Thanks Arthur, this is an interesting bit of digging, I'll pass it
around for others to read.

On Thu, 9 Oct 2003 06:56:16 -0700, you wrote:

>It has often been raised in this forum a comparison of fuel cells 
>versus batteries for operating cars.  But I've seen no hard 
>documented data.  So I decided to look some up.
>
>The Electric Storage Association has a website 
><http://www.electricitystorage.org> that describes various energy 
>storage technologies and their efficiencies.  Under Li-Ion 
><http://www.electricitystorage.org/tech/technologies_technologies_liion.htm>, 
>they cite an efficiency rate of nearly 100%.  Unfortunately, they do 
>not cover the efficiency of NiMH nor of hydrogen.
>
>The Toyota current Fuel Cell prototype FCHV-4 
><http://www.toyota.co.jp/en/tech/environment/fchv/fchv12.html> has a 
>well-to-tank efficiency of 58% (if the hydrogen is produced from 
>natural gas) and tank-to-wheel efficiency of 50% (with hybrid 
>technology) for an overall efficiency of 29%.  Toyota's ideal fuel 
>cell vehicle has a well-to-tank efficiency of 70% and a tank-to-wheel 
>efficiency of 60% for an overall efficiency of 42%.  They observe 
>that the well-to-tank efficiency of gasoline is 88%.  The Prius 2003 
>had a tank-to-wheel efficiency of 32%, for an overall well-to-wheel 
>efficiency of 28%.  The Prius 2004 has a tank-to-wheel efficiency of 
>37% (2004_Prius_Tech_Pres_08-22-03.ppt).  Under the well-to-tank 
>efficiency of 88% (quoted on Toyota Fuel Cell website), the Prius 
>2004 overall efficiency is 33%.  Under the well-to-tank efficiency of 
>79% (quoted in Prius presentation), the Prius 2004 overall efficiency 
>is 29%, the same as the overall efficiency of the commercial fuel 
>cell vehicle (presumably Toyota FCHV-4) cited at 29% in both places.
>
>Some interesting comparison charts can be found at 
><http://www.worldenergy.org/wec-geis/global/downloads/NZConf/2_08.pdf>.
>
>A detailed article comparing well-to-wheel efficiency is at 
><http://www.memagazine.org/mepower03/gauging/gauging.html>.  They 
>quote battery + all electric as having a "tank"-to-wheel efficiency 
>of only 44% (it is tied for first place with 3 others on their chart).
>
>The 1998 Toyota RAV4-EV was rated 
><http://avt.inel.gov/fsev/rav4/toyrav98.pdf> at 245 Wh/mile (from 
>battery) and 432 Wh-AC/mile (from grid).  That would make 
>"tank"-to-wheel efficiency at 57%.  [At 10 cents/Wh, they quote 4.32 
>cents/mile.]  Note that the 1998 Toyota RAV4-EV had a *conductive* 
>charger, so it was more efficient than the later *inductive* charger. 
>Note that this "tank"-to-wheel efficiency of 57% is comparable to 
>Toyota's 60% tank-to-
>
>So if the ultimate source of energy is electricity, then a battery 
>electric car is the most efficient and beats hydrogen hands down. 
>(If the electricity is locally generated, then the "well"-to-"tank" 
>efficiency would be 100%.  Otherwise, there are decreases that need 
>to be made for )
>
>On the other hand, if the ultimate source of energy is natural gas, 
>then combined heat and power systems can be over 75% efficient (see 
><http://www.aceee.org/energy/nrgeffbrief.pdf> slide 4).  For example, 
><http://www.oceta.on.ca/profiles/admic/admic_tech.html> generates 
>heat with 55% efficiency and electricity with only 30% efficiency. 
>(That's also the figure quoted in 
><http://www.naturalgas.com/consumer/>.)  In that case, well-to-wheel 
>efficiency of the 1998 Toyota RAV4-EV is 30% times 57% or only 17%, 
>while the Toyota FCHV-4 is at 29%.
>
>Conclusions:
>
>If electricity is produced from renewable sources (solar, wind, and 
>even hydro), then there is zero air pollution for battery electric 
>vehicles, and they have the highest efficiency of 57%.
>
>If the energy source is natural gas (and note that usage is eclipsing 
>supply), then Toyota's ideal fuel cell hybrid vehicle would be 42%.
>
>If the energy source is oil, then the Prius 2004 has a well-to-wheel 
>efficiency of 29-33%.


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