Newsgroups: sci.energy

A great deal is made of the following calculations, which basically try
to indicate how many kilowatt hours per mile my car should use, vs
my own evidence.

In particullar, Mr. De Armond, Mr. Coffman, and Mr. Cage attempt to put 
forth the notion that these calculations are based on undenyable physical
principles, when in fact, there are a considerable number of questionable
assumptions involved.

I can only go by my own results, however I would like to point out some
of the inconsistencies in this posting:

>gary@ke4zv.uucp (Gary Coffman)
>In article <+vnh4=@dixie.com> jgd@dixie.com (John De Armond) writes:
>>bg055@cleveland.Freenet.Edu (Stewart Rowe) writes:
>>
>>
>>>This attempts to summarize the various postings on this and other
>>>boards regarding the question: Do electric cars reduce the emission
>>>of carbon dioxide compared with gasoline-fueled cars?
>>> 
>>>I. Power requirement of electric car:
>>> 
>>>Paul Houtz says his converted Ford Tempo goes 50 miles on an 8 KWH charge.
>>>This figures to   ** 0.16 ** kwh/mile
>>>John DeArmond quotes Kornhaus as saying Houtz uses
>>>                ** 1.5 ** kwh/mile

   Okay, let's take this figure.  1.5 kwh/mile.   This is what the 
   anti-electric crowd would like you to believe as "reasonable".

   I travel on average about 32 miles per day in my car from Solar Electric.
   I judge my kwh consumption by figuring the average amperage registering
   from the charging ammeter over an 8 hour period, times the 8 hours, times the
   110 volts from the outlet.

   For the sake of argument, however, I will use the "1.5 kwh/mile" figure
   and do some calculations:

    32 miles * 1.5 kwh = 48 kwh per day
    30 days * 48 kwh per day = 1,440 kwh per month.

   This figure is double what my normal PGE usage is, around 600 - 700 kwh
   per month.   If I ADDED this to my former usage, the amount is nearly
   2200 kwh per month.   This is what I SHOULD be seeing, if this figure is 
   correct.   Is this what I am seeing?   Of course not.

   Then what ARE my results.   The bill has increased (as near as I can make
   out with varying usage from other appliances) about $10 to $22 per month,
   or 280 - 310 kwh per month, and divided by 30, this comes out to around
   5 - 8 kwh per day.   The calculation is not completely accurate, as I am
   using $.07 for the rate, and it is actually slightly higher than this, 
   but there is a discount for the first 330 kwh used, so the formula is
   complex.

   Obviously, however, from my direct experience, the 1.5 kwh per mile
   figure is completely wrong, so far off as to be laughable.

>>Thanks for the nice summary.  I just want to clarify one thing.  I am
>>very uncomfortable with the power per mile figures we're using.  I 
>>used the 1.5 kwh/mile figure only to be consistent with others' calculations.

   Good for you.   It is obviously WAY off.

>>Coastdown tests I've done on a few cars indicate that from 12 to 20 hp 
>>are needed to maintain 50 mph on level ground.  This is also consistent

   Yet I have seen figures in the 2 - 4 hp range for 50 mph.   So, I am
   not clear on your reference.   Perhaps you could post a source for 
   such numbers, then we could all be satisfied.

>>with numbers I've seen published in auto magazines.  If these numbers are
>>true, that would indicate (at 746 watts per HP) that between 9 kw
>>and 15 kw continuously would be required.  At 50 mph, that would be 
>>between 0.18 and 0.3 kwh/mile.  working backward, given 85% efficiency

   I would be interested in how you came to the conclusion that 15% of
   the power is lost between the batteries and the wheels.   For instance,
   you have not even specified what the drive wheel configuration is. 
   This statement is so innaccurate as to be ludicrous.  Are you talking
   about a front wheel drive vehicle or a rear wheel drive vehicle?


>>from battery to wheels, that would be 0.21 to 0.35 kwh/mile.  Using 

   So this assumption is entirely meaningless...

>>70% charging efficiency, it works out to 0.35 to 0.44 kwh/mile.

   And I have to question this assumption, as well.  I have no 
   idea what the charge efficiency of MY charger is.

>>As a check, I went back and looked at this from another angle.
>>Consider a car that gets 25 mpg.  Using 18,500 BTU/lb for the 
>>energy content of gasoline and 6.2 lbs/gal for density (_Internal
>>Combustion Engine Fundimentals_, John Heywood), I calculate a 
>>gross energy usage of 1.344 kwh/mile.  At 30% efficiency, that 
>>works out to 0.40 kwh/mile net.  This compares very good with the 
>>0.35 to 0.44 kwh/mile figure estimated in the previous paragraph.

   So, you are using the efficiencies of a gasoline engine to
   determine if the your calculations regarding an electric engine
   are sensible.   Scientifically speaking, this is total hogwash.

>John, my calculations back this up, using Paul's Tempo as a model I
>get .46 kWh/mile *rear wheel* at 65 MPH. But please note that that 

   Now, you have switched from 50 MPH to 65 MPH.  Interesting.  
    
   And, you indicate "rear wheel", which makes me believe you are 
   talking about a rear wheel drive vehicle, and speaking of the end
   of the drive train.   

   This gives you an idea of how totally off these calculations are.

   To give you the benefit of the doubt, I *never* drive my car at
   65 MPH, except downhill, not because it won't go that fast, but 
   because I see no need.  It is also illegal on all the freeways
   within my 30 mile one-way range.  I make no apology for this.  It
   is a simple fact for electric cars.   If you want to argue about
   limited range, then you will finally be on FACTUAL ground.

   So, I have *no* idea what the efficiency is at 65 MPH.  It wouldn't 
   surprise me if it is *terrible*.  My vehicle can hardly maintain 65 MPH 
   on any but the slightest of inclines.      


>calculation was for level ground, steady speed, no wind, and *no hills*. 
>In real world driving with accelerations and hill climbing, and no 
>regenerative braking, the situation is at least three times worse 
>according to Southern California Edison's fleet experiments.
 
    I would very much like to see you post information about these fleet 
    experiments, Gary.   Since you know about them, it is likely that you 
    have the information at hand.  Please post it.  


Basically, the calculations that Cage, Coffman, et al, have posted in an
attempt to discredit my figures about my electric car are such a mish-mash
of assumptions and occaisional fact that they are useless in making any 
predictions about my energy usage.

 I believe that the results I am getting represent REAL reductions in
 per mile CO2 output and fossil fuel usage, and nothing posted so far
 has successfully disputed my results.

 
Newsgroups: sci.energy