Wind speed for wind turbines: unlocking optimal output

The cut-in speed is the minimum speed required for a turbine rotor to overcome friction and begin generating electricity. When the wind is below cut-in, the turbine remains idle. As wind speed increases, power output escalates until the rated wind speed is achieved and the turbine produces maximum or rated power.

Beyond that, turbines maintain performance by adjusting blade pitch. Exceeding the wind turbine maximum wind speed, known as the cut-out speed, leads to automatic shutdown to avoid structural damage.

Wind speeds between 3.5 and 4 metres per second are regarded as suitable for small wind turbines, whereas wind speeds between 5.8 and 8 metres per second are considered suitable for commercial wind turbines.

A turbine’s rotational speed depends on its design and local wind, but they generally make between 10 and 20 revolutions per minute. Wind tip speed is dependent on the length of the blades. Smaller blades may spin at 75 to 100 mph, while larger blades may easily top speeds of 150 mph.

The tip speed ratio of a wind turbine expresses how fast blade tips move relative to wind speed. Optimal values hover around 6–8 for three-bladed turbines, ensuring efficient energy extraction. Higher values increase noise and wear, while too low a ratio reduces efficiency.

Wind speed largely determines the amount of electricity generated by a turbine. Higher wind speeds generate more power because stronger winds allow the blades to rotate faster. Faster rotation translates to more mechanical power and more electrical power from the generator.

Small increases in wind speed yield large gains in power – doubling the wind increases the power eightfold. However, conversion is limited by Betz’s Law, a wind energy principle developed in 1919 by German physicist Albert Betz. This theory states that at most, only 59 per cent of the kinetic energy from wind can be used to spin the turbine and generate electricity.

Low wind speed turbine models are specifically designed for sites where wind speeds seldom exceed 8 metres per second. One example is the N169/5.X, created by the Nordex Group to address the challenge of low wind speeds. This turbine features a larger rotor diameter of 169 metres and a power rating of up to 5.5 MW, significantly enhancing energy yield in low to medium wind speeds.

Professor Erin Bachynski-Polić of the Norwegian University of Science and Technology (NTNU) notes, “Building smaller turbines that work well at lower wind speeds can be an advantage over very large turbines that work best at higher wind speeds”. The “LowWind Project” shows that turbines with larger rotor diameters and lower cutoff speeds can be economical in Northern Europe, despite lower average wind speeds.

Norway has become a global leader in researching, testing and manufacturing wind turbines optimised for a wide range of wind conditions. SINTEF’s WindRise project, supported by Aker Solutions, focuses on foundations for offshore turbines in deep waters where wind speeds are generally higher and more variable.

In floating offshore wind, Equinor’s Hywind Tampen farm proves the viability of turbines in high‑wind environments. Meanwhile, Norway’s Marine Energy Test Centre (METCentre) has secured permits to test five new floating turbines, adding to earlier projects like Zefyros and TetraSpar, which provide valuable knowledge about floating wind farms in strong wind areas. Collectively, these technological strides may pave the way for broader adoption and integration of wind energy into the global power grid.