Re: four elements for EV acceptance - or one alternative

["Darryl McMahon" <darryl@econogics.com>]

Hello again, Peter.  You wrote:
> Your calculations may be correct, but since we are not heating a house
> they are irrelevant.
> 
> A.  Cars don't run on BTUs.
Actually, as I understand it, the internal combustion engine is a 
heat engine, therefore it runs precisely on BTUs.  BTUs being a 
measure of heat energy.  The internal combustion engine 
harnesses a small amount of this energy (from the rapid expansion 
of the content of the cylinder resulting from the burning of the 
gasoline resulting in heating of the gasoline and oxygen in the 
cylinder).  The remainder of the heat energy released from burning 
the gasoline is normally wasted (cabin heating and defrosting being 
minor exceptions).  The fact that we generally choose to rate such 
engines by their optimum mechanical energy output ability does 
not change this.  The internal combustion engine is a means of 
converting chemical energy to heat energy to mechanical energy.

> B.  Relative efficiency is different for EVs than it is for ICEs.
To me efficiency is efficiency.  It is the ratio of useful energy out 
relative to available energy consumed.  In a practical EV, it seems 
to come out around 70% (electricity from the wall socket to power 
at the wheels).  In a typical ICE, it is about 15% (fuel from the 
pump to power at the wheels).
> 
> To put it simply:  a typical EV goes about as far on 10kw of electricity
> (from the outlet) as a similar ICE goes on 1 gallon of gas.
Agreed.  My point is that gasoline is so cheap we can accept the 
fact that it is only used with 20% of the efficiency in an ICE as 
electricity is used in an EV (15% vs 75% in round and evenly 
divisable numbers) and still be competitive on a cents/mile basis.
> 
> Arguing about potential BTUs doesn't change this relationship.  For
> example how many BTUs are available on 1 sq. meter of surface area in full
> sunlight at noon?  
I believe it is generally accepted that a "full sun" is about 1 kWh 
per square meter.  So about 3,412 BTUs.

> These BTUs are free but how far will they move your car?
Depends on what assumptions you care to use.  This is just 
another conversion exercise.  The sunlight can be converted to 
heat for my house, which would offset my fossil-fuel heating 
requirements.  This fuel could then run an appropriately configured 
vehicle (e.g. CNG powered).  There are conversion losses in the 
heating (reflected/absorbed by glazing), but I suppose as much as 
50% might actually be transformed to usable heat energy after 
allowing for the energy used by fans, controls, etc.  (This is 
probably slightly optimistic, but it is a nice round number.)  Taking 
that 50% as CNG fuel, and running it through a 15% efficient ICE, 
gives an effective net efficiency of about 7%. (7.5)

For a slightly higher capital cost than the solar heating collectors, I 
could install photovoltaic panels.  These typically have an efficiency 
of about 9% (commercial grade) converting the available sunlight 
into electricity under near-optimum conditions. (Better efficiency 
panels are available, but I can't afford those.)  Taking this 9% and 
running through a 70% efficient EV, gives an overall efficiency of 
about 6%. (6.3)  

I expect I would not get far with either conversion mode. Nasty 
conversion losses either way.  Assuming I can get about 90 Watts 
peak from a square meter of solar cells for an hour, this is 90 Watt 
hours.  My EV gets about 3 miles to the kWh, so 90 Watt-hours 
would get my EV about a 1/4 of a mile.

Sorry to have rambled on.


Darryl McMahon          48 Tarquin Crescent,
Econogics, Inc.         Nepean, Ontario K2H 8J8
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