Engineers have gone to great lengths to make wind turbines as exposed as possible, placing their blades on high towers on hilltops or in desolate, unprotected seas miles from shore. A new study presents an interesting curveball that could open up new avenues for renewable energy generation, demonstrating that turbines placed behind hills can actually produce more energy than those in open areas.
The study was carried out at a university in the Netherlands. Scientists are trying to explore how wind turbines could actually benefit from being placed behind hills in certain situations. The scientists achieved this through an aerodynamic modeling technique called large eddy simulation, which allowed them to simulate the effects of three-dimensional hills on downwind turbine performance.
The simulation was based on a 90 meters (295 feet) turbine with 63 meters (207 feet) blades that was placed 756 meters (2500 feet) behind a hill 90 meters (300 feet) above sea level. In contrast, the team found that this particular arrangement actually increased the turbine's power output by about 24 percent under some conditions.
Dr Stevens explained: "The wind speeds are slower close to the hills and this creates an area of low pressure. This area of low pressure draws in air from above, where winds are much stronger than near the ground. This means wind turbines don't need to be taller to take advantage of strong winds at high altitudes."
This effect is combined with another related to the change in wind direction, which pushes up the strength of the forces sweeping through the turbines as the wind blows over the hills. "Also, the wind above the hill blows differently than the wind near the ground," Stevens said. "This causes the slow-moving air flow to change direction away from the wind turbines, allowing the turbines behind the hill to benefit from the strong airflow."
While the study suggests that some turbines placed behind hills can produce more power in some environments, there are other factors to consider. The simulations showed that this increase in wind would lead to more turbulence, which would cause more wear and tear on the turbine. Scientists are continuing to study whether these benefits outweigh the types of damage that turbines can cause, and whether this performance boost can be replicated in a wider range of real-world settings.