Types Of Wind Turbines: Everything You Need To Know

Uneven heating of the earth by the sun is what causes wind, creating a renewable source of energy. Wind turbines harness the kinetic energy in wind to create electricity and power grids. Turbines are systems made up of turning blades and a generator that makes electricity. They are a great source of renewable source of energy in urban and rural settings.

Turbines in varying sizes, and the blade length is the biggest factor that determines the amount of electricity a wind turbine can generate. Smaller turbines are capable of generating up to 10 kilowatts of electricity, which is enough to power 1-3 households. Some of the largest turbines can generate 10,000 kilowatts, and are often grouped together to create wind farms.

Wind turbines rely on a central axis that feeds into a generator to produce electricity. Depending on its placement, turbines can be classified into horizontal axis and vertical axis.

Horizontal Axis Wind Turbines

Horizontal axis turbines can be traced to the 1820s when they were used in American wind farms. They have a rotor with up to 20 flat sheet metal blades. A tail vane is responsible for ensuring that the rotor faces into the wind. Turning the wheel off the wind direction helps prevent over speeding and operational governance is automatic.

Traditionally, horizontal axis turbines were used to pump water. Modern models have 1-4 metal blades that rotate at higher speeds than ordinary windmills. The blades are twisted like airplane propellers and their rotation is automatically governed. This ensures that a constant generator speed is maintained.

One of the most popular horizontal axis turbines is the Jacobs three-bladed windmill. It was used between 1930 and 1960, and had the ability to produce 1 kilowatt of power at a speed of 6.25 meters per second.

Large horizontal axis turbines with two blades have been developed in recent years. One of the first such devices was installed in 1976 in Ohio. It has a diameter of 11.6 meters and its power was rated at 100 kilowatts. Another one installed in Oahu has an axis that is 76 meters above the ground and a rotor diameter of 122 meters. Its output at an average wind of 32 meters per second is 6200 kilowatts.

Advantages of Horizontal Axis Turbines

Most horizontal axis turbines are self-starting
They have the ability to pitch rotor blades in a storm, thus minimizing damage
The tall tower can be placed on uneven land and offshore locations
Ability to wing warp gives the blades the best angle to attack
Blades are located on the side of the turbine’s center of gravity for better stability
Tall towers provide better access to wind in areas affected by wind shear

Disadvantages of Horizontal Axis Turbines

They cannot operate efficiently in areas with near ground winds
Taller cranes and skilled operators are required for installation
Horizontal axis turbines are not easy to maintain
The cost of transportation is high i.e. 20% of equipment cost
Local opposition to aesthetics
They require stronger tower construction

Vertical Axis Wind Turbines

The main rotor shaft of a vertical axis turbine is set transverse to the wind while the main components are located at the base of the turbine. Because the gearbox and generator are close to the ground, maintaining them is easy. Vertical axis turbines don’t have to be pointed to the wind during installation, and this eliminates the need for wind sensing and orientation mechanisms.

The axis of these turbines is vertical to the ground and perpendicular to the wind streamlines. Vertical axis turbines were used in Middle ages and later in 1922, when S.J. Savonius invented a new rotor. The rotor had semicircular blades made from sections of an oil drum and cut in half along the vertical axis. They were welded together to form an open S.

An advanced version of the Savonius rotor was installed in the 1970s in Manhattan. It produced 5 kilowatts of electricity at a speed of 12 meters per second. The most recent vertical axis turbine is based on the device patented by G.J.M. Darrieus in 1931. It has two blades with twisted metal strips that are tied to the shaft at the top and bottom. The blades bow down in the middle, much like those of a food mixer. The Darrieus turbine installed in New Mexico generated 60 kilowatts at an average of speed of 12.5 meters per second.

Advantages of Vertical Axis Turbines

They are omni-directional and as such don’t require complex mechanisms to pitch the blades or yaw the rotor
Their gearbox takes less fatigue compared to that of a horizontal axis turbine
Vertical axis turbines can be grouped in wind farms to increate power generated per unit area
They perform better in high wind speed conditions than their horizontal counterparts
They can be installed below pre-existing horizontal axis turbines to supplement power production
A carefully designed wind farm of vertical axis turbines can produce up to 10x more electricity than a horizontal axis wind turbine farm
Gearbox replacement and maintenance is simpler since the gearbox is located at ground level
Most effective on hilltops, ridgelines, mesas and passes

Disadvantages of Vertical Axis Turbines

Blades are prone to variation in applied forces during rotations
They have low starting torque and as such, may require energy to start running
Blades have a tendency to constantly spin back into the wind, causing drag

Ducted Wind Turbines

These are less popular turbines designed to produce electricity from the airflow on the side of a building. They are positioned on the edge of the building such that when the air flows upwards, it hugs the building and enters the ducts. They are small and their blades have an average diameter of 600mm.

Advantages of Ducted Turbines

Minimal visual impact on buildings
Meets energy need to be met on site. This prevents transmission losses, which are associated with central power generation.
Makes use of unused roof space in urban areas

Disadvantages of Ducted Turbines

More research is required to determine energy production potential
Only effective for high rise buildings in cities and not households
Uni-directional and only produce power if wind blows in the right direction

Conclusion

A lot of work needs to be done to improve the efficiency of wind energy. There has been considerable progress over the past few decades, with vertical axis turbine technology making headway. That said, we hope you know more about different types of turbines and understand how they work.