Why is the efficiency of vertical axis wind turbines low?

The main reasons for the lower efficiency of vertical axis wind turbines (VAWT) compared to horizontal axis wind turbines (HAWT) involve various factors such as aerodynamic characteristics, structural design, and operating environment. The following is a detailed analysis:
1. Low aerodynamic efficiency

Poor self starting ability: The angle of attack of most vertical axis wind turbines (especially Dario type) blade airfoils constantly changes during rotation, making it difficult to generate sufficient starting torque at low wind speeds and requiring additional devices or external forces to start.

Dynamic stall problem: When the blades rotate to the upwind side, the direction of the airflow relative to the blades changes dramatically, which can easily cause dynamic stall and result in energy loss.

Interference between blades: The blades of a vertical axis fan will pass through the downstream wake region during rotation, and are affected by the turbulence of the front blade wake, reducing aerodynamic efficiency.

2. Structural design and material limitations

Fatigue stress concentration: The support structure (such as cables or pillars) and blade roots of vertical axis fans are subjected to cyclic alternating loads, which are prone to damage due to fatigue and limit large-scale design.

Manufacturing complexity of blades: The manufacturing process of curved blades (such as Daryl type) is more complex, costly, and difficult to apply for efficient airfoil design compared to straight blades with a horizontal axis.

3. Low wind energy utilization coefficient (Cp)

Theoretical limit low: The theoretical maximum wind energy utilization coefficient of vertical axis fans is about 0.4, while that of horizontal axis fans can reach 0.59 (Bates limit).

Actual efficiency gap: The actual wind energy conversion efficiency of vertical axis fans is usually only 10% -30%, while modern horizontal axis fans can reach 40% -50%.

4. Insufficient environmental adaptability

Sensitive to changes in wind direction: Although vertical axis fans can theoretically accept any wind direction, it is difficult to maintain the optimal blade angle of attack in actual turbulent or frequently changing wind environments.

Weak wind resistance: Large vertical axis fans are prone to stability issues due to structural vibration under strong winds, and the braking system design is more complex.

5. Application scenarios and technological maturity

Scale limitation: Vertical axis wind turbines are mostly used for small and medium-sized distributed power generation (such as urban environments), but large-scale commercial wind power projects are still dominated by horizontal axis, which has been optimized for decades and has high technological maturity.

Less R&D investment: Due to a small market share, technological progress in aerodynamic optimization, material research, and control systems for vertical axis fans is relatively slow.

Advantages and Applicable Scenarios of Vertical Axis Fans

Despite its low efficiency, vertical axis fans still have some unique advantages:

No need for yaw system: can capture wind in any direction.

Low noise and safety: Low speed, low noise, and relatively safe blade movement trajectory for birds.

Convenient maintenance: The generator and other equipment can be placed on the ground for easy maintenance.

Therefore, vertical axis wind turbines are more suitable for application in urban environments with strong turbulence and variable wind directions, or small off grid power supply systems, rather than large-scale wind farms.

summary

The core reason for the low efficiency of vertical axis wind turbines is the inherent lack of aerodynamic characteristics, which limits their ability to capture wind energy. In addition, structural fatigue and scale challenges make it difficult to compete with horizontal axis wind turbines. In the future, with the development of new materials and flow control technologies such as active flaps and vortex generators, the efficiency of vertical axis wind turbines is expected to improve, but they may still play a complementary role in the mainstream wind energy market.