Traditional Propeller-type turbines experience shaking and irregular forces when their blades pass through turbulent wind. Turbulence is often associated with mid-level wind layers and wake from other tall turbines. The shaking causes problematic fatigue issues for their gearboxes, blades, and bearings.
Although placing propeller-type turbines on shorter, less expensive towers in locations with excellent mid-level wind speeds (i.e., most wind farms in California) would be preferable, this is not practical due to the fatigue damage they would endure. Instead, they are installed high above the ground, where the wind flow is smoother, more laminar, and often faster. Horizontal axis wind turbines also must be placed far enough apart to escape turbulent wake shedding from their neighbor’s blade tips. On the plus side, the wind speed is usually faster above the ground, making up for the added costs of making and installing taller towers and leaving the mid-level wind resource unused.
Vertical axis H-type turbines like Wind Harvesters can be extremely durable and have long been considered much more capable of withstanding turbulence because of the following:
- Two connection points from each blade to the rotor shaft prevent the shaking and unsteady forces that propeller-type blades experience in turbulence.
- The physics involved with the Wind Harvester’s NACA 0018 shaped blades causes them to stall in high winds. This naturally regulates blade loads and keeps the rotor from overspeeding.
- When a propeller turbine is not facing directly into the wind, its blades experience added fatigue loads. Vertical axis wind turbines don’t have a “yaw” mechanism and are immune to any added loads due to changes in wind direction.
- A vertically oriented driveshaft is not subject to cyclic loads due to gravity – unlike the horizontally aligned driveshaft of a propeller turbine.
- Propeller-type turbines work best when the wind is steady and the turbulence is low. In contrast, the blades of vertical axis turbines are designed to withstand a cyclically varying wind speed and extract energy from turbulence while having little impact on their fatigue life.
- Three-bladed vertical axis turbines have been shown to be less susceptible to harmful harmonic resonance conditions.
