New turbine design

[Tom Foster]

New turbine design maintains output at low windspeed http://www.tradewindturbines.com

[Nick Grant]

It may well turn in low winds as did the old Cretan windmill at CAT in the 80s but the laws of physics remain unchallenged and the power in the wind is proportional to the cube of the speed.

[Tom Foster]

And the power captured is proportional to sail area – yes? So if as wind speed halves, sail area unfurls eightfold, then power captured remains unchanged.

I don't know what the unfurl to windspeed ratio is in this case but it's far greater than the effect of unfeathering a prop-turbine's blades – which AFAIK isn't intended to be used progressively for this purpose anyway. The idea is to allow a small/cheap/lightweight turbine/tower to carry unprecedentedly large sail area, when winds are light, and progressively furl the sails as the wind strengthens.

However, that's seen as a secondary benefit; the main things are its silence, its portability if reqd (MoD sponsored the project), and they are hoping to provide the best kWp per £ on the market (the Proven 8 being 'the competition'). Certified performane figures in a month's time.

[Anonymous]

I too hope it does work out but I'm not convinced by the website.

I'm a bit nervous about the lack of hard technical data on the website and the apparent lack of any specific wind generation or even aerodynamic knowledge and experience in the team biographies.

As regards the design itself, there seem to be a lot of moving parts exposed to the weather for something with high reliability. I'd also like to see the high wind performance analysis, because there are a lot of non-aerodynamic components and especially a lot of wires. Wires have surprisingly high drag coefficients. So the drag will be quite large, perhaps leading to a poor lift-drag ratio in strong winds. The improvement in aspect ratio as it furls will help a bit.

Many traditional windmills furled their sails in strong winds, so there is some precedent, but it will take good performance numbers and a successful extended trial of several turbines in an exposed site to convince me it works well.

[Author]

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