IDAU & EM + others

Folding or feathering propellers have been used on sailing boats to reduce drag when under sail. Variable pitch propellers are used on ships to control speed at set engine RPM.

I suppose that so far, it has been cheaper to jam or brake wind turbines. In the UK, the operators get paid subsidies if it is too windy, and subsidies are more important than anything else in wind turbine economics.

It doesn't add up

Quite possibly. The graph in your link shows increasing output from the cut-in windspeed to the windspeed at which rated power is achieved.

My generator physics is very rusty. IIRC you have to maintain constant rpm to produce 50Hz AC. Can a generator absorb more torque to generate more power while maintaining constant rpm?

Alan Kendall & SandyS The Great Tea Race of 1866 (see Wikip) represented the peak performance of cargo carrying by sailing ships. The opening of the Suez Canal changed the economics, as sail only ships could not use this shorter route. Average speeds for Clippers were over 15 knots, with the right wind behind them.

The temperature of the seawater was not relevant, and windspeed would have been estimated by use of the Beaufort Scale. What is Jonathan Leake making comparisons with, to determine speeds have increased?

Nobody knows what the Chinese data was, that was lost by Phil Jones. Of course, that includes Phil Jones. Perhaps there will be an academic argument about the types of bucket used for recording wind speed. Alternatively, there could be constructive discussion about the degree of accuracy required to throw this data into a bucket.

Tea Clippers were designed for Trade Wind Sailing. The sails were predominantly square rigged, and not suitable for sailing towards the wind. A modern variation of the Square Rigged Sailing Ship is Maltese Falcon Yacht (Wikip) I am not aware that any commercial shipping company has shown serious interest..

Smaller wind turbines will be stall regulated, rather than pitch regulated. The effect is that they actually tend to have a drop off in power output at higher wind speeds below cut-out.

Pitch vs stall

Entropic man

I doubt the output from the windmills is constant over the wind speed range you cite. 0.5MW is probably the maximum, but I would guess that isn't reached until over 10 m/s wind speed.

Rhoda

IIRC the turbines up the road from me turn at 30 rpm and are governed to turn a 6-pole generator at 300rpm and generate 0.5 megawatt each. This remains constant between windspeeds of 2M/sec and 20M/sec.

Below 2M/sec there is insufficient torque to turn the generator. Above 20M/sec the blades feather to limit the stress.

rhoda:

Only over a portion of the range of wind speed does the actual output rise roughly in line with the theoretical cube law.

At higher speeds, it gets limited, and higher still it gets curtailed altogether. At low speeds there's not enough energy to operate.

Basic guide

Doesn't power out of a wind turbine vary as the cube of windspeed?

Sandy S. A question I asked myself, especially as they couldn't rule out El Nino as a cause. This seems to imply observations over a rather short time period. But I only had the ST news item to go on. I posted it because I thought it interesting, and because it might stimulate some other BHer to look at it further.