This may or may not have been said yet and if it has, then i apologize for the repeat.
Also let me start by saying that i am a proponent of efficient tech and sacrifices(cost) necessary for clean tech and i am, in fact, currently engaged
in prototyping some of this stuff. That being said, i'd like to point out a few errors in some thinking as it relates to cars, energy, and
When discussing energy and its use, one must consider the entire sequence, starting at the actual energy source and going to the final energy sink,
taking into account all the conversions (and losses) along the way. So lets do this for each option: there are four that i think are worth
considering (many others are fringe and have yet to prove themselves)... and am not including fuelcells here: too expensive.
1. heat engine (any fuel consuming prime mover)
2. pure electric
3. expander (air powered)
4. hybrid (heat engine + electric)
: Directly converts chemical energy into car locomotion. Roughly 30% thermo efficiency(give or take depending on cycle)
: Converts stored electric potential into car locomotion. Roughly 80-90% electric efficiency (losses at battery, motor and
controller). But this stored electricity comes from power plants at transmission losses. These plants operate at roughly 30% also (baring modern
cogen [turbine + steam] plants). So we start with 30% heat efficiency, take 5% off for transmission losses (not even considering stress to maxed
electric grid) and the 30% drops to 28%. Now remove the 20% (ish) losses at vehicle itself and 28% drops to 22%.
This is a significant reduction compared with pure heat engine conversion. That being said, i also appreciate that many more complicated factors can
be added to this analysis (heat engine idling being just one) that may change this arithmetic.
Finally, if pure electric is directly solar thermal/electric sourced, the math swings heavily in pure electric's favor, particularly if the source is
local (means on the property)
(air powered). This device converts stored gas pressure (usually air) into auto locomotion, and like electric, it does so with out
any emissions (at the vehicle). Also, like electricity, the air is an energy media used as an energetic transfer from some primary source and again,
like pure electric, this source is a heat engine.
Only this time we add one more step in the transfer: that of first compressing the air. The process is: heat engine, compressor, expander (car
'engine'), motion.... and there are major losses at compression. In fact, roughly 50% of the energy used to compress the gasses are lost to heat.
Nobody talks about this: 50% of the energy bound in compressed gasses are in the form of heat. In a heat engine, this heat is useful and used
(largely). In an air motor, all this heat is gone (thermally leaked back into the environment) and only the actual pressure is used.
So our 30% becomes 15%. Add the 10% (ish... i'm being generous here: most expanders are roughly 80% efficient) losses at the vehicle and we have a
total of 13% ish over all thermodynamic efficiency.
In my opinion,The expander is the worst of the lot.
(heat engine + electric). In my opinion, this is the very best choice (barring solar sourced pure electric). We have the benefits of a
heat engine prime source (even better if using the Atikinson cycle) added to most of the benefits of pure electric (no idling at stops for one: quite
traffic jams!) with one more huge advantage over pure heat engine.
This comes in the form of regenerative braking: the conversion of braking forces into energy or kinetic energy recapture. This is why hybrids get
better millage in the city vs. the highway: they recapture (some portion) of their kinetic energy and recharge the battery as a result.
The overall thermodynamic picture changes and we can see a net increase (due to recapture). I have no numbers to give quantitative values to this
assertion, but the logic is sound.
Imagine hybrid trucks reconverting the uphill fuel use into downhill energy storage. Given the masses of the vehicles, the energy saving would be
mark my words: ultra-clean heat engines + electric (regenerative) drive trains with on board storage will dominate.
edit on 1-3-2012 by galactix because: edit