Types of Wind Turbines: Explained & Compared

 

The wind is a renewable energy source caused by uneven heating on the earth’s surfaces by the sun. Devices known as wind turbines have been invented to convert wind power into electricity. There are many types of wind turbines. The turbines are environmentally friendly because no harmful chemicals are emitted into the environment when generating power. The wind turbines made of blades are connected to a generator producing electricity once turned by the wind.

Types of Wind Turbines Are:

The horizontal axis and the vertical axis are the two main types of turbines. Other types of wind turbines are Diffuser-augmented, multi-rotor, and Co-axial wind turbines, among others.

Wind Turbine Type Sizes

Wind turbines vary in size. The length of a blade is the determinant of the amount of electricity to be generated. The largest wind turbine can generate power of up to 10,000 kilowatts. A single home can use 10 Kilowatts generated power from the small wind turbines. Many turbines are combined to create a wind farm or a wind power plant to provide electricity grids.

 

Horizontal Axis Wind Turbines (HAWT)

 

What are horizontal axis wind turbines?

Horizontal-axis wind turbine is the most used type of turbine. Its components include a shaft, generator, and blades. The blades are made facing the wind. The blades are hit by the wind causing the shaft to rotate. The generator is turned on by a gear connected to the shaft, and the production of electricity starts and is sent to the power grid.

Horizontal Wind Turbines Key Elements

To add efficiency to the turbine, the wind turbine has some key elements. In the Nacelle, also known as the head, there is a wind vane, an anemometer, and a controller that reads the speed and direction of the wind. In case of a change in the winding course, a motor turns the Nacelle to ensure the blades face the wind. In extreme winds, there is a break on the turbine to slow the speed of the shaft. The brake prevents the turbines from damage in severe conditions.

The horizontal axis turbines have airplanes like propellers with three blades. The largest is nearly a 20 story building with 100 feet long blades. The taller the turbine, the more electricity is produced. The horizontal type is almost used in all the turbines.

 

Horizontal Axis Wind Turbine Advantages and Disadvantages

 

Advantages

• The blades are positioned to the side of the center to help with stability.
• Has the ability to wing wrap, giving the blades an angle to attack
• Has the ability to pitch the rotor blades in case of a storm hence minimizing possible damages
• A tall tower allows easy access to stronger winds
• A tall tower can be placed on uneven land or offshore locations
• It can be set in the forest among the tall trees
• Most of them are self-starting

Disadvantages

• Difficult to operate on ground winds
• Difficult to transport
• Challenging to install since it requires skilled operators and cranes
• Difficult to maintain
• The proximity affects the radar

Vertical Axis Wind Turbines (VAWT)

 

What is a Vertical Axis Wind Turbine?

In a vertical axis turbine, the shaft and the blade are connected vertically to the ground. The main components are all close to the ground. The wind turbines of the vertical one are near the ground, unlike the horizontal ones. The vertical axis wind turbine has two types, namely: lift-based and drag-based turbines. The lift design is more efficient than the drag or paddle-based design. The vertical axis turbines are in the shape of an egg beater, and the blades are attached at the top and bottom of a rotor placed vertically.

Darrieus Wind Turbine

The Darrieus wind turbine is another common type of vertical axis turbine named after French engineer Georges Darrieus. He patented the design in the year 1931 looks like a giant egg beater with two blades. Some of the versions used are the 100 feet and 50 feet vertical axis turbines. These turbines are rarely used because the horizontal performs better.

 

Vertical Axis Wind Turbine Advantages and Disadvantages

Advantages

• Easy maintenance
• Low transportation and construction cost
• They are not directional
• Effective on a ridgeline, hilltops, mesas, and passes

 

Disadvantages

• Less efficient
• Blades spin back to the wind causing a drag
• Operate in low and more turbulent wind
• It has a low starting torque and requires energy to run.

 

Other Wind Turbine Designs

 

Diffuser-augmented Wind Turbine

A diffuser-augmented wind turbine is modified with cone-shaped wind diffusers to increase the effectiveness of converting wind power into electricity. The diffuser increases the speed; thus, the efficiency is increased. In the traditional bare turbines, rotor blades are mounted vertically on the support shaft or tower. In the Diffuser-augmented wind turbine, rotor blades are installed in the diffuser. It is then placed at the top of a shaft or support tower. To increase the efficiency of the device, more modifications have been carried out on the diffuser.

 

Twin Bladed Rotor

Nearly all modern wind turbines use a three-bladed rotor, but there are specific ones with two blades. GROIWAN was a two-bladed unit that was under experiment at Kaiser-Wilhelm-Koog in Germany from 1983 to 1987. The two-bladed turbines were used by Eemmeerdijk Wind Park, located in Zeewolde, Netherlands. The manufacturers of the two-blade turbines were Nordic Windpower that came up with a model such as N 100. NedWind has also manufactured other turbines.

 

Downwind Rotor

Approximately all the wind turbines have a rotor placed in the Nacelle front when the wind blows. In some turbines, the rotor is placed behind the Nacelle. The design is advantageous because the turbines align themselves with the wind reducing the cost. The disadvantage is the load on the blade changes as it passé behind the tower, thus increasing the fatigue load and resonance in the other structures of the turbine.

 

Co-axial, Multi-Rotor

On the drive shaft, more than three rotors can be mounted. They are combined as the wind passes through each rotor by the space between an angle from the direction of the wind. Research by Douglas Selsam in 2004 proved that the co-axial multi-rotor produced a considerable amount of power. The first one was used in California with the 12 feet separation of the propellers. Due to the new rotor, the diameter was 2.1 meters. Aerospace engineers from Lowa State University have optimized the turbines, among others. The turbine proved a 10 to 20% increase in power and was less efficient than the counter-rotating design.

 

Counter-Rotating Horizontal Axis

When the mass is accelerated in one direction, it causes a proportion but in the opposite direction. There is a significant amount of rotational air that takes place. In a single rotor, too much tangential airflow goes to waste. To make it more useful, an extra rotor is added to increase the production of extra power. Another advantage of contra-rotation is the absence of a gearbox and an auto-centering on the turbines.

The turbines in the counter-rotating horizontal axis are located on the same side while the placed are mounted at the front angled to prevent hitting the rear ones. Whenever the blade is on the opposite side of the tower, the blades at the back should be smaller than those at the front. With few common multiples, the turbines should turn at a ratio of 7:3 to reduce the vibration. It allows the generator to function even with a wide speed range.

 

Savonius Wind Turbine

The turbine has aerofoils that are mounted vertically on the shaft and grounded on a station. From above, the turbine has an S shape and rotates slowly. It is used to grind grains, pump water, and do other tasks. There is no production of power because of the slow rotation of the wind turbine.

 

Flapping Panel Wind Turbines

A flap turbine, also known as the check valve turbine, is a vertical axis turbine where the blades are adjustable flaps. When the blades are combined, they act as a sail. When the wind is flowing, the flaps close, allowing no wind to pass through the sail. The wind is blocked, causing the turbine to begin to rotate.

 

Giromill Wind Turbine

A giro mill wind turbine is powered by two or three aerofoils attached vertically to the center with horizontal support. It works well with turbulent wind conditions, and they are an affordable option. In this type of turbine, the standard horizontal axis windmill is unsuitable.