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Theoretical power extracted from wind depends on air density, swept rotor area, wind speed cubed, and the turbine's power coefficient (Cp). Real turbines achieve Cp of 0.25–0.45.
Annual_kWh = 0.5 × ρ × A × V³ × Cp × 8760Rotor swept area determines how much kinetic energy the turbine captures. Doubling rotor diameter quadruples swept area and potential output.
A = π × (D/2)²Divide net installed cost by annual energy value. Include tower cost, interconnection fees, and maintenance. Small wind typically requires 50 ft+ tower height for viable ROI.
Payback = Cost / (kWh × rate)Updated: July 2026
A 7 m diameter turbine on a 80 ft tower at 5.5 m/s average wind speed.
→ Annual output: ~12,000 kWh; at $0.14/kWh payback: ~33 years — marginal without incentives
A 5 kW turbine at 6.5 m/s on open agricultural land with $0.18/kWh rate.
→ Annual output: ~10,500 kWh; value: $1,890/yr; payback: ~18.5 years
Replacing $0.45/kWh diesel generation with a 3 kW turbine at a remote site.
→ Annual savings: $2,025; payback: ~12 years — viable off-grid economics
Wind speed increases with height. A 5 m/s reading at 10 m may be 6.5 m/s at 80 ft hub height. Use wind shear exponent (typically 0.14–0.20) to extrapolate.
Turbines need clear exposure for 300 ft upwind and 100 ft downwind. Trees, buildings, and ridgelines create turbulence that reduces output 20–40% below predictions.
Budget $500–1,500/year for inspections, lubrication, and component replacement. Gearbox and bearing failures on small turbines are common after year 7–10.
Small wind turbines (1–100 kW) can offset rural or off-grid electricity costs when sited in Class 3+ wind resources. This calculator estimates annual energy production from rotor geometry and wind speed, then computes payback against installed cost and local electricity rates.