens between these wind speeds at most wind turbine locations. The annual kilowatt hours produced by a 2MW Lux turbine is expected to be approximately 10-20% more than most other 2MW HAWT. The Lux turbine has a lower capital cost than HAWT because it does not need a tower, a pitch system or a yaw system. The blades are easier to manufacture and a robust foundation is not required. This is why we say this turbine can produce more power at a lower cost.

+ Problems such as vibrations and torque ripple were common with past VAWT. How does the Lux wind turbine negate these issues?

The Lux turbine uses 5 or more blades instead of 2 or 3. As the blade of a VAWT rotates through one complete revolution, the relative wind direction produces torque, no torque, torque, and no torque. By using multiple blades that are supported with cross cables, this torque pattern is diminished and these problems are eliminated.

+ The Lux turbine only uses a short tower or bottom structure. Does this impair the power output because the equator is lower than the hub height of HAWT?

Although it is true that higher wind speeds are found at higher elevations, the Lux turbine still extracts more power because the rotor is larger. An expensive tower is not required to produce more power. The equator on a megawatt sized Lux turbine can be as high or higher than the hub of most HAWT of equal power rating, therefore, the Lux turbine does utilize the winds at higher elevations.

+ The Lux turbine rotates at a slower speed than other turbines of equivalent rating and will require a more expensive gearbox or direct drive generator. How does this turbine deal with this issue?

First of all, a slower rotating rotor with vertical blades may be easier for birds to see and therefore easier to avoid. We use a Traction Drive system that is similar to the well-proven technology of the locomotive and rail system where steel wheels transfer 6000HP to the steel rails. Our steel on steel Traction Drive is low cost and increases the output shaft speed without using an expensive gearbox. The hydraulic pump using cylinders is also an excellent low cost method for extracting power from a slow rotating output shaft.

+ HAWT must be spaced at large distances from each other to avoid interference. Do the Lux turbines need the same spacing?

Researchers such as Dr. Dabiri at Stanford University have developed computer models and experimented with as many as 18 VAWT in various configurations. They believe that counter rotating VAWT placed in close proximity can extract 10 times more power from a given area of land than can HAWT. More research is required in this area but most people believe turbines like the Lux turbine can be spaced much closer together.

+ Can the Lux turbine operate offshore?

It is an excellent candidate for offshore use because of its very low center of gravity and lightweight. Instead of having the heavy gearbox, nacelle, generator and blades positioned high above the water level it is much easier to float or stabilize a lightweight rotor and have the heavier components such as the Traction Drive, generator and support structure near water level. Also, the components that require maintenance are at water level.