From: stead@skadi.CSS.GOV (Richard Stead)
Newsgroups: sci.electronics,sci.energy,rec.autos
Subject: Re: Flywheel batteries as EV power source
Date: 23 Dec 92 17:48:12 GMT
Followup-To: sci.energy

In article <1992Dec23.015933.24919@erg.sri.com>, rat@erg.sri.com (Ray Trent) writes:
> Is anyone here missing the point that flywheel powered cars need far
> less total energy to go a certain distance (stop and go) than a
> gasoline powered car? Car designers aren't completely stupid, you
> know, they do try to recover kinetic energy during braking in a
> vehicle that is capable of doing so (gasoline engines aren't). Also,

In city driving, that is where a major portion of the energy is lost,
but not in highway driving.  Regenerative braking is not terribly
efficient, especially if you want safe brakes that can act quickly,
gradually, bring you to a full stop or just slow you down a bit.
Even if you can get regeration to 50% efficiency, and have really bad
stop and go traffic so that 50% of the energy is going to re-acceleration,
then you've only saved 25% of the energy.  So 400 MJ goes to 300 MJ,
300MJ is still a huge explosion.

> flywheel vehicles aren't really intended to provide as high a range as
> gasoline powered vehicles, nor are they intended to be used for
> towing. We're talking commuter cars here.

But the Company making the claims talked about a 600 mile range in
Popoular Science.  That's not a short commute.

> Additionally, gasoline engines are basically heat pumps. A large
> percentage of the energy escapes in the form of heat out the exhaust
> pipe in normal operation. This much energy, at least, would not
> present in a flywheel.

Q losses would be present however, as well as losses involved in maintaining
vacuum and maintaining magnetic suspension.  These are energy losses that
occur before the power ever gets to the motor.

> Electric motors are much more efficient than gasoline engines, there's
> absolutely no question about that...the inefficient part about using
> electric motors in cars is getting the electricity into the car in
> usable form (charging losses, discharging losses, efficiency of power
> plants, efficiency of power lines, etc).

Absolutely true, however they aren't 100% efficient either.

I would like to point out that an electric motor is the same thing you
have in a standard electric vehicle, and that regeneration applies
equallly well to this vehicle.  The "big problem" with lead-acid storage
is the weight.  All of the savings associated with vehicle design
changes can be applied to the standard electric as well.  Then the battery
problem becomes less and will remain more practical than flywheels
for any vehicle design.

> The actual amount of non-lossy energy it theoretically takes to get
> from point A to point B is much smaller than you might think in terms
> of heat.

Depends on what you consider loss.  The standard physics environment
of no gravity, smooth frictionless plane, no air, etc., says the only
energy that is real (not "loss") is that required to accelerate the car
initially.  That is tiny indeed, but irrelevant.  The real world has
air, friction, vibration, inefficiencies, etc.  The whole discussion
of the energy involved to this point, including all the forgoing
computations has assumed that the electric vehicle is much more
efficient than the gas one.  Are there any gas vehicles that
can go 600 miles on 2 gallons of gas?

> Actually, though, the thing I'm curious about is: how do they manage
> to find strong enough materials to make the mounts that connect the
> counter-rotating flywheels? There's one hell of a lot of precessional
> energy released in a change of orientation of even minor proportions,

And if this energy is not recovered, it represents more losses.


--
Richard Stead
Center for Seismic Studies
Arlington, VA
stead@seismo.css.gov