From tim.jervis@gmail.com Mon Nov 10 08:57:36 2008
From: Tim Jervis
To: David John Cameron MacKay
Subject: Lamp post chargers
Cabling is rated to 16 amps at 240v
= 3.84 kW max
Regenerative\index{brakes!regenerative}\index{regenerative brakes}
brakes make a difference during city driving,
not motorway driving. Using the brakes less in the city makes a similar
difference; how can you use the brakes less? By using the accelerator less.
So measures that smooth traffic flow, reducing a car's variations in speed,
will help.
Reducing the \ind{frontal area}\index{area!frontal}
of cars\index{car!frontal area} and enhancing
\ind{streamlining}
make a difference to \uk{motorway}{freeway} energy consumption.
% The best \ind{drag coefficient}
% of cars on the market is 0.25.
% {\em (This discussion is assuming familiarity with
% material from the technical chapter)}
% When comparing cars' drags, don't forget to multiply their drag coefficient
% by the frontal area. Small cars are better.
To have the biggest impact on your energy consumption, sell
the car, and ride a bike. If you insist on keeping a car,
you can have a huge impact on your consumption by {\em driving slower}.
If everyone who drives for one hour per day relocated their home
%% moved house
such that they could drive at half the speed for the same
duration (perhaps in an appropriately
lower-powered vehicle), energy consumption by transportation would fall
to one eighth of current levels; stinky emissions would fall to one eighth of current levels;
and serious injuries to pedestrians and cyclists would fall even more.
Now, let me remind you, I'm not trying to tell anyone what to do.
I'm trying to make the numbers clear so you can evaluate
alternative suggested policies. So, just in case you are interested
in reducing transportation costs,
let's sum up policies that would reduce energy consumption significantly.
Reducing the mass of the car makes a difference
to consumption during city driving, but not \uk{motorway}{freeway} driving.
Prototype
tZero (precursor of Venturi, Tesla, and Wrightspeed.)
Lithium ion battery gives 4 times the range,
and is slightly more efficient than lead acid.
% (Tzero does 180\,Wh/mile, compared
% to 165\,Wh/mile for lead acid.)
% http://www.acpropulsion.com/tzero/efficiency.htm
% http://www.acpropulsion.com/tzero/efficiency.htm
tZero does
% 170\,Wh/mi.
% 10.6
11\,kWh/100 km.
% 2 passengers
% Just better than a Honda Insight hybrid.
% (Assuming natural gas power station.)
\item[AVT-100E]
\myurl{www.avt.uk.com}
Range: 100 miles with lithium-ion batteries.
15\,kW motor.
Top speed over 100\,mph.
How does this compare with the consumption of an ordinary petrol-powered car?
At {\tt{www.goinggreen.co.uk}}, they claim that the G-Wiz does
``600\,miles per gallon,'' but that's misleading.
% which take 2.5 hours to charge to 80%
% complete charge 7 hours, gives range of 80km. Website now says 48 miles
At 9.7\,kWh per 77\,km, the energy consumption is
220\,miles per gallon -- about
7 times better than a typical car that does 33\,miles per gallon.
This comparison treats a unit of electrical energy as having equal
value to a unit of chemical energy.
If you prefer to redo the comparison
with the exchange rate achieved by a
40\%-efficient fossil-fuel power station,
2.5\,kWh of chemical energy for 1\,kWh of electricity,
you'll find that the G-Wiz, on its best behaviour,
is equivalent to
a 90\,miles-per-gallon car.
%% updated Sat 26/4/08
I say ``on its best behaviour'' because