Vertical-Axis Wind Turbine Drafting
A recent study into vertical-axis wind turbines (VAWTs) showed that their efficiency could be improved by arranging them into clusters to exploit drafting, i.e., placing VAWTs in the wake of other VAWTs.
Clusters (wind farms) of horizontal-axis wind turbines (HAWTs) are currently the most efficient way to convert wind energy into electrical power. However, HAWTs have fairly stringent location and spacing requirements. The efficiency of a HAWT is particularly sensitive to the wake of other HAWTs. The most efficient arrangement of HAWTs requires a relatively large separation between them.
The two main attractions of standalone VAWTs compared to HAWTs are:
- Insensitivity to wind direction
- Ability to perform useful work (e.g., generate electricity) in turbulent air close to the ground
Arranging VAWTs into clusters to exploit drafting can improve the efficiency of each individual VAWT, but the improvement is now sensitive to the direction of the wind. Just goes to show that engineering is all about compromise - rarely is there an ideal solution, or, to quote Voltaire, "The perfect is the enemy of the good."