Wind Turbine Tower Height Wind Speed Boost Calculator
Calculate wind speed boost from raising a turbine tower.
Use the wind shear power law to compare hub-height speeds at 30, 50, 80, or 100 feet up.
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:
| Terrain | α (alpha) |
|---|---|
| Open water, smooth | 0.10 |
| Open prairie / smooth grassland | 0.14 |
| Crops, hedgerows | 0.17 |
| Suburban, trees | 0.22 |
| Wooded, complex terrain | 0.28 |
| Urban / built-up | 0.34 |
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):
| Hub Height | Wind Speed | Power Multiplier |
|---|---|---|
| 33 ft (10 m) | 10.0 mph | 1.0× (baseline) |
| 50 ft | 11.0 mph | 1.35× |
| 80 ft | 12.2 mph | 1.81× |
| 100 ft | 12.8 mph | 2.10× |
| 140 ft | 13.7 mph | 2.59× |
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 cost 30-50% of total system cost. Industry rule: tower cost is typically justified if hub-height wind ≥ 11 mph annual average — the “Class 3” threshold.
Site assessment matters more than tower: A poor site with a 100-ft tower beats a great site with a 30-ft tower? Often yes — but not always. Always do a 1-year wind logger study before committing to a tall tower install.