The following data is summarized from a presentation by Paul Kühn, Fraunhofer-Institut für Windenergie und Energiesystemtechnik (IWES), at Husum, Germany, March 20, 2010 based on observations of performance of 253 small wind turbines from 1989 to 2003.

In the fall of 2009, Herr Kühn surveyed 51 operators by telephone.

Kühn divides small turbines into two classes.

- S: <200 m2 (~16 m dia.), <75 kW; examples; Lagerwey 15/75, Aeroman 14.8 m, Krogman 15/50, nearly any Danish wind turbine from the mid-1980s.
- XS: <40 m2 (~7 m dia.), <10 kW; examples, LMW 2500, Easywind.

The Bergey Xcel and Southwest Windpower’s Skystream would fall within Kühn’s XS category.

The most important question was, “Are they still running?”

- S: 22 are still running, 6 not
- XS: 8 are still running, 15 are not

Of the SX category two-thirds are not running, only one-third are.

Second important question, how many years have they been operating?

- S: 17 years for those still running, 13 years for those not running
- XS: 12 years for those still running, 7 years for those not running

Most surprising, and possibly most damning is the average annual reoccurring cost. For comparison, large turbines (L), the average cost in the IWES program is €0.015/kWh.

- S: €0.035/kWh ($0.05 CAD/kWh, $0.05 USD/kWh)
- XS: €0.16/kWh ($0.23 CAD/kWh, $0.22 USD/kWh)

Equally damning is the average performance. The Average Annual Specific Yield for small wind turbines is a fraction of that for large wind turbines. For comparison, the yield at a good site in Germany is more than 1,000 kWh/m²/yr and at interior sites in the range of 800 kWh/m²/yr.

- S: 250 kWh/m²/yr
- XS: 100 kWh/m²/yr

Kühn also observed that small Vertical-Axis Wind Turbines typically use much higher rated wind speeds than typically found on small Horizontal-Axis Wind Turbines.

Kühn and IWES provide a handy Small Wind Turbine Yield Estimator that can be downloaded in English.

Presentation by Paul Kühn, IWES (auf Deutsch)