Re: [Phys-l] Wind generator output versus wind speed.

[Brian Whatcott <betwys1@sbcglobal.net>]

At 09:44 AM 4/3/2008, Rick Tarara, you wrote:
> ...
> We have the Pasco Energy Transfer Generators and are putting together a wind
> energy lab, but we're also seeing a linear dependency (using a three speed
> fan). ...

> Rick

This is a scientific observation, and I would like to understand it correctly.
Rick correctly relates wind speed and the available wind power as a cubic,
or perhaps even better, the difference of two cubics.

In his model environment, he has a wind source provided by a three speed
fan.     One can suppose he measures the electrical power input to the fan
and also its output wind speed.
   He may possibly see a cubic relation between electrical power input and
wind speed output on a three point graph, but probably not, because the
fan is  (I imagine) a fixed blade arrangement.   And he may be directing
 the airflow into a generator fitted with fixed blades.
 He may then be measuring the generator output voltage, and may possibly
 be providing the generator with a variable load, which he can vary so as
 to maximize the electrical power generated at given airspeeds?
 I apologize for the number of assumptions I am putting into action here
- I have no insights into Pasco's recommended protocol as you may have
 guessed.

It seems to me better to proceed from this example experiment,
 and generalize from its data where possible.

 Just reading this description of Rick's experimental arrangement
(in my imagined form at least) may already be allowing you to think,
 "Did I really expect to deploy two energy conversions both nominally
 involving cubics, but with numerous sources of speed sensitive
inefficiencies, and expect to see a neat cubic curve emerge?"

The same sort of considerations may also be applied to the
 slide 11 curves - though one assumes that the windmill blades are
provided with variable pitch arranged for constant speed given
sufficient wind.



Brian Whatcott    Altus OK    Eureka!