Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

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



Rick,

you found a rotor generator arrangement that gives an output that is linear
in power versus wind speed.
V^2/R proportional to wind speed suggests that with V proportional to
rotation rate and probably proportional to wind speed, you are not extracting
as much power as you expect at higher wind speeds.
How might you do that?
Suppose that if the rotor ran faster, it might provide more power.
One way to encourage that (hoped for) state of affairs might be to unload the
generator, for example with a load resistance of 140 ohms.
Even better, a rheostat to tune power at any wind speed.

Thanks for sharing your results so far.

Brian

At 05:45 AM 4/4/2008, you wrote:
As to your assumptions:

Both the source (fan) and the generator have fixed bladed rotors (fan blade
styles). The load of the generator is fixed (100 ohms) and the output is
fed to a voltage/current sensor and then to a program which calculates and
displays the average power versus time. Once the orientations of fan and
generator are optimized, that power is fairly constant. There is a separate
device (rotational motion sensor) that is used to measure wind speed and we
were careful to keep the distances and orientations as constant as possible.

I did not expect the generator power to wind speed to be cubic but was
somewhat surprised when I found it (admittedly one time through--will redo
the experiment this weekend) to be linear (including 0,0). My 'gut' was to
expect something more quadratic (and indeed I've analyzed some data from a
2MW Illinois generator that fits nicely with a v^2 dependency), but realized
we had a lot of transfers going on--ignored the electrical to fan, but wind
to blade and blade rotation to generator--and also had a fairly narrow range
of velocities (.35-.55 m/s). With John's more complete description it is
clear that we have a very complex system. [Just last weekend drove by a new
wind farm going up in Western Indiana with one of the towers very near the
highway. I did note the twist in the blades and a bend at the end--sort of
like a 747 wing. None of those turbines were yet running--near (and I mean
NEAR) the town of Earl Park, Indiana.]

Rick


----- Original Message -----
From: "Brian Whatcott" <betwys1@sbcglobal.net>
>
> 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!
>

_______________________________________________
Forum for Physics Educators
Phys-l@carnot.physics.buffalo.edu
https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l


Brian Whatcott Altus OK Eureka!