energy in the future:
trends and unknowns
This closing chapter offers no forecasts; there is no need to add to the
large, and growing, volume of that highly perishable commodity.
Reviews show that most long range (more than ten to ﬁfteen years
ahead) energy forecasts—whether at sectoral, national or global
level, and no matter if they were concerned with the progress of individual
techniques, the efﬁciency gains of a particular process, overall
energy demand and supply, or the price levels of key commodities—
tend to fail in a matter of years, sometimes months. Given the postWorld
War II penchant for long range forecasting, it is now possible
to recite scores of such failures. Perhaps the most tiresomely
notorious is the ever-elusive further ﬁfty years that will be needed
to achieve commercial nuclear fusion (generating electricity by
fusing the nuclei of the lightest elements—the same kind of reactions
that power the Sun). Common failures include forecasts of the
imminent global peak oil production, and some of the most spectacular
misses include the predictions of future crude oil prices (too
high or too low, never able to catch the reality of highly erratic
ﬂuctuations).
Even if some individual numbers come very close to the actual
performance, what is always missing is the entirely new context in
which these quantities appear. Imagine that in 1985 (after the
collapse of crude oil prices and a sharp drop in global oil production),
you accurately forecast global oil production in 2005. Could
anybody in 1985 have predicted the great trio of events that changed
the post-1990 world: the peaceful collapse of the USSR (ﬁrst leading to
156
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a rapid decline and then to an impressive resurgence of its oil output),
the emergence of China as the world’s second largest economy (soon
to be the world’s second largest importer of oil), and September 11,
2001 (with its manifold consequences and implications for the
world in general, and the Middle East in particular)?
No forecasts then, only brief reviews of some key factors that will
determine the world’s future quest for a reliable and affordable
energy supply, and the major resource and technical options we can
use during the next half-century. During that time, the basic nature
of global energy supply will not drastically change, and the world will
remain highly dependent on fossil fuels. At the same time, we know
our fossil-fueled civilization to be a relatively short-lived phenomenon,
and the next ﬁfty years will see an appreciable shift toward
non-fossil energy resources. At the beginning of the twentieth century,
the world derived about sixty per cent of its energy from coal,
crude oil and (a very little) natural gas. A century later, the three
kinds of fossil fuels account for about eighty per cent of the world’s
total primary energy supply; the rest is about equally split between
primary electricity (hydro and nuclear) and phytomass fuels.
Even if the recoverable resources of fossil fuels (particularly those
of crude oil and natural gas) were much larger than today’s best
appraisals, it is clear they are not large enough to be the dominant
suppliers of energy for an afﬂuent civilization for more than a few
centuries. Conversely, the combination of rapidly rising demand
and the escalating costs of fuel extraction may limit the fossil fuel era
to the past and present centuries—and the rapid progress of pronounced
global warming, clearly tied to the combustion of fossil
fuels, may force us to accelerate the transition to non-fossil energies.
As already stressed in Chapter 1, the overall magnitude of renewable
energy ﬂows is not a constraint.
Biomass energies have been with us ever since we mastered the
use of ﬁre: wood, charcoal, crop residues, and dung are still used by
hundreds of millions of peasants and poor urban residents in Asia,
Latin America, and particularly throughout sub-Saharan Africa,
mostly for cooking and heating. Our best estimates (there are no reliable
statistics, as most of these fuels are collected or cut by the users
themselves) put the worldwide energy content, at the beginning of
the twenty-ﬁrst century, of traditional biomass energies at about
45 EJ, roughly ten per cent of the world’s aggregate primary energy
consumption. But the share is much lower when comparing useful
energies, because most of the biomass is burned very inefﬁciently in
energy in the future: trends and unknowns 157
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primitive stoves. As already noted in Chapter 3, these wasteful uses
also have considerable health costs, due to indoor air pollution, and
there are also the serious environmental problems of deforestation
and the reduced recycling of organic matter. Biomass energies could
make a difference only when harnessed by modern, highly efﬁcient
techniques without serious environmental and social impacts:
achieving this will be an enormous challenge.
Hydroenergy is the only kind of indirect solar energy ﬂow
extensively exploited by modern techniques, but, outside Europe,
North America and Australia, there is still considerable untapped
potential. We have only just begun to harness the other major indirect
solar ﬂow, wind, but it is not clear to what extent the recent
European enthusiasm for large-scale wind farms will translate into
worldwide and sustained contributions. Potentially the most
rewarding, and by far the largest, renewable energy resource is the
direct solar radiation that brings close to 170 W/m2
to the Earth—
but, so far, its direct conversion to electricity (by photovoltaics) has
succeeded only in small niche markets that can tolerate the high cost.
There is also the possibility of new designs of inherently safer and
more economic nuclear electricity generation. I will review the
advantages and drawbacks of all of these major non-fossil options.
But before doing so I must stress the magnitude of future energy
needs against the background of enormous consumption disparities
and long-term energy transitions.
The extent of future global energy needs cannot be understood without
realizing the extent of existing consumption disparities. The
per caput annual energy consumption in the US and Canada is
roughly twice as high as in Europe or Japan, more than ten times as
high as in China, nearly twenty times as high as in India, and about
ﬁfty times as high as in the poorest countries of sub-Saharan Africa.
Because of this highly skewed (hyperbolic) consumption pattern, the
global annual average of about 1.4 toe (60 GJ) is largely irrelevant:
only three countries (Argentina, Croatia, and Portugal) have consumption
rates close to it; the modal (most frequent) national average
is below 0.5 toe, and high-income countries average above 3 toe.
energy: a beginner’s guide158
energy needs: disparities, transitions, and
constraints
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energy in the future: trends and unknowns 159
The enormous disparity in access to energy is most impressively
conveyed by contrasting the national or regional share of the
global population with their corresponding share of world-wide
primary energy consumption: the poorest quarter of humanity
(including most of sub-Saharan Africa, Nepal, Bangladesh, the
nations of Indochina, and rural India) consumes less than three
per cent of the world’s primary energy supply while the thirty or so
afﬂuent economies, whose populations add up to a ﬁfth of the
global total, consume about seventy per cent of primary energy
(Figure 30). The most stunning contrast: the US alone, with less
than ﬁve per cent of the world’s population, claims twenty seven
per cent of its primary commercial energy.
No indicator of high quality of life—very low infant mortality,
long average life expectancy, plentiful food, good housing, or
ready access to all levels of education—shows a substantial gain
once the average per caput energy consumption goes above
about 2.5 toe/year. Consequently, it would be rational to conclude
that the world’s afﬂuent nations have no need to
increase their already very high averages, ranging from just over
8 toe/caput for the US and Canada, to just over 4 toe for Europe
UNEQUAL ACCESS TO MODERN ENERGY
numberofcountries
per capita energy consumption (GJ/year)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
>200
oren curve of global commercia
energy consumption
shareoftheglobalTPES
share of the global population
0
10
20
30
40
50
60
0
0 20 40 60 80 100
20
40
60
80
100
Figure 30 Distribution of average national per caput energy consumption
and a Lorenz curve of global commercial energy consumption
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To achieve a modicum of economic security, the average annual
per caput consumption rates should at least triple in sub-Saharan
Africa, more than double in India (currently at less than 0.4 toe) and
nearly double in China (now at roughly 1 toe). It is clear that future
energy use in the world’s most populous and rapidly expanding
economies will conform (with variations for national characteristics)
to the general pattern of energy transitions that has taken place
in afﬂuent countries. Their two principal components were noted in
Chapter 4: the declining share of coal in total primary consumption
(although in China that share will remain relatively high, because it
derives about two-thirds of its energy from coal), and a steady rise of
oil and natural gas consumption, leading to higher demand for
imported liquids and gases.
Another key ingredient of the world-wide transition of commercial
energy use has been the rising share of electricity in ﬁnal consumption.
In 1900, less than a generation after the beginning of
electricity generation, little more than one per cent of fossil fuels was
converted to electricity; by 1950 the global share rose to ten per cent
energy: a beginner’s guide160
and Japan. At the same time, there are still hundreds of millions of
people in the poorest countries who do not directly consume any
fossil fuels.
Because almost all the world’s population growth during the ﬁrst
half of the twenty-ﬁrst century will take place in low- and mediumincome
countries (afﬂuent populations, with the exception of the
US, will either be stagnant or in decline), most future increases
in fossil fuel and electricity consumption will be in Asia, Latin
America, and Africa. But there is no easy way to forecast this new
demand, as it is a complex function of population growth and economic
expansion, the changing composition of the primary energy
supply and ﬁnal energy uses (energy-intensive heavy industries
compared to light manufacturing and service industries), and the
adoption of new inventions and higher-efﬁciency innovations
(ﬂuorescent rather than incandescent lights, high-efﬁciency
natural gas furnaces rather than coal stores, or subcompacts
instead of SUVs).
UNEQUAL ACCESS TO MODERN ENERGY (cont.)
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and by 2000 surpassed thirty per cent. The US share is now about
thirty-ﬁve per cent, and, remarkably and despite a large economic
gap between the two countries, China’s share, at about thirty
per cent, is not far below that. Nearly everywhere, electricity use has
been growing at a much faster rate than the consumption of fuels,
because during the second half of the twentieth century fossil-fueled
generation was extensively augmented by hydroenergy and nuclear
ﬁssion.
The continued rapid growth of average per caput electricity consumption
in low- and medium-income economies will be the only
way to narrow the existing disparities. The US annual per caput
average is now more than 12 MWh, Japan’s is nearly 8 MWh, and
Europe averages almost 7 MWh. In contrast, China’s annual per caput
mean is about 1.1 MWh, India’s 0.5 MWh, and in sub-Saharan Africa
(excepting South Africa) it remains generally below 0.25 MWh.
Despite decades of electriﬁcation programmes, nearly two billion
people (mainly in India, Southeast Asia and sub-Saharan Africa) still
do not have access to electricity. Consequently, the global disparity
in average per caput electricity use is greater, and the need for future
production increases more acute, than is primary energy consumption.
This is perhaps most vividly portrayed by composite nighttime
satellite images, which starkly contrast brightly-lit afﬂuent
countries with the huge areas of darkness, or at best sparse light, over
large parts of Asia, Africa, and Latin America.
While the overall efﬁciency of energy use in low- and mediumincome
countries is dismally low and should be greatly improved
through technical innovation and better management, future higher
energy needs cannot be met solely, or even mostly, through higher
efﬁciency. Positive steps in this direction are essential. China’s
post-1980 achievements (roughly halving the energy use per unit of
Gross Domestic Product (GDP)) show their fundamental importance:
without them, China would be now consuming about twice as
much energy for every unit of its economic product as it now does,
as well as burdening its already highly degraded environment with
even more pollutants. High-efﬁciency conversions clearly beneﬁt
economies and the environment, but they reduce overall energy use
only on an individual or household level, or for a single company,
particular industrial process, or entire production sector.
On national and global levels, the record shows the very opposite;
there is no doubt that higher efﬁciencies of energy conversions have
led to steadily greater consumption of fuels and electricity. This
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paradox was noted for the ﬁrst time by Stanley Jevons (1835–1882),
a prominent English economist, in 1865. In his words: “It is wholly a
confusion of ideas to suppose that the economical use of fuels is
equivalent to a diminished consumption. The very contrary is the
truth.” Jevons illustrated the phenomenon by contrasting the huge
efﬁciency improvements of eighteenth-century steam engines (from
Savery and Newcomen’s extremely wasteful machines to Watt’s
improved design) with the large increases in British coal consumption
during the same period.
Two examples illustrate this common phenomenon for modern
energy-consuming activities. First, in 2005, the average American
passenger vehicle (including SUVs) consumed about forty per cent
less fuel per kilometer than in 1960, but more widespread ownership
of automobiles (two people per vehicle in 2005, compared to nearly
three in 1970) and the higher annual average distance driven
(roughly 20,000 km, compared to 15,000 km in 1960) resulted in an
average per caput consumption some thirty per cent higher. Second,
during the twentieth century, the efﬁciency of British public street
lighting rose about twenty-fold, but the intensity of this illumination
(MWh per km of road) rose about twenty-ﬁve times, again more
than eliminating all efﬁciency gains.
So higher efﬁciencies have not resulted in lower overall demand
for energy. Its growth has continued, albeit at a slower pace (as
expected), even in mature, post-industrial economies. In the 1990s,
despite deep economic problems and the stagnation of its GDP,
Japan’s average per caput energy consumption grew by ﬁfteen
per cent; in the same period the already extraordinarily high US and
Canadian rates grew by about 2.5%, and France’s by nearly ten
per cent. Between 1980 and 2000 China, despite the unprecedented
achievement of halving the energy intensity of its economy, more
than doubled its per caput energy consumption. Replicating similar
achievements during the coming decades would be challenging
under any circumstances, but we now face the entirely new constraint
of possibly rapid global warming.
We have three choices if we wish to keep on increasing energy
consumption while minimizing the risks of anthropogenic climate
change (due mostly to rising combustion of fossil fuels) and keeping
atmospheric levels of greenhouse gases from rising to as much as
three times their pre-industrial level: we can continue burning fossil
fuels but deploy effective methods of sequestering the generated
greenhouse gases, we can revive the nuclear option, or we can turn
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increasingly to renewable energy. None of these options is yet ready
for large-scale commercial adoption, none could be the sole solution,
and all have their share of economic, social and environmental
problems.
Despite of a great deal of theoretical research, and much interest
shown by industries and governments, CO2
sequestration is only in
the very early experimental stages; its eventual contribution to the
management of the global warming challenge is uncertain. In contrast,
we have half a century of experience of large-scale commercial
generation of nuclear electricity, which has shown us what to avoid
and what techniques to favor. The general expert consensus is that
any development of the nuclear industry cannot be a replica of the
ﬁrst generation; there has been no shortage of new, ingenious
designs aimed at minimizing or eliminating the concerns that contributed
to the stagnation (and in some countries even retreat) of
nuclear electricity generation. Several, so-called, inherently safe
nuclear reactor designs provide passive guarantees of fail-proof
performance: even operator error could not (as it did in Chornobyl)
lead to a core meltdown. Its adoption would be made easier by
ﬂexible sizing: a helium-cooled reactor, fuelled by hundreds of thousands
of ﬁst-sized graphite spheres ﬁlled with tiny particles of
uranium oxide, could be built in modules as small as 120 MW.
Increased concerns about the possibility of terrorist attacks in the
post-9/11 world are a powerful counter-argument to substantial
expansion of nuclear generation. But the future of the industry will
not depend primarily either on better designs (they have been available
since the mid-1980s), or on the fears of a terrorist attack (there
are already hundreds of reactors in operation, and many other highproﬁle
targets). What has to change is the public acceptance of this,
potentially risky, but very rewarding, form of electricity generation,
and I have argued that there is little chance of any substantial
worldwide return to nuclear generation unless led by the world’s
largest economy. But in 2005, US nuclear plans seem no less confused
and uncertain than they were in 1995 or in 1985: there is constant
talk of the industry’s future importance, indeed inevitability,
but no practical steps toward making it happen, and no sign that the
public distrust of nuclear generation has eased. As the endless wrangling
about the location and operation of the country’s permanent
repository of high-level radioactive wastes shows, the combination
of executive intents, legislative delays, and legal appeals makes for
decades of irresolution and offers little hope for any determined
energy in the future: trends and unknowns 163
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state-sanctioned nuclear-based solution to the country’s future
electricity needs.
All that may change, but not because the public ﬁnally appreciates
the real relative risks of various electricity-generating options, as
these have been known for decades. Two developments may bring
this shift about: a quicker than expected decline in worldwide crude
oil production, and clear signs of exceptionally rapid and highly pronounced
global warming. The nuclear option is not greenhouse gas
free: we need coke to make the plant’s many steel components, and
the cement for its massive concrete structures comes from fossil fuelﬁred
kilns. But in comparison with today’s dominant (coal-ﬁred)
mode of generation, nuclear plants produce at least ninety-ﬁve
per cent less CO2
per unit of electricity. If our civilization were to
face a true global warming shock, this would be very appealing.
Consequently, the most rational strategy of future energy supply
would be to combine improvements in conversion efﬁciency
(particularly in industrialized economies) with reduced rates of
overall energy demand (especially in afﬂuent countries), keep the
nuclear option open during the development of innovative reactor
prototypes, and increase the contributions of non-fossil sources as
quickly as economically feasible and environmentally acceptable.
Because capital investment considerations and infra-structural
inertia mean that it takes several decades for any new energy source
or conversion to claim a substantial share of the market, we should
not waste any time in aggressively developing and commercializing
suitable renewable options.
Biomass energies could only become an important component of
future energy supply after the development of large-scale, intensive
production of selected crop and tree species convertable, by
advanced techniques, into liquid or gaseous fuels or electricity. This
strategy has three fundamental drawbacks. First, as explained in
Chapter 2, photosynthesis operates with an inherently very low
energy density, and hence any large-scale biomass fuel production
would claim extensive areas of farmland (and it would have to be
farmland, rather than marginal land, to sustain high productivity).
Second, humanity already claims a very high share (possibly as
much as two-ﬁfths) of the biosphere’s net primary productivity
energy: a beginner’s guide164
renewable energies: biomass, water, wind, solar
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(through harvests of food, feed, wood, grazing, and deliberately set
grassland, and forest ﬁres), and adding a further burden through
massive fuel production would lead to a further loss of biodiversity
and greater environmental degradation. Finally, the overall costs
(economic, energetic and environmental) of large-scale biomass
energy production are very high.
Low power densities translate into very large land requirements
(Figure 31). For example, replacing just a quarter of the world’s fossil
fuel consumption with cultivated woody biomass would require
(even with high average yields of 15 t/ha and high combustion
efﬁciencies) tree plantations larger than the area of total combined
forested land in Europe and the US, clearly an impossible option. If
all American cars were to run on corn-derived ethanol, the country
would have to put all its farmland under that energy crop, another
impossible option. Devoting even limited areas to biomass crops
energy in the future: trends and unknowns 165
highrises
houses
industry
cities
steel mills,
refineries
0.1
m2
1
m2
10
m2
100
m2
1000
m2
1
ha
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ha
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km2
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gy p
area (m2)
photovoltaics
wind
phytomass
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Figure 31 Comparison of power densities of energy consumption and
renewable energy production
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would be irrational for the scores of densely populated countries
that already have shortages of the arable land needed to secure their
basic food supply and so are major food importers. Creating new
biomass plantations would lead to further loss of natural grasslands,
wetlands, and lowland tropical forests. Only a few countries (Brazil
and US above all), could spare signiﬁcant shares of their farmland
for large-scale fuel production.
Moreover, a number of energy analyses show that ethanol production
from US corn entails a net loss of energy (due to the combined
energy cost of machinery, fertilizers, irrigation, and the grain’s fermentation
to alcohol). Other studies show a small net energy gain, but
efﬁcient and inexpensive enzymatic conversion of cellulose and hemicellulose
(making it possible to use corn stalks and leaves) rather than
just starches (that is, fermenting only grain corn) would radically
improve the overall energy balance. In contrast Brazilian ethanol,
made from sugar cane, has a positive energy return, because the fermentation
process can be fuelled by bagasse, the ﬁbrous residue
remaining after the expressing of the sweet juice from the cane stalks.
But even when biomass crops and their processing produce a net
energy gain, their cultivation would still have undesirable environmental
impacts, above all increased soil erosion, soil compaction, and
contamination of aquifers and surface waters by nitrogen and phosphorus
lost from fertilizers, causing aquatic eutrophication (that is,
the enhanced growth of algae, which disrupt the existing ecosystem).
Until we have bioengineered micro-organisms, able to convert
non-starch phytomass into reasonably priced liquid fuels, we should
continue to use efﬁciently all biomass wastes (logging and lumber
mill residues, and crop residues not needed for protecting soils
against excessive erosion and recycling nutrients), and limit the production
of liquids from biomass to tropical sugar cane grown in
countries with abundant farmland. Expanding fuelwood groves for
household use and planting fast-growing species for commercial
wood deliveries is desirable in areas with good growing conditions,
or regions with plenty of available barren slopeland, where afforestation
may not only improve regional fuel supply but also reduce soil
erosion. But any dreams of a modern urbanized civilization fuelled
by biomass should remain, for the sake of a reliable food supply and
limited environmental impacts, just that.
Hydrolectricity is the largest modern non-fossil source of primary
energy; the combination of relatively low cost, high suitability
to cover peak demand, and the multi-purpose nature of most large
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reservoirs (they serve as sources of irrigation and drinking water, a
protection against downstream ﬂooding, recreation sites, and,
increasingly, places for aquacultural production) should make it one
of the most desirable choices in a world moving away from fossil
fuels. This conclusion seems to be strengthened by the fact that on
the global scale most of this clean renewable energy resource
remains untapped: the International Commission on Large Dams
put the global potential of economically feasible projects at just over
8 PWh, roughly three times the current rate of annual generation. As
expected, the remaining potential is unevenly distributed. Europe,
North America, Australia, and Japan have already developed as
much of their large-scale hydrogenerating capacity as they can (there
is always the potential for microstations), but Latin America has so
far tapped less than a quarter, Asia less than a seventh, and Africa not
even a twentieth, of their respective potentials.
This untapped potential would seem especially welcome, as it is
precisely those continents where future demand will be highest, but it
now appears that the development of hydrogeneration in those
regions will not proceed either as rapidly or as exhaustively as was
assumed two decades ago. In an important shift of perception,
hydroenergy has changed, from a clean, renewable, and environmentally
benign resource, to a much more controversial cause of socially
and environmentally disruptive, and economically questionable,
developments. As a result, there has been a spreading international
and internal opposition to megaprojects (plants with multigigawatt
capacities), and a marked decline in the willingness of governments
and international lending agencies to ﬁnance such developments.
Sweden has banned further hydrostations on most of its rivers,
Norway has set aside all existing plans, in the US, since 1998, the
decommissioning rate for large dams has overtaken the construction
rate, and many countries in Asia (most notably in India) and Latin
America have seen vigorous public protests against new projects.
energy in the future: trends and unknowns 167
In 2000, the World Commission on Dams published a report which
stressed that all future projects should consider social and environmental
effects to be as important as the, traditionally dominant,
economic beneﬁts of electricity generation (or of irrigation or
CONCERNS ABOUT LARGE DAMS
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energy: a beginner’s guide168
water supply). While some recent criticism has been ideologically
motivated and clearly overwrought, there is no doubt that large
hydroprojects bring a number of serious social and environmental
changes. In Chapter 4 I noted the major concerns: the large
numbers of people displaced by the creation of major reservoirs,
the excessive silting of many storages, the aging of average river
runoff and the fact that water reservoirs are (much like fossil fuels)
sources of greenhouse gas emissions, as they release CO2
and CH4
from submerged and decaying trees and shrubs.
A new concern has emerged, as we see more indications of the
inevitable deterioration of aging dams and contemplate the costs
of their eventual decommissioning: these matters were given no, or
insufﬁcient, attention when they were built. We can only speculate
about the ultimate life expectation of such massive structures, and
have no good strategies to deal with the excessive silting and premature
ﬁlling of reservoirs, which reduces their useful life span (in
parts of monsoonal Asia affected by severe deforestation the
process has already cut the expected duration of some reservoirs by
as much as half). All this makes it much more unlikely that the
remaining hydrogeneration potential will be developed as aggressively
as it was in the twentieth century.
But even without any obstacles to their construction, new hydrogeneration
capacities could supply only a part of the expected
demand, and then only by claiming large expanses of river valleys,
forests, grasslands, settlements, and agricultural land. The average
power density of existing hydrostations (actual generation rather
than installed capacity: this adjustment is necessary because dry
years curtail generation at many dams) equates to about 1.7 W/m2
and they claim some 175,000 km2
of land. If all of the remaining
potential were to be realized during the ﬁrst half of the twenty-ﬁrst
century, new reservoirs would claim roughly 500,000 km2
, an area
as large as Spain. But hydroenergy can be also harnessed on a
smaller scale, and many Asian, African, and Latin American countries
have excellent potential for developing stations, with capacities
less than 10–15 MW, which would not make much of a dent in
a nationwide supply of a populous country, but could sufﬁce to
electrify a remote region or an island.
CONCERNS ABOUT LARGE DAMS (cont.)
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Wind energy, harnessed by large and efﬁcient turbines, has
emerged in the 1990s (less than a decade after a failed mini-boom
during the 1980s) as the leading renewable energy choice, thanks
largely to aggressive promotion and adoption in a number of
Western European countries. Better designs, and larger sizes, of
wind machines made a big difference: ratings rose from 40–50 kW
during the early 1980s to 500–750 kW by the late 1990s, when the
ﬁrst turbines with capacities of more than 1 MW went on line.
Danish designs have led the way, and the country also leads in
per caput wind capacity, but Germany (thanks to a guaranteed high
ﬁxed price for wind-generated electricity) has become the country
with the highest aggregate capacity, followed by Spain. More than
seventy per cent of installed wind turbine capacity is in Europe,
Denmark gets about twenty per cent and Germany and Spain more
than ﬁve per cent of their electricity from wind. But there is a long
way to go before wind power becomes a substantial player on the
global scale: by the end of 2004 it generated just over one per cent of
the world’s electricity.
To avoid conﬂict, much future wind power will be in large offshore
wind farms (some already operate in Denmark, Sweden,
Holland and the UK), or re-powering of old sites with larger turbines.
Wind power will remain the fastest growing segment of
renewable electricity generation for years to come, but its ultimate
extent is uncertain. It is an immense resource, and even a restrictive
appraisal (taking into account suitable wind speeds and siting
restrictions) shows a global potential of about 6 TW, or about ﬁfty
per cent larger than the world-wide electricity-generating capacity
in 2005. But this grand total is largely irrelevant, because the wind
power cannot be relied on either to cover the high base-load
demanded by modern societies or meet spiking peak loads.
This inability is due to the high, poorly predictable, variability in
wind speeds (on time scales from daily to annual), and to the fact
that optimum wind ﬂows do not correlate well with periods of the
highest electricity demand. Strong winds are as undesirable as
protracted calm, because to avoid structural damage, modern wind
turbines cut out at speeds greater than 25 m/s (90 km/h). European
studies show that wind capacities of up to twenty per cent of
installed power can be successfully integrated into a national supply,
especially when a relatively small nation is well connected to
neighboring countries (as in Denmark)—but there is no realistic
way to make wind power, even in regions where the resource greatly
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surpasses actual electricity demand, the sole provider of the base
load supply.
Other factors that complicate large-scale reliance on wind-driven
turbines range from the sudden, substantial (10–20%), loss of power
due to the soiling of leading blade edges by swarms of summer
insects, to the damage that could be inﬂicted on towers and blades by
hurricane- and tornado-strength winds. Environmental concerns
range from the well-documented risks to migrating birds, to esthetic
objections, both to turbines massed in large onshore wind farms and
the size of the largest machines (nearly twice as high as the Statue of
Liberty). As with any major engineered system, it is far too early to
appraise the overall reliability of the technique. We have to accumulate
operating experience with a very large number of units to be
able accurately to assess the long-term availability and reliability of
wind turbines: how will offshore wind farms fare in hurricanes, how
will the machines be affected by heavy icing, or to what extent will
the smooth blades surfaces be pitted by abrasive airborne particulate
matter?
Compared to wind-powered electricity generation—with recent
worldwide annual increments of the order of 5–8 GW and aggregate
installed capacity in 2005 of over 50 GW—photovoltaics (PV) is still
a minor affair: its worldwide capacity was below 3 GW in 2005, with
just three countries (Japan, Germany, and the US) accounting for
more than eighty per cent of the total. Moreover, the power ratings
of PV units are not directly comparable with other modes of electricity
generation, because they are expressed in peak watts measured
under high irradiance (1,000 W/m2
, the equivalent of
mid-day, clear-sky insolation) rather as an average performance.
Three fundamental reasons make the PV conversion of solar radiation
into electricity the most appealing of all renewable sources: the
unparalleled magnitude of the resource, its relatively high power
density, and the inherent advantages of the conversion technique
(no moving parts, silent operation at ambient temperature and pressure,
and easy modularity of units), but the two key reasons for its
rather limited commercial penetration are the relatively low conversion
efﬁciency and the high unit cost. Efﬁciencies have risen from
less than ﬁve per cent during the early 1960s, when the ﬁrst PV cells
were deployed on satellites, to almost twenty-ﬁve per cent for highpurity
silicon crystals in the laboratory, but the best ﬁeld efﬁciencies
are still below ﬁfteen per cent, which eventually deteriorate to less
than ten per cent. PV ﬁlms, made of amorphous silicon (or gallium
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arsenide, cadmium telluride, or copper indium diselenide), have
reached as much as seventeen per cent in the laboratory, but deliver
much less than ten per cent in ﬁeld applications. Although these
advances have lowered the unit cost of PV cells, the modules are still
too expensive to compete, price-wise, with fossil-fueled generation.
But their marketing has ﬁnally moved beyond specialized, lowpower
applications to larger, grid-connected capacities, and sales are
rising worldwide, from less than 50 MW (peak capacity) a year in
1990 to more than 700 MW in 2003.
Competitive and reliable PV would be a most welcome breakthrough,
because of its relatively high power densities: efﬁciencies
close to twenty per cent would translate to electricity generation
rates between 20–40 W/m2
, two orders of magnitude better than
biomass conversion, and one better than most hydro and wind projects.
Problems with the natural randomness of the resource, outside
the predictably sunny subtropical desert regions, cannot be easily
overcome: converting diffuse radiation in cloudy regions is much
less efﬁcient than using direct sunlight; and there are no techniques
for large-scale storage of electricity on the commercial horizon.
Consequently, grid-connected PV could work very well in providing
a sizeable share of overall electricity demand, while reducing the
need for fossil-fueled generation, during sunny hours, but not (until
a number of technical breakthroughs become commercial) as the
dominant means of base-load supply.
The most welcome advance would be a large-scale affordable means
of electricity storage: without this even a combination of affordable
wind-driven and PV electricity generation could not provide a
reliable base-load supply. But no imminent breakthroughs are
expected, and pumped storage remains the only effective way of
storing surplus electricity on a large scale. This uses two water reservoirs
at least several hundred meters apart in height; electricity not
needed by the grid is used to pump water from the lower to the
upper storage, where it is kept until released for generation during
periods of peak demand. The world-wide capacity of pumped storage
is close to 100 GW; the largest units surpass 2 GW. But pumped
storages are expensive, and the requirement for reservoirs in high
relative elevations makes them inconceivable in densely populated
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innovations and inventions: impossible forecasts
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lowlands. Batteries cannot store energy on such a large scale, because
they are too expensive, their energy density is too low, they are difﬁcult
to charge, and have very short life cycles. This is why large-scale
electricity generation based on variable ﬂows of renewable energies
would beneﬁt from using hydrogen as a major energy carrier.
energy: a beginner’s guide172
Hydrogen cannot, contrary to what so many popular writings
repeatedly imply, be a signiﬁcant source of energy. Unlike
methane, it is not present in huge reservoirs in the Earth’s crust,
and energy is needed to produce it, from either methane or water.
But some of its properties make it an outstanding energy carrier. Its
key advantages are superior energy density (liquid hydrogen contains
120 MJ/kg compared to 44.5 MJ/kg for gasoline), a combustion
that yields only water, and the possibility of using it in fuel
cells.
The key advantages of fuels cells (electrochemical devices that
combine hydrogen and oxygen to produce electricity) are the
absence of moving parts, a quiet and highly efﬁcient (commonly in
excess of sixty per cent) operation, and their modularity (they can
be made small enough to power a laptop or large enough to generate
electricity in multi-megawatt plants). An enormous amount of
research interest in fuel cells has recently led to exaggerated
expectations of their early commercialization, but their cost
(except for a few relatively small niche markets) is still prohibitive,
and many innovations are needed to make them affordable and reliable
converters. There are also major problems in setting up a distribution
system for hydrogen—and unless this is in place,
carmakers will be reluctant to mass-produce hydrogen-powered
cars. Niche conversions (ﬂeet vehicles such as buses, taxis, and
delivery trucks, which can be fuelled at just a few points in a city),
might be better than pushing hydrogen for passenger cars.
The transition to hydrogen-powered vehicles will also be complicated
by the need for energy-dense storage and safe handling.
Uncompressed hydrogen occupies 11,250 l/kg; pressurizing it into
a high pressure (hence dangerous) steel tank reduces this to 56 l/kg,
but this is equivalent to less than three liters of gasoline, or enough
fuel to move an efﬁcient compact car less than ﬁfty kilometers.
HYDROGEN AS ENERGY CARRIER
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Moving toward a system dominated by hydrogen is clearly consistent
with the long-term decarbonization of the modern energy
supply, but the progress will be gradual and we should not expect
any large-scale transition to a hydrogen economy during the coming
generation (Figure 32). The hydrogen:carbon (H:C) ratio of dominant
fuels has moved from around 0.1 in wood, to about 1.0 in coal,
energy in the future: trends and unknowns 173
Liqueﬁed hydrogen occupies only 14.1 l/kg but needs to be kept
below –241 °C—an immense engineering challenge in a small
vehicle. Adsorption on special solids with large surface areas, or
absorption by metal hydrides seem to be the most promising
options.
The safety of hydrogen distribution is no smaller challenge.
While the highly buoyant gas leaks quickly and it is non-toxic
(making its spills more tolerable than those of gasoline) its ignition
energy is only one-tenth that of gasoline, its limit of ﬂammability
is lower, and its range of ﬂammability much higher. These will
mean much stricter precautions at hydrogen stations than those
now in place at gasoline ﬁlling stations.
HYDROGEN AS ENERGY CARRIER (cont.)
gy pp y
tC/TJ
1975 2000 1900 1925 1950 1975 2000
18
20
22
24
26
Figure 32 Decarbonization of the world’s energy supply
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and 2.0 in crude oil. The continuation of this trend points ﬁrst to the
emergence of natural gas (with H:C of 4) as the leading source of
global primary energy, and eventually (but almost certainly not
during the ﬁrst half of the twenty-ﬁrst century) to a hydrogendominated
world. But trends can be derailed or accelerated by social
or political upheavals, or enter frustrating culs-de-sac, and only
those that are strongly entrenched and rely on mature techniques
have a high probability of continued adoption, accompanied by further
innovation. Neither hydrogen nor a strong revival of the nuclear
option belong to this category, and hence any forecasts of future
milestones or diffusion rates of these techniques are just guesses.
In contrast, there is no doubt that the combustion of fossil
fuels—gradually becoming more efﬁcient, cleaner and less carbonintensive—will
dominate the global energy supply during the next
two generations. As electricity will be supplying a steadily higher
share of the world’s ﬁnal use of energy, its already generally highlyefﬁcient
conversions will become even better. The greatest room for
improvement is in lighting, and light emitting diodes are a most
promising innovation. They have been around for many years as the
little red or green indicator lights in electronic devices, and
(although you may think you have a light bulb there) are now
common in car brake lights, tail-lights, and turn signals, and also in
trafﬁc lights. But they will make the greatest impact once their fullspectrum
prototypes (producing daylight-like light) become commercial.
So our grandchildren will use lights that may be, on average,
at least ﬁfty per cent more efﬁcient than ours.
There is also little doubt that our continued reliance on fossil
fuels will be ﬁrst augmented and then progressively supplanted by
renewable energies: major hydroenergy projects in Asia and Africa
and by wind-powered electricity generation and PV conversions
on all continents (Figure 33). And history makes it clear that the
train of human ingenuity is not about to stop. Although major
inventions tend to come in irregularly spaced clusters rather than an
orderly progression, half a century is long enough to see the emergence,
and even substantial diffusion, of several new inventions
whose universal adoption could transform the energy foundations
of late-twenty-ﬁrst century civilization. Such developments are
highly probable, but their nature and their timing are entirely
unpredictable: remember the two major late twentieth century
examples; the emergence of mass air travel thanks to the invention of
the gas turbine and its much improved turbofan designs, and the
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invention of solid state electronic devices (transistors, integrated
circuits, and microprocessors).
The transition to an energy system based predominantly on
non-fossil resources is in only its earliest phase. In some ways this
appears to be a greater technical and social challenge than the last
epochal shift (from animate energies and biomass fuels to coal,
hydrocarbons, engines, and electricity). But, given the knowledge
and resources at our command, this challenge should be manageable.
After all, we now have much more powerful scientiﬁc and technical
means to come up with new solutions, and we also have the
beneﬁts of unprecedented information sharing and international
co-operation, and can take advantage of various administrative,
economic, and legal tools aimed at promoting the necessary adjustments,
from more realistic pricing to the sensible subsidies required
to kick-start new and promising techniques or help them to achieve
a critical market mass more quickly.
The task ahead is daunting, because the expectations for energy
futures are high. They combine the anticipation of continued supply
improvements (in access, reliability, and affordability) in already
afﬂuent (or at least fairly well-off) countries (whose populations
total about one billion), not only with the necessity of substantial
increases in average per caput energy consumption among the
world’s (roughly ﬁve billion) less fortunate people, but also with the
energy in the future: trends and unknowns 175
Figure 33 Albany wind farm
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need to harness, distribute, and convert these massive energy ﬂows
in ways compatible with long-term maintenance (and in many cases
major enhancement) of local and global environmental quality.
Such challenging, fundamental transformations offer the best
opportunities for creative solutions and effective adaptations. The
evolutionary and historical evidence shows that humans are
uniquely adapted to deal with change. While our past record of
ingenuity, invention, and innovation is no guarantee that another
fairly smooth epochal energy transition will take place during the
next few generations—it is a good foundation for betting that our
chances are far better than even.
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