A 3 kW nameplate on the brochure is not 3 kW at your chimney. Small wind economics live or die on hub-height wind speed, and hub-height wind speed obeys v³ arithmetic—not marketing optimism.
Cubic power: the non-negotiable math
If average wind rises from 4 m/s to 5 m/s:
P₂/P₁ = (5/4)³ ≈ 1.95 → nearly double the energy
Drop from 6 m/s to 4 m/s:
(4/6)³ ≈ 0.30 → 70% less power from the same rotor
That is why installers obsess over one more m/s on the mast. It is also why a “breezy” backyard at ground level may be a poor turbine site at 12 m.
Tower height and obstacles
Wind near the ground is slowed by friction and turbulence. Houses, tree lines, and berms create:
- Wake deficits downwind of obstacles
- Turbulence intensity that fatigues small rotors and cuts efficiency
- Vertical shear — wind may be 50–100% stronger just above the roofline
Rules of thumb for planning (not permitting):
| Practice | Why |
|---|---|
| Hub well above roof/trees (often 10 m+ clear) | Escape slow, chaotic layer |
| Prevailing wind sector open | Unobstructed fetch |
| Avoid mounting on short patio masts | Looks cheap, performs worse |
Measure at proposed hub height for a year if possible. Ground-level handheld readings mislead.
When small wind pays vs. solar-only
Favors wind:
- Open rural parcel with documented mean wind > 5–6 m/s at hub
- Night loads (EV, heat, backup) you want to offset
- Existing tall tower or barn with structural path
Favors solar first:
- Suburban lot with tree canopy
- Weak mean wind (< 4 m/s) even after mast
- HOA / noise / shadow flicker constraints
Run the calculator with conservative wind and realistic efficiency (30–40%). Compare annual kWh to a PV array occupying similar budget.
Small wind is not “free energy.” It is cubic energy—paid for in steel height and honest wind data. Skip either and the turbine becomes lawn art.