Re: [Phys-L] electric cars

[Hugh Haskell <haskellh@verizon.net>]

At 2:03 PM -0500 6/20/12, David Marx wrote:
> While we are on the subject, I thought I'd share some information I 
> got at a lecture on battery
> technologies given by one of the developers of the baterries for the 
> Chevy Volt.
>
> The maximum energy density for liquid fuels such as octane, 
> methanol, etc. is 11 000 W-h/kg.
>
> The energy density for the Chevy Volt batteries is 150 W-h/kg, with 
> a maximum theoretical value for
> the current chemistry is about 500 W-h/kg.
>
> The next generation battery chemistries (Ni-Co-Mn, Li-Ti-O) 
> currently being developed will give us
> three times the current energy density, but not be available on the 
> market until after 2020.
>
> This is why vehicle range will continue to hinder the development 
> and sales of electric vehicles going
> forward.
>
> In addition, a 2007 vehicle report in which the lifetime costs, from 
> producing raw materials to usage to
> disposal, were reported for a wide range of vehicles indicated that 
> the costs of hybrid sedans are three
> times greater than the costs of a conventional sedan.  One of the 
> reasons why hybrids are more
> expensive is that there is a much greater number of different kinds 
> of materials that go into them, and
> many of these materials have to be produced all around the world, 
> processed, pre-formed, and
> transported to the assembly location.  The disposal costs are also 
> greater.  This isn't an economies of
> scale problem, so the prices cannot come down that significantly 
> with greater sales volume.

Clearly, the primary limit on the range of an electric vehicle is the 
size of the battery it can carry. But the great disparity in energy 
density of the fuel (gas vs. battery) is partly compensated for by 
the significant improvement in road efficiency of an electric 
vehicle. A quick calculation shows that a ICE-propelled vehicle 
today, using gasoline whose energy density corresponds to the value 
David, gives about 1.3 km per kWh of energy used (assuming it has a 
fuel use rate of about 25 mpg), while a typical electric vehicle 
travels about 2 km on the same energy--about 50% farther than the 
traditional gasoline-powered engine on the same amount of energy.

To travel 500 miles (800 km), then, an electric car would require a 
battery of about 400 kWh capacity, which, even by the optimistic 
future possibility of 1.5 kWh/kg means that the battery will weigh at 
least 270 kg, while the gasoline-powered vehicle will need only about 
60 kg of gasoline, or just under 20 gal, a typical gasoline tank size 
for a mid-size car.

A quick search failed to turn up any data on mass density for these 
batteries, so I am assuming something like 1000-1500 kg/m^3, based on 
the density of lithium and whatever structural materials will be 
needed to construct the battery. I'm also not including any allowance 
for the total capacity of a battery capable of delivering 400 kWh 
without recharging, Given those limitations the battery capable of 
delivering the necessary energy for this hypothetical trip will have 
a volume of at least 200 liters, while the fuel tank of the 
conventional car has a volume of about 75 liters (I know that the 
liter is not a very sensible unit for a solid battery but it does 
enable a straightforward comparison between the two).

I don't see the weight disparity as very important since the electric 
car will not need things like a large engine or a transmission, so 
its weight can easily be quite comparable to a similar-size 
conventional car.

I think the point here is that the range issue is not quite as 
serious as has been claimed, and the special components needed for 
the electric car may not be as serious a problem as we are afraid it 
could be. The 2007 study David mentioned almost surely was based on 
the design of "parallel" drive systems such as in the Prius, whereas 
serial drive hybrids like the Volt are not nearly as complex as the 
Prius system. Furthermore, if we can resurrect the lithium mining 
industry in this country, the problem of providing hard-to-get 
materials for the electric vehicles should largely go away. The US 
has substantial lithium reserves (less so for some of the rare earths 
needed, although other nations nearer our borders do). The main 
problem with lithium and the rare earths recently has been the fact 
that the Chinese government has been undercutting the price of these 
materials in order to gain control over the markets. That cannot 
continue forever--China will eventually run out of the easy-to-dig-up 
stuff and international pressure against their policy of dumping the 
materials at artificially low prices will grow. Lithium can also be 
recovered from worn out batteries, much as lead is currently 
recovered from worn out standard automobile batteries

And if all else fails and we cannot make batteries that will have 
sufficient range, then the next possibility is swappable batteries. 
This idea makes lots of sense anyway. The batteries are kind of 
analogous to gasoline in the sense that when we buy a car, we don't 
buy its gasoline for its lifetime, we add gasoline as needed. Since 
we cannot add electrical energy to the batteries quickly, we can take 
the process to the next step, and make the batteries interchangeable 
(much like we do now with the propane tanks many people use to power 
their outdoor grills) and they can be recharged at the leisure of the 
battery swapping station. This will, of course require some degree of 
standardization of the batteries so they can be changed quickly, but 
that doesn't seem to be an insurmountable challenge. The company 
Better Place is experimenting with that system now in several 
locations, including Denmark and Israel. At one point they were 
planning something for the SF Bay area, but I don't know what its 
status is.

Even if there are no great technological breakthroughs about 
batteries, the problems are not insurmountable. And if we require all 
companies that create or consume natural resources to pay for the 
externalities they presently dump on the taxpayers, then most if not 
all of the cost differentials will go away. Its also comforting to 
remember that back in the early years of the 20th century we managed 
to convert our private transportation system from horsepower to 
gasoline power in about 20 years. With a bit of careful planning we 
should be able to make the transition from gas to electricity in a 
not-much-longer time than that--at most 30 years. I don't understand 
why the electric power industry isn't already all over this problem, 
especially as efficiency in home and industrial use of electricity 
continues to reduce demand for their product, in some areas even 
below the growth in demand due to population growth.

Hugh

--
Hugh Haskell
mailto:hugh@ieer.org
mailto:haskellh@verizon.net

I have been wondering for a long time why some of our own defense 
officials do not
put more emphasis on finding a good substitute for oil and worry less 
about where
more oil is to come from.  Our people are ingenious. New discoveries 
are all around
us, and when we have to make them, we nearly always do.

						Eleanor Roosevelt
						February 13, 1948