London Banter - View Single Post - Electric or Hybrid Card or something car, suggestions?

Sales! · April 2nd 04, 12:38 PM posted to uk.rec.cars.misc,uk.transport.london

Apparently on date Thu, 1 Apr 2004 10:20:20 +0000 (UTC),
(D.P.Round) said:

Gives overall efficiency of EVs at 28% compared to 14% for ICE engined
vehicles. Do you have better figures? If not EVs are twice as efficient

The site above is very misleading though

Of course. Best I could find in a hurry. If you find some better facts
please let me know. I think we can manage to see the valuable facts
behind the sales talk.

- Table 5, "comparison of fuel efficiency" which is your figures' source,
is a masterpiece of obfustication.

My figures come from table 4. Table 5 is poor science at best with lots
of cludges. Table 4 however it rather more useful. Lets stick to that
shall we?

Table four merely plucks the two figures out of the air. It doesn't derive them
or explain how it came to these figures, it just says "88%" versus "15%".

One of the issues I have with the comparison is it ignores things like vehicle
range and carrying capacity.

Petrol, as a fuel, carries around 30 MJ / kilogram, might be 40 MJ. Somewhere
around twice the energy capacity of wood, and in this I'm assuming the fuels
are used for combustion, in terms of the energy you can get from them. A car
fuel tank contains about thirty kilos / litres of petrol, which means it has
something of the order of 1000 MJ of energy contained within it, and weighs
about 30 kilograms with the engine adding another 70 kilograms, just for the
same of comparison. That is, 1000 MJ of energy costs about 100 Kg of payload
for a 1000 Kg car to manage about 400 miles of travelling.

Now consider a battery, with the same energy capacity as a car fuel tank.

Batteries also use chemical reactions to derive their energy output, but in far
less explosive and exothermic ways, and that means they deliver far less
energy, put plain and simple. A lead acid battery contains about 0.2 MJ of
energy per kilogram.

You can get more from nicads, if you don't mind the fact that you are utilising
a fairly expensive and polluting metal Cadmium, you can bump this up to maybe 1
MJ, and if lithium polymers work out in practice, this type may reach 2 MJ per
kilogram, not counting the containment chamber, which has to be much heavier
and more durable than a petrol tank, partly because the energy conversion is
going on inside the fuel chamber. Note that these types of battery require
considerable investment of energy to manufacture them, and they have to be
replaced quite often. This means serious expense to the owner of a vehicle
using them, e.g. 5,000 quid a year for replacement batteries as a ballpark
estimate.

For an equivalent range to the car above, with a 30 Kg fuel capacity, you will
need about 500 kilograms of the expensive, lithium polymer type of battery and
you haven't yet included a motor to convert the energy into motion. Using lead
acid, you have about 2.5 tonnes of batteries to cart about in a 1 tonne
vehicle, which isn't in the right ballpark. You can propose electric motors
that are more efficient in terms of energy conversion - although these will not
generally be true when the comparison is for a constant speed - but you are
still only halving the requirement, and that means a battery with a car
attached and low power, lightweight motors in all but the most ideal
theoretical examples.

So, battery powered, electric vehicles have lower range, and / or greatly
reduced sustainable power output, simply because there is no way to build
batteries which can liberate the sort of chemical energies that combustion of
highly reactive flammable fuels can liberate. This is, and always will be,
fact.

Sometimes people trot out the notion that future technologies will mean
batteries with higher and higher energy capacity and power outputs, and this
has some relevance as this is what development tends to do. However, people
*have* been developing battery power for mobile phones, laptops and PDAs for
some time and there are no easy leaps in technology to come due to the fact
that a battery must be capable of not exploding / melting / thermal runaway
release of the energy in it.

The conclusion I have come to long since, is petrol cannot be replaced by
battery powered vehicles without some seriously inconvenient changes in what a
vehicle is used for, e.g. we have single person vehicles with short ranges,
rather than cars able to carry shopping, passengers, etc along the motorways.

This is why, I do not tend to accept the websites / people who push or promote
a technology that I already can see will never be able to compete with the
existing technology on equal terms. It's an expensive, out of date concept that
is only popular among those who do not understand the situation and is intended
to solve a problem that no longer exists in any serious extent, which is the
emission of nitrous oxides and incomplete combustion products by passenger
vehicles in city environments, i.e. the reduction of smog. Modern cars in
roadworthy condition produce almost no smog even in cities.

The idea we have to use mains power instead of a diminishing petrol resource
fuels is conjoined with the notion that nuclear power is inherently clean and
inexhaustible, which can only be convincing when mains power is primarily clean
and inexhaustible, not when it is a less efficient way to burn the same
carboniferous resources

And the fear of releasing fossil carbon into the biosphere is as yet
unconvincing and is a gradual issue which can be reversed quite easily by a
reversionary economic model, e.g. fuel processing where the carbon and hydrogen
used to produce the fuel is extracted from the air by what may be a nuclear or
solar (or wind, or tidal) plant which is clean and inexhaustible, and produces
petrol which can then be used in passenger vehicles which release harmless
natural chemicals back into the atmosphere from where they were extracted.
Which is more or less what plant / animal life does at the moment.

Personally, I would adopt the final model using hydrogen as a fuel, because
hydrogen fuel contains far more chemical energy per kilogram* and converts into
clean water when used in a fuel cell. And it is much easier to liberate
hydrogen than to build petrol hydrocarbons. Course, this model only becomes
economical when there isn't an easily exploited source of hydrocarbon fuel
lying about ready to be used with less investment in processing.

Either way, battery powered vehicles are an expensive dead end for all but the
most radical and people-unfriendly transport models, mad in a democracy, not
very convincing even in a dictatorship like the socialist states which gave up
on battery vehicles even quicker.

(* - this is why space rockets use hydrogen fuel, it's pretty much the best
combustion fuel available for calorific capacity, and that is even when you
have to carry the oxygen to burn with it, which is 80% of your fuel load in a
space rocket, and a passenger vehicle burns it much slower so will take oxygen
from the atmosphere instead, which means a quarter of the weight that can take
you into orbit.)