Our wind turbine: measured output

It's becoming clear from our results that the sales brochures of "rated output" from some wind turbine manufacturers are way out.

Government is promoting wind turbines to show how much it loves the environment. Sales literature is therefore unlikely to become more realistic.

We have a 1.4 metre diameter turbine in a windy field mounted at a height of several metres. It's coupled up to a 200Ah battery. We have a continuous load of 30 watts, day and night, and it's lit all the time. The output is - you guessed it - about 30 watts.

Recently the wind speed over a three day period went up to 20 knots, according to Met Office data; which is about 25 mph. We replaced the 30W load with a 60W; it was lit for the windy period, but fizzled out 8 hours after the wind dropped to about 10 mph.

The output is therefore somewhere between 30W and 60W, and rather closer to the lower figure. We're satisfied with this; it's enough for an independent power supply. 30W continuous means 90W if we use it a third of the time (eight hours a day). On the basis of this we would expect a 3m diameter turbine to have an output of about 120W.

For students with a serious interest in fiction, here are published "rated outputs" for 1.5 and 3 metre diameter turbines from different makers. Our measured figures are at the top.

preliminary figures, habitat21 turbine

This is in reasonable agreement with a recent report from Germany where their projected 48 GW of wind power is expected to to deliver 2 GW. The concept of "rated output" is not useful. The sooner it disappears the better. In fairness, it should be said that some turbine companies produce tables of output against windspeed which agree quite well with our preliminary tests.

Nigel Deacon

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