While the specific wind velocity needed to obtain "useful energy" depends greatly on the application and technology used, a commonly cited minimum wind speed for electricity generation is approximately 15 km/h (or about 9.3 mph).
However, let's break down what makes energy "useful" and how wind velocity impacts this:
Factors Affecting Useful Energy from Wind
- Technology: Different wind turbines have different cut-in speeds (the minimum wind speed needed to start generating power). Smaller turbines might have lower cut-in speeds than larger, utility-scale turbines.
- Application: "Useful energy" can mean different things. For example, a small wind turbine powering a remote cabin might find lower wind speeds useful, while a large wind farm needs higher, more consistent winds to be economically viable.
- Efficiency: The efficiency of a wind turbine, and thus the amount of useful energy it can produce, increases significantly with wind speed. This is because the power available in the wind is proportional to the cube of the wind speed (P ∝ v3).
- Location: Local wind conditions, including average wind speed, turbulence, and direction, significantly impact the overall energy output.
- Definition of Useful: What constitutes "useful" depends on energy needs and the cost-benefit analysis. Even low wind speeds can provide some energy, but whether that energy is worth the investment depends on many factors.
Wind Turbine Cut-in Speeds
- Typical Range: Most modern wind turbines have a cut-in speed around 3-4 meters per second (approximately 6.7 - 8.9 mph or 10.8 - 14.4 km/h).
- Utility-Scale Turbines: Larger turbines often have slightly higher cut-in speeds.
Beyond Electricity Generation
It's important to remember that "useful energy" from wind isn't limited to electricity generation. Historically, wind power has been used for:
- Sailing: Wind propulsion for boats and ships.
- Grinding Grain: Windmills for milling grain.
- Pumping Water: Wind pumps for irrigation and livestock watering.
These applications can be "useful" even at lower wind speeds than those required for efficient electricity generation.
In conclusion, while a wind speed of approximately 15 km/h (9.3 mph) is often cited as a minimum for efficient electricity generation with modern wind turbines, the true minimum speed to obtain "useful energy" depends heavily on the specific application, the technology used, and the definition of "useful."
