Re: [Phys-l] [ncnaapt] another crackpot idea from the California legislative assembly

["John Clement" <clement@hal-pc.org>]

I agree that the first law is not the whole story, but some of the schemes
mentioned here do have some first law components that make them not so
attractive.

Capturing the air flow from passing cars will likely produce a back wave
which would increase air resistance for the cars.  In which case the air
turbines are robbing energy from the autos.  The piezo electric idea means
you now have springs under the roadbed which will likely make it more
elastic.  This would again would probably decrease auto efficiency.  The
audio energy source would have negligible interaction, but also negligible
power output.  You have to find schemes which will not rob usable energy
from one source to power another source.  The result of doing that is a
decrease in usable energy due to the second law.

Indeed the devil is in the details.  There are much larger sources of energy
which are more easily tapped such as wave motion.  Thermal and light energy
from the Sun has been tapped in many ways.  This is a case of wasting money
to look at a very small source of energy which is extremely expensive to
tap.  Actually you probably would get more energy from engine shake than
from roadbed deformation.  How about developing more efficient road
surfaces?  Does soft blacktop waste more energy than bare concrete?  Both
should be better than gravel, and certainly better than sand.

A simple way of looking at this is to compare railroad efficiency with auto
efficiency.  Both deform the roadbed, but the railroads are much more
efficient in operation.  So the amount of energy absorbed by roadbed
deformation is not a large percentage of the energy expended by the engines.
If you were to try piezo generation first do it with railroad tracks.  They
have definite points where it is easy to insert the piezo generators.  You
can actually see the tracks deform, but how much do non elevated roadbeds
deform?  The swaying of bridges probably has more energy than the roadbed
downwards deformation, "Galloping Gertie" excepted.  Of course Gertie was
wind driven.

Incidentally the roadbed idea is generating the energy at the wrong time.
It is needed when people are at work or home, not when they are commuting.

The legislature has slipped a decimal point because they can't figure the
amount of energy and the expense of this scheme.  Who came up with it, and
who is paying them for it?

John M. Clement
Houston, TX

> The question that needs to be asked, and I don't know the answer with
> respect to Piezoelectric energy generation, is whether the energy is
> captured energy that would escape into the environment if it were not
> captured by the piezoelectric generator, or if it is a more direct form of
> energy generation, like a generator.
>
> For example, you could set up wind turbines that would capture the wind
> produced by passing cars, or large microphones to capture the sound
> generated by the passing cars.  Neither of these methods would cost any in
> gasoline consumption because they are capturing wasted energy.  No
> violation of the the First Law.  I can think of many others, such as
> capturing the heat that rises from the road, or heat generated by the
> tires on the road.  Some, like capturing the heat generated by the tires
> on the road, might actually improve the gas milage of the cars.
>
> A naive application of the first law is not always going to tell the whole
> story.  Hell, that's why hybrid cars are more efficient!  Look to the
> Second Law!