NREL’s field test report on Renewable Devices Swift in 2011 can be found here: Power Performance Test Report for the SWIFT Wind Turbine.

The report is important because in 2008 I wrote (see Renewable Devices Swift Mk II AEO), “Cascade claims on its web site that the Swift Mark II will generate 2,000 kWh/year.

Can it do so?”

Yes, but at sites unlikely to be found in Michigan where Cascade is located and at heights where the turbine was likely to be installed.

The Swift was a 2.1 m diameter wind turbine that swept about 3.5 m². A wind turbine of this size requires an average annual wind speed of about 7 m/s at hub height to generate more than 2,000 kWh/year. Sites this windy are rare in Michigan, especially at the rooftop heights that this turbine is intended to be used.

According to NREL’s tests, the turbine reached its 1.25 kW at 12.5 m/s, not far off from the advertised 1.5 kW in the brochure I have from 2006. However, the web site was still up when this was written and it said that 12 m/s is the rated speed. If that’s the case the turbine reached 1.14 kW or 24% less than advertised. In either case, that’s not bad as far as small turbines go. The turbine’s performance was about par.

Nevertheless, it would take an average wind speed of more than 6 m/s to produce 2,000 kWh per year and more than 7 m/s to generate 3,000 kWh per year based on NREL’s tests. These are not wind speeds found at rooftop, and certainly not in urban areas. These are wind speeds that might be found on a well-exposed tall tower in the Orkney’s or on the west coast of Scotland.

As I wrote—correctly—in 2008 and earlier, the Swift could possibly produce what Cascade Engineering claimed at the time—at only the very best sites, but the turbine could not meet the more outlandish claims of the British manufacturer.