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
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.
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.
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