Friends,
doug wrote:
> Dawie Coetzee wrote:
>
>> A practical rooftop turbine has been quite elusive. If this works it would
>> be something of a breakthrough. The design seems quite simple, its unique
>> feature being that its alternator is attenuated to an annular ring. In
>> principle that's quite open to artisanal manufacture. I wonder how it will
>> work in practice.
>>
>> -Dawie Coetzee
>>
>>
> Indeed, it seems like a simple enough idea to be taken into consideration for
> the DIY designer...
Power in the wind is related to the cube of the velocity. This is one of
the prime reasons that designers of wind electric machines are not
concerned about winds of 2 mph. The fact that this design can generate
power at low velocities is nice/interesting but as a practical matter
more or less irrelevant.
The basic equation for the power available from the wind is power equals
one half rho times area times velocity cubed. Generally that term would
be multiplied by an efficiency factor of anything less than 1. ("rho" in
the equation refers to the density of the air at the location being
measured.)
One can assume a standard sea level air density (0.0024 slugs per cubic
foot), in which case the equation becomes 0.0001423 AV^3 , where A is
expressed in square feet and V is in MPH. This results in a figure for
instantaneous power in watts. Area is of course pi times the radius squared.
Given that this turbine has a swept diameter of 6 feet, it promises to
give us 0.032 watts (dribble, dribble) at 100% efficiency. It is of
course highly unlikely that the turbine would get anywhere near 100%
efficiency, particularly at low windspeeds. When the wind is blowing at
8 MPH, the turbine should generate 64 times the power, but in fact the
efficiency will probably climb along with wind speed up to some point
(20 MPH??) and thereafter will fall again.
d.
--
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
"Make no search for water. But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)
http://bahai.us/
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