Hub height
The height of a wind turbine's rotor centre above ground or sea level; taller hubs reach stronger, steadier winds and are a main driver of rising capacity factors.
Wind speed increases with height because ground friction slows the air nearest the surface, a profile known as wind shear. Raising the hub therefore increases both mean wind speed and energy yield, while also reducing turbulence.
Representative hub heights:
- Onshore, 2000s: 60–80 m
- Onshore, mid-2020s: 100–140 m typical; forested German sites up to 160–170 m; US average around 100 m (Berkeley Lab Land-Based Wind Market Report)
- Offshore: 110–150 m above mean sea level for 12–15 MW machines
Using the power-law shear profile with a typical onshore exponent of 0.2, moving from 80 m to 140 m raises wind speed by about 12% and the power available by roughly 40%:
The trade-offs are cost and logistics. Steel tubular towers are limited by transport diameter (about 4.3–4.5 m in many road networks), so taller towers use hybrid concrete-steel, lattice, bolted-shell or on-site wound designs. Hub height also defines the rotor's lower tip clearance and the turbine's total tip height, a key parameter in planning rules, aviation radar and visual impact assessments. Low-shear sites, such as open plains or offshore, gain less from extra height.
Related terms
All terms →- Wind shear
The change in wind speed (and sometimes direction) with height above the surface, driven by surface roughness and atmospheric stability.
- Swept area
The area of the circle traced by a turbine's rotating blades; wind turbine power output is directly proportional to it, and it grows with the square of rotor diameter.
- Weibull distribution
A two-parameter probability distribution used to describe how often each wind speed occurs at a site, defined by a scale factor c and a shape factor k.
- Wind power density
The mean power available in the wind per square metre of area perpendicular to the flow, in W/m², the standard measure of wind resource quality.
- Repowering
Replacing ageing generating equipment at an existing site with newer, usually larger and more efficient technology, most commonly applied to wind farms after 15 to 25 years.