Swept area

The Swift has a blade diameter of 2.10 metres. This means it has a swept area, or capture area of 3.46 square metres. This is all important when comparing wind turbines, since it directly relates to the amount of passing wind energy the turbine blades can intercept.

Swift power output curve

The graph below shows the power produced (in watts) for the Swift at different wind speeds, based on data supplied by the manufacturer.

The green line shows the actual output that the wind turbine achieves at the given wind speed, according to the manufacturers.The dashed line in the graph shows the theoretical maximum energy that this turbine could extract from the wind, according to Betz's Law (59.3%). At a typical wind speed of 5 m/s, the Swift is extracting 68 Watts of power from the wind, which is an efficiency of 25.54%.

How efficient is the Swift?

Wind turbines can only convert some of the energy in the wind into electricity. The graph here shows how efficient the turbine is across the range of wind speeds you might get.

The orange line in the above graph shows the efficiency ranging from 0 to 1. The grey line is the previously mentioned maximum efficiency - The Betz Limit. If this limit is exceeded, the manufacturer's claims are not to be trusted!

While these graphs give an indication of the instantaneous power and efficiencies you might expect from the Swift turbine, working out annual power production is more complex.

Read more about the Power Predictor

The power output curve as published by Swift is shown below.

Around £5,500 for the system, plus installation which would probably cost about £1,500. The Swift is eligible for grant funding from the Low Carbon Building Programme and the Scottish Community and Householders Renewables Initiative (30% domestic and 50% community) bringing the final capital cost to the end user down to between £3500 and £5000. You must use an accredited installer (you cannot DIY).

An exciting proposition, especially as the claims say there is virtually no noise. It's an elegant design, but when we saw one at an exhibition, it seemed like a fairly large thing to be strapping to the side of your house, and there are of course well-documented problems with roof-mounted machines (as mentioned elsewhere on this site and others).

2.10 metres

1400

Swift have government accreditation so the turbines are eligible for up to 30% grant funding depending on where you live in the UK.

Unclear, but expected lifespan of 20 years

Renewable Devices / Swift

0131 535 3301

UK

Permanent magnet

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Dynamic brake