Since Wh/mi is not only a logical measurements
("how many 'pounds' of electrical energy does it take
to move my car this distance" - comparable to volume of petrol)
it is also speed-dependent: you can trade speed (more time invested)
against more electrical energy invested, for example I know that my pack
holds a
theoretical 30kWh of which about half is available due to the rate of
discharge of the lead-acids (Peukert).
At freeway speeds, my inefficient truck uses more than 600 Wh/mi so I
can barely get 25 mi range, but if I use secondary roads and the
consumption drops to below 500 Wh/mi (still very inefficient due to the
automatic transmission that converts a lot of useful energy into heat)
then I can eek out a range of 30 miles if I really need to. (It also
helps that Peukert will back off at lower rate of discharge, so I can
use a little more of the stored energy in my batteries)
Cor van de Water
Chief Scientist
Proxim Wireless Corporation http://www.proxim.com
Email: [email protected] Private: http://www.cvandewater.info
Skype: cor_van_de_water Tel: +1 408 383 7626
-----Original Message-----
From: [email protected] [mailto:[email protected]] On
Behalf Of Roger Stockton
Sent: Monday, March 25, 2013 3:42 PM
To: [email protected]; Electric Vehicle DiscussionList
Subject: Re: [EVDL] EVLN: 10 questions for a Ford electrification
Jim wrote:
> I like to use watt-hours per mile as it gives a more accurate measure
of
> efficiency, but then I'm detail oriented.
Yes, Wh/mi is a sensible way to measure EV energy use, though mi/kWh is
probably an easier way to express it for those used to mi/gal fuel
consumption values (mi/kWh and mi/gal both express energy use in terms
of how far one can travel on a certain amount of energy, and this makes
it easier, I think, for people to get the point once they substitute the
$ cost of a gallon of fuel or kWh of electricity into the expression ;^)
> One of my EV's gets 426 whr per mile and another gets 185.
One of the issues with Wh/mi or mi/kWh is that the value might be
measured at the AC outlet or from the battery, and this can lead to
confusion when comparing values from one source to those from another.
>From an operating cost perspective, it is the Wh/mi or mi/kWh from the
AC outlet that people need to appreciate the difference in EV and ICE
operating costs.
> It's no harder
> to calculate than saying 2.35 miles per Kw or 5.4 miles per Kw.
You need to be careful with units mi per kW is meaningless; the ICE
equivalent is mi per hp.
It is mi per kWh that makes sense.
> Everyone knows what gasoline costs per gallon but few ICE drivers know
> what they pay per KWH for electricity. It certainly gets some of them
> to thinking after they get to the "Wow" part of the conversation when
> educating someone on the economics of driving electric.
>
> Jim - Glendale, AZ (where electricity is 4.125 cents per Kw after 9pm)
(where I'm sure electricity is actually priced by the kWh at all times
of day ;^)
Cheers,
Roger.
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