# Small, airborne and traditional wind: Efficiency

Why small turbines catch so little of the wind

Source page: https://www.materialinsights.org/energy/e_small_wind/efficiency/

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](https://arxiv.org/abs/2010.00982) | 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](https://doi.org/10.1016/j.rser.2012.02.056) | Commercial | Maximum averaged power coefficient reported for most tested configurations (review of experiments and simulations) |
| **Best modified Savonius rotors** | 40%^[11](https://www.mdpi.com/2227-9717/11/5/1473) | Record | Power coefficient of the best blade-shape modifications reported in a 2023 review |
| **Large three-blade turbines, for comparison** | 40 to 50%^[1](https://arxiv.org/abs/2010.00982) | Commercial | Power coefficient between cut-in and rated wind speed |
| **US small wind (up to 100 kW), 2025** | 14%^[3](https://www.pnnl.gov/sites/default/files/media/file/DW%20Energy%20Tech%20Data%20Update%20-%202026%20Summary.pdf) | In service | Average capacity factor across 69 projects |
| **Wind-assisted ships** | 5 to 20%^[7](https://www.ajot.com/news/wind-powered-cargo-ships-sail-past-the-100-vessel-milestone) | 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 factor^[3](https://www.pnnl.gov/sites/default/files/media/file/DW%20Energy%20Tech%20Data%20Update%20-%202026%20Summary.pdf) |

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

1. [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))](https://arxiv.org/abs/2010.00982) arXiv (author manuscript of peer-reviewed paper), 2021
2. [A review on the performance of Savonius wind turbines (Akwa, Vielmo and Petry, Renewable and Sustainable Energy Reviews 16(5), 3054-3064)](https://doi.org/10.1016/j.rser.2012.02.056) Elsevier, 2012
3. [Distributed Wind Energy Technologies Data Update: 2026 Summary (calendar year 2025 data)](https://www.pnnl.gov/sites/default/files/media/file/DW%20Energy%20Tech%20Data%20Update%20-%202026%20Summary.pdf) Pacific Northwest National Laboratory, 2026
4. [Wind-powered cargo ships sail past the 100-vessel milestone](https://www.ajot.com/news/wind-powered-cargo-ships-sail-past-the-100-vessel-milestone) American Journal of Transportation, 2026
5. [Investigation of performance enhancements of Savonius wind turbines through additional designs (Altan and Gultekin, Processes 11(5), 1473), review](https://www.mdpi.com/2227-9717/11/5/1473) MDPI, 2023

## Other sections

- [Summary](https://www.materialinsights.org/energy/e_small_wind/index.md)
- [Overview](https://www.materialinsights.org/energy/e_small_wind/overview/index.md)
- [Correlation](https://www.materialinsights.org/energy/e_small_wind/correlation/index.md)
- [Techniques](https://www.materialinsights.org/energy/e_small_wind/techniques/index.md)
- [Resources and labour](https://www.materialinsights.org/energy/e_small_wind/resources/index.md)
- [Impact on the biosphere](https://www.materialinsights.org/energy/e_small_wind/biosphere/index.md)
- [Relationships](https://www.materialinsights.org/energy/e_small_wind/links/index.md)