. 11
( 13)


1850 1900 1950 2000 2050

a WEC study on renewable energy,7 a substantial growth in the share
of primary energy supply coming from new renewable energy sources
(˜modern™ biomass, solar, wind and so on). A growth in world energy
supply from these new renewable sources from two per cent in 1990 to
twelve per cent in 2020 (by when 1.4 Gtoe per year would be coming
from these sources) is considered feasible if their development is given
suf¬cient support. By the year 2050 under scenario C, twenty per cent
of energy supply is assumed to come from new renewable sources and
by 2100, ¬fty per cent. The WEC report points out that ˜cost effective
research, development and installation involving ¬nancing which only
governments can supply will be needed if these sources of energy are
to be implemented on the large scale shown in the Ecologically Driven
Case C™. Renewable energy sources will be discussed further later in the
During the last few years many organisations have developed miti-
gation energy scenarios for the twenty-¬rst century under a wide variety
of assumptions regarding the growth of total energy, renewable energy
and energy ef¬ciency.8 As one example of these, Figure 11.7 shows a
scenario developed by the Shell Oil Company which is called ˜Dynamics
276 Energy and transport for the future

as Usual™. The ¬gure illustrates the large transitions that have occurred
in energy sources in the past and those that will have to take place in the
The following sections address how increased energy conservation
and ef¬ciency can be achieved and what developments can be realised in
new renewable energy sources; these are the technical means through
which the necessary reductions in carbon dioxide emissions will be
achieved in the energy sector.

World Energy Council scenarios
The World Energy Council (WEC) is an international non-governmental
organisation with representation from all parts of the energy industry and
from over ninety countries. The Council has developed four energy scen-
arios for the period to 2020, each representing different assumptions in
terms of economic development, energy ef¬ciencies, technology transfer
and the ¬nancing of development round the world. The WEC emphasises
that they have been developed to illustrate future possibilities and they
should not be considered as predictions.
All four cases assume that there will be signi¬cant environmental and
economic pressures to achieve major improvements in energy ef¬ciency
compared to historic performance, although to different degrees within
the various economic groupings of countries. One of them, scenario
C, assumes very strong pressure to reduce the emissions of greenhouse
gases in order to combat global warming. Table 11.1 presents the detailed
assumptions underlying the four scenarios.
Table 11.1 refers to the ˜energy intensity™ (see box on page 272),
which is a measure of energy ef¬ciency. When averaged over the world,
over the past ¬fty years it has been falling by about one per cent per year. A
more demanding rate of reduction in energy intensity than this is assumed
for all the scenarios; for case C, the ecologically driven scenario, the rate
assumed is considered very demanding indeed. The main difference
between the modi¬ed reference case B1 and the reference case B is that,
in B1, the rate of reduction of energy intensity assumed for the economies
in transition is less than in case B and for the developing countries is
only half that in case B.
With somewhat less detail, scenarios A, B and C have been extended
to the year 2100 (Figure 11.4). Global energy demand can be expected to
continue to increase, but by that time the availability of fossil fuels will
be more limited and new renewables will contribute substantially to the
energy mix for all scenarios. Some of the characteristics of the scenarios
out to 2100 are listed in Table 11.2 “ similar details of the scenarios for
2020 are in Figure 11.6.
Future energy projections 277

Table 11.1 Assumptions underlying the four WEC energy scenarios. See glossary
for explanation of abbreviations

Case (name)

A B1 B C
Assumptions (High growth) (Modi¬ed reference (Reference) (Ecologically driven

Economic growth % p.a. High Moderate Moderate Moderate
OECD 2.4 2.4 2.4 2.4
CEE/CIS 2.4 2.4 2.4 2.4
DCs 5.6 4.6 4.6 4.6
World 3.8 3.3 3.3 3.3
Energy intensity
reduction % p.a. High Moderate High Very high
’1.8 ’1.9 ’1.9 ’2.8
’1.7 ’1.2 ’2.1 ’2.1
’1.3 ’0.8 ’1.7 ’2.4
’1.6 ’1.3 ’1.9 ’2.4
Technology transfer High Moderate High Very high
improvements (world) High Moderate High Very high
Possible total demand Very high High Moderate Low
(Gtoe) 17.2 16.0 13.4 11.3

From Energy for Tomorrow™s World: the Realities, the Real Options and the Agenda for Achievement.
WEC Commission Report. New York: World Energy Council, p. 27.

Table 11.2 Some characteristics of the WEC scenarios out to the year 2100


1990 2050 2100 2050 2100 2050 2100
Global energy demand (Gtoe) 8.8 27 42 23 33 15 20
Fossil fuels (% of primary energy) 77 58 40 57 33 58 15
Nuclear (% of primary energy) 5 14 29 15 28 8 11
New renewables
(% of primary energy) 2 15 24 14 26 20 50
Annual CO2 emissions
from fossil fuels (Gt carbon) 6.0 14.9 16.6 12.2 11.7 7.3 2.5
Annual CO2 emissions from
fossil fuels (% change on 1990) 152 181 107 98 24

From Energy for Tomorrow™s World: the Realities, the Real Options and the Agenda for Achievement.
WEC Commission Report. New York: World Energy Council, p. 304.
278 Energy and transport for the future

Energy conservation and ef¬ciency in buildings
If we turn lights off in our homes when we do not need them, if we turn
down the thermostat by a degree or two so that we are less warm or if
we add more insulation to our home, we are conserving or indeed saving
energy. But are such actions signi¬cant in overall energy terms? Is it
realistic to plan for really worthwhile savings in our use of energy?
To illustrate what might be possible, let us consider the ef¬ciency
with which energy is currently used. The energy available in the coal,
oil, gas, uranium, hydraulic or wind power is primary energy. It is either
used directly, for instance as heat, or it is transformed into motor power
or electricity that in turn provides for many uses. The process of energy
conversion, transmission and transformation into its ¬nal useful form
involves a proportion of the primary energy being wasted. For example,
to provide one unit of electrical power at the point of use typically requires
about three units of primary energy. An incandescent light bulb is about
three per cent ef¬cient in converting primary energy into light energy;

Thermodynamic ef¬ciencies
When considering the ef¬ciency of energy use, it can be important to
distinguish between ef¬ciency as de¬ned by the First Law of Thermo-
dynamics and ef¬ciency as de¬ned by the Second Law. The second
particularly applies when energy is used for heating.
A furnace used to heat a building may deliver to heating the building
say eighty per cent of the energy released by full combustion of the fuel,
the rest being lost through the pipes, ¬‚ue, etc. That eighty per cent is
a First Law ef¬ciency. An ideal thermodynamic device delivering 100
units of energy as heat to the inside of a building at a temperature of
20 —¦ C from the outside at a temperature of 0 —¦ C would only require just
under seven units of energy. So the Second Law ef¬ciency of the furnace
is less than six per cent.
Heat pumps (refrigerators or air conditioners working in reverse)
are devices that make use of the Second Law and deliver more energy
as heat than the electrical energy they use.12 Although typically their
Second Law ef¬ciencies are only about thirty per cent, they are still able
to deliver more heat energy than the primary energy required to generate
the electricity they use. Because of their comparatively high capital and
maintenance costs, however, heat pumps have not been widely used. An
example of their substantial use is their contribution to district heating
in the city of Uppsala in Sweden where 4 MW of electricity is employed
to extract heat from the river and deliver 14 MW of heat energy.
Energy conservation and ef¬ciency in buildings 279

unnecessary use of lighting reduces the overall ef¬ciency to perhaps
no more than one per cent.9 Assessments have been carried out across
all energy uses comparing actual energy use with that which would be
consumed by ideal devices providing the same services. Although there
is some dif¬culty in de¬ning precisely the performance of such ˜ideal™
devices (see box below for a discussion of thermodynamic ef¬ciencies),
assessments of this kind come up with world average end-use energy
ef¬ciencies of the order of three per cent. That sort of ¬gure suggests
that there is a large amount of room for improvement in energy ef¬ciency,
perhaps by at least threefold.10 In this section we look at the possibilities
for energy saving in buildings; in later sections we shall consider possible
savings in transport and in industry.11
To be comfortable in buildings we heat them in winter and cool them
in summer. In the United States, for instance, about thirty-six per cent

Ef¬ciency of appliances
There is large potential for reducing the electricity consumption from
appliances used in domestic or commercial buildings. If, in replacing
appliances, everyone bought the most ef¬cient available, their total elec-
tricity consumption could easily drop by more than half.
Take lighting for instance. One-¬fth of all electricity used in the USA
goes directly into lighting. This can easily be reduced by the wider use of
compact ¬‚uorescent light bulbs that are as bright as ordinary light bulbs,
but use a quarter of the electricity and last eight times as long before
they have to be replaced “ with signi¬cant economic savings to the user.
For instance, a 20-W compact ¬‚uorescent bulb (equivalent to a 100-W
ordinary incandescent light bulb) costing £5 or less will use about £20
worth of electricity over its lifetime of twelve years. To cover the same
period eight ordinary bulbs would be needed costing about £4 but using
£100 worth of electricity. The net saving is therefore about £80. A further
large increase in the ef¬ciency of lighting will occur when light emitting
diodes (LEDs) giving out white light become commonplace.14 The latest
such device that is about one square centimetre in size and consuming
only 3-W, produces the same light as a 60-W incandescent bulb.
The average daily electricity use from the appliances in a home
(cooker, washing machine, dishwasher, refrigerator, freezer, TVs, light-
ing) for typical appliances bought in the early 1990s amounts to about
10 kWh per day. If these were replaced by the most ef¬cient available
now, electricity use would fall by about two-thirds. The extra cost of
the purchase of ef¬cient appliances would soon be recovered in the sav-
ings in running cost. Similar calculations can be carried out for other
Insulation of buildings
About one and a half thousand million people live in cold climates where some heating in
buildings is required. In most countries the energy demand of space heating in buildings is far
greater than it need be if the buildings were better insulated.
Table 11.3 provides as an example details of two houses, showing that the provision of
insulation in the roof, the walls and the windows can easily lead to the energy requirement for
space heating being more than halved (from 5.8 kW to 2.65 kW). The cost of the insulation is
small and is quickly recovered through the lower energy cost.
If a system for circulating air through the house is also installed, the number of necessary
air changes with outside air is less and the total heating requirement further reduced. In this
case it is worthwhile to add more insulation to reduce the heating requirement still further.

Table 11.3 Two assumptions (one poorly insulated, and one moderately well insulated)
regarding construction of a detached, two-storey house with ground ¬‚oor of size 8 m — 8 m,
and the accompanying heat losses (U -values express the heat conduction of different
components in watts per square metre per —¦ C)

Moderately well
Poorly insulated insulated

Brick + cavity + block U -value Brick + cavity + block with
Walls (150 m2
total area) 0.7 insulation in cavity of 75 mm
thickness: U -value 0.3
Roof (85 m2 area) Uninsulated U -value 2.0 Covered with insulation of
thickness 150 mm: U -value 0.2
Floor (64 m2 ) Uninsulated U -value 1.0 Includes insulation of thickness 50
mm: U -value 0.3
Windows (12 m2 Single glazing Double glazing with low
total area) U -value 5.7 emissivity coating: U -value 2.0

Heat losses (in kW) with 10 —¦ C
temperature difference from
inside to outside

Total heat loss (kilowatts) 4.2 1.05
Add heat (in kilowatts) needed
for air changes
(1.5 per hour) 1.60 1.60
Total heating required 5.8 2.65
Energy conservation and ef¬ciency in buildings 281

of the total use of energy is in buildings (about two-thirds of this in
electricity), including about twenty per cent for their heating (including
water heating) and about three per cent for cooling.13 Energy demand
in the buildings sector grew by about three per cent per year averaged
worldwide from 1970 to 1990 and, apart from countries with economies
in transition, has been growing during the last decade by about 2.5% per
year. How can these trends be reversed?
Substantial energy savings can be made in buildings by improving
their insulation (see box above) and by improving the ef¬ciency of appli-
ances (see box on page 279). Many countries, including the UK and the
USA, still have relatively poor standards of building insulation compared,
for instance, with Scandanavian countries. Improvements in building de-
sign to make better use of energy from sunlight can also help (see box
on page 301). There are also large possibilities for the improvement of
the ef¬ciency of appliances at relatively small cost.
The results of a study in the USA have identi¬ed some of the large
savings that could be made in the electricity used in buildings. The
cost of such action would be less than the cost of the energy savings;
overall therefore there would be a substantial net saving (Figure 11.8).
The twelve options in Figure 11.8 together cover about forty-¬ve per
cent of the amount of electricity used in residential buildings in the
USA, which in 1990 was about 1700 TWh or about ten per cent of
the USA™s total energy use. The four options that provide the largest
savings (together adding up to sixty per cent of the savings) are in the
areas of commercial lighting, commercial air conditioning, residential
appliances and residential space heating. Electricity companies in
some parts of the USA are contracting to implement some of these
energy-saving measures as an alternative to the installation of new
capacity “ at signi¬cant pro¬t both to the companies and its customers.
Similar savings would be possible in other developed countries. Major
savings at least as large in percentage terms could also be made in
countries with economies in transition and in developing countries if
existing plant and equipment were used more ef¬ciently.
Further large savings can be realised when buildings are being
planned and designed by the employment of integrated building design.
When buildings are designed, the designs of the systems for heating, air
conditioning and ventilation are commonly carried out separately from
the main design. The value of integrated building design is that energy-
saving opportunities can be taken up associated with the synergies be-
tween many aspects of the overall design and the design (including the
sizing) of the systems where much of the energy use occurs. Many ex-
amples exist of low energy buildings, where integrated building design
has been employed, that consume less than half the energy and are often
282 Energy and transport for the future


Cost of conserved electricity (US cents per kWh)


4 10

2 6

0 200 400 600 800
Electricity savings (TWh year

Figure 11.8 Cost of various options (at 1989 prices) for saving electricity in
buildings. If the cost of conservation is less than the cost of the electricity saved
over the lifetime of the application, a net saving results. The various options are:
(1) use of white surfaces to reduce the need for air conditioning; (2) residential
lighting; (3) residential water heating; (4) commercial water heating; (5)
commercial lighting; (6) commercial cooking; (7) commercial cooling; (8)
commercial refrigeration; (9) residential appliances; (10) residential space
heating; (11) commercial and industrial space heating; (12) commercial
ventilation. The shaded areas are all below 7.5 cents per kWh (the all-sector
average electricity price) and 3.5 cents per kWh (typical operating cost of US
electricity generation). The total savings in the ¬gure add up to about forty-¬ve
per cent of the electricity use.

more acceptable and user-friendly than those that have been designed in
more traditional ways.15 Some recent examples demonstrate the possi-
bility of more radical building designs that aim at Zero Emission (fossil-
fuel) Developments (ZED). The box illustrates a recent development in
the UK along these lines.
Recent studies17 suggest that with aggressive implementation of
energy-ef¬cient policies and measures, carbon dioxide emissions from
buildings in both developed and developing countries could be reduced
by about twenty-¬ve per cent in 2010 and about ¬fty per cent in 2050. If
however growth in energy demand in the buildings sector continues to
increase at the current rate, these savings in emissions due to increased ef-
¬ciency will mostly go to compensate for the growth in demand. Further
increases in ef¬ciency, however, could be achieved by new technolo-
gies that are in prospect such as the use of LEDs for lighting (see box
above on appliances). What is clearly necessary also is a switch to non-
fossil-fuel energy sources to which we shall be turning in later sections.
Energy savings in transport 283

Example of a ZED (Zero Emission (fossil-fuel)
BedZED is a mixed development urban village constructed on a brown-
¬eld wasteland in the London Borough of Sutton, providing eighty-two
dwellings in a mixture of apartments, maisonettes and town houses to-
gether with some work/of¬ce space and community facilities.16 The
combination of super-insulation, a wind-driven ventilation system in-
corporating heat recovery and passive solar gain stored within each unit
in thermally massive ¬‚oors and walls reduces the energy needs so that a
135-kW wood-fuelled combined heat and power (CHP) plant is suf¬cient
to meet the village™s energy requirements. A 109-kW peak photovoltaic
installation provides enough solar electricity to power forty electric cars,
some pool, some taxi, some privately owned. The community has the
capacity to lead a carbon neutral lifestyle “ with all energy for buildings
and local transport being supplied from renewable sources.

Energy savings in transport
Transport is responsible for nearly one-quarter of greenhouse gas emis-
sions worldwide. It is also the sector where emissions are growing
most rapidly. Road transport accounts for the largest proportion of this,
over eighty per cent in industrialised countries; air transport is next at
thirteen per cent. Since 1970, the number of motor vehicles in the United
States has grown at an average rate of 2.5% per year, in the rest of the
world the growth has been almost twice as rapid at nearly ¬ve per cent
per year (Figure 11.9). The latter trend will continue or increase as there
remain very large differences in the degree of car ownership between
different countries “ for instance about 1.5 persons per car in the USA
and a little over 100 persons per car in India and China. The advantages
conferred by the motor car, the convenience, freedom and ¬‚exibility that
it brings, mean that growth in its use is bound to continue. Increased pros-
perity also brings with it increased movement of freight. In the transport
sector the achievement of reductions in carbon dioxide emissions will
be particularly challenging.
There are three types of action that can be taken to curb the energy use
of motor transport.18 The ¬rst is to increase the ef¬ciency of fuel use. We
cannot expect the average car to compete with the vehicle which, in 1992,
set a record by covering over 12 000 km on one gallon of petrol “ a journey
which serves to illustrate how inef¬ciently we use energy for transport!
However, it is estimated that the average fuel consumption of the current
¬‚eet of motor cars could be halved through the use of existing technology
284 Energy and transport for the future

Figure 11.9 Growth of world
motor vehicle population,

(see box below) “ more ef¬cient engines, lightweight construction and
low-air-resistance design “ while maintaining an adequate performance.
The second action is to plan cities and other developments so as to
lessen the need for transport and to make personalised transport less
necessary “ work, leisure and shopping should all be easily accessible
by public transport, or by walking or cycling. Such planning needs also
to be linked with a recognition of the importance of ensuring that public
transport is reliable, convenient, affordable and safe. The third action is to
increase the energy ef¬ciency of freight transport by making maximum
use of the most energy-ef¬cient forms of freight transport, e.g. rail or
water rather than road or air and by eliminating unnecessary journeys.
Air transport is growing even faster than motor transport. Global
passenger air travel, as measured in passenger-km, is projected to grow at
about ¬ve per cent per year over the next decade or more and total aviation
fuel use “ including passenger, freight and military “ is projected to
increase by about three per cent per year, the difference being due largely
to increased fuel ef¬ciency.19 Further increases in fuel ef¬ciency are
expected but they are unlikely to keep up with the increase in the volume
of air transport. A further problem with air transport, as mentioned in
Chapter 3 page 52, is that its carbon dioxide emissions are not the only
contributor to global warming; increased high cloudiness due to other
emissions produce an effect of similar or even greater magnitude. Further
research directed at understanding the climatic effects of aircraft and how
they may be reduced is urgently required.

Energy savings in industry
Substantial opportunities exist for ef¬ciency savings in industry. The
installation of relatively simple control technology often provides large
Energy savings in industry 285

Technologies for reducing carbon dioxide emissions
from motor cars20
An important recent development is that of the hybrid electric motor car
that combines an internal combustion engine with an electric drive train
and battery. The gains in ef¬ciency and therefore fuel economy achieved
by hybrid vehicles are typically around ¬fty per cent. They mainly arise
from: (1) use of regenerative braking (with the motor used as a generator
and captured electricity stored in the battery), (2) running on the bat-
tery and electric traction only when in slow moving or congested traf¬c,
(3) avoiding low ef¬ciency modes of the internal combustion engine and
(4) downsizing the internal combustion engine through the use of the
motor/battery as a power booster. Both Toyota and Honda have intro-
duced commercially available hybrid models and other manufacturers
are not far behind.
Other signi¬cant ef¬ciency improvements have come from the use
of lower weight structural materials, improvements in low-air-resistance
design and the availability of direct injection diesel engines, long used
in heavy trucks, for automobiles and light trucks.
Biofuels generated from crops can be employed to fuel motor ve-
hicles thereby avoiding fossil fuel use. For instance, ethanol has been
extensively produced from sugarcane in Brazil and from maize in the
USA. Biodiesel is also becoming more widely available. However, such
fuels can as yet only compete with fossil fuels if they are strongly sub-
During the next few years we will begin to see the introduction of
vehicles driven by fuel cells (see Figure 11.15) based on hydrogen fuel
that can potentially be produced from renewable sources (see page 310).
This new technology has the potential to have a large in¬‚uence on the
transport sector.

potential for energy reduction at a substantial net saving in cost. The
co-generation of heat and power, which already enables electricity gen-
erators to make better use of heat which would otherwise be wasted, is
particularly applicable to some industrial plants where large amounts
of both heat and power can be required. To take an example: British
Sugar in 1992 with an annual turnover of £700 million spent £21 million
p.a. on energy. Through low-grade heat recovery, co-generation schemes
and better control of heating and lighting, in 1992 the spend on energy
per tonne of sugar had been reduced by forty-one per cent from that in
1980.21 Other potential decreases in carbon dioxide emissions can occur
through the recycling of materials, the use of waste as an energy source
Table 11.4 Estimates of potential global greenhouse gas emission reductions in 2010 and in 2020

Historic emission Potential emission Potential emission
Historic Ceq
in 1990 annual growth rate in reductions in 2010 reductions in 2020 Net direct costs per tonne
Sector 1990“1995(%) of carbon avoided
(MtCeq yr ) (MtCeq yr’1 ) (MtCeq yr’1 )

Buildingsa 1650 1.0 700“750 1000“1100 Most reductions are available at
CO2 only
negative direct costs.
Transport 1080 2.4 100“300 300“700 Most studies indicate net direct costs
CO2 only
less than $US 25/tC but two suggest
net direct costs will exceed $US 50/tC.
Industry 2300 0.4
CO2 only
Energy ef¬ciency 300“500 700“900 More than half available at net negative
Material ef¬ciency direct costs. Costs are uncertain.
∼200 ∼600
Industry 170
Non-CO2 gases N2 O emissions reduction costs are
∼100 ∼100
$US 0“10/tCeq .
Agricultureb 210 Most reductions will cost between
CO2 only
1250“2800 n.a 150“300 350“750
Non-CO2 gases $US 0 and 100/tCeq. with limited
opportunities for negative net direct
cost options.
Wasteb 240 1.0 About 75% of the savings as methane
CH4 only ∼200 ∼200
recovery from land¬lls at net negative
direct cost; 25% at a cost of
$US 20/tCeq .
Montreal Protocol 0 n.a. n.a. About half of reductions due to
Non-CO2 gases ∼ 100
replacement difference in study baseline and SRES
applications baseline values. Remaining half of the
reductions available at net direct costs
below $US 200/tCeq .
Energy supply and (1620) 1.5 50“150 350“700 Limited net negative direct cost
CO2 only
conversionc options exist; many options are
available for less than $US 100/tCeq .
Total 6900“8400d 1900“2600e 3600“5050e

Buildings include appliances, buildings, and the building shell.
The range for agriculture is mainly caused by large uncertainties about CH4 , N2 O and soil related emissions of CO2 . Waste is dominated by land¬ll methane and the
other sectors could be estimated with more precision as they are dominated by fossil CO2 .
Included in sector values above. Reductions include electricity generation options only (fuel switching to gas/nuclear, CO2 capture and storage, improved power
station ef¬ciencies, and renewables).
Total includes all sectors for all six gases. It excludes non-energy related sources of CO2 (cement production, 160 MtC; gas ¬‚aring, 60 MtC; and land use change,
600“1400 MtC) and energy used for conversion of fuels in the end-use sector totals (630MtC). Note that forestry emissions and their carbon sink mitigation options
are not included.
The baseline SRES scenarios (for six gases included in the Kyoto Protocol) project a range of emissions of 11 500“14 000 MtCeq for 2010 and of 12 000“16 000
MtCeq for 2020. The emissions reduction estimates are most compatible with baseline emissions trends in the SRES-B2 scenario. The potential reductions take into
account regular turn-over of capital stock. They are not limited to cost-effective options, but exclude options with costs above $US 100/tCeq (except for Montreal
Protocol gases) or options that will not be adopted through the use of generally accepted policies.
Source: Table SPM-1 from Metz, Climate Change 2001: Mitigation, Chapter 3. Further information in Moomaw and Moreira et al., Chapter 3 in Metz et al. Climate
Change 2001: Mitigation.
288 Energy and transport for the future

and through switching to less carbon intensive fuels. Many studies in
industrialised countries indicate that savings of thirty per cent or more
could be made in the industrial sector at a net saving in overall economic
Given appropriate incentives, substantial savings of carbon dioxide
emissions can also be realised in the petrochemical industry that can
result in signi¬cant savings in cost. For instance, British Petroleum has
set up a carbon emissions trading system within the company that en-
courages the elimination of waste and leaks from their operations and
the application of technology to eliminate the venting of methane. In
its ¬rst three years of operation, 600 million US dollars were saved and
carbon emissions reduced to ten per cent below 1990 levels.23
There is also room for increased ef¬ciency in large power stations
or other installations burning fossil fuels. The ef¬ciency of coal-¬red
power stations, for instance, has improved from about thirty-two per
cent, a typical value of twenty years ago, to about forty-two per cent
for a pressurised, ¬‚uidised bed combustion plant of today. Gas turbine
technology has also improved providing ef¬ciency improvements such
that ef¬ciencies approaching sixty per cent are reached by large modern
gas-turbine-combined cycle plants. Such improvements are very signif-
icant in environmental terms and it is important that means be provided
for the latest, most ef¬cient technology to be available and attractive
to rapidly industrialising countries such as China and India. Substan-
tial further gains in overall ef¬ciency can be realised by making sure
that the large quantities of low-grade heat generated by power stations
is not wasted but utilised, for instance in combined heat and power
(CHP) schemes. For such co-generation, the ef¬ciencies attainable in
the use of the energy from combustion of the fuel are typically around
eighty per cent.
Table 11.4 provides summary estimates of the contributions differ-
ent sectors or industries could make to greenhouse gas reductions by
2010 and 2020 respectively. In total they amount to about half of the
emissions from these industries or sectors in 1990. Many of the contri-
butions summarised in the table and most of the proposals described in
this section fall into the category of ˜no regrets™ proposals “ mentioned in
Chapter 9. In other words, not only do they lead to substantial reductions
in greenhouse gas emissions but they are good to do for other reasons “
they lead to increased ef¬ciency, cost savings or improvements in per-
formance or comfort. It remains the case, however, that basic energy
is generally so cheap, that without both encouragement and incentives,
progress with the implementation of many of the proposals will be lim-
ited. Some of the policy instruments mentioned later can address this
Capture and storage of carbon dioxide 289

Capture and storage of carbon dioxide
An alternative to moving away from fossil fuel sources of energy is to
prevent the carbon dioxide from fossil fuel burning from entering the
atmosphere. This can be done either by removing it from the ¬‚ue gases
in a power station, or the fossil fuel feedstock could, in a gasi¬cation
plant, be converted through the use of steam,24 to carbon dioxide and
hydrogen. The carbon dioxide is then relatively easy to remove and the
hydrogen can be used as a versatile fuel. The latter option will become
more attractive when the technical and logistic problems of the large-
scale use of hydrogen in fuel cells to generate electricity have been
overcome “ we mention this again later in the chapter.
Various options are possible for the disposal (or sequestration) of
the very large amounts of carbon dioxide which result. For instance,
the carbon dioxide can be pumped into spent oil or gas wells, into deep
saline reservoirs or into unminable coal seams.25 Other suggestions have
also been made such as pumping it into the deep ocean, but these are
more speculative and need careful research and assessment before they
can be realistically put forward. In the most favourable circumstances
(for instance when power stations are close to oil or gas ¬elds and when
the extraction cost is relatively small), the cost of removal, although
signi¬cant, is only a small fraction of the total energy cost. For instance,
in Norway where there is carbon tax of $US l5 per tonne of carbon, a
company is ¬nding it economic to pump over one million tonnes per year
of carbon dioxide removed from a natural gas stream into storage under
the North Sea. In other circumstances estimates of the cost are larger
(perhaps up to 100% on top of the energy cost) “ the cost of extraction
being generally larger than the cost of storage.
The technology of carbon capture and storage could enable contin-
uing use of fossil fuels without the deleterious effects of carbon dioxide
emissions. The global potential for underground carbon dioxide storage
is large. For instance, it has been estimated that over 200 Gt of carbon
as carbon dioxide could be stored in geological reservoirs in north west
Europe alone. How much it is used will depend more on the cost than
on the availability of suitable storage sites.

Renewable energy
To put our energy use in context it is interesting to realise that the energy
incident on the Earth from the Sun amounts to about 180 thousand million
million watts (or 180 000 terawatts, 1 TW = 1012 W). This is about
14 000 times the world™s average energy use of about 13 million million
watts (13 TW). As much energy arrives at the Earth from the Sun in
290 Energy and transport for the future

forty minutes as we use in a whole year. So, providing we can harness
it satisfactorily and economically, there is plenty of renewable energy
coming in from the Sun to provide for all the demands human society
can conceivably make.
There are many ways in which solar energy is converted into forms
that we can use; it is interesting to look at the ef¬ciencies of these con-
versions. If the solar energy is concentrated, by mirrors for instance,
almost all of it can be made available as heat energy. Between one and
two per cent of solar energy is converted through atmospheric circula-
tion into wind energy, which although concentrated in windy places is
still distributed through the whole atmosphere. About twenty per cent of
solar energy is used in evaporating water from the Earth™s surface which
eventually falls as precipitation, giving the possibility of hydropower.
Living material turns sunlight into energy through photosynthesis with
an ef¬ciency of around one per cent for the best crops. Finally, photo-
voltaic (PV) cells convert sunlight into electricity with an ef¬ciency that
for the best modern cells can be over twenty per cent.
Around the year 1900, very early in the production of commer-
cial electricity, water power was an obvious source and from the begin-
ning made an important contribution. Hydroelectric schemes now supply
about six per cent of the world™s commercial energy. Other renewable
sources of commercial energy, however, have been dependent on recent
technology for their implementation. In 1990, only about two per cent of
the world™s commercial energy came from renewable sources other than
large hydro26 (these are often collectively known as ˜new renewables™).
Of this two per cent (Table 11.5), about three-quarters was from ˜mod-
ern™ biomass (called ˜modern™ when it contributes to commercial energy
to distinguish it from traditional biomass), the other 0.5% being shared
between solar, wind energy, geothermal and small hydro sources.
Returning to commercial energy generation, in order to put renew-
able sources into context, it is useful to inspect the detailed projection of
the WEC (Table 11.5) for the contributions from different ˜new renew-
able™ sources which make up the twelve per cent of total energy supply
in the year 2020 assumed for the WEC scenario C. The main growth
expected is in energy from ˜modern™ biomass and from solar and wind
energy sources. Table 11.6 provides detailed summary information about
the status and cost of different renewable energy sources.
In the following paragraphs, the main renewable sources are de-
scribed in turn and their possibilities for growth considered.27 Most of
them are employed for the production of electricity through mechanical
means (for hydro and wind power), through heat engines (for biomass and
solar thermal) and through direct conversion from sunlight (solar PV).
In the case of biomass, liquid or gaseous fuels can also be produced.
Hydro-power 291

Table 11.5 Contributions to world energy supply (in millions of tonnes
of oil equivalent) from renewable sources in 1990 and as assumed
under the WEC scenario C in 2020

1990 2020

% of world % of world
Mtoe energy Mtoe energy

˜Modern™ biomass 121 1.4 561 5.0
Solar 12 0.1 355 3.1
Wind 1 0.0 215 1.9
Geothermal 12 0.1 91 0.8
˜Small™ hydro 18 0.2 69 0.6
Tides, waves and 0 0.0 54 0.5
tidal streams
Total (new 164 1.8 1345 11.9
renewable sources)
˜Large™ hydro 465 5.3 661 5.8
˜Traditional™ biomass 930 10.6 1060 9.3
Total (all renewables) 1559 17.7 3066 27.0

From Energy for Tomorrow™s World: the Realities, the Real Options and The
Agenda for Achievement. WEC Commission Report. 1993. London: World En-
ergy Council, p. 94.

Hydro-power, the oldest form of renewable energy, is well established and
is competitive economically with electricity generated by other means.
Some hydroelectric schemes are extremely large. The world™s largest, the
Three Gorges project on the Yangtze river in China, when completed will
generate about 20 000 MW of electricity. Two other large schemes, each
of over 10 000 MW capacity, are in South America at Guri in Venezuela
and at Itaipu on the borders of Brazil and Paraguay. It is estimated28
that there is potential for further exploitation of hydroelectric capacity
to three or four times the amount that has currently been developed,
much of this undeveloped potential being in the former Soviet Union and
in developing countries. Large schemes, however, can have signi¬cant
social impact (such as the movement of population from the reservoir
site), environmental consequences (for example, loss of land, of species
and of sedimentation to the lower reaches of the river), and problems
of their own such as silting up, which have to be thoroughly addressed
before they can be undertaken.
292 Energy and transport for the future

Table 11.6 Current status and potential future costs of renewable energy technologies. The costs can
be compared with typical current costs of fossil fuel supplied energy of 3 to 6 ¢US kWh’1

installed Potential
capacity Operating Energy Turnkey Energy future
in last ¬ve capacity production, investment cost in energy
years “ end year Capacity 1998 costs year 1999 cost
($US kW’1 ) (¢US kWh’1) (¢US kWh’1)
1998 GWa factor (%) TWha
Technology (% p.a.)

Large 640 (e) 35“60 2510 (e) 1000“3500 3“8 3“8
Small 23 (e) 20“70 90 (e) 1200“3000 5“10 4“10
Electricity 40 (e) 25“80 160 (e) 900“3000 5“15 4“10
Heatb >200 (th) 25“80 >700 (th) 250“750 1“5 1“5
∼3 18 — 10 litres
Ethanol 120 3“9 2“4
(= 420 PJ)
∼ 30
Wind electricity 10 (e) 20“30 18 (e) 1100“1700 5“13 3“10
∼ 30
Solar PV 500 (e) 8“20 0.5 (e) 5000“10 000 25“125 5 or 6“25
Solar thermal 400 (e) 20“35 1.0 (e) 3000“4000 12“18 4“10
Low temperature 18 (th) 8“20 14 (th) 500“1700 3“20 2 or 3“10
solar heat
Electricity 8 (e) 45“90 46 (e) 800“3000 2“10 1 or 2“8
Heat 11 (th) 20“70 40 (th) 200“2000 0.5“5 0.5“5
Tidal 0 300 (e) 20“30 0.6 (e) 1700“2500 8“15 8“15
Currentc 25“35 2000“3000 8“15 5“7
Wavec 20“35 1500“3000 8“20

(e) refers to electrical energy and (th) to thermal energy.
Heat embodied in steam (or hot water in district heating) often produced by CHP using various forms of biomass.
Still in experimental phase.
Source: Goldemberg, J. (ed.) World Energy Assessment: Energy and the Challange of Sustainability. Table 4 from
Biomass as fuel 293

But hydroelectric schemes do not have to be large; Table 11.5 dis-
tinguishes between large and small hydroelectric sources. Many units
exist generating a few kilowatts only that may supply one farm or a
small village. The attractiveness of small schemes is that they provide a
locally based supply at modest cost. Substantial growth in ˜small hydro™
has occurred during the last decade or so, from around 20 000 MW in
1990 to about 40 000 MW in 2000.29 Installations in China account for
about half of this latter ¬gure where the growth has been about twice
as rapid as in the rest of the world. Many more possibilities still exist
for the exploitation of the potential of small rivers and streams in many
parts of the world.
An important facility provided by some hydro schemes is that of
pumped storage. Using surplus electricity available in off-peak hours,
water can be pumped from a lower reservoir to a higher one. Then, at
other times, by reversing the process, electricity can be generated to
meet periods of peak demand. The ef¬ciency of conversion can be as
high as eighty per cent and the response time a few seconds, so reducing
the need to keep other generating capacity in reserve. In 1990 about
75 000 MW of pumped storage capacity was available worldwide with
a further 25 000 MW under construction.30

Biomass as fuel31
Second in current importance as a renewable energy source is the use
of biomass as a fuel. The annual global primary production of biomass
of all kinds expressed in energy units is about 4500 EJ (= 107 Gtoe).
About one per cent of this is currently turned into energy mostly in de-
veloping countries “ we have labelled it ˜traditional biomass™. It has been
estimated that about six per cent of the total could become available for
energy crops taking into account the economics of production and the
availability of suitable land.32 The energy so generated would represent
about seventy-¬ve per cent of current world energy consumption “ a sub-
stantial contribution to global energy needs. It is a genuinely renewable
resource in that the carbon dioxide which is emitted when the biomass
is burnt is turned back into carbon, through the process of photosynthe-
sis, in the renewed biomass when it is grown again. The word biomass
not only covers crops of all kinds but also domestic, industrial and agri-
cultural dry waste material and wet waste material, all of which can be
used as fuel for heating and to power electricity generators; some are
also appropriate to use for the manufacture of liquid or gaseous fuels.
Since biomass is widely distributed, it is particularly appropriate as a
distributed energy source suitable for rural areas.
294 Energy and transport for the future

In much of the developing world, most of the population live in
areas where there is no access to modern or on-grid energy. They rely
on ˜traditional biomass™ (fuelwood, dung, rice husks and other forms of
biofuels) to satisfy their needs for cooking and heating. Ten per cent or
so of world energy originates from these sources supplying over one-
third of the world™s population. Although these sources are renewable, it
is still important that they are employed ef¬ciently, and a great deal of
room for increased ef¬ciency exists. For instance, a large proportion of
each day is often spent in collecting ¬rewood especially by the women,
increasingly far a¬eld from their homes.
The burning of biomass in homes causes serious health problems
and has been identi¬ed by the World Health Organization as one of
the most serious causes of illness and mortality especially amongst
children.33 For instance, much cooking is still carried out on open ¬res
with their associated indoor pollution and where only about ¬ve per
cent of the heat reaches the inside of the cooking pot. The introduc-
tion of a simple stove can increase this to twenty per cent or with a
little elaboration to ¬fty per cent.34 An urgent need exists for the large-
scale provision of stoves using simple technology that is sustainable “
although there is often considerable consumer resistance to their intro-
duction. Other means of reducing fuelwood demand are to encourage
alternatives such as the use of fuel from crop wastes, of methane from
sewage or other waste material or of solar cookers (mentioned again
later on). From the existing consumption of ˜traditional biomass™ there
is the potential to produce sustainable ˜modern™ energy services with
much greater ef¬ciency and much less pollution for the two billion or
so people who currently rely on this basic energy source. A particular
challenge is to set up appropriate management and infrastructure for the
provision of these services in rural areas in developing countries (see box
Firstly, consider the use of waste.37 There is considerable public
awareness of the vast amount of waste produced in modern society. The
UK, for example, produces each year somewhat over thirty million tonnes
of domestic solid waste, or about half a tonne for every citizen; this is
a typical value for a country in the developed world. Even with major
programmes for recycling some of it, large quantities would still remain.
If it were all incinerated for power generation (modern technology en-
ables this to be done with negligible air pollution) about 1.7 GW could
be generated, about ¬ve per cent of the UK™s electricity requirement.38
Uppsala in Sweden is an example of a city with a comprehensive dis-
trict heating system, for which, before 1980, over ninety per cent of the
energy was provided from oil. A decision was then made to move to
renewable energy and by 1993 energy from waste incineration and from
Biomass as fuel 295

Biomass projects in rural areas in the developing world

In much of the developing world, most of the popu- create more jobs “ all of which in turn increases the
lation live in areas where there is little or no access ability of people to pay for improved energy ser-
to electricity or modern energy services. There is vices. A ˜mutuality of interest™ is created between
large potential for creating local biomass projects biomass fuel suppliers, electricity users and plant
to provide such services. The use of sugar cane as operators.
biomass provides one example of what is beginning
Integrated biogas systems, Yunnan, China
to be provided; three other examples are given of
pilot projects in different countries,35 all of which The South-North Institute for Sustainable Devel-
opment has introduced a novel integrated biogas
could be replicated many times.
system in the Baima Snow Mountains Nature Re-
Sugar cane as biomass
serve, Yunnan Province. The system links a biogas
A sugar cane factory produces many different digester, pigsty, toilet and greenhouse. The biogas
byproducts that can be ef¬ciently employed as generated is used for cooking and replaces the burn-
sources of energy “ either for biofuels or for elec- ing of natural ¬rewood, the ˜greenhouse™ pigsty in-
tricity production. creases the ef¬ciency of pig-raising, the toilet im-
Sugar cane production yields two kinds of proves rural environmental hygiene, and vegetables
biomass fuel suitable for gasi¬cation (Figure and fruits planted in the greenhouse increase the in-
11.10), known as bagasse and barbojo. Bagasse is come of local inhabitants. Manure and other organic
the residue from crushing the cane and is thus avail- waste from the pigsty and toilet are used as the raw
able during the milling season; barbojo consists of material for biogas generation that delivers about
the tops and leaves of the cane plant, which could be 10 kWh per day of useful energy. The operation of
stored for use after the milling season. It has been es- ¬fty such systems has considerably reduced local
timated that, using these sugar cane sources, within ¬rewood consumption.
thirty years or so, the eighty sugar-cane-producing
Biomass power generation and coconut
countries in the developing world could generate
oil pressing, the Philippines
two-thirds of their current electricity needs at a price
competitive with fossil fuel energy sources.36 The Community Power Corporation (CPC) has
developed a modular biopower unit that can run
Rural power production, India
on waste residue or biomass crops and can en-
Decentralised Energy Systems India Private Lim- able village-level production of coconut oil. CPC
ited are piloting the ¬rst independent power projects and local partners are using the modular biopower
of around 100 kW capacity in rural India owned and unit fuelled by the waste coconut shells to pro-
operated by village community co-operatives. An vide electricity to a low-cost mini-coconut-oil-mill
example is a small co-operative in Baharwari, Bi- (developed by the Philippines Coconut Authority
har State, where a biomass gasi¬cation power plant and the University of Philippines), sixteen of which
is used as a source of electricity for local enter- are now operating in various Philippine villages.
prises, for instance for pumping water in the dry sea- Furthermore, the biopower unit generates waste
son. Local income is thereby generated that enables heat which is essential to drying the coconuts prior
villagers to expand their micro-industries and to pressing.
296 Energy and transport for the future

Figure 11.10 The processes involved in the sugar cane industry.

other biomass fuel sources provided nearly eighty per cent of what is
required for the city™s heating.
But what about the greenhouse gas generation from waste inciner-
ation? Carbon dioxide is of course produced from it, which contributes
to the greenhouse effect. However, the alternative method of disposal is
land¬ll (most of the waste in the UK currently is disposed of that way).
Decay of the waste over time produces carbon dioxide and methane in
roughly equal quantities. Some of the methane can be collected and
used as a fuel for power generation. However, only a fraction of it can
be captured; the rest leaks away. Because methane is a much more ef-
fective greenhouse gas, molecule for molecule, than carbon dioxide,
the leaked methane makes a substantial contribution to the greenhouse
effect. Detailed calculations show that if all UK domestic waste were
incinerated for power generation rather than land¬lled, the net saving
per year in greenhouse gas emissions would be equivalent to about ten
million tonnes of carbon as carbon dioxide.39 Since this is about ¬ve
per cent of the total UK greenhouse gas emissions, we can infer that
power generation from waste could be a signi¬cant contribution to the
reduction in overall emissions.
Other wastes resulting from human or agricultural activity are wet
wastes such as sewage sludge and farm slurries and manures. Bacterial
Wind energy 297

fermentation in the absence of oxygen (anaerobic digestion) of these
wastes produces biogas, which is mostly methane and which can be used
as a fuel to produce energy. There is room for an increasing contribution
from these sources. If the potential for power generation from agricultural
and industrial waste was taken into account, the savings in emissions
arising from domestic waste already mentioned could be approximately
Turning now to the use of crops as a fuel, the potential is large.
Many different crops can be employed as biomass for energy production.
In Brazil, for instance, since the 1970s large plantations of sugar cane
have produced alcohol for use as a fuel mainly in transport, generating,
incidentally, much less local pollution than petrol or diesel fuel from
fossil sources. A lot of potential has been recognised for the sugar cane
industry to produce both sugar and energy together with other byproducts
as well (see box above). Biomass from wood plantations on agricultural
land no longer needed for food crops features as an important future
source in Sweden™s energy plans40 ; the most ef¬cient use of the biomass
is ¬rst to turn it into biogas and then burn it in a gas turbine to produce
electricity. For the UK, trials indicate that the most promising option is
willow and poplar grown in coppices.41
Because of the low ef¬ciency of conversion of solar energy to
biomass, the amount of land required for signi¬cant energy production
by this means is large “ and it is important that land is not taken over
that is required for food production. However, there is in principle no
shortage of land for this purpose. Plenty of suitable crops are available
which could be grown on land only marginally useful for agriculture. In
many developing countries biomass plantations can provide suitable fuel
for local electricity generation more competitively than other means of
The growth of the use of biomass for energy in industrialised coun-
tries (Table 11.6) is substantial but is limited by the cost differential that
exists between energy from biomass and that generated from fossil fuels
(Table 11.6). This problem is addressed later in the chapter.

Wind energy
Energy from the wind is not new. Two hundred years ago windmills were
a common feature of the European landscape; for example, in 1800 there
were over 10 000 working windmills in Britain. During the past few years
they have again become familiar on the skyline especially in countries
in western Europe (for instance, Denmark, Great Britain and Spain) and
in western North America. Slim, tall, sleek objects silhouetted against
the sky, they do not have the rustic elegance of the old windmills, but
they are much more ef¬cient. A typical wind energy generator will have
298 Energy and transport for the future

a two- or three-bladed propeller about 50 m in diameter and a rate of
power generation in a wind speed of 12 ms’1 (43 kmh’1 , 27 mph or
Beaufort Force 6), of about 700 kW. On a site with an average wind
speed of about 7.5 ms’1 (an average value for exposed places in many
western regions of Europe) it will generate an average power of about
250 kW. The generators are often sited close to each other in wind farms
that may include several dozen such devices.
From the point of view of the electricity generating companies the
dif¬culty with the generation of electrical power from wind is that it
is intermittent. There are substantial periods with no generation at all.
The generating companies can cope with this in the context of a national
electricity grid that pools electrical power from different sources pro-
viding that the proportion from intermittent sources is not too large.42
Some public concern about wind farms arises because of loss of visual
amenity. The use of more off-shore sites may therefore be more generally
acceptable than too much concentration in windy sites on-shore.
Rapid growth has occurred in many countries in the installation of
wind generators over the past decade “ a growth that continues unabated.
But most of the growth has been for electricity generation. Over 30 GW
peak operating capacity has now (2002) been built worldwide. With
this large growth, economies of scale have brought down the cost of
the electricity generated so that it is approaching the cost of electricity
generated from fossil fuels (Table 11.6). Because the power generated
from the wind depends on the cube of the wind speed (a wind speed
of 12.5 ms’1 is twice as effective as one of 10 ms’1 ) it makes sense to
build wind farms on the windiest sites available. Some of the windiest
sites available are to be found in western Europe where some of the most
rapid growth in wind generation has occurred. In Denmark for instance,
twenty per cent of electricity is now generated by wind “ increasingly
being built offshore.43 Eventually, it is envisaged the proportion could
rise to forty to ¬fty per cent. Similar estimates of the eventual resource
are being made for the UK where rapid expansion, again especially of
off-shore wind energy generation, is envisaged.44 Developing countries
are also making increased use of wind energy. For instance, it has been
estimated that India could be generating up to 10 GW of electrical power
(about a quarter of current needs) from wind by 2030.45 With the growth
that is occurring, the proportion of global energy needs supplied from
wind energy could be substantially greater than that envisaged by the
projection in Table 11.5.
Wind energy is also particularly suitable for the generation of elec-
tricity at isolated sites to which the transmission costs of electricity from
other sources would be unacceptable. Because of the wind™s intermit-
tency, some storage of electricity or some back-up means of generation
Energy from the Sun 299

Wind power on Fair Isle
A good example46 of a site where wind power has been put to good ef-
fect is Fair Isle, an isolated island in the North Sea north of the Scottish
mainland. Until recently, the population of seventy depended on coal
and oil for heat, petrol for vehicles and diesel for electricity generation.
A 50-kW wind generator was installed in 1982 to generate electricity
from the persistent strong winds of average speed over 8 ms’1 (29 kmh’1
or 18 mph). The electricity is available for a wide variety of purposes;
at a relatively high price for lighting and electronic devices and at a
lower price controlled amounts are available (wind permitting) for com-
fort heat and water heating. At the frequent periods of excessive wind
further heat is available for heating glasshouses and a small swimming
pool. Electronic control coupled with rapid switching enables loads to
be matched to the available supply. An electric vehicle has been charged
from the system to illustrate a further use for the energy.
With the installation of the wind generator, which now supplies over
ninety per cent of the island™s electricity, electricity consumption has
risen about fourfold and the average electricity costs have fallen from
13 pkWh’1 to 4 pkWh’1 . A second wind turbine of 100 kW capacity
was installed in 1996/7 to meet increasing demand and to improve wind

has to be provided as well. The installation on Fair Isle (see box) is a
good example of an ef¬cient and versatile system. Small wind turbines
also provide an ideal means for charging batteries in isolated locations;
for instance, about 100 000 are in use by Mongolian herdsmen. Wind
energy is often also an ideal source for water pumps “ one million small
wind turbines are used for this purpose worldwide.47
In the longer term it can be envisaged that wind generation could
expand into areas remote from direct electrical connection providing an
effective means for energy storage (for instance, using hydrogen; more
of that possibility later in the chapter) is developed.

Energy from the Sun
The simplest way of making use of energy from the Sun is to turn it into
heat. A black surface directly facing full sunlight can absorb about 1 kW
for each square metre of surface. In countries with a high incidence of
sunshine it is an effective and cheap means of providing domestic hot
water, which is extensively employed in countries such as Australia,
Israel, Japan and the southern states of the USA (see box above).
300 Energy and transport for the future

Solar water heating
The essential components of a solar water heater (Figure 11.11) are a set
of tubes in which the water ¬‚ows embedded in a black plate insulated
from behind and covered with a glass plate on the side facing the Sun. A
storage tank for the hot water is also required. A more ef¬cient (though
more expensive) design is to surround the black tubes with a vacuum
to provide more complete insulation. Ten million households worldwide
have solar hot water systems.48

Figure 11.11 Design of a solar water heater: a solar collector
connected to a storage tank through a circulating pump. Alternatively,
if the storage is above the collector, the hot water will collect through
gravity ¬‚ow.

In tropical countries, a solar cooking stove can provide an ef¬cient al-
ternative to stoves burning wood and other traditional fuels. Thermal
energy from the Sun can also be employed effectively in buildings
(it is called passive solar design), in order to provide a modest boost
towards heating the building in winter and, more importantly, to pro-
vide for a greater degree of comfort and a more pleasant environment
(see box).
Solar heat can also be employed to provide heating to produce steam
for the generation of electricity. To produce signi¬cant quantities of
steam, the solar energy has to be concentrated by using mirrors. One
arrangement employs trough-shaped mirrors aligned east-west which
focus the Sun on to an insulated black absorbing tube running the length
of the mirror. A number of such installations have been built, particularly
in the USA, where solar thermal installations provide over 350 MW
of commercial electricity. The high capital cost of such installations,
Energy from the Sun 301

Solar energy in building design

case it is known as ˜solar wall™ (Figure 11.12).49 Its
All buildings bene¬t from unplanned gains of so-
lar energy through windows and, to a lesser extent, construction enables sunlight, after passing through
through the warming of walls and roofs. This is an insulating layer, to heat the surface of a wall of
called ˜passive solar gain™; for a typical house in heavy building blocks that retain the heat and slowly
the UK it will contribute about ¬fteen per cent of conduct it into the building. The insulating layer, al-
the annual space heating requirements. With ˜pas- though allowing sunlight to pass through, prevents
sive solar design™ this can relatively easily and in- thermal radiation from passing out. A retractable
expensively be increased to around thirty per cent, re¬‚ective blind can be placed in front of the insula-
while increasing the overall degree of comfort and tion at night or during the summer when heating of
amenity. The main features of such design are to the building is not required. A set of student resi-
place, so far as is possible, the principal living dences for 376 students at Strathclyde University in
rooms with their large windows on the south side of Glasgow in southwest Scotland has been built with
the house, with the cooler areas such as corridors, a ˜solar wall™ on its south-facing side. Even under
stairs, cupboards and garages with the minimum of the comparatively unfavourable conditions during
window area arranged to provide a buffer on the winter in Glasgow (the average duration of bright
north side. Conservatories can also be strategically sunshine in January is only just over one hour per
placed to trap some solar heat in the winter. day) there is a signi¬cant net gain of heat through
The wall of a building can be designed specif- the wall to the building.
ically to act as a passive solar collector, in which

Figure 11.12 Construction of a ™solar wall™. The insulation material is about 100 mm thick and consists of
open honeycomb channels of transparent polycarbonate material.
302 Energy and transport for the future

The photovoltaic solar cell

The silicon photovoltaic (PV) solar cell consists of posited in this way and, because they have higher
a thin slice of silicon into which appropriate impu- ef¬ciencies than amorphous silicon, are likely to
compete with silicon for the thin ¬lm market.53
rities have been introduced to create what is known
as a p“n junction. The most ef¬cient cells are so- However, since typically about half the cost of a
phisticated constructions using crystalline silicon solar PV installation is installation cost, the high
as the basic material; they possess ef¬ciencies for ef¬ciency of single crystal silicon, which means a
the conversion of solar energy into electricity typ- smaller size, remains an important factor.
ically of ¬fteen to twenty per cent; experimental Cost is of critical importance if PV solar cells
cells have been produced with ef¬ciencies well over are going to make a signi¬cant contribution to en-
twenty per cent.51 Single crystal silicon is less con- ergy supply. This has been coming down rapidly.
venient for mass production than amorphous sili- More ef¬cient methods and larger scale produc-
con (for which the conversion ef¬ciency is around tion are bringing the cost of solar electricity down
ten per cent), which can be deposited in a contin- to levels where it can compete with other sources.
uous process on to thin ¬lms.52 Other alloys (such Projections up to the year 2020 of the likely cost of
as cadmium telluride and copper indium selenide) generating electricity from PV sources are shown in
with similar photovoltaic properties can also be de- Figure 11.13.

($ per Watt-peak)
PV Module cost



2002 (four-fold reduction 1982“2002)

(two-fold reduction 2002“2012?)
1 10 100 1 000 10 000 100 000

Cumulative installed capacity (in MW)

Figure 11.13 The falling cost of PV modules over the last twenty years and as projected for the next
twenty years. Note the twenty per cent reduction in cost for every doubling of installed capacity.

however, assuming a reasonable pay-back period, translates into an elec-
tricity cost which, at the moment, is at least three times that from most
conventional sources. Generating plants which incorporate integrated
solar and fossil fuel heat sources in combined cycle operation are cur-
rently under development that promise signi¬cantly lower costs.50
Energy from the Sun 303

Sunlight can be converted directly into electricity by means of photo-
voltaic (PV) solar cells (see box on page 302). Solar panels on spacecraft
have provided electrical power for spacecraft from the earliest days of
space research nearly ¬fty years ago. They now appear in a variety of
ways in everyday life; for instance, as power sources for small calcu-
lators or watches. Their ef¬ciency for conversion of solar energy into
electrical energy is now generally between just under ten per cent and
twenty per cent. A panel of cells of area one square metre facing full
sunlight will therefore deliver between 100 and 200 W of electrical
power. A cost-effective way of mounting PV modules is on the surface
of manufactured items or built structures rather than as free-standing
arrays. In the fast-growing building-integrated-PV (BIPV) sector, the
PV fa¸ ade replaces and avoids the cost of conventional cladding. In-
stalled on rooftops in cities, they provide a way for city dwellers to
contribute renewably to their energy needs. Japan has done the most to
encourage rooftop solar installations and by 2000 had installed 320 MW
capacity. The USA and Germany follow as countries with large rooftop
programmes, the USA with a target by 2010 of one million roofs and
Germany with programme for 100 000. The cost of energy from solar
cells has reduced dramatically over the past twenty years (see box below);
so much so that they can now be employed for a wide range of appli-
cations and can also begin to contribute to the large-scale generation of
Small PV installations are also suitable, especially for developing
countries, to provide local sources of electricity in rural areas. About a
third of the world™s population have no access to electricity from a central
source. Their predominant need is for small amounts of power for light-
ing, for radio and television, for refrigerators (for example, for vaccines
at a health clinic) and for pumping water. The cost of PV installations for
these purposes is now competitive with other means of generation (such
as diesel units). Over the twenty years to the year 2000, approximately
1.1 million ˜Solar Home Systems™and ˜Solar Lanterns™ had been in-
stalled in Asia, Africa and South American countries.54 Solar Home
Systems provide typically 15“75 W from a solar array (Figure 11.14)
and cost in the range of $US 200“1200. Smaller ˜solar lanterns™ (typi-
cally 10“20 W) provide lighting only. Larger installations are required
for public buildings, although they need not be that much larger. Many
small hospitals can bene¬t from an electrical power source as small
as 1“2 kW. For instance, by 1995, seventy small hospitals in Sri Lanka,
through assistance from the Australian government, had installed 1.3-kW
solar arrays, backed up by 2200 amp-hour batteries, to provide for light-
ing, refrigeration for vaccines, autoclave sterilisation, pumping for hot
water (produced through a solar-thermal system) and radio. Over
304 Energy and transport for the future

Figure 11.14 A simple ™solar home system™ now being marketed in many
countries in Africa, Asia and South America for a cost of a few hundred US$. An
array of thirty-six solar cells, covering an area of 60 cm — 60 cm, provides
around 40 W of peak power. This is suf¬cient to charge a car battery that can
power up to three 9-W ¬‚uorescent lights and three hours of radio and one hour
of television per day. With more restricted use of these devices or with a larger
solar array, a small refrigerator can be added to the system.

20 000 water pumps are now powered by solar PV and thousands
of communities receive drinking water from solar-PV-powered puri-
¬ers/pumps. The potential for further growth and development of so-
lar systems is clearly very large. For instance, mini-electrical grids
powered by a combination of solar PV wind, biomass and diesel are
beginning to emerge especially in the remoter parts of China and
The total installed world capacity of PV grew from about 500 MW
peak in 1998 to about 1500 MW peak in 2002, an increase of about
thirty per cent per year. With that rate of continued growth it should be
possible to more than meet the projected contribution by PV solar cells
to world energy supply in WEC scenario C of at least 150 GW56 by
the year 2020 (Table 11.5). In the short term, increased development of
local installations is likely to have priority; later, with the expectation of
a signi¬cant cost reduction (Figure 11.13), penetration into large-scale
electricity generation will become more possible. Eventually, because of
its simplicity, convenience and cleanliness, it is expected that electricity
from solar PV sources will become one of the largest “ if not the largest “
of the world™s energy sources.
Other renewable energies 305

Other renewable energies
We have so far covered the renewable energy sources for which there
is potential for growth on a scale that can make a substantial contribu-
tion to overall world energy demand. We should also mention brie¬‚y
other renewable energy technologies which contribute to global energy
production and which are of particular importance in certain regions,
namely geothermal energy from deep in the ground and energies from
the tides, currents or waves in the ocean.
The presence of geothermal energy from deep down in the Earth™s
crust makes itself apparent in volcanic eruptions and less dramatically
in geysers and hot springs. The energy available in favourable loca-
tions may be employed directly for heating purposes or for generating
electrical power. Although very important in particular places, for in-
stance in Iceland, it is currently only a small contributor (about 0.3%)
to total world energy; its contribution could rise to the order of one per
cent during the next few decades (Table 11.5).
Large amounts of energy are in principle available in movements
of the ocean; but in general they are not easy to exploit. Tidal energy
is the only one currently contributing signi¬cantly to commercial en-
ergy production. The largest tidal energy installation is a barrage across


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