Small, airborne and traditional wind: Efficiency

Why small turbines catch so little of the wind

What this tab covers How much of the energy available is actually captured or extracted, in per cent: theoretical limits, laboratory records, typical new equipment and in-service averages, each with exactly what is being measured.

Every open rotor, large or small, is bound by the 59.3% Betz limit. Small turbines sit in slower, more turbulent wind near the ground, so their annual output is low: US small turbines averaged a 14% capacity factor in 2025.

Chart: Efficiency ranges

Theoretical limit Commercial Record In service

Efficiency by measure

Measure	Range	Type	What is measured
Betz limit	59.3%¹	Theoretical limit	Maximum share of wind kinetic energy through the rotor area that any open rotor can capture
Savonius (drag-type vertical-axis) rotors	5 to 30%²	Commercial	Maximum averaged power coefficient reported for most tested configurations (review of experiments and simulations)
Best modified Savonius rotors	40%¹¹	Record	Power coefficient of the best blade-shape modifications reported in a 2023 review
Large three-blade turbines, for comparison	40 to 50%¹	Commercial	Power coefficient between cut-in and rated wind speed
US small wind (up to 100 kW), 2025	14%³	In service	Average capacity factor across 69 projects
Wind-assisted ships	5 to 20%⁷	In service	Share of a ship's propulsive energy supplied by retrofitted sails or rotors

Where the energy is lost

Step	Loss
Low and gusty wind near the ground and around buildings	main reason small turbines average 14% capacity factor³

Small turbines lose out on two counts. Drag-type rotors such as the Savonius extract much less than lift-type blades. More importantly, small turbines sit on short masts where wind is slow and turbulent; since wind power rises with the cube of speed, a modest drop in wind speed cuts output sharply. Airborne systems aim to escape this by flying at up to 800 m. Sails on ships are judged differently: their output is thrust, measured as the share of propulsion energy they replace.

Sources

Physical limits of wind energy within the atmosphere and its use as renewable energy: from the theoretical basis to practical implications (Kleidon, Meteorologische Zeitschrift 30(3)) arXiv (author manuscript of peer-reviewed paper), 2021
A review on the performance of Savonius wind turbines (Akwa, Vielmo and Petry, Renewable and Sustainable Energy Reviews 16(5), 3054-3064) Elsevier, 2012
Distributed Wind Energy Technologies Data Update: 2026 Summary (calendar year 2025 data) Pacific Northwest National Laboratory, 2026
Wind-powered cargo ships sail past the 100-vessel milestone American Journal of Transportation, 2026
Investigation of performance enhancements of Savonius wind turbines through additional designs (Altan and Gultekin, Processes 11(5), 1473), review MDPI, 2023