\amarginfig{b}{
\begin{center}
\begin{tabular}{@{}c@{}}
%\mbox{\epsfxsize=53mm\epsfbox{../../images/CarsBMWSpaceship4.jpg.eps}} \\
\lowres{\epsfxsize=53mm\epsfbox{../../images/CarsBMWSpaceship3S.jpg.eps}}%
{\epsfxsize=53mm\epsfbox{../../images/CarsBMWSpaceship3.jpg.eps}} \\
%\lowres{\epsfxsize=53mm\epsfbox{../../images/CarElephantS.jpg.eps}}%
%{\epsfxsize=53mm\epsfbox{../../images/CarElephant.jpg.eps}} \\
\end{tabular}
\end{center}
\caption[a]{
Cars. A red \ind{BMW} dwarfed by a \ind{spaceship}
from the \ind{planet Dorkon}.
}
}
For our first chapter on consumption, let's
study that icon of modern civilization:
% that symbol of
% individual freedom:
the \ind{car} with a lone person in it.
% invalid carriage.
% Invalid carriages give enhanced
% mobility to physically-disabled people.
% Invalid carriages are also popular with able-bodied people,
% who tend to call these one-tonne metal boxes `cars'.
% 50 km is 31 miles.
How much power does a regular car-user consume?
Once we know the conversion rates, it's simple arithmetic:
\beqa
\mbox{\begin{tabular}{@{}c@{}}energy used\\[-0.1mm]per day\end{tabular}} \!&\!=\!&\! \frac{
\mbox{distance travelled per day}
}{ \mbox{distance per unit of fuel }}
\,\times\, \mbox{energy per unit of fuel} .
% \\
\eeqa
For the {\bf{distance travelled per day}}, let's use 50\,\km\ (30 miles).\label{pageAveragecar}
% 60 miles = 96.56
% 100 kilometers = 62.1371192 miles 50 km is 31 miles
% 50 km/d is 18,000 km per y
For the {\bf{distance per unit of fuel}}, also known as the {\bf\ind{economy}}
of the car, let's use 33 miles per UK gallon (taken from an advertisement
for a\label{mileage}
% diesel-engined
family car):
%% in today's newspaper).
%% box this
\[
33\, \mbox{miles per imperial gallon}
%%% = 27.5 \,\mbox{miles per US gallon}
%% 27.478236
\simeq 12\,\km\ \per\ \litre.
\]
% 33 * (miles per Imperial gallon) = 11.6821994
(The symbol ``$\simeq$'' means ``is approximately equal to.'')
%% figure for motor gasoline: 44,000 kJ/kg (net cal value)
%% biodiesel 37,000 kJ/kg
What about the {\bf{energy per unit of fuel}}
(also called the {\bf{calorific value}} or {\bf{energy density}})?
Instead of looking it up,\index{calorific value!butter}
it's fun to estimate this sort of quantity
by a bit of lateral thinking. Automobile fuels (whether
diesel or petrol)\index{energy density!butter}\index{calorific value!fuel}
%% and aviation fuels
are all hydrocarbons;\index{energy density!fuel}\index{fuel!energy density}
and \ind{hydrocarbon}s can also be found on our breakfast table,
with the calorific value conveniently written on the side:
roughly 8\,kWh\index{butter!calorific value}\index{fuel!calorific value}
% 30\,000\,\kJ\
per \kg\ (\figref{fig.butter}).
\amarginfig{b}{
\begin{center}
\begin{tabular}{c}
\lowres{\epsfxsize=50mm\epsfbox{../../images/butterS.jpg.eps}}%
{\epsfxsize=50mm\epsfbox{../../images/butter.eps}} \\
%\mbox{\epsfxsize=50mm\epsfbox{../../images/butterNutrition2.eps}} \\
%\mbox{\epsfxsize=50mm\epsfbox{../../images/butter/energy2.eps}} \\
\lowres{\epsfxsize=50mm\epsfbox{../../images/butter/energy1S.jpg.eps}}%
{\epsfxsize=50mm\epsfbox{../../images/butter/energy1.eps}} \\
\end{tabular}
\end{center}
\caption[a]{%%% for BUTTER FLOATS figure see _cars.tex
Want to know the energy
in car fuel?
Look at the label on a pack of \ind{butter} or \ind{margarine}.
The \ind{calorific value} is 3000\,kJ per 100\,g,
or
% 30\,000\,\kJ\ per \kg.
about 8\,kWh per kg.
}
\label{fig.butter}
}%
%% energy density of gasoline
%% http://hypertextbook.com/facts/2003/ArthurGolnik.shtml
%% 12.7 kWh/kg or 8.76kWh/l
Since we've estimated the economy
of the car in miles per unit {\em{volume}\/} of fuel,
we need to express the
\index{energy density}\ind{calorific value} as an energy per unit {\em{volume}}.
To turn our fuel's ``8\,kWh
% 30\,000\,\kJ\
per \kg'' (an energy per unit
{\em{mass}})
into an energy per unit volume, we need to know the
density of the fuel.
What's the density of \margarine? Well, \margarine\ just\label{butter}
floats on water, as do fuel-spills, so its density must be a
little less than water's, which is 1\,\kg\ per litre.
If we guess a density of 0.8\,\kg\ per litre\label{pageDensity},
%% 0.7 is a better figure for gasoline
%% volume of one kilogram
% and assume \margarine\ and \ind{petrol} are the same,
we obtain
a \index{energy density}\ind{calorific value} of:
\[%beq
% 30\,000\,\kJ\,
8\,\kWh\ \per\ \kg \times 0.8\,\kg \ \per\ \litre
\simeq
% 24\,000\,\kJ
7\,\kWh\ \per\ \litre .
\]%eeq
% Putting this into our preferred energy unit, the kilowatt-hour
% ($1\,\kWh = 3600\,\kJ$),
% the calorific value of fuel is estimated to be about 7\,\kWh\,per\,litre.
Rather than willfully perpetuate an inaccurate estimate,
let's switch to the actual value, for petrol, of
% 8.8\,\kWh\,per\,litre. 9.7
10\,kWh per litre.\nlabel{pageFuel}
%
\beqa
\mbox{energy per day}\! &\!=\!& \!\frac{
\mbox{distance travelled per day} }
{ \mbox{distance per unit of fuel }}
\times \mbox{energy per unit of fuel}
\\
&\!=\!& \frac{ 50 \,\km / \uday }
{{ 12 \,\km / \litre }} \times 10 \,\kWh /\litre
\\
&\!\simeq\!& \Red{40 \,\kWh / \uday} .
\eeqa
% 80.8 accurate ; 83.3 is what you get from this calculation
%
Congratulations!
\amarginfig{b}{
% \begin{figure}
\begin{center}
\begin{tabular}{@{}cc}
{\small\sc Consumption}& {\small\sc Production}\\
\mbox{\epsfbox{metapost/stacks.21}} & \\
%% {\mbox{\epsfbox{crosspad/cars3.ps}}} & ? \\
\end{tabular}
\end{center}
% }{
\caption[a]{Chapter \protect\ref{ch.car}'s conclusion:
a typical car-driver uses about 40\,kWh per day.
}\label{fig.carCon}
}%
% \end{figure}
We've made our first estimate of consumption.
% For ease of memorization, let's round this figure to
% 70\,\kWh\ per day.
I've displayed this estimate in the left-hand stack in \figref{fig.carCon}.
% Subsequent chapters will alternate add to the right-hand stack
The red box's height represents 40\,kWh per day per person.
This is the estimate for a typical car-driver driving a
typical car today. Later chapters will discuss
the {\em{average}\/} consumption of all the people in Britain, taking
into account the fact that not everyone drives. We'll also
discuss in Part II what the
consumption {\em could\/} be, with the help of other technologies
such as electric cars.
% come back to the question of the car's economy, asking:
Why does
the car deliver 33 miles per \uk{gallon}{imperial gallon}? Where's that energy going?
Could we manufacture cars that do 3300 miles per gallon?
If we are interested in trying to reduce cars' consumption,
we need to understand the \ind{physics} behind cars' consumption.
% We've not finished with cars yet. In a later chapter we'll
% These are questions that can be addressed with the
% help of a
%% *** TENSE CONSISTENCY?
These questions are answered in the accompanying
% appendix
technical chapter
\ref{ch.cars2} (\pref{ch.cars2}), which provides a
cartoon theory of cars' consumption.
I encourage you to read the
% appendices
technical chapters
if formulae
like $\frac{1}{2} m v^2$ don't give\index{formula!kinetic energy}
you medical problems.
% The appendices make use of formulae like $\frac{1}{2} m v^2$;
% I encourage you to read the appendices if such formulae don't give
% you medical problems.
Chapter \protect\ref{ch.car}'s conclusion:
a typical car-driver uses about 40\,kWh per day.
% Now we need to find out about sustainable production.
%
Next we need to get the sustainable-production stack going, so
we have something to compare this estimate with.
\section{Queries}
\qa{What about the energy-cost of {\em{producing}\/}
the car's fuel?}{
Good point.
When I estimate the energy consumed by a particular
activity, I tend to choose a fairly tight ``\ind{boundary}''
around the activity.
This choice makes the estimation easier, but I agree that
it's a good idea to try to estimate the full energy impact of an activity.
It's been estimated that making each unit of petrol
requires an input of 1.4 units of oil and other primary fuels
\citep{TreloarLoveCrawford}.
%% *** MJB says to check Shell for LCA on this. He predicts 10 or 15%
}
\qa{What about the energy-cost of {{manufacturing}}
the {\em{car}}?}{
Yes, that cost fell outside the boundary of this calculation too.
We'll talk about car-making in \chref{ch.stuff}.
}
% \newpage
% \newpage
%\beginfullpagewidth
\small
\section*{Notes and further reading}
\nopagebreak
\beforenotelist
\begin{notelist}
\item[page no.]
% In USA 77% of people drive to work
% Norfolk: 213k out of 359k working get to work by car or van
% In England and Wles 55% drive car or van to work. 6.3% are passengers in a car
% or van
\item[\npageref{pageAveragecar}]
{\nqs{For the {{distance travelled per day}}, let's use 50\,km.}}
This corresponds to 18\,000\,km (11\,000 miles) per year.
\amarginfig{b}{
\begin{center}
\mbox{\epsfxsize=53mm\epsfbox{../data/transportmode.eps}} \\
\end{center}
\label{fig.transportmode}
\caption[a]{
How British people \ind{travel} to work,\index{data!commuting}\index{commuting, data}
according to the 2001 census.
}
}%
Roughly half of the British population drive to work.
% Average distance travelled per person per year by car
% is 3660 miles as driver (2033 as passenger) 16km
The total amount of car travel in the UK
is 686 billion passenger-km per year,
% 2006
which
corresponds to an ``average distance travelled by car per
\ind{British person}''\index{average travel}\index{travel!average}
of 30\,km per day.
Source: Department for Transport
% 686 billion passenger km per year / 60e6 /365.25
% website the average distance travelled
%> in a car per year per person is about 5,500 miles (
% Section 2.4 of
%% http://www.dft.gov.uk/stellent/groups/dft_transstats/documents/page/dft_transstats_026290.hcsp
%% http://tinyurl.com/wqm2z
% this link has gone bad
% new link is
\tinyurl{5647rh}{http://www.dft.gov.uk/pgr/statistics/datatablespublications/tsgb/}.
% \tinyurl{wqm2z}{http://www.dft.gov.uk/stellent/groups/dft_transstats/documents/page/dft_transstats_026290.hcsp}.
% {\url{http://{\breakhere}www.{\breakhere}dft.{\breakhere}gov.{\breakhere}uk/{\breakhere}stellent/{\breakhere}groups/{\breakhere}dft\_transstats/{\breakhere}documents/{\breakhere}page/{\breakhere}dft\_transstats\_026290.hcsp}}
As I said on \pref{typicalaffluent},
I aim to estimate the consumption of a ``typical
moderately-affluent person'' -- the consumption that many people
aspire to.
Some people don't drive much. In this chapter,
I want to estimate the energy
consumed by someone who chooses to drive, rather than depersonalize
the answer by reporting the UK average, which mixes together the drivers
and non-drivers.
% If you'd prefer to use different figures, feel free.
If I said ``the average use of energy for car driving
in the UK is 13\,kWh/d per person,'' I bet
%%%% CORRECT 24 to 13 (at pump) or 18 (upstream primary energy cost)
%%%% source http://www.dft.gov.uk/pgr/statistics/datatablespublications/tsgb/
%%% see http://www.inference.phy.cam.ac.uk/wiki/sustainable/en/index.php/Chapter_3
%%% 21.68e6 tonnes per year * 13 kWh per kg / 60e6 in kWh per day
%%% 12.86 kWh per day per person (not including upstream costs)
%%% The total petroleum used by all road transport is 38.5 Million tonnes per year. (about 23 kWh per day per person).
some people would misunderstand and say: ``I'm a car driver
so I guess I use 13\,kWh/d.''
%% 2006: 511 billion vehicle km
%% from http://www.dft.gov.uk/pgr/statistics/datatablespublications/trends/current/transporttrends2007
%% of which cars:
%% 402 billion vehicle kilometres. (2006)
%% average car occupancy is 1.58 (2006)
%% average traffic speed in urban areas is 21 mph on peak, and 24 mph off peak.
%% in London, average traffic speed in urban areas is 15 mph morning peak, and 18 mph off peak.
%% there are 30 million private and light goods vehicles . and 33.3M total of all vehicles
%% 25% of households have no car
%% 30% of adults have no driving license
\setcounter{latestnotepage}{0}% hack to ensure page number given
\item[\npageref{mileage}]
{\nqs{\ldots\ let's use 33 miles per UK gallon.}}
In the European language, this is 8.6\,litres per 100\,km.
% 8.56.
% (I got this number
% from an advertisement
% for a family car).}
33 miles per gallon was the average for UK cars in 2005
\tinyurl{27jdc5}{http://www.dft.gov.uk/pgr/statistics/datatablespublications/
energyenvironment/
tsgb-chapter3energyandtheenvi1863}.
% edited this URL to fix problem (added -)
Petrol cars have an average fuel consumption of 31\,mpg; diesel cars, 39\,mpg;
new petrol cars (less than two
years old), 32\,mpg \citep{TSGB}.\label{tabCar80}
% Is this too low a figure?
% SMMT figures also show that the average Combined
% economy of all new registrations has risen from
% 42mpg in 2004 to 43.4mpg in 2006.
% For comparison,
% The website of
\ind{Honda}, ``the most fuel-efficient auto company in America,''
records that its fleet of new cars sold in 2005 has an average
top-level fuel economy of
% 29.2 miles per US gallon, which is
35 miles per UK gallon
%% which is 12\,\km \,\per\, \litre.
\tinyurl{28abpm}{http://corporate.honda.com/environmentology/}.
\item[\npageref{pageDensity}]
{\nqs{Let's guess a \ind{density} of 0.8\,kg\ per litre.}
} \Gasoline's density is 0.737.
Diesel's is 0.820--0.950
{\tinyurl{nmn4l}{http://www.simetric.co.uk/si_liquids.htm}}.
\item[\npageref{pageFuel}]
{\nqs{\ldots\ the actual value of
10\,kWh per litre}.}
ORNL \tinyurl{2hcgdh}{http://cta.ornl.gov/data/appendix_b.shtml} provide
the following \ind{calorific value}s:
\ind{diesel}: 10.7 kWh/l; \ind{jet fuel}: 10.4 kWh/l; \ind{petrol}\index{gasoline}:
9.7 kWh/l.
\marginpar{\small
%\margintab{
\begin{tabular}{cc}\toprule
\multicolumn{2}{c}{\sf{\index{energy density}\ind{calorific value}s}} \\
\midrule
petrol & 10\,\kWh\ per litre\\
diesel & 11\,\kWh\ per litre\\
\bottomrule
\end{tabular}
% \caption[a]{ Facts worth remembering: petrol and diesel. }
}
When looking up calorific values, you'll find ``gross calorific
value'' and ``net calorific value'' listed (also known
as ``\ind{high heat value}'' and ``\ind{low heat value}'').\index{calorific value!net}
These differ by only 6\%
for motor fuels, so it's not crucial to distinguish them here,
but let me explain anyway. The \ind{gross calorific value}\index{calorific value!gross}
is the actual
\ind{chemical energy}\index{energy!chemical}
released when the fuel is burned.
One of the products of \ind{combustion} is water, and in most engines
and power stations, part of the
energy goes into vaporizing this water.\index{energy!of vaporization}
The net calorific value measures how much energy is left over
assuming this energy of vaporization is discarded and wasted.
When we ask ``how much energy does my lifestyle consume?'' the
\ind{gross calorific value} is the right quantity to use.
The \ind{net calorific value},
on the other hand, is of interest to a power station \ind{engineer},
who needs to decide which fuel to burn in his power station.
Throughout this book I've tried to use gross calorific values.
A final note for party-pooping \ind{pedant}s who say ``\ind{butter} is not
a \ind{hydrocarbon}'':
OK, butter is not a {\em{pure}\/} hydrocarbon; but it's a good approximation
to say that the main component of butter is long hydrocarbon chains, just
like petrol.
The proof of the pudding is, this approximation got us within 30\% of the
correct answer. Welcome to \ind{guerrilla physics}.
% The gross calorific value of \ind{DERV} is 45.5\,GJ/tonne;
% of aviation fuel, 46.2; of motor spirit, 47\,GJ/tonne
%{\tinyurl{ybh97n}{http://www.cefic.be/sector/shared/ecoprofile/appendix/a04.htm}}.
% The net calorific value is 6\% smaller.
% Not that it makes any difference,
% but in these calculations I use the gross calorific value, since that's
% the energy guzzled.
% Thus the calorific value of \ind{petrol} is 10\,\kWh\,per\,litre.
% For easy memorization, I've rounded this figure to 9\,\kWh\,per\,litre.
%% gross cal value of gasoline is 45.85 MJ/kg; net cal val=42.95
%% ROUGHLY 12 kWh/ kg
%% 6% difference.
% Diesel's calorific value is slightly higher\index{diesel} -- about 11\,kWh\,per\,litre.
% Correction Tue 11/12/07:
% Wikipedia says petrol is 34.6 megajoules per litre, which is 9.61 kWh per litre.
% So I think petrol should be 10 and diesel (38.6 MJ/l) 11 kWh/l. (10.7)
% petrol : 44.4MJ/kg; diesel 45.4MJ/kg.
% This bumps up all my car figures by 10\%. DONE
% Wikipedia's source is \tinyurl{2hcgdh}{http://cta.ornl.gov/data/appendix_b.shtml}.
% diesel: 138700 Btu/gal ; jet fuel 135000 Btu/gal ; gasoline 125000 Btu/gal
% 10.74 kWh/l 10.45 kWh/l 9.7 kWh/l
% 10.7 kWh/l 10.4 kWh/l 9.7 kWh/l
% 37.6 MJ/l
\end{notelist}
\normalsize
\normalsize
%\ENDfullpagewidth
\amarginfig{t}{
\begin{center}
\begin{tabular}{@{}c@{}}
\mbox{\epsfxsize=53mm\epsfbox{../../images/ExhaustPipe.jpg.eps}} \\
\end{tabular}\label{Claire1}
\end{center}
% \caption[a]{ }
}
%Commute for an office
%
%For that Exeter branch of PF, their average commute per person per
%workday was 30 (averaged over 75 employees at the site, using
%post-codes from a travel survey), with 47 work weeks per year.