Wind Turbine Tower Height Wind Speed Boost Calculator

Wind Shear Power Law

Wind speed increases with height due to surface friction. The power-law model relates ground-level wind to hub-height wind:

V₂ / V₁ = (H₂ / H₁) ^ α

Where:

• V₁ = reference wind speed at H₁ (typically 10 m / 33 ft)
• V₂ = wind speed at hub height H₂
• α = wind shear exponent (depends on terrain)

Wind shear exponent (α) by terrain:

Why this matters for small wind turbines:

Power output scales with the cube of wind speed: Power ∝ V³

So a 25% increase in wind speed → (1.25)³ = 1.95× the power output, almost double.

Practical examples (10 mph at 33 ft, suburban α = 0.22):

The “120-foot rule”: For most small-wind installations, every doubling of tower height adds ~30-50% more energy. Going from 60 ft to 120 ft typically improves output 30-45%, despite higher tower cost. Most small-wind experts recommend at least 80 ft of clearance above the highest obstacle within 500 ft.

Cost-benefit at hub height: A 100-ft monopole tower can run to 30-50% of the total system cost. The industry rule of thumb is that the tower pays for itself if hub-height wind averages 11 mph or more over a year, which is the “Class 3” threshold.

Site assessment beats tower height A mediocre site with a 100-ft tower usually does beat a good site with a 30-ft tower, because 30 feet puts the rotor in the turbulent, obstacle-shadowed layer where the power law stops applying at all. But that is an argument for measuring, not for buying steel. Run a wind logger for a full year before committing to a tall tower: a single windy month proves nothing, and the seasonal swing at most sites is larger than the difference between two tower heights.

Terrain classes here match the wind shear correction calculator, which does the same arithmetic in metres and lets you set the measurement height. Use this page for a small turbine measured at the standard 33 feet, and that one for anything else.