Wind energy is leading the renewable energy revolution across the globe, becoming a new favorite for large-scale utility power plants while reducing carbon emissions in the process. While many of us are familiar with the Horizontal Axis Wind Turbine—the kind you’ve likely seen in pictures—how these turbines produce electricity can be difficult to wrap your head around. Here’s a crash course on the interesting physics, earth science, and engineering behind wind turbines to get you up to speed. 

Above: Offshore Horizontal Axis Wind Turbines. Image courtesy of ScienceNewsExplores. 

How do wind turbines spin?

Wind turbines don’t spin from the direct force of air against their blades, like the force you feel walking into a stiff breeze. Rather, their blades act like the wings of an airplane. The teardrop-shaped cross-section of the blade creates a pressure differential on both sides, generating lift and causing the rotor to spin.

Above: Diagram of lift generation by a wind turbine blade. Image courtesy of Code7700. 

The angle of attack, or the angle between the blade and incoming wind, is directed by the orientation of the blade and influences the power output of the turbine. To draw the most power from low winds, the blades will rotate into their most efficient angle of attack: think, for example, of a plane angling upwards to climb in elevation. Under extreme conditions, like hurricanes, wind turbines shut off to protect themselves using the same principle. The blades rotate into an unfavorable position, like a plane in a steep descent. 

Why don’t I see more wind turbines?

Despite the growing number of wind turbines, chances are you haven’t seen many of them near your hometown. Due to the way wind interacts with the Earth’s surface, the locations with the most wind often have a low human population. Trees and buildings block and slow down incoming wind, making landscapes like forests and cities unfavorable at ground level for high winds. Even elevated turbines are inefficient in these areas as blocked winds near ground level will slow down winds higher up. 

Above: Map of surface level wind speed in North America. Image courtesy of NREL. 

On land, wind farms thrive in plains or hilly environments. Offshore, the flat ocean is ideal for sustained gusts. While these sites optimize wind turbine efficiency, transmitting electricity from these remote locations to densely populated regions has brought challenges of its own to the wind industry. 

‍How do wind turbines make electricity?

Wind turbines turn slower than you might expect at about 12 rotations per minute (RPM). You can spin faster than this in your desk chair. The key is that wind turbines spin with extremely high torque. In other words, it takes a lot of force to slow them down.  

Above: Nacelle of a wind turbine. Image courtesy of OBO.

Traditional wind turbine designs have used gearboxes as a middleman to turn a high-speed, low-torque shaft at around 1,800 RPM. This shaft then powers a generator, which in turn produces electricity. The electricity is sent through a converter, which converts it to alternating current, and is then pushed to the grid to be used by consumers. 

There’s more than meets the eye when it comes to electricity generation by wind turbines. Their global deployment is a testament to interdisciplinary collaboration. From materials science to meteorology to economics, if you can name the subject, it probably has a role in the growing industry.