Three differences between horizontal and vertical wind turbines that should be kept in mind when choosing a wind turbine.
1°/ Structural constraints of wind turbines
Vertical axis wind turbines ( VAWT ) and horizontal axis wind turbines ( HAWT ) each have their own structural constraints.
Thus, during each rotation, the blades of horizontal-axis wind turbines are subject to the combined effect of inertial force and gravity. The direction of the inertial force is subject to change, while gravity remains constant, so the blades of horizontal wind turbines bear an alternating load . This is a significant fatigue stress for this type of wind turbine . Furthermore, the wind turbine itself, which generates the electricity, is generally several tens of meters above the ground, leading to numerous repair and maintenance challenges for this generator.
Regarding the rotation process of vertical axis wind turbine blades , the conditions for receiving the effects are better than those of horizontal axis wind turbines because the respective directions of inertial force and gravity are both constantly stable. Consequently, the blades receive a constant load during their rotation, and their lifespan is greatly improved compared to horizontal axis wind turbines . The generator of vertical axis wind turbines is generally located directly below the rotor or at ground level. This makes it easy to repair or perform routine maintenance.
2°/ The start-up of the wind turbines
Wind speed at the start-up of a wind turbine is an important performance criterion, and the most commonly held opinions on this subject are not necessarily perfectly correct.
It is generally accepted that horizontal-axis wind turbines start easily. However, it has been observed that small horizontal-axis wind turbines require an average wind speed of approximately 4 to 5 m/s to start, with a maximum of 5.9 m/s. This is clearly not satisfactory.
In the field of wind turbines , it is commonly claimed that vertical-axis wind turbines suffer from poor start-up , particularly Darrieus-type turbines, which have virtually no self-starting capability. This is a significant obstacle to the commercial development of vertical-axis wind turbines . However, observations have led to the opposite conclusion: when properly configured, the H-shaped structure specific to Darrieus turbines can start with a wind speed of 2 m/s, which is undoubtedly preferable to the start-up of horizontal-axis wind turbines in general.
3°/ Environmental problems caused by wind turbines
What are the nuisances caused by horizontal wind turbines?
Although wind power is inherently a clean energy source and clearly compatible with the ecological imperative of sustainable development for the planet, the proliferation of large wind farms is not without its problems. These are essentially of two kinds: those related to the noise generated, and those concerning the negative impact on the local ecological environment .
The ratio of wind speed to blade speed of horizontal wind turbines is generally 5 to 7. At such a speed, significant aerodynamic noise is produced by the blades cutting through the air, while many birds do not escape blades traveling at such speeds.
The ratio of wind speed to blade speed in vertical-axis wind turbines is typically 1.5 to 2, which is significantly lower than in horizontal-axis models. Such low rotational speeds produce virtually no aerodynamic noise, and are therefore silent . The benefits are clear, as this resolves the past problem of being unable to install wind turbines in certain locations, such as urban public spaces or near residential areas. From this perspective, vertical-axis wind turbines will have a wider range of applications than horizontal-axis models.
