Are Vertical Axis Wind Turbines the Future of Urban Energy?
The race to cut carbon emissions and build sustainable cities has reignited interest in vertical axis wind turbines (VAWTs). These machines — which trace their roots back to ancient Persian windmills — are now seen as a promising solution for future urban energy. Their compact, omnidirectional design outperforms the horizontal spinning giants of open landscapes, particularly in space-constrained cities seeking new power sources.
What Are Vertical Axis Wind Turbines?
VAWTs are wind-catching machines that spin around a vertical pole instead of the traditional sideways setup that resembles a fan. Their average power is 7.4 kilowatts — for reference, most standard wind turbines generate 2.5 to three megawatts. There are four types of VAWTs.
1. Savonius
This drag-type machine consists of two or more half-barrel-shaped blades. The curved design allows it to spin easily at low wind speeds. However, it has low rotational performance, meaning it can’t whirl fast, which limits energy generation.
2. Darrieus Rotor
The vanes of a Darrieus rotor look like egg beaters, with thin, curved wings that spin using aerodynamic lift. Wind flows around the structure, creating suction at the front of the unit, which drives rotation. These turbines rotate faster than Savonius models. A three-blade Darrieus can even start independently under certain conditions. It’s the most common type of VAWT.
3. H-Darrieus
Unlike the curved aerofoils of a standard Darrieus turbine, the H-Darrieus uses straight blades mounted on a central vertical shaft, forming an “H” shape. It’s one of the most promising vertical generators for areas where wind direction changes frequently. Like other Darrieus types, it relies on aerodynamic lift but struggles with self-starting at low speeds.
4. Helix Shape
This turbine features helical blades. These ribbon-like, twisted structures improve performance over traditional straight-vaned designs, especially in variable environments. Studies show that helical angles of 80 degrees demonstrate the best wind-catching performance.
Advantages of VAWTs
Wind energy adoption is predicted to surge 7% from 2023 to 2030. However, nearly all operating turbines operate on a horizontal axis. Here’s why more VAWTs could be beneficial in urban environments.
Omnidirectional
Vertical turbines can catch wind from any direction without being pointed toward it. In comparison, horizontal axis wind turbines (HAWTs) require complex orientation since they are unidirectional and optimized to capture energy from a single airflow direction.
Space-Efficient
VAWTs can vary significantly, ranging from a few meters in diameter to tens of meters. However, they’re still smaller than side-facing turbines, which can be as tall as 20-story structures with 100-foot-long blades. Wind in open plains can consistently turn HAWTs. The compactness of VAWTs makes them well-suited for denser areas like urban environments, where buildings often create turbulent, unpredictable airflow.
Operable at Lower Wind Speeds
Some turbines require speeds of seven to 11 mph to operate, while vertical generators can function at much lower airflow rates. In Malaysia, VAWTs have been shown to capture wind as low as one meter per second or about 2.2 mph, making them ideal for urban areas where strong, consistent breezes are rare.
Simpler to Maintain
The blades of large horizontal wind turbines can be as big or even bigger than airplane propellers, making them difficult to maintain. In addition to their size, they are often located in remote areas with strong, consistent winds, creating harsh onshore and offshore conditions. As a result, regular maintenance, inspections, and repairs can be challenging.
In contrast, vertical wind turbines are significantly smaller, and the generator and gearbox are easier to access since they’re closer to the ground. However, they still present unique maintenance challenges due to their distinctive shape.
The Disadvantages of VAWTs
Despite significant benefits, VAWTs also have limitations.
Lower Efficiency
Vertical units are usually less efficient than side-facing turbines, especially where winds are strong and steady. Some models also suffer from torque ripple, which is an uneven spinning that causes vibrations and power to fluctuate. These vibrations can lead to mechanical fatigue and reduce turbine lifespan.
Installation Challenges
VAWTs are typically ground-mounted, so installing them at greater heights to access stronger winds is challenging. Because airflow is weaker at ground level, where they are usually placed, offshore installations can lead to high costs due to the need for specialized equipment, skilled personnel, and robust foundations that withstand wind loads and environmental stresses.
Dynamic Stall
Dynamic stall occurs when the blades temporarily lose lift as airflow separates from the vane during rotation. This increases drag and reduces energy output, resulting in unsteady loads.
How to Use VAWTs in Urban Areas
Ongoing design advancements are helping to overcome many of these limitations, making VAWTs an increasingly practical option to achieve sustainable energy generation using the following urban applications:
> Rooftop installations: VAWTs can be installed on the roofs of residential buildings, commercial complexes, and high-rise apartments to generate electricity for on-site consumption.
> Building facades: VAWTs can be mounted on the sides of buildings, potentially expanding their swept area and increasing energy output.
> Integration with smart cities: VAWTs can be part of smart city initiatives, working with solar panels and smart grids. They can contribute to energy efficiency by providing a renewable source for street lighting, traffic signals, and EV charging stations.
> Off-grid power solutions: In areas with unreliable grids, VAWTs can serve as backup sources for critical infrastructure like hospitals, police stations, and telecom towers. They can also power remote urban locations and reduce reliance on diesel generators.
> Retrofitting existing architecture: Some companies are developing VAWTs to retrofit onto structures like lamp posts and bridges, harvesting wasted airflow from vehicles.
The Winds of Change Are Vertical
As cities search for cleaner energy solutions, VAWTs are making a noticeable spin in the right direction. They may not replace every horizontal axis giant, but they can be impactful in dense cities where space is tight and the breeze is unpredictable.
