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

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

I would think a few calculations involving how much energy is dissipated,
and where it goes would be in order.  Then a few calculations involving the
cost of the scheme would most probably make it extremely cost ineffective.
The idea of recovering some of the lost efficiency of autos is certainly
attractive, but I doubt that more than a small fraction goes into the
roadway.  Actually a better proposal might be to put pipes under the roadway
and use it as a heat source for a generator.  Or put panels over the roadway
for electrical generation.  Roadways are nice open areas which would be
ideal for solar power generation, without significant ecological
consequences.

A better solution than piezoelectric generation would be to make cars more
efficient.  Changing the rolling friction dissipation could save significant
amount of energy and this could be done by better tires.  Hybrids do some of
the braking by conventional means, so being able to do all of the braking
with the motors might save a lot of energy.  And finding a way to reduce
road flexing might be much more cost effective and cheaper than using
piezoelectric generators.

In the end I am pretty sure they slipped a decimal point.  The amount of
energy generation is probably miniscule compared to other possibilities, and
the cost would be prohibitive.  A simple low cost study could reveal that it
is a crackpot idea.  Indeed it might even be possible to do it on the back
of an envelope.  Unfortunately envelopes are not becoming scarce!

John M. Clement
Houston, TX

> As Boris Korsunsky said on physlrnr, this idea does not sound 'obviously
> ridiculous' to him, nor to Charles I think, nor to me. I'm not sure the
> roadway piezo-electric proposal can be dismissed simply by appeal to
> 'conservation of energy', without considering the various energy
> transformations involved, both with and without the roadway piezo-electric
> transducers in place.  Let's assume that some energy is normally
> dissipated as 'heat' in the roadway anyway as cars pass over it and deform
> it slightly. If some of this were to generate energy in piezo-electric
> transducers instead, then energy remains conserved, just in a more usable
> form now, without requiring more energy from the car. The roadway would
> not get as warm presumably? Of course I know nothing of the details or
> mechanism of the proposed system so correct me if I am missing something,
> but I'm just conserving energy without taking more from the car.
> David
> ----