P. E. HODGSON is Senior Research Fellow Emeritus
in Physics at Corpus Christi College, Oxford.
The world demand for energy is rapidly
increasing. We need energy to warm
our homes, to cook our meals, to travel and
communicate, and to power our factories.
The amount of energy available to us determines
not only our standard of living, but also
how long we live. Detailed statistics from
many counties show that in countries where
the available energy is 0.15 tons of coal
equivalent per person per year the average
life expectancy is about forty years, whereas
countries in Europe and America where the
available energy is a hundred times greater
have an average life expectancy of about
seventy-five years. It is well to remember
that a shortage of energy is a minor inconvenience
to us, but for people in poorer countries
it is a matter of life and death.
The world energy demand is increasing
due to population growth and to rising living
standards. World population in doubling
about every thirty-five years, though the
rate of growth is very different in different
countries. The world energy use is doubling
every fourteen years and the need is increasing
faster still. One of the main energy
sources is oil and the rate of production is
expected to peak in the next few years. There
are still plentiful supplies of coal, the other
principal energy source, but it is even more
seriously polluting than oil, leading to acid
rain and climate change. This combination
of increasing need and diminishing supply
constitutes the energy crisis. The world urgently
needs a clean energy source that is able
to meet world energy needs.
This is without doubt the most serious
problem facing mankind. If we simply let
things take their course, the world is heading
for a catastrophe during the present century.
To see what can be done about it, all possible
energy sources have to be critically examined
and their potential evaluated (1).
Before considering the various energy
sources in detail it is useful to list some of the
difficulties in doing so. These arise partly
from the complicated nature of the subject,
which involves a range of scientific and
technological specialities, and partly from the
fierce political debates that surround it. The
only way to assess the various criteria is to
express them numerically as far as possible.
Without the numbers it is all just a matter of
words spiced with emotion, and it is never
possible to reach an objective decision. These
numbers seldom have the precision of scientific
measurements, and some of them are
inherently imprecise but it is better to have
approximate numbers rather than no num-
bers at all. It is important to distinguish
between precise measurements, reasonable
estimates, guesses, commercial or political
propaganda, and speculations. The speculations
can be plausible and in accord with
known scientific laws, or in contradiction to
such laws. A further complication is that new
scientific data often alter the picture; this is
notably the case for climate change. The
people providing the information can be
completely objective, or they can be strongly
influenced by commercial and political concerns.
The criteria used to assess the various
energy sources are their capacity, reliability,
cost, safety, and effects on the environment.
No single source satisfies all these criteria so
an energy mix is essential for each country.
The optimum energy mix depends on the
natural resources of that country, and so there
is no general solution; each country must be
considered separately.
No energy source is completely safe, so it
is relatively easy to make a case against any
particular source by emphasising its hazards.
What is needed is an objective comparison
between the hazards of all the energy sources,
based on numbers. This may be done by
estimating the numbers of workers killed and
injured in the course of producing a stated
amount of electricity. This excludes the contribution
of long-term effects. It is worth
mentioning that the casualties due to energy
production are small compared with those
due to natural disasters. Thus, for example,
the Chinese Seismological Bureau estimated
that in the years from 1949 to 1976 about 27
million people died and 76 million were
injured following about a hundred earthquakes.
Huge numbers were also killed by
tsunamis and hurricanes.
Every energy source has to be constructed
and maintained, and this requires energy. It
is thus some time before the energy produced
by a device is sufficient to pay back the
energy used initially. This payback time is an
important parameter when comparing energy
sources, but data are rather sparse.
There is one general classification of energy
sources that provides a useful guide.
This is the degree of concentration. To do
anything useful the energy must be concentrated.
Energy sources can be divided into
three categories: the concentrated sources
wood, oil, coal, gas, and nuclear; the intermediate
category of hydro which is partly
concentrated by the mountain valleys; and
the least concentrated such as wind, solar,
geothermal, wave, and tidal. These sources
contain vast amounts of energy but it is thinly
spread and only becomes useful when it is
concentrated.
We tend to think that environmental
degradation is a recent problem, beginning
only with the Industrial Revolution; but in
ancient times, when wood was the main fuel,
the forests of the Mediterranean were cut
down, often leaving deserts. Later on, many
of the forests of northern Europe were also
cut down for fuel. Wood together with crop
residues and dried animal dung is still the
principal fuel for most people in poorer
countries. This practice impoverishes the soil
and makes more deserts. Other ancient energy
sources like wind mills and water wheels,
although less polluting, produce limited quantities
of power. The windmill is especially
unreliable, although the waterwheel has developed
into hydro-electric power in modern
times.
Before considering the possible energy
sources individually it is useful to make a few
general remarks. While it is essential to
express as much as possible numerically, the
limitations on the numbers must be borne in
mind. These numbers are vital to a proper
assessment but are inevitably approximate.
They differ from one county to another, and
vary with time as new safety measures are
introduced. They include all the direct haz
ards; in the case of coal for example, they
include mining and transport hazards as well
as those involved in the day to day running
of the power stations. The manufacture of
safety devices in factories brings with it more
hazards, so it is just not possible to make any
energy generating device absolutely safe.
The costs of energy generation vary from
one country to another and with the distance
from mine to power station, where appropriate.
Power stations remain in operation
for many decades, and during that time
inflation affects the costs. The rate of interest
on the dividends paid to the shareholders has
a critical effect on the final cost.
The power output from energy generating
devices estimated by the designer often
differs substantially from what is actually
achieved. It is therefore necessary to base
figures for the power output and the costs on
actual operating experience over a number
of years. It is thus practically impossible to
evaluate a new device without running it for
several years.
It is often said that our energy problems
could be solved if we used energy more
carefully and avoided waste. There is certainly
much that can and should be done. We
can insulate our homes to conserve heat and
avoid heating rooms that are not used. We
can turn the heating down and wear more
clothing. We can install energy-saving light
bulbs. We can walk or use smaller automobiles
and avoid unnecessary journeys. If
everyone were to carry out these and many
similar measures the energy use would be
much reduced. It has even been suggested
that in this way we can reduce energy use by
a factor of four (2). Some of these measures
are easy and some are not. It is much easier,
for example, to build an energy-saving house
than to modify an existing house. Many of
these measures, such as insulating our homes,
require new materials that have to be made
in factories. This inevitably requires energy,
and we have to consider how long it will take
to recover the energy expended. The main
difficulty is to convince people to change
their way of life. Certainly we have a serious
obligation to do what we can to reduce
energy use, but even if we do we will still
need to generate large amounts of energy.
Energy-saving measures are most important.
They can ameliorate the situation but
are not able to avoid the energy crisis. We
must therefore consider how the available
sources of energy can be enhanced and used
wisely.
Coal
Coal, together with oil and natural gas, is one
of the fossil fuels, which come from the decay
of vegetation many millions of years ago.
They are all very reliable sources of energy
and are not unreasonably expensive. Their
main disadvantage is the pollution they cause,
of the land, the sea, and the atmosphere.
The world consumption of coal has risen
from 100 millions tons of oil equivalent
energy in 1860, to 330 in 1900, to 1300 in
1950 and to 2220 in 2000. In 1950 it was by
far the world’s largest energy source, but by
2000 it was easily exceeded by oil. The
lifetime of world coal supplies is often calculated
by dividing the coal reserves by the
annual consumption, and this gives about
250 years. However Lomborg (3) has found
that this ratio seems to stay the same from
year to year, the increased consumption
being balanced by the discovery of new
reserves. This cannot go on indefinitely, but
we can conclude that the above figure is an
underestimate. There is plenty of coal for the
foreseeable future.
The main concern about coal is the pollution
it causes. A typical coal power station
produces as solid waste over a million tons of
ash, 21,000 tons of sludge, and half a million
tons of gypsum and discharges into the atmosphere
eleven million tons of carbon dioxide,
16,000 tons of sulphur dioxide, 29,000 tons
of nitrogen oxides, and a thousand tons of
dust, plus smaller amounts of aluminium,
calcium, iron, potassium, nickel, titanium,
and arsenic.
This anthropogenic pollution can be compared
with that due to natural causes, such as
bush fires due to lightning strikes and volcanic
eruptions. Although the short term effects
may be severe, the earth has great natural
recuperative powers; and once the source of
pollution is removed the land, lakes, and seas
return to their previous state.
Unlike these natural events the pollution
from energy generation builds up continuously,
and so the earth cannot recover. The
solid waste has to be deposited somewhere,
often in the sea, hazarding aquatic life. The
atmospheric waste produces acid rain and
climate change. The acid rain causes plants
and trees to weaken and die, and renders
lakes sterile and kills the fish. By the 1980s,
nearly 4,000 lakes in Scandinavia were dead
and 5,000 had lost most of their fish.
It has been suggested that the carbon
dioxide, which is the principal ingredient in
atmospheric pollution, could be sequestered,
that is put into liquid form and pumped into
empty oil wells. This process is expensive and
could increase the price of coal by a factor of
two or three. Even if this were done, there
would still remain the hazards of the other
atmospheric discharges.
The vicinity of a coal power station is
hardly an object of beauty. The waste from
burning the coal is usually stored nearby and
forms large, unsightly, and dangerous slag
heaps. They are dangerous because after
heavy rain they can collapse, overwhelming
nearby buildings. This happened some time
ago in the Welsh village of Aberfan. The slag
flowed over the village school, killing over a
hundred children.
Coal is by far the most hazardous of the
energy sources. Mining is dirty and dangerous;
over 80,000 miners were killed in accidents
from 1873 to 1938. A detailed study (4)
found that about forty miners are killed to
produce a thousand megawatt years of energy,
and many hundreds of thousands have
had their health permanently impaired by
silicosis and other diseases. For all these
reasons it is imperative to phase out coal
power stations as soon as possible.
Oil
The world consumption of oil increased very
rapidly throughout the twentieth century,
partly because it is easier to extract from the
earth than coal and partly because it is easier
to transport by pipeline or tanker from well
to power station. It also has a higher calorific
content than coal. In 1900 the world oil
production was twenty million tons, 470 in
1950, and 3400 in 2000.
The safety of oil occupies an intermediate
position with about ten deaths per thousand
megawatt-years. This is mainly due to oil
well fires. There were 63 accidents in the
period 1969-1986, with an average of fifty
deaths per accident.
Oil is serious threat to the environment
because tankers are sometimes wrecked and
the oil discharged into the sea, killing fish and
seabirds, and destroying marine plant life.
The polluted area soon recovers and it is
worth mentioning that more oil pollution is
caused by tankers cleaning out their tanks.
The main disadvantage of oil is that world
oil production is expected to peak in about
ten years and thereafter fall. This may be
offset by new discoveries, although no large
oilfields have been discovered since 1980.
The demand for oil continually increases.
Burning oil also produces large quantities of
carbon dioxide, just like coal. Furthermore,
oil is a valuable chemical with many applications
principally as airplane fuels and in the
pharmaceutical industry, and so burning it is
very wasteful. A further complication is that
the bulk of the remaining oil reserves are in
the Middle East.
Oil can also be extracted from tar sands.
There are enormous deposits in Northern
Canada, estimated to be able to yield at least
170 billion barrels compared with about 260
billion barrels in Saudi Arabia. Venezuela
also has substantial reserves. The oil is extracted
by boiling water, and is an expensive
and very polluting process. It costs about $25
to extract a barrel of oil, so the process is
economic as long as it remains less than that
from oil wells, as is the case at present.
Oil in the form of ethanol can be extracted
from sugar cane and from maize. Already
there are large plantations growing crops for
this purpose; Brazil plans to plant 120 million
hectares and an African consortium 380 million
hectares. This takes up valuable agricultural
land, however, leading to food shortages,
and is also highly polluting. It is, therefore,
unwise to rely on oil, even from vegetable
sources, for our future energy supplies.
Natural Gas
Sometimes associated with oil and sometimes
on its own, gas is an attractive energy source.
It comes out of the ground easily and can be
transported over large distances either by
pipeline or less conveniently in liquid form
by road, rail, and ship. It is widely used for
domestic heating and cooking It is one of the
cheapest and safest energy sources, so many
gas power stations are now being built. These
power stations can be brought into action
rapidly and so are useful when dealing with
fluctuating demand. Natural gas is also the
safest energy source, with an average of half
a death per thousand megawatt years.
The contribution of natural gas to world
energy consumption has risen from 170
million tons of oil equivalent in 1950 to 2020
million tons in 2000. A large gas field in
Siberia now supplies around 20 percent of
western European gas. Gas consumption in
Britain is rising rapidly and with it the price.
The calculated lifetime is about sixty years,
but as in the case of coal and oil this is likely
to be an underestimate. Ultimately gas production
will fall, like that of oil.
The Renewable Energy Sources
Recognition of the pollution caused by fossil
fuel power stations has led to strong advocacy
of what are sometimes termed the
“benign renewables.” This label is somewhat
misleading, as statistics show that they are by
no means benign. The word “renewable”
implies that they do not rely on sources that
are limited in amount; they rely on the
practically inexhaustible sun. In all cases the
energy available is enormous, but it is thinly
spread and therefore costly to concentrate. It
is regrettable that this renders most of them
uneconomical for large-scale energy generation,
except for hydro where nature does
the concentrating for us. They have many
attractive and valuable features, but the laws
of physics are inexorable.
Hydropower
Hydropower (hydro for short) is a wellestablished
and reliable source that supplies
most of the electrical power in mountainous
countries like Norway and Switzerland. It is
however limited worldwide by the number
of suitable mountains and cannot ever supply
more than about three per cent of the world’s
energy needs. There are untapped sources in
remote areas, but the electricity produced
there has to be transported over long distances
and the power lines are exposed to
attacks by guerillas.
Hydropower is relatively safe, with a
death rate of about four per thousand megawatt
years. The dams that hold back the
water seem so solid that even this hazard is
surprising. However, it sometimes happens,
especially with earthen dams, that water
starts to trickle through small channels, gradually
weakening the dam until it collapses. A
wall of water then surges down the valley,
obliterating everything in its path. If people
are living there, a large number could be
drowned. In the period 1969-1986 there have
been more than eight dam collapses, with an
average death toll of more than 200 people.
In one case, about 2500 people were killed.
The lakes behind the dams provide a
habitat for wild life, and they can be popular
for boating. However in times of drought the
water level falls and exposes ugly bands of
mud. In addition, these lakes often inundate
picturesque valleys and their villages, and
destroy valuable agricultural land.
Wind
Of the remaining renewable energy sources,
wind is the most promising. Windmills have
been used since ancient times, and now wind
turbines are a familiar sight in the countryside.
They have several disadvantages, however,
the main one being that the wind does
not always blow and so the power output
fluctuates instead of remaining steady. The
fluctuations are magnified because the power
output is proportional to the cube of the wind
velocity. This means that energy is available
only over a limited range of wind velocities;
when the velocity is small very little energy
is produced, while if it exceeds the safety
limit the blades have to be feathered to avoid
catastrophic damage.
The total energy in the wind is more than
enough to satisfy all our energy needs but this
cannot be realized because of the high cost
(two or three times that of coal power), the
unreliability, and the large amount of land
required. It may however make a useful
contribution if the costs can be substantially
reduced.
Wind power is surprisingly dangerous at
five deaths per thousand megawatt-years.
This is due to the large number of turbines
required, about a thousand, to equal the
output of one coal power station. These have
to be made in factories by processes which are
inevitably hazardous. In addition, there are
the hazards of construction and maintenance.
The environmental impact of wind turbines
is increasingly recognised. They must
be built in exposed positions where they can
be seen for miles around. They emit a persistent
humming sound which people living
nearby find intolerable. Often people who
moved to the country for peace and quiet are
forced to leave and then find that no one
wants to buy their house. Wind farms can
also be built offshore but this increases the
cost and may pose a danger to shipping.
In spite of intensive work over many years
wind power is still uneconomical, and in
most cases it relies on massive Government
subsidies. It is fair to propose that research
continues until this difficulty is overcome,
but that until this is achieved it is unwise to
deploy wind turbines on a large scale.
It is sometimes argued against wind power
that turbine blades kill large numbers of
birds, estimated to be about 70,000 a year in
the United States. This figure should be put
into perspective by comparing it with the
numbers killed on motorways, amounting to
57 million per year in the United States, by
colliding with glass windows (98 million per
year), and by domestic cats (55 million a year
in Britain) (3).
At present wind contributes only about
0.2 percent of Britain’s energy. The Government
has announced that the energy from
all the renewables must be raised to 10
percent by 2010. This requires about 8,400
turbines spread over an area of about 1300
square kilometres. There is no hope of doing
this, and even if it were achieved there would
still be the problem of generating the remaining
90 percent. The situation is very similar
in the United States.
Tidal
Some river estuaries are so formed that they
experience high tides. When there is a high
tide, the sea water flows in, sometimes to a
surprising distance from the sea. Around low
tide this water flows again back to the sea. If
a barrier is put across the river the water flows
through pipes to the sea. It is then easy to
make this flow rotate a turbine and generate
electricity. Such a device has operated in the
La Rance estuary in France for many years,
producing 65MW. It is reliable, although the
peak periods vary according to the moon and
not the sun, so the electricity is not always
available when it is needed.
A similar though much larger scheme has
been proposed for the Severn estuary between
England and Wales. It would cost
about fifteen billions pounds spread over
about ten years to build and would produce
about 7GW. The environmental effects are
expected to be severe as the whole ecology of
the area would be altered. The cost of the
energy produced would be about twice that
from a conventional power station. It is a
practicable but hardly attractive prospect.
Wave
Once again the energy in the waves is
enormous, but it is difficult to concentrate. A
number of devices to do this have been built,
but the output is not cost-effective. One such
device, costing over a million pounds, had a
power output of 75 kW, enough for 25
domestic electric heaters. Wave machines
are, moreover, always at the mercy of storms,
which can destroy them in a few minutes.
Solar
The sun pours energy on to the earth at the
average rate of about 200 watts per square
metre so that the amount of energy that we
obtain is proportional to the area of the
collectors. It has been estimated that to supply
the energy needs of four houses requires a
collector the size of a large radio telescope.
The sunlight can be used directly to heat
domestic water circulating in pipes on the
roof. This process is reasonably economic
and is widely used. Nevertheless, there has to
be an additional source of energy for times
when the sun is not shining. On a larger scale
it is possible to focus the sun’s rays on a boiler
at the center of an array of hundreds of
mirrors. The steam produced can be used to
drive a small turbine to produce electricity.
The disadvantage is that the mirrors have to
be constantly turned by servomechanisms to
keep the sun’s rays focussed on the boiler so
the whole process is uneconomic.
Electricity can also be obtained using photoelectric
cells. These are expensive to make
and produce electricity with a low voltage.
They are not economic for large-scale generation,
but are very useful to generate electricity
in situations where the other sources are
impossible or impracticable, such as in satellites
and traffic signals in remote areas.
Thus solar power has useful but small-scale
applications that will certainly be developed
further when the cost of photoelectric cells is
reduced. It is not a practical economic source
of energy for the major needs.
Geothermal
The interior of the earth is hot, and in some
places hot water gushes out. This can be used
as an energy source, but on a small scale in
rather few places. Elsewhere it is possible to
drill two nearby shafts, pulverise the rock
between their ends, and then pump water
down one and extract it by the other. Passing
through the rock, the water is heated and is
an energy source. However if the shafts are
close the heat in the vicinity is soon used up,
whereas if they are far apart the water has
difficulty in passing from one shaft to the
other. Trials show that this process is absolutely
uneconomical.
Costs
In our society, costs are crucial. Even a small
difference is enough to ensure the dominance
of one product over another. With energy
sources the situation is more complex because
the choice depends on weighing the
advantages and disadvantages of each source.
This is difficult because they are often incommensurable:
how much, for example,
are we prepared to pay for increased safety or
to reduce the effects on the environment?
Finally, it is impossible to estimate the cost of
delayed damage, such as that due to global
warming and climate change. These costs
could well be the greatest of all.
Several studies
have been made of
the costs of generating
electricity in
various ways, and
these are given in
the Table. Oil is not
included because
the impending
shortage will drive
its cost upwards, and
it is not a long-term
option.
Examination of
this Table shows
both a fair measure of agreement as well as
substantial differences among various authorities.
This is to be expected because of differing
criteria and the uncertainties of the estimates.
It is clear that anyone wanting to make a case
for a particular source can choose his figures
accordingly. The costs quoted for wind are
uncertain because they are not based on actual
experience for a sufficient number of years.
It is sometimes said that more research will
improve existing sources and thus remove
some current disadvantages. Generally this is
true. But in some cases the disadvantage is a
consequence of the laws of physics, and then
it can never be overcome. An example is the
fluctuating nature of wind energy; it is just
not possible to make the wind blow steadily
all the time.
The worldwide need for energy is so urgent
that it is essential to use existing energy
sources. It is of course necessary to continue
research into new sources, but we cannot wait.
Already over the years millions of people have
been killed or had
their lives impoverished,
by energy
shortages.
This survey
shows that at a
time of increasing
energy demands
the sources
listed all have serious
disadvantages:
oil and
natural gas are fast
running out, and
in any case, all
fossil fuels, especially coal, are polluting.
Hydropower is limited, and wind and solar
energy are unreliable. If that were the end of
the story the future would be bleak indeed.
However there is another energy source, the
nucleus of the atom. The potentialities of this
energy source, its advantages and disadvantages,
will be considered in the next article.
References:
- There are many books where more
detailed accounts may be found: Wolf Hafele, ed.,
Energy in a Finite World: A Global Systems Analysis
(Ballinger Publishing Company, 1981). P. E. Hodgson,
Nuclear Power, Energy and the Environment (Imperial College
Press, 1999). - E. von Weiszacker, A. B. Lovins, and
L. H. Lovins, Factor of Four: Doubling Wealth – Halving
Resources (Earthscan Publications Ltd, 1996). - Bjørn
Lomborg, The Skeptical Environmentalist (Cambridge:
Cambridge University Press, 1998). - H. Inhaber, Risk
of Energy Production (Ottawa: Atomic Energy Control
Board, 1981).
