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Renewable Energies DOI: 10.1002/anie.200602373
The Future of Energy Supply: Challenges and
Opportunities
Nicola Armaroli* and Vincenzo Balzani*
Keywords:
hydrocarbons · natural resources · photochemistry ·
renewable energies · science and society ·
solar energy conversion
Dealing with Change
“Questions are never indiscrete, answers
sometimes are.”
Oscar Wilde
Each generation is confronted with
new challenges and new opportunities.
In a restricted system like the Earth,
however, opportunities discovered and
exploited by a generation can cause
challenges to the subsequent ones. Fossil
fuels have offered astounding opportu-
nities during the 20th century in the rich
countries of the western world, but now
mankind has to face the challenges
arising from fossil-fuel exploitation.
The proven reserves of fossil fuels are
progressively decreasing,[1] and their
continued use produces harmful effects,
such as pollution that threatens human
health and greenhouse gases associated
with global warming. Currently the
worlds growing thirst for oil amounts
to almost 1000 barrels a second,[2] which
means about 2 liters a day per each
person living on the Earth (Figure 1).[3]
The current global energy consumption
is equivalent to 13 terawatts (TW), that
is, a steady 13 trillion watts of power
demand. How long can we keep running
this road?
Energy is the most important issue
of the 21st century. Here is the funda-
mental challenge we face, here are many
vital and entangled questions that we
are called to answer. Can well-being, or
even happiness, be identified with the
highest possible amount of per capita
energy consumption? Should we pro-
gressively stop burning fossil fuels? Can
scientists find an energy source capable
of replacing fossil fuels? Can chemistry
help in solving the energy problem?
Will it be possible for all the Earths
inhabitants to reach the standard of
living of developed countries without
devastating the planet? Will science and
technology alone take us to where we
need to be in the next few decades?
Should we, citizens of the western world,
change our lifestyle and shift to innova-
tive social and economic paradigms?
Can people living in poor countries
improve their quality of life?
Forty years ago, looking at the first
photos of the Earth seen from space, we
fully realized that our planet is a space-
ship that travels without any destination
in the infinity of the universe. As
passengers of this spaceship we are
deeply interested in finding solutions
to the energy crisis. As parents, we wish
to leave our planet in a good shape for
the benefit of future generations. As
scientists, we do have the duty to con-
tribute to the discussion on the impend-
ing energy crisis. As chemists, we can
help improving energy technologies
and, hopefully, finding scientific break-
throughs capable of solving the energy
problem at its root. Finally, as citizens of
the affluent part of the world, first class
passengers of spaceship Earth, we
should ask ourselves how can we really
help passengers now traveling in much
worse compartments of this spaceship.
We know that our lifestyle, based on
consumerism, may cause disparities.
Disparity is, indeed, the most prominent
characteristic among the Earths inhab-
itants and, in the long run, the most
dangerous problem. Finding a correct
solution to the energy crisis could offer
the opportunity to reduce disparity and
create a more peaceful world. Our
[*] Dr. N. Armaroli
Molecular Photoscience Group
Istituto per la Sintesi Organica e
la Fotoreattivit
Consiglio Nazionale delle Ricerche
Via Gobetti 101, 40129 Bologna (Italy)
Fax : ( +39)051-639-9844
E-mail: nicola.armaroli@isof.cnr.it
Prof. Dr. V. Balzani
Dipartimento di Chimica “G. Ciamician”
Universit di Bologna
Via Selmi 2, 40126 Bologna (Italy)
Fax : ( +39)051-209-9456
E-mail: vincenzo.balzani@unibo.it
Figure 1. In this 1970 picture, an average
American family is surrounded by the barrels
of oil they consume annually. Now this con-
sumption is about 40 % higher.
“Currently the world’s growing
thirst for oil amounts to almost
1000 barrels a second.”
Essays
52 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2007,46,52–66
generation will ultimately be defined by
how we live up to the energy challenge.
An Unsustainable Growth in an
Unequal World
“My grandmother used to say: there are
but two families in the world, have-much
and have-little.”
Miguel de Cervantes, Don Quixote
Energy is the number one but, by no
means, the unique problem for human-
ity. Food, water, health, environment,
education, population, war, democracy
are other important problems. It can be
noted that all of them, perhaps except
for democracy, are strictly dependent on
the availability of energy.[4] It is easy to
understand that a hospital consumes a
huge quantity of energy. Perhaps it is
more difficult to reckon the colossal
amount of energy embodied in and
consumed by a stealth bomber. Modern
agriculture, which provides any kind of
food and delicacies to Western consum-
ers, is one of the most energy intensive
human activities. For example, the en-
ergy of 7 liters of oil is needed to
produce 1 kg of beef. Some people say
that modern industrial agriculture is, in
fact, the use of land to turn oil and gas
into food.
Excluding the light coming from the
Sun, the Earth is a closed system. The
second law of thermodynamics states
that, in a closed system, there are
limitations that cannot be overcome;
apparently, several economists are not
acquainted with this simple principle.
We must never forget that human econ-
omy vitally depends on the planets
natural capital (e.g. oxygen, water, bio-
diversity, etc). Fortunately, part of this
capital is regenerated for free by the
direct and indirect action of sunlight on
the biosphere, but drawing on the nat-
ural capital beyond its regenerative
capacity results in depletion of the
capital stock. Humanitys load corre-
sponded to 70% of the capacity of the
global biosphere in 1961, and grew to
100% in the 1980s and to 120 % in
1999.[5] This statistic simply means that
we are living above our possibilities.
Furthermore, we make extensive use of
resources that cannot be regenerated by
the biosphere. This is not only the case
of fossil fuels, that are irremediably
consumed when used, but also that of
metals.[6] Clearly, spaceship Earth has a
limited carrying capacity. It has been
calculated that if all the worlds 6.5 bil-
lion inhabitants were to live at current
North American ecological standards,
we should look around for another two
Earths to accommodate them.[5] Of
course also Europe is heavily contribu-
ting to unsustainable Earth exploitation:
European terrestrial biosphere absorbs
only 10% of Europes anthropogenic
CO2production.[7]
Known and Hidden Costs of
Energy
“The struggle for existence is the struggle
for available energy”
Ludwig Boltzmann
What is energy? The answer is not
simple. We might apply to energy what
Saint Augustine argued about time
(Confessions, XI, 14): “What is time? If
nobody asks me, I know; if I wish to
explain to him who asks, I know not.”
Energy is an ubiquitous entity look-
ing like heat, electricity, motion that,
unnoticed, shapes and drives every sin-
gle instant of our life (Figure 2). How-
ever, even the most educated people of
developed countries do not care much
about its importance. There is indeed a
big disproportion between the extensive
use we make of energy and the scarce
knowledge we have of it. This situation
is not good for a society willing to
become knowledge-based as Europe is
supposed to do.[8]
If you ask simple questions to com-
mon people, for example, How energy is
produced? How much energy do you
consume? What is the cost of electric-
ity? How can you save energy? you will
most likely get poor answers. As educa-
tors we should ask ourselves: how
energy is taught in our schools and
universities?
In recent years the price of energy
has substantially increased; the common
belief is that energy is now extremely
expensive. But can we really complain?
The current “high” price of the most
valuable energy source, oil, is around
$70/barrel, that is, $0.44/liter. Hence,
crude oil is cheaper than some mineral
waters one can find on the supermarket
shelves. Currently, the cost of petrol in a
gas station in Europe (ca. E1.3 L1)is
“Our generation will ultimately
be defined by how we live up to
the energy challenge.”
Figure 2. The power at the disposal of energy-affluent people: to run a TV set the continuous
muscular work of 2 people would be needed, while for a complete cycle with an energy-efficient
washing machine the number is increased to 15. To take-off a fully loaded Boeing 747,
1.6 million “energy slaves” would be required. These examples give an idea of how much energy
we use.
“There is a big disproportion
between the extensive use we
make of energy and the scarce
knowledge we have of it.”
Angewandte
Chemie
53Angew. Chem. Int. Ed. 2007,46, 52 – 66 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org
lower than that of water in a restaurant.
Thus it is still cheaper for a car to drink
than for a human being.[9]
Our energy bonanza, however,
comes at a price that is not paid directly
by individuals or by energy companies,
but by the society as a whole in terms of
socio-economic and environmental
damage. For instance, in Europe health
care for people injured by car accidents
(i.e., energy intensive transportation) is
paid with public money and this con-
tributes to burden national budgets. The
hidden costs of energy (“externalities”)
deal with short term negative impacts
related to the discovery, extraction, dis-
tribution, and conversion of power re-
sources as well as long-term effects, such
as health damage arising from air-pollu-
tion exposure.[10,11] Externalities are
probably the greatest taboo of the
energy puzzle. Some side-effects of en-
ergy consumptions are transmitted to
future generations (e.g., nuclear waste) ;
others, in the form of huge military costs
related to securing energy supply, fur-
ther burden our society. In this regard it
is sufficient to recall that the first
Persian Gulf War (PGWI, 1990–1991)
cost approximately $80 billion, most
likely a tiny value if compared to the
unknown cost of the ongoing PGW II
(Figure 3). Even in peace time there is a
gigantic security machine operating to
safeguard key energy corridors and
facilities (pipelines, sea routes, refiner-
ies, etc.) and these costs are not directly
charged on the oil barrel.
Europe is leading the way to estab-
lish a scientifically sound account of
energy externalities.[12] The European
Union (EU) has recently estimated the
extra-cost of electricity production by
different sources. For example, electric-
ity generated by coal in Germany im-
plies an extra cost of 0.73Ecents per
kWh, that is, 10-times higher than wind
energy.[13] From these and related data it
becomes clear that, if externalities were
included in energy accounting, some
renewable technologies would be al-
ready competitive with traditional tech-
nologies on a purely economic basis.
Probably the heavier externality that
big energy consumers are inflicting to all
of the citizens of the world is the forcing
of the carbon cycle that fosters global
warming. The amount of carbon we are
injecting in the air (ca. 7 Gt/year) looks
little if compared to the naturally occur-
ring exchange between the biosphere
and the atmosphere (ca. 200 Gt/year).
However this is enough, on the long
term, to steadily increase CO2concen-
tration (+30 % since industrial revolu-
tion), alter the Earths radiation bal-
ance, and trigger artificial climate var-
iations that overlap with natural oscil-
lations.[14] The most likely scenarios
imply an increase of extreme weather
events, such as top scale hurricanes,
droughts, heavy precipitations, heat
waves. Of course, the most exposed to
the “external” effects related to climate-
change are deprived people, as shown in
the aftermath of Katrina in New Or-
leans. In other words, affluent energy
consumers will mainly generate the
damage, the poor will suffer most.
Energy and Quality of Life
“You can never get enough of what you
don’t need to make you happy”
Eric Hoffer
Energy is embodied in any type of
goods and is needed to produce any kind
of service. This is the reason why it takes
energy to improve peoples standard of
living. Since more energy yields more
goods and more services, one could
believe that the well-being of people
increases with increasing consumption
of energy. This, however, is not always
the case. The quality of life is highly
correlated with energy consumption
during basic economic development,
but it is almost completely uncorrelated
once countries are industrialized.[11]
When the per capita energy consump-
tion reaches a value of about 2.6 ton of
oil equivalents (toe) per year there is no
further improvement. There is in fact a
strict parallelism between overcon-
sumption of energy and food. The
nation with the highest number of over-
weight or obese people (USA: 130 mil-
lion, or 64%) is also the one with the
highest energy consumption per capita
(8 toe per year). An American con-
sumes as much energy as 2 European,
10 Chinese, 20 Indian, or 30 African
people.[11] Calories are both biologically
and socially healthy only as long as they
stay within the narrow range that sepa-
rates enough from too much.[15] Over a
definite threshold, energy inputs in-
crease inefficiency of personal life (obe-
sity) as well as of social life (traffic
jams), cause more waste, boost medical
expenses and, last but not least, increase
inequality.
Figure 3. The so-called “energy strategic ellipse”, an area stretching from Arabian Peninsula to
Western Siberia, where about 70% of the world’s proven oil and gas reserves are concentrated.
“Some side-effects of energy
consumption are transmitted
to future generations; others,
burden our society.”
“The quality of life is almost
completely uncorrelated with
energy consumption once
countries are industrialized.”
Essays
54 www.angewandte.org 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2007,46,52–66
As soon as a black-out takes place in
a country, for whatever reason, the
solution proposed by most politicians
and economists is that of making new
power plants. This, for example, was the
case for the nationwide black-out that
occurred in Italy on a Saturday night in
September 2003, when the power de-
mand was less than 30% of the national
capacity production. The wisest decision
to take in front of any “energy crisis” in
developed countries is not that of in-
creasing energy supply, but that of
reducing energy demand. It is not diffi-
cult to demonstrate that affluent coun-
tries can cut the energy consumption by
25% at virtually no sacrifice for peo-
ple.[16] Since a substantial amount of the
consumed energy is embodied in indus-
trial products, avoiding production of
useless things and increasing the lifetime
of products would save a lot of energy.
Unfortunately this goal does not fit
with the mantra of endless economic
growth.
Fossil Fuels
“Is fossil solar energy the only one that
may be used in modern life civiliza-
tion? That is the question”
Giacomo Ciamician
Oil is the most valuable commodity
in world trade. It can be estimated that,
at current prices, roughly six billion
dollars a day change hands in worldwide
petroleum transactions.[17] We currently
consume 85 million barrels of oil a day
and demand is growing mainly as a
result of increasing car ownership in
Asian countries. If China and India, with
now less than 20 cars for 1000 people,
should reach the car saturation level of
European countries (about 700 cars per
1000 people), their automotive fleet
would need 28 million barrels of oil a
day, that is, almost three times the
current production of Saudi Arabia.
Our oil-addicted civilization is going
to face a problem that might change the
energy scenario dramatically, the so-
called oil peak.[18] Starting from early
20th century the demand of oil has
steadily increased and the supply has
always been able to cope with such a
demand: we needed more oil and we
extracted it easily. There will come a
time, however, in which the supply will
not be able to satisfy the ever increasing
demand. That day the oil reserves will
not be exhausted, but the golden age of
“easy oil” will be over. The pessimists
believe that we are now at the oil peak,
the optimists[19] shift it 30 years later.
Actually, even if the latter are right, the
oil peak problem will not be moved too
far away: after all, the babies today will
be still young in 30 years time.
Oil is the ideal fuel since, being
liquid, it is easy to extract and transport.
For some applications oil is practically
impossible to replace: can we conceive
to run a Boeing-747 Jumbo Jet with solid
or gas fuels?
The gas peak is expected to occur
later than oil peak. However, the short-
age in the supply of Russian natural gas
to Europe in winter 2006 has shown that
the distribution infrastructure of this
valuable energy source is rigid and
fragile. We should also consider that in
the future a substantial share of Russian
gas could take the direction south to
developing Asian countries. The distri-
bution problem can be limited, in prin-
ciple, by building liquid natural gas
(LNG) tankers and regasification termi-
nals. These infrastructures, however, are
extremely expensive and imply severe
security issues. This is probably the
reason why most California LNG termi-
nals were built off the Mexican coast.[20]
The risk of accident is limited, but …
you never know.
Coal is the most abundant and dirt-
iest of fossil fuels. Basically, the problem
of coal in the next 100 years is not
availability, but environmental sustain-
ability. Just to give a visual impression, a
standard 1000 MW plant consumes a
100-trainloads of coal a day. The trend in
the use of the most greenhouse-inten-
sive fuel is in conflict with ongoing
efforts for a world-scale climate policy.
In the hope to mitigate the climate
impact of coal, considerable resources
are being invested on projects for coal
gasification and carbon sequestration
underground. The latter technology,
that aims at capturing CO2from sta-
tionary sources (e.g., power plant flue
gases) thereby preventing its release in
the atmosphere, encounters a wealth of
environmental, technical, economical,
and political obstacles.[21,22] Coal has
another significant drawback: in many
cases it requires someone digging it
underground, which is not exactly the
easiest job one can dream of. Probably,
the lowest vocation rate for this career is
found among the biggest energy con-
sumers of affluent countries.
In conclusion, it is clear that, sooner
or later, we will face an energy transition
from fossil fuels to some kind of renew-
able energy source (Figure 4),[23]
Nuclear Energy
“The nuclear power industry remains as
safe as a chocolate factory”
The Economist, March 29th 1986 (4 weeks
before the Chernobyl catastrophe)
Nuclear energy can be obtained by
fission or fusion. While fission is largely
used to produce electrical energy, fusion
Figure 4. The famous paper “The Photochemis-
try of the Future” also published in Science by
Giacomo Ciamician in 1912 (ref. [23]), where
he pointed out the need for an energy transi-
tion from fossils to renewables. One century
later this call is more urgent than ever.
“The wisest decision to take in
any energy crisis in developed
countries is that of reducing
energy demand.”
Angewandte
Chemie
55Angew. Chem. Int. Ed. 2007,46, 52 – 66 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org
is still at the level of preliminary labo-
ratory experiments[24] (except for
bombs). The most technically advanced
nations have recently joined to launch a
project called ITER that should demon-
strate by 2050 the possibility to use
nuclear fusion for civil purposes. It is
difficult to forecast whether this project,
which is extremely complex and very
expensive (about 10 billion E, which
means approximately 2 Efor each per-
son on the Earth) will be successful.
Presently there are 441 operating
fission power plants in the world. In
the next few years this number will
likely decrease because, while waiting
for new planning and regulation clear-
ance, the 26 plants that are now under
construction will hardly replace the old-
est reactors close to decommissioning.[25]
Development of fission nuclear energy
faces a number of difficulties. In princi-
ple, modern reactors are safe, but people
cannot forget the Chernobyl accident,
whose terrible material and psycholog-
ical consequences are still difficult to
evaluate. The problem of safe disposal
of nuclear waste has not yet been solved
even in the United States, in spite of the
huge effort to construct a national
deposit in the Yucca Mountain,[26]
whereas leaving nuclear deposits radio-
active for thousands of years to future
generations raises moral concern. Civil
nuclear energy is tightly and ambigu-
ously linked with weaponry technology
(see the current Iran affair) and prolif-
eration of nuclear weapons is the last
thing we need on our fragile spaceship
Earth. Nuclear plants are primary tar-
gets for terrorists and are hugely expen-
sive to build, safeguard, and decommis-
sion.
The development of nuclear energy
has been heavily subsidized in different
ways. In U.S., for example, the Price–
Anderson act poses a cap of $200 mil-
lion on the cost of private insurance, that
would otherwise be prohibitive. When
required, resources are ultimately pro-
vided by taxpayers. Observers note that
it is questionable if any nuclear plants
would have been constructed in the U.S.
without this support.[10]
To contribute significantly to our
future energy needs, nuclear energy
should provide 10 TW of power for an
extended period of time. Production of
such a large amount of energy would
require 10 000 one-gigawatt-electric (1-
GWe) nuclear fission plants which
means that a new power plant should
be constructed somewhere every other
day for the next 50 years.[27, 28] Once that
level of deployment was reached, the
terrestrial uranium resource base would
be exhausted in 10 years. Spent fuel
should then be reprocessed and breeder
reactor technology should be developed
and disseminated to countries wishing to
meet their additional energy demand in
this way.[29] Conventional fuel reprocess-
ing, however, requires the separation of
plutonium from radioactive material,
making much easier plutonium stealing
for atomic weapons. The Bush admin-
istration has recently asked Congress to
provide $40 billion start-up funding for
an ambitious program called Global
Nuclear Energy Partnership (GNEP)
that aims at launching an improved
nuclear recycling process.[29] If the proj-
ect were successful, by 2025 the U.S. and
its partners would provide fresh nuclear
fuel and small nuclear reactors to devel-
oping nations. In return, these user
nations would agree not to build urani-
um enrichment and to give back spent
fuels to the original supplier for reproc-
essing. This kind of initiative, however,
would render developing countries
heavily depend on foreign technology
and their political freedom could be
substantially compromised.
Solar Energy
“Life is a water mill: the effect produced
by the falling water
is achieved by the rays of the sun.
Without the sun the wheel of life cannot
be kept going.
But we have to investigate more closely
which circumstances and laws of Nature
bring about this remarkable transfor-
mation
of the sunrays into food and warmth.”
Wilhelm Ostwald
As mentioned before, spaceship
Earth is a closed system. We are lucky,
however, to have an inexhaustible en-
ergy flow coming from the sun and
deposited on the surface of the Earth:
120000 TW of electromagnetic radia-
tion. It is a quantity of energy far
exceeding human needs. Covering
0.16% of the land of the Earth with
10% efficient solar conversion systems
would provide 20 TW of power (Fig-
ure 5),[30] nearly twice the worlds con-
sumption rate of fossil energy and the
equivalent of 20 000 1-GWenuclear
fission plants.
Solar energy has enormous potential
as a clean, abundant, and economical
energy source, but cannot be employed
as such; it must be captured and con-
“Civil nuclear energy is tightly
and ambiguously linked with
weaponry technology.”
Figure 5. The production of 20 TW of power, the world’s mid-century projected demand, would
require covering 0.16% of Earth’s land (red squares) with 10 %-efficient solar panels (courtesy
of Prof. Nathan Lewis, Caltech, Pasadena).
Essays
56 www.angewandte.org 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2007,46,52–66
verted into useful forms of energy. Since
solar energy is diffuse (ca. 170 Wm2)
and intermittent, conversion should in-
volve concentration and storage. Cur-
rently, none of the many routes used to
convert solar energy into heat, electric-
ity, and fuel is competitive with fossil
fuels at todays world market price.
However, if the “external” costs of
energy from fossil fuels were consid-
ered, the cost comparison would give
quite different results.
Some scientists believe that in the
future it will be possible to collect
energy from the space by solar power
satellites (SPS) and then send micro-
wave power beams back to Earth. We
will not consider these futuristic appli-
cations in the following.
Solar Thermal Conversion
The most broad-scale way of making
use of solar energy is that of solar
thermal collectors, in which a liquid is
heated to supply hot water for direct use
or home heating. These systems are very
simple and do not need sunlight con-
centration. The market for solar thermal
collectors grew some 50 % between 2001
and 2004. The EU accounts for 13%
(1.6 million square meters installed in
2004).[31] The highest density of solar
thermal systems is in Israel (740 m2per
1000 inhabitants; in Germany, it is ten-
times less), where most buildings are
required by law to have solar hot-water
collectors. The 110 million square me-
ters of installed collector area (77 ther-
mal gigawatts, GWth, of heat production
capacity) worldwide correspond to al-
most 40 million households, about 2.5%
of the roughly 1.6 billion households
that exist worldwide.[31] It is important
to point out that, contrary to common
perception, over 50% of energy use in
modern houses is spent in the most
trivial fashion: warm up water for heat-
ing, washing, and cooking. Hence wide
diffusion of solar thermal conversion
would substantially alleviate the energy
and environmental bill of the residential
sector.
It has been estimated that in 2004
the use of solar energy in the place of
fossil fuels to obtain hot water has
avoided production of 25–30 million
tons of CO2. A number of major cities
around the world, lead by Barcelona
and Oxford, have enacted ordinances
requiring solar thermal systems in new
buildings, with very significant results.
An important improvement of solar
thermal conversion would be to con-
struct systems capable of accumulating
heat during the day, storing it in an
embedded phase transition, and release
it in a controlled manner.
The Suns energy can also be con-
verted into high-temperature heat by
using mirrors to concentrate the radia-
tion. Once the sunlight is concentrated,
heat can be converted into electricity by
heat engines or used for thermochem-
ical processes such as methane reform-
ing and metal oxide reduction.[28] After a
stagnant period which lasted until a few
years ago, high-temperature solar ther-
mal systems have recently regained
interest. Spains market is emerging
and some developing countries have
planned projects.[31] Breakthrough di-
rections are materials that can withstand
the high temperatures and corrosive
chemical environments in solar furna-
ces.
Solar Electricity
Solar electricity can be produced
from photovoltaic (PV) cells and related
devices, or from high-temperature sys-
tems. The first method is by far the most
promising for diffuse electricity produc-
tion. PV cells have many applications.
They are particularly well suited to
situations where electrical power from
the grid is unavailable. About 1.6 billion
people still do not have access to
electricity and a substantial portion of
the worlds poor lives in areas where the
cost of extending the electric grid is
prohibitive. In developed countries, so-
lar cells (in the form of modules or solar
panels) on building roofs can be con-
nected through an inverter to the elec-
tricity grid in a net metering arrange-
ment (grid-connected PV systems).
From 2002 to 2004, grid-connected solar
photovoltaics grew by 60 % per year, to
cover more than 400 000 rooftops (of
which 200 000 in Japan, and 150000 in
Germany).[31]
In conventional PV cells electrons
and holes created by absorption of
photons with energies above the semi-
conductor band gap lose their excess
energy as heat. The thermodynamic
limit for energy conversion efficiency
under these conditions is 31 %. In prin-
ciple, this limit can be overcome by
second-generation systems made of
semiconductor p–n junctions arranged
in tandem configuration (multijunction
solar cells).[28]
The most common, first-generation
PV cells, consisting of single-crystalline
silicon, have efficiencies between 5 and
15%, a lifetime of about 30 years and a
cost for grid-connected electricity of
about 0.20–0.40 $/kWh, to be compared
to electric grid supplies from fossil fuels,
which vary between 0.03 (off-peak,
developed country) and 0.80 $/kWh
(rural electrification).[31] The energy
payback time of a solar cell is of the
order of 2–4 years and in its lifetime a
cell may produce electricity with a value
of something in the order of 10 times its
cost of production.[28] Total world cumu-
lated installed capacity of PV amounted
to 1.8 GW in 2004.[31]
Solar electricity is already cost-com-
petitive with fossil and nuclear electric-
ity if externalities are taken into consid-
eration. Furthermore, it can reasonably
be expected that an intense research
effort in this field will produce new
concepts, designs, materials, and tech-
nologies capable of increasing cell effi-
ciency and reducing cost.
During the past decade, solid-state
PV cells based on molecular-based or-
ganic systems like those used in video
display technology have been devel-
oped. Their energy conversion efficien-
cy is still low (less than 5 %), but they
offer great potential for construction of
low-cost, lightweight, large-area, flexi-
ble solar cells. The development of high-
efficiency organic solar cells could lead
to solar conversion paints that would
allow extensive capture and conversion
of solar energy.[28]
Solar energy can be converted into
electrical power also by photoelectro-
“Over 50 % of energy use in
modern houses is spent in
warming up water for heating,
washing, and cooking.”
Angewandte
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chemical cells based on a semiconductor
electrode in contact with an electrolyte
containing an electron relay. The most
stable, and therefore most used semi-
conductor is TiO2which, however, does
not absorb much of the sunlight because
its band gap is too high (3.0 eV, ca.
410 nm). To overcome this problem, dye
molecules are adsorbed onto thin films
of sintered nanocrystalline particles of
TiO2.[32] The dye molecules, when excit-
ed by sunlight, inject electrons into the
TiO2, producing the charge-separation
process. These dye-sensitized solar cells
are attractive because of the low cost of
TiO2and the potential simplicity of their
manufacturing process. Laboratory
scale devices of 11 % efficiency have
been demonstrated, but larger modules
are much less efficient.
Solar Fuels
Liquid fuels are the best form of
energy since they can be stored and
transported. Because of the intermittent
nature of solar energy, its conversion
into useful chemical fuels is even more
advisable. Solar electricity can be con-
verted into chemical fuels through the
electrolysis of water to produce H2and
O2, but it is a very expensive method.
Therefore, direct production of fuels
from sunlight (perhaps including meth-
anol)[33] would be much more advanta-
geous.
Natural photosynthesis: Natural
photosynthesis converts sunlight into
fuels, producing biomass and, over geo-
logical time, fossil fuels. Fossil fuel
production rate, however, is about
500,000-times slower than our current
consumption rates. The maximum po-
tential photosynthetic conversion of
sunlight to chemical energy is about
6.7%, but only a fraction of this is
realized. Globally, only 0.3 % of the
solar energy falling on land is stored in
plant matter, and only a fraction of this
can be harvested.[11] Improving upon the
efficiency of natural photosynthesis
would of course be a very important
result. To reach this goal, elucidation of
the molecular basis of the overall pro-
cess is essential (Figure 6). In photo-
synthetic organisms, light is harvested by
antenna systems consisting of pigment-
protein complexes. The captured exci-
tation energy is then transferred to
reaction center (RC) proteins, where it
is converted by an excited-state elec-
tron-transfer process into electrochem-
ical potential energy. The quantum effi-
ciency of the charge-separation process
is close to 100 %. The resulting oxidizing
and reducing equivalents are then trans-
ported, by subsequent thermal electron-
transfer steps, to catalytic sites, where
they are used to oxidize water and
produce fuels, such as carbohydrates.
Artificial photosynthesis: The need
and possibility to achieve artificial pho-
tosynthesis[34] was anticipated by the
Italian chemist Giacomo Ciamician
(Figure 7) about one century ago :[23]
“Where vegetation is rich, photochemis-
Figure 6. A very simplified sketch representing key processes in natural photosynthesis: solar
light harvesting by pigments, energy transfer to the reaction center, charge separation,
production of carbohydrates and oxygen (courtesy of Dr. Lella Serroni, University of Messina).
D donor, A acceptor, P photosensitizer.
Figure 7. Giacomo Ciamician, pioneer of photochemistry and prophet of the energy transition,
while watching his flasks under solar irradiation on the roof of his laboratory at the University of
Bologna, Italy, circa 1910.
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try may be left to the plants and, by
rational cultivation, solar radiation may
be used for industrial purposes. In the
desert regions, unsuitable to any kind of
cultivation, photochemistry will artifi-
cially put their solar energy to practical
uses. On the arid lands there will spring
up industrial colonies without smoke and
without smokestacks; forests of glass
tubes will extend over the plants and
glass buildings will rise everywhere; in-
side of these will take place the photo-
chemical processes that hitherto have
been the guarded secret of the plants,
but that will have been mastered by
human industry which will know how
to make them bear even more abundant
fruit than nature, for nature is not in a
hurry and mankind is. And if in a distant
future the supply of coal becomes com-
pletely exhausted, civilization will not be
checked by that, for life and civilization
will continue as long as the sun shines!”.
The efficient production of clean
solar fuels would indeed represent the
most important breakthrough of mod-
ern science. Although this task presents
many scientific challenges, some results
so far obtained are encouraging.[35]
For solar fuel production to be
economically and environmentally at-
tractive, the fuels must be formed from
abundant, inexpensive raw materials
such as water and carbon dioxide. Water
should be split into molecular hydrogen
and molecular oxygen,[36] and carbon
dioxide in aqueous solution should be
reduced to ethanol with the concomitant
generation of dioxygen. These are the
two reactions on which research is
presently focused. The best way to
construct artificial photosynthetic sys-
tems for the practical production of
solar fuels is that of mimicking the
molecular and supramolecular organi-
zation of the natural photosynthetic
process: light harvesting should lead to
charge separation, that must be followed
by charge transport to deliver the oxi-
dizing and reducing equivalents to cata-
lytic sites where oxygen evolution and
hydrogen evolution (or CO2reduction)
should separately occur. While some
progress has been made on each aspect
of artificial photosynthesis, integration
of the various components in a working
system has not yet been achieved (Fig-
ure 8).[37]
Difficulties arise because formation
of hydrogen and oxygen from water (as
well as reduction of CO2) are multi-
electron processes, whereas light ab-
sorption is a one-photon process that
results in a one-electron charge-separa-
tion process. Therefore catalysts are
necessary to couple single photon events
to processes capable of accumulating
the redox equivalents needed for fuel
production. Efficient catalysts, particu-
larly for oxygen generation, however,
have not yet been found. The recent
discovery of the structure of the oxygen
evolving center of natural photosynthe-
sis[38] may help in designing efficient
artificial catalytic systems.
More successful has been the study
of hybrid natural–artificial systems, for
example, the construction of a proton
pump using an artificial donor–acceptor
triad and ATP synthase incorporated in
a liposome.[39]
Fuels from biomass: Biomass has
been, and continues to be, an important
resource for energy production partic-
ularly in developing countries where it is
often used to provide energy in small-
scale industries and more generally as
fuel-wood in stoves causing severe
health problems.[40] Substantial energy
production from biomass requires very
large areas of cultivable land, and huge
amounts of water. It has been estimated
that, at current consumption rate, the
substitution of a mere 5% of gasoline
and diesel fuels for Europe and U.S.
would claim about 20 % of their culti-
vable land.[41]
In the industrial countries, biomass
is employed to produce heat and elec-
tricity using mainly solid biomass, or to
obtain liquid fuels, such as ethanol and
biodiesel, from crops (33 billion liters in
2004, about 3 % of the 1 200 billion liters
of gasoline consumed globally).[31] Eth-
anol is extracted from sugarcane in
Brazil and from corn in the U.S. The
Brazil cane–ethanol system converts
33% of the harvested primary energy
into ethanol[42] providing, in 2004, 44 %
of all (non-diesel) motor-vehicle fuel
consumed as pure ethanol (E95) or a
25 %-ethanol/75 % gasoline blend
(E25). More than half of all new cars
sold in Brazil are flexible-fuel vehicles
Figure 8. A very simplified sketch representing key processes in artificial photosynthesis: solar
light harvesting by molecular antennas, energy transfer to a reaction center, charge separation,
water splitting with production of hydrogen and oxygen on the two sides of a membrane
(adapted from ref [37]).
“The efficient production of
clean solar fuels would repre-
sent the most important
breakthrough of modern
science.”
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that run with pure ethanol or the
ethanol/gasoline blend. Use of ethanol
as E85 and E10 blends (that is 85% or
10% ethanol) is increasing in the U.S.,
where the corn–ethanol system is re-
ported to convert 54 % of the harvested
primary energy.[43] Mandates for blend-
ing biofuels into vehicle fuels have been
appearing in several countries including
India and China. In Europe, several
countries produce biodiesel and provide
tax exemption for this fuel. In Germany,
biodiesel production grow by 50 % in
2004. EU has a biofuels target of 5.75 %
for 2010. Notably, the net energy gain in
the production of biodiesel from soy-
beans is substantially higher than that of
bioethanol from corn.[44]
Current research directions on bio-
mass focus on 1) increasing cellulose-to-
sugar conversion for the production of
ethanol,[16,45] and 2) gasification technol-
ogies to produce synthesis-gas (syngas),
a mixture of CO and H2for use in fuel-
forming reactions.[28]
Wind, Hydro, and Other Renew-
ables
“Praised be You my Lord with all Your
creatures,
especially Sir Brother Sun,
Who brings the day and through whom
You give us light.
And he is beautiful and radiant with
great splendor.
Praised be you, my Lord, through
Brother Wind,
Praised be You, my Lord, through Sister
Water,
Praised be You, my Lord, through Sister
Mother Earth,”
Saint Francis, Canticle of the Creatures
Wind
Producing electricity by wind im-
plies a number of hard-to-rival advan-
tages such as 1) guaranteed perpetual
zero cost of the primary “fuel”; 2) no
emissions in the atmosphere or heat to
dissipate; 3) a relatively simple technol-
ogy; 4) short times of construction and
wide tunability of installed capacity
from a few kW to hundreds of MW.
Inevitably, the price of wind-made elec-
tricity will continue to decrease on the
long term, making it a stronger and
stronger competitor for traditional tech-
nologies. Disadvantages are related to
the natural variability of winds, the
distance between wind farms and con-
sumption centers, and aesthetic and
ecological objections. The total amount
of globally extractable wind power has
been estimated to be 2–6 TWe.[30]
The wind-power market is concen-
trated in a few primary countries, with
Spain, Germany, India, U.S., and Italy
leading expansion in 2004, but new
large-scale commercial markets are tak-
ing the first steps in several countries
such as Russia, China, and Brazil. The
wind-power industry produced more
than 6000 wind turbines in 2004, at an
average size of 1.25 MW each.[31] Ac-
cording to the European Wind Energy
Association,[46] by the end of the current
decade 75 000 MW of wind turbines will
be installed in Europe, able to satisfy the
residential electricity need of almost
200 million European citizens. The vast
European wind-energy potential, in
principle, would be able to satisfy all
our electricity needs.
Hydroelectric Energy
Hydrogeneration is one of the oldest
technologies for electricity production,
thus it is easier to evaluate advantages
and disadvantages.[16] Among the latter,
invasivity comes first. The land occupied
by the world hydroelectric infrastruc-
ture is estimated to be roughly
300000 km2(approximately the area of
Italy), although hydroelectric plants
provide just 3 % of world total primary
energy supply (TPES).[47] The construc-
tion of big dams has caused the forced
displacement of 40-to-80 million (usual-
ly poor) people in developing countries
during the 20th century, with unaccount-
able social and economic penalties.
Reservoirs have often inundated ar-
cheological sites as well as many unique
natural ecosystems and life in down-
stream rivers (e.g., the Colorado) has
often been dramatically affected. Re-
cently it has also been shown that water
reservoirs can be significant sources of
CO2and CH4from decaying vegetation.
Despite these drawbacks, hydroelectric
power exhibits many important advan-
tages such as 1) the lowest operating
cost and a longer plant lifetime than any
other mode of electricity production;
2) easy harvesting of potential energy
for peak electricity demand, available
within seconds; 3) reliable supply of
irrigation and drinking water; 4) protec-
tion against recurrent, and sometimes
destructive, floods. In principle the
Earth untapped hydro potential is sim-
ply huge, however only a small fraction
of it can be utilized in a sustainable
fashion from an economic and environ-
mental standpoint. According to recent
estimates, the remaining exploitable
hydroelectric resource is less than
0.5 TW.[28]
As far as Europe is concerned, the
potential for new big hydroelectric
plants is minimal, but small size and
widely distributed facilities can give a
significant contribution to tomorrows
energy mix. This situation is also true for
developing countries where tens of mil-
lions of rural homes already receive
power from small hydroelectric plants,
mostly in China.[16,31]
Other Renewables
Mother nature donates us a few
other options to draw energy from our
Earth spaceship. The most important of
these is probably geothermal energy,
related to the heat stored in the depths
of our progressively cooling planet. In
some selected areas, as demonstrated in
Italy over a century ago, underground
thermal energy can be extracted and
used as heat or converted into electric-
ity. Geothermal direct-heat utilization
capacity has nearly doubled from 2000
to 2005 (13 GWth increase), with at least
13 countries using geothermal heat for
the first time.[31] The total geothermal
energy at the surface of the Earth,
integrated over all the land area of the
continents, is 12 TW, of which only a
small fraction could practically be ex-
tracted. The global potential electric
energy generated in this way could cover
3–5% of current consumption, which is
certainly interesting especially for re-
gions of the planet where exploiting
geothermal energy is practical.[16]
Other, minor energy resources could
be obtained by taking advantage of the
ocean and lake temperature gradients,
currents, and waves, while the Earth–
Moon gravitational energy can be ex-
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ploited in some selected coastal areas of
the northern hemisphere where tides
move large volumes of sea water in a
relatively short time. The cumulative
energy in all tides and ocean currents in
the world amounts to less than 2 TW.
However, in our quest for an increas-
ingly diversified energy portfolio, they
must be carefully considered, especially
on the local scale. A recent interesting
example is the use of the deep cold
waters of Lake Ontario to provide air-
conditioning to thousands of Torontos
offices and houses.[48]
The Hydrogen Economy
““I believe that water will one day be
employed as fuel, that hydrogen and
oxygen which constitute it, used singly or
together, will furnish an inexhaustible
source of heat and light, of an intensity of
which coal is not capable … . Water will
be the coal of the future””
Jules Verne, The Mysterious Island
According to media and press it
seems that the energy problem will
shortly be solved by hydrogen (Fig-
ure 9), that sometimes is described as a
fuel obtainable for free from water.
Policy-makers have strongly biased
opinions on the hydrogen issue.[49] Most
scientists believe that the shift to a
hydrogen economy will not occur soon
and might also not occur at all unless a
large research effort is set up to over-
come several scientific and technologi-
cal obstacles.[49–52]
Combustion of molecular hydrogen,
H2, with oxygen produces heat and
water, and combination of molecular
hydrogen and oxygen in a fuel cell
generates electricity, heat, and water.
Clearly, if hydrogen could promptly
replace oil, both the energy and the
environmental problems of our planet
would have been solved. Unfortunately,
however, there is no molecular hydro-
gen on the Earth. Molecular hydrogen
cannot be “mined”, but it has to be
“manufactured”, starting from hydro-
gen rich compounds, by using energy.
Therefore, hydrogen is not an alterna-
tive fuel, but a secondary form of
energy. This is the central (but not
unique) problem of hydrogen economy.
Like electricity, hydrogen must be pro-
duced by using fossil, nuclear, or renew-
able energy and then it can be used as an
energy vector, with the advantage, with
respect to electricity, that it can be
stored.
Although a proper use of hydrogen
is not expected to cause big environ-
mental problems, one cannot say that
hydrogen is a “clean” form of energy. In
fact, hydrogen is “clean” or “dirty”
depending of the primary energy form
used to produce it. Hydrogen obtained
by spending fossil fuels or nuclear en-
ergy incorporates all the problems of
using those primary energy sources.
Burning fossil fuels in remote regions
to produce hydrogen as a clean fuel for
metropolitan areas would be an ineffec-
tive solution, owing to the transboun-
dary nature of atmospheric pollution.[53]
Clearly, clean hydrogen can only be
obtained by exploiting renewable ener-
gies, and this can be done, in principle,
through the intermediate production of
electricity (e.g., by wind or photovoltaic
cells) followed by water electrolysis, or
by photochemical water splitting.
Growth and Potential of
Renewable Energies
“The only way to discover the limits of
the possible is to go beyond them into
the impossible”
Arthur C. Clarke
In the last few years, the use of
renewable energies has grown rapidly.
From 2000 to 2004, the average annual
growth rate was: grid-connected solar
PV 60 %, wind power 28 %, biodiesel
25%, solar hot water/heating 17 %, off-
grid solar PV 17 %, geothermal heat
capacity 13 %, and ethanol 11 %.[31] Such
a generalized increase in all the fields of
renewable energies is very important
since it allows each country to construct
a diversified energy portfolio.
Solar water heaters are fully com-
petitive with conventional water heat-
ers; ethanol in Brazil is competitive with
gasoline; hydro, geothermal, and some
forms of biomass power generation are
already competitive with power from
fossil fuels (2–4 $cents/kWh) and nucle-
ar energy 4–6 $cents/kWh; wind power
is competitive at good sites, and solar
PV power is expected to become com-
petitive before 2010 even in developed
countries at high insolation regions.
While waiting for progress in solar-
fuel production, solar thermal and solar
electricity can already supply a notice-
able amount of energy. Chinas target
for solar thermal is to reach 230 million
square meters by 2015, more than twice
the amount of worldwide collectors to-
day. Solar thermal conversion can in-
deed replace much of the heat now
supplied by burning fossil fuels and
biomass.
Solar electricity can be profitably
exploited in developing as well as de-
veloped countries. By 2005, more than
2 million households in developing
countries have received electricity from
solar home systems. An idea of how
necessary development in this field is
and how huge this market is, comes from
the estimate that 350 million households
worldwide do not have access to central
power networks. The spreading of de-
centralized electricity generation sys-
tems could eliminate the need to build
up an extensive and costly transmission
grid, in the same way as mobile tele-
communications has allowed the leap-
Figure 9. A hydrogen fuel-cell bus in Iceland.
The water splitting and recombination reac-
tions are figuratively represented by the open-
ing and closing of the door.
“According to the media it
seems that the energy problem
will shortly be solved by
hydrogen.”
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frogging of cabled telephone lines in
some developing regions of the world.
In some developed countries, de-
mand for grid-connected PV systems
outstrips production. Solar PV is indeed
one of the worlds fastest growing, most
profitable industries. Chinese module
production capacity doubled during
2004. Indias primary solar PV manu-
facturer expanded production capacity
from 8 MW in 2001 to 38 MW in 2004.
Large production is expected from new
plants installed in the Philippines, Thai-
land, and other countries. Substantial,
but not sufficient, increase in production
is taking place also in Europe, where at
the end of 2004 the top two producers
were Q Cell in Germany (75 MW) and
Isofoton in Spain (53 MW).[31]
The harnessing wind energy is also
increasing worldwide. Considering the
current level of deployment of on-shore
and off-shore wind farms, especially in
Europe, it is outdated to consider them
as “alternative” energy stations.
In new buildings, solar thermal and
PV systems can be integrated and in-
corporated into roof and walls. Blending
of small wind turbines with PV and/or
solar heaters is also possible. Standar-
dized “plug and play” full-scale house-
hold off-grid PV systems are produced
and shipping containers with integrated
systems consisting of PV modules, small
turbines, and advanced batteries are also
available. Indeed, the sophistication of
many segments of the renewable-energy
industry increases year by year.
At least 48 countries worldwide, in-
cluding all 25 EU and 14 developing
countries, have now some type of re-
newable-energy promotion policy. For
example, an European Solar Thermal
Technology Platform has just been cre-
ated to promote and ease the develop-
ment of industries with high technolog-
ical potential.[54] European renewable-
energy targets are 21 % electricity and
12% total energy by 2010. Large com-
mercial banks, venture-capital investors,
and leading global companies are
strongly interested in renewable ener-
gies, whose growth is supported by at
least 150 marked facilitation organiza-
tions. More than 1.7 million jobs have
been estimated to be directly involved in
renewable energies in 2004, including
400000 jobs in the Brazil ethanol indus-
try, 250 000 jobs in the China solar hot-
water industry, 130 000 jobs in Germany
from all renewables, and 15000 jobs in
the European wind industry.[31] Detailed
studies are available on the estimation
of direct jobs that can be created by the
development of the various kinds of
renewables.
There is strong evidence that solar
and other renewable energies can take
off with great benefit for people and the
environment. Policy can play a funda-
mental role to support this develop-
ment. Key points are durability and
reliability of political support and direct
involvement of local authorities. A vari-
ety of renewable-energy promotion pol-
icies have been adopted in farsighted
countries.
In spite of such a fast growth, the
contribution of renewable energy to the
overall energy supply is still very low.
Renewables (excluding hydroelectric)
provide 0.5 % of world TPES and 2 %
of world electricity;[55] more than one
third of the latter share is produced in
Europe.[56] There is a need to accelerate
the development of renewable energies,
but this acceleration can only be based
on scientific research. If suitable re-
search projects are launched and sup-
ported, a wealth of more efficient and
less expensive materials to construct
systems for solar energy conversion into
heat and electricity can reasonably be
expected in a few years and production
of solar fuels by artificial photosynthesis
is a likely achievement in the long run.
As pointed out by the Basic Energy
Science Workshop on Solar Energy
Utilization in April 2005,[28] research in
solar-energy conversion lies at the cross-
roads where physics, chemistry, and
biology meet nanoscience. Sciences
greatest advances have always occurred
on the frontiers, at the crossroads of
different disciplines, where the most
profound questions are posed. Solving
the energy problem is indeed a great
question that needs to be tackled by an
interdisciplinary scientific effort. Since
great questions often make good sci-
ence,[57] research aimed at solving the
energy problem will also lead to abun-
dant positive outcomes in other fields.
Answers to Fundamental
Questions
“Better to expect the foreseeable than be
caught out by the unexpected”
Andr= Isaac
At the beginning of this essay we
pointed out that the energy problem is
entwined with many other social issues,
and that we need to know the answers to
several entangled questions before tak-
ing decisions that could heavily affect
our lives and, even more so, those of our
children and grandchildren. After the
above discussion, we are in the position
to propose some answers that are, of
course, as much entangled as the corre-
sponding questions.
Can well-being, or even happiness, be
identified with the highest amount of per-
capita energy consumption? NO. In-
crease in energy consumption helps
material development, but in developed
countries it does not help people to
solve their nonmaterial problems. We
have to change the paradigm that gov-
erns our energy policy. The energy crisis
in a wealthy society cannot be over-
whelmed by increasing energy produc-
tion. To expand our happiness we should
make room for our nonmaterial values
and to human relationships.
Should we progressively stop burning
fossil fuels? YES, for three important
reasons: 1) fossil fuels are a not renew-
able energy source that is going to
exhaust; 2) use of fossil fuels causes
severe problems to human health and
irreversible damages to the environ-
ment; 3) fossil fuels should be preserved
as raw material for the chemical indus-
try. Energy from fossil fuels should
progressively be used only for creating
the conditions for a smooth transition
toward the development of new energy
sources.
Can scientists find an energy source
capable of replacing fossil fuels? YES.
There are two abundant energy sources,
solar energy (that broadly speaking
includes the other renewable energies)
and nuclear energy. These two forms of
energy are completely different not only
“Research aimed at solving the
energy problem will also lead to
abundant positive outcomes in
other fields.”
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for technical reasons, but also from the
social viewpoint.
Nuclear energy obtained by the
presently available technology (fission)
is neither clean nor inexhaustible. Fur-
thermore, it is a very concentrated form
of energy that has to be produced under
strict technical, political, and military
control because of its high capital cost,
possible catastrophic accidents, difficul-
ty to dispose wastes, misuse of nuclear
material, proliferation of nuclear arma-
ments. Development of nuclear energy
will favor energy overuse, increase dis-
parities among rich and poor nations,
and lead to a more fragile world.
Solar energy is abundant and inex-
haustible. It can be exploited all over the
world by a variety of friendly, but still
relatively expensive technologies, some
of which are very simple. Solar energy is
a diluted and diffuse form of energy,
which can be transformed without fear-
ing big accidents, misuse, and military
applications. Being not concentrated,
solar energy will discourage energy
overuse and reduce pressure on the
consumption of the Earths other re-
sources; being diffuse all over the world
(Figure 10), it will reduce disparities
among the worlds nations. Most poor
countries have abundant solar energy
and development of related technolo-
gies can contribute to poverty allevia-
tion.
Can chemistry help in solving the
energy problem? YES. The three con-
version routes of solar energy (solar
heat, solar electricity, solar fuel) require
special materials and two of them in-
volve chemical processes. New material
systems, guided by the interplay be-
tween rational design and experimental
screening, can greatly improve the per-
formance of light absorbers, energy
converters, and energy-storing systems.
Chemistry can play a key role in im-
proving any kind of energy-related tech-
nology and can even find novel solu-
tions. Finding a breakthrough for solv-
ing the energy crisis is indeed the “grand
challenge” of chemistry.[27,28, 57]
Will it be possible for all Earths
inhabitants to reach the standard of living
of developed countries without devastat-
ing the planet? NO. Even if, as expected,
the population growth will soon reach a
plateau, there are not enough resources
for all people to live at the level reached
today by developed countries. To keep a
decent level of life we will be forced to
exploit sunlight for recycling the most
important raw materials.
Will science and technology alone
take us to where we need to be in the next
few decades? NO. Even if science and
technology will fully succeed in taking
advantage of solar energy, we should
never forget that spaceship Earth, ex-
cept for solar energy, is a closed system
and that we are already using the natural
capital beyond its regenerative capacity.
Therefore, there is a need to reduce our
pressure on the Earth and to recycle
resources as much as we can, especially
in view of population growth. We must
become aware that the Earth is not an
open place in which we live, but a closed
system which we belong to and whose
destiny we share.[59]
Should we, citizens of the western
world, change our lifestyle and shift to
innovative social and economic para-
digms? YES. We should change our
lifestyle for two reasons. First, the no-
tion of endless economic expansion
cannot be maintained because it contra-
dicts the second principle of thermody-
namics. Second, we know that our life-
style, based on consumerism, increases
disparities.
In affluent countries we live in
societies where the concepts of
“enough” and “too much” have been
removed. At most, we agree on the need
of increasing efficiency of energy con-
sumption. Higher efficiency, however,
will not lead us towards the promised
land of sustainability because not only is
efficiency still consumption, but it can
even increase consumption. For exam-
ple, if we increase energy efficiency of
some cars, consumers will presumably
use the saved money to buy other items,
perhaps more dangerous from a sustain-
ability viewpoint (e.g., faster cars). To
live in the third millennium, we need
new thinking and new ways of perceiv-
ing worlds problems. We need to over-
come the logic of efficiency and enter a
logic of sufficiency to attain ecological
stability.[60]
Can people of poor countries im-
prove their well-being? YES, they can.
Figure 10. Yearly sum of solar irradiation on horizontal surface in Europe in kWh m2; there is
only a factor of 1.6 between the values for Rome and London (data from European Commission
Joint Research Center). Isolated red dots are major metropolitan areas.
“In affluent countries the con-
cepts of ’enough’ and ’too
much’ have been removed.”
Angewandte
Chemie
63Angew. Chem. Int. Ed. 2007,46, 52 – 66 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org
What is not clear is whether we wish to
help. To contribute to this effort, we
should change somewhat our lifestyle.
Between 2002 and 2030, consumption in
U.S./Canada is expected to increase by
5.7 mbpd (million barrel of oil equiva-
lent per day) as a result of a population
increase of 88 million. By comparison, a
population increase in India of 383 mil-
lion will be responsible for an additional
1.4 mbpd, or an increase in China of
164 million will be responsible for an
additional 1.5 mbpd.[61]
To diminish the huge disparity in
energy distribution among rich and poor
one might propose to stop the growth in
affluent countries while raising energy
supply to poor countries. This is certain-
ly more realistic than imposing a de-
crease of energy consumption among
rich. Unfortunately, however, this strat-
egy is inadequate because there are not
enough resources on the planet for
6.5 billion energy voracious people.
Any action to restore equity has thus
to focus on lowering the standard of life
of the rich while attempting to raise that
of the poor.
What we can do as scientists is help
developing countries to build their own
research capacity for generating appro-
priate solutions to their specific prob-
lems involving energy resources, public
health, agriculture, ecology, and basic
education. Providing modern energy
services is crucial for the eradication of
extreme poverty as called for in the UN
Millennium Development Goals.[62]
Conclusion
“If our black and nervous civilization,
based on coal, shall be followed by a
quieter civilization based on the utiliza-
tion of solar energy that will not be
harmful to progress and to human hap-
piness”
Giacomo Ciamician
Prompt global action to solve the
energy crisis is needed. Such an action
should be incorporated in a more gen-
eral strategy based on the consciousness
that the Earths resources are limited.
The first step of this strategy is to
drastically reduce consumption of fossil
fuels. This is a task that mainly concerns
the affluent countries, where a wrong
model of life ignores any limit, dissipates
enormous amounts of resources, produ-
ces huge quantities of waste, and causes
an intolerable increase in disparity
among the worlds nations. The second
step is to launch, without any further
delay, a massive and concerted plan for
research and development of renewable
energies. This is again a task of devel-
oped countries where most of scientific
research is currently performed.[63] The
various forms of renewable energy
should be carefully considered on the
local scale. As technology improves, it
will become easier for each community
and each country to exploit the renew-
able energies available in its territory
and to have a more and more diversified
energy portfolio.
Political leaders of all nations should
put energy as the number one priority in
the agenda. The way out of the fossil-
fueled civilization is indeed a global
problem, bristling with difficulties. Since
it will take a long time, any further delay
will increase our responsibility towards
future generations.
Scientists have to provide the tech-
nological advancements to make energy
transition a reality, but not only that.
They have the moral duty to inform the
general public of the urgency and com-
plexity of the energy problem and they
must speak up with politicians on a key
issue: the energy conundrum must be
framed on a longer temporal perspec-
tive than that of political careers. Scien-
tists, who are well aware of the conse-
quences of the Second Principle of
Thermodynamics, should also convince
economists and politicians that sustain-
ability requires that we reject the notion
of endless economic expansion.[64]
Let us not forget that there is no
renewable power source on Earth that
can beat our wastefulness and igno-
rance. Each nation, community, and
even every single citizen should identify
thresholds of real needs. Consuming
resources above such a threshold is not
a necessary condition for a successful
society and prevents the construction of
a peaceful world. Indeed, the ultimate
strategy to cope with the future is
learning to say “enough”. Initially it
may be difficult, but living on the Earth
believing that there is no need for the
concept of “enough” is already quite
risky and will clearly become impossible
in a few decades. Perhaps most people,
including politicians, will understand
this “enough” if explained by responsi-
ble scientists.
The energy crisis is a challenge, but,
indeed, also an opportunity. It offers a
precious chance to become more con-
cerned about the world in which we live
and the society that we have construct-
ed. It is actually an opportunity for
scientists to take an active role in
protecting the Earth and helping to
change what is wrong in our social and
political organization, beginning with
the huge disparity between the rich
and the poor. We are well aware that
the stability of human society decreases
with increasing disparities. Ronald Rea-
gans trickle-down approach to the
world problems does not work and, if
things do not change, sooner or later the
poor will rise up against the rich. We try
to set aside the problem of disparity, but
in the long run it cannot be eluded. The
fragile spaceship Earth is in our hands.
Are we wise enough to develop, beside
science and technology, a civilization
capable of reducing disparity and creat-
ing a more peaceful world? Besides wise
politicians, we need concerned scientists
capable of knowing whether where we
are going is the right place for us to go.
Of course, new energy sources may
be found in the next decades, since
science and technology will continue to
advance. Nuclear fusion, if successfully
exploited, could solve the energy prob-
lem at the root. Unfortunately, however,
we cannot rely on what is presently
unknown. Reducing energy consump-
tion and using renewable energies are
“Scientists have the moral duty
to inform the general public of
the urgency and complexity of
the energy problem.”
“The Earth is in our hands.
Are we capable of reducing
disparity and creating a more
peaceful world?”
Essays
64 www.angewandte.org 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2007,46,52–66
options already available. Someone may
find the expansion of solar technologies
unrealistic. In this regard, it is nice to
recall that horse traders laughed at the
first automobiles, shortly before going
out of business. “Mainstream forever”,
namely new gas and oil explorations,
seems to be the most audacious recipe of
many analysts for the energy crisis. They
sound like dinosaurs in a world under
continuous evolution and are reminis-
cent of the 1970s information technol-
ogy gurus, who did not even imagine the
personal computer era.
We would like to close this Essay
with a few comments on the role of our
continent, Europe. The EU regions
enjoy the highest quality of life but are
the poorest as far as conventional en-
ergy reserves are concerned.[56] Oil pro-
duction in the North Sea peaked in late
1990s and is now inexorably declining.
Norway and Britain the greatest Euro-
pean oil producers, possess a mere 1.2%
of the worlds proven oil reserves. The
combined gas reserves of Norway and
the Netherlands, account for just 2.1%
of the total. The situation is not better
with coal, with Germany and Poland
holding 2.3 % of the worlds recoverable
amount. It might sound distasteful to
some nuclear energy supporters, who
talk about “energy independence”, that
not a single European region is listed
among uranium and thorium reserve
holders. If a prompt action to energy
transition is needed for the world, it is
simply imperative for Europe.
Given the scarcity of conventional
energy resources, energy conservation is
mandatory for Europe: we must make
use of our limited energy resources in a
smarter way. Just an example: to get one
unit of light service by using a traditional
tungsten lamp, we feed a power station
with 100 units of primary energy, simply
wasting 99 units as heat in the electricity
production/transmission and in the bulb
itself. We can perform better by using
combined heat and power facilities
(CHP)[65] and shifting progressively to
solid-state lighting.[66]
Renewable energies are fairly well
distributed all over the world, including
Europe. As an average, solar power is
only 1.5-times higher in Italy than in
Germany (Figure 10). Europe must
strengthen its role as world leader in
renewable energies. Today we need to
buy energy resources from other con-
tinents, tomorrow we must be able to
share and sell our energy know-how to
the rest of the world. Our European
institutions give us the hope that this can
be done in the framework of fairer
international relationships than those
established during the present oil era.
Europe must lead the way for a real,
albeit gradual, structural economic re-
form: passing from the intensive use of
non-renewable energy resources (fossil
fuels) to the use of the abundant, inex-
haustible, less harmful primary energy
source provided by the Sun. Our con-
tinent has the intellectual, cultural, and
economic resources to lead this crucial
endeavor.
European universities have a most
important role in creating a new gener-
ation of conscious and responsible citi-
zens who feel active members of soci-
ety,[67] according to the strategic objec-
tive of the Council of Europe meeting in
Lisbon (2000): “to become the worlds
most dynamic and competitive knowl-
edge-based economy capable of achiev-
ing a sustainable economic growth with
new and better jobs and a greater social
cohesion”.[8] Values such as conscious-
ness, compassion and care have to be the
roots of such a knowledge-based econ-
omy. And if the diluted nature of solar
energy will force us to substantially
modify our way of living, this will not
necessarily mean that our lives will be
less enjoyable in a more peaceful world.
Certainly the existence of billions now
underprivileged will be better than right
now.
Published online: November 14, 2006
[1] M. R. Simmons, Twilight in the Desert,
Wiley, Hoboken, NJ, 2005.
[2] P. Tertzakian, A Thousand Barrels a
Second, McGraw-Hill, New York, 2006.
[3] R. A. Kerr, R. F. Service, Science 2005,
309, 101.
[4] Though, curiously, nowadays a “war for
energy” is sometimes propagandized as
a “war for democracy”.
[5] M. Wackernagel, N. B. Schulz, D. Deum-
ling, A. C. Linares, M. Jenkins, V. Kapos,
C. Monfreda, J. Loh, N. Myers, R.
Norgaard, J. Randers, Proc. Natl. Acad.
Sci. USA 2002,99, 9266– 9271.
[6] R. B. Gordon, M. Bertram, T. E. Grae-
del, Proc. Natl. Acad. Sci. USA 2006,
103, 1209 – 1214.
[7] I. A. Janssens, A. Freibauer, P. Ciais, P.
Smith, G. J. Nabuurs, G. Folberth, B.
Schlamadinger, R. W. A. Hutjes, R.
Ceulemans, E. D. Schulze, R. Valentini,
A. J. Dolman, Science 2003,300, 1538 –
1542.
[8] 2000 Lisbon European Council, Presi-
dency Conclusions, can be found under
http://www.europarl.europa.eu/sum-
mits/lis1_en.htm
[9] In affluent countries tap water is of
excellent quality and very cheap. Never-
theless, quite often, people prefer to
drink mineral water or soft drinks which
are as much as 1000 times more expen-
sive. This is a classical example of the
luxurious energy attitude of affluent
societies: a lot of energy is consumed
to supply drinkable water to households,
which is mostly used to flush the toilet or
sprinkle the garden. On the other hand
big energy investments are made to
bring a variety of drinks, sometimes
abused and unhealthy, on our tables.
[10] D. M. Kammen, S. Pacca, Annu. Rev.
Environ. Resour. 2004,29, 301 – 344.
[11] V. Smil, Energy, Oneworld, Oxford,
2006.
[12] See for example http://www.externe.in-
fo/
[13] European Commission, 2003,External
Costs—Research Results on Socio-Envi-
ronmental Damages due to Electricity
and Transport, can be found under
http://www.externe.info/externpr.pdf
[14] R. A. Kerr, Science 2006,311, 1698 –
1701.
[15] I. Illich, Energy and Equity, The Trinity
Press, London, 1974.
[16] V. Smil, Energy at the Crossroads, MIT
Press, Cambridge, MA, 2003.
[17] D. ORourke, S. Connolly, Annu. Rev.
Environ. Resour. 2003,28, 587 – 617.
[18] K. S. Deffeyes, Beyond Oil, Hill and
Wang, New York, 2005.
[19] P. W. Huber, M. P. Mills, The Bottomless
Well, Basic Books, New York, 2005.
[20] P. Roberts, The End of Oil, Mariner
Books, Boston, 2004.
[21] S. Anderson, R. Newell, Annu. Rev.
Environ. Resour. 2004,29, 109 – 142.
[22] R. H. Socolow, Sci. Am. 2005,293,49–
55.
[23] G. Ciamician, Science 1912,36, 385 –
394.
[24] W. E. Parkins, Science 2006,311, 1380.
“If a prompt action to energy
transition is needed for the
world, it is simply imperative
for Europe.”
Angewandte
Chemie
65Angew. Chem. Int. Ed. 2007,46, 52 – 66 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim www.angewandte.org
[25] M. Inman, Science 2005,309, 1170 –
1171.
[26] J. Johnson, Chem. Eng. News 2005,
83(June 6), 32 – 34.
[27] R. Eisenberg, D. G. Nocera, Inorg.
Chem. 2006,45, 6799 – 6801.
[28] US Department of Energy Office of
Science, Basic Research Needs for Solar
Energy Utilization,2005, can be found
under http://www.er.doe.gov/bes/
reports/files/SEU_rpt.pdf
[29] G. Hess, Chem. Eng. News 2006,84-
(March 27), 34 – 36.
[30] R. F. Service, Science 2005,309, 548 –
551.
[31] Worldwatch Institute, Washington, DC,
2005,Renewables 2005—Global Status
Report, can be found under http://
www.worldwatch.org/press/news/2005/
11/06/
[32] M. Grtzel, Inorg. Chem. 2005,44,
6841 – 6851.
[33] G. A. Olah, A. Goeppert, G. K. S. Pra-
kash, Beyond Oil and Gas: The Meth-
anol Economy, Wiley-VCH, Weinheim,
Germany, 2006.
[34] Artificial Photosynthesis (Eds.: A. Col-
lings, C. Critchley), Wiley-VCH, Wein-
heim, 2005.
[35] K. Maeda, K. Teramura, D. L. Lu, T.
Takata, N. Saito, Y. Inoue, K. Domen,
Nature 2006,440, 295.
[36] V. Balzani, L. Moggi, M. F. Manfrin, F.
Bolletta, M. Gleria, Science 1975,189,
852 – 856.
[37] V. Balzani, A. Credi, M. Venturi, Mo-
lecular Devices and Machines,Chap. 5,
Wiley-VCH, Weinheim, 2003.
[38] K. N. Ferreira, T. M. Iverson, K. Magh-
laoui, J. Barber, S. Iwata, Science 2004,
303, 1831 – 1838.
[39] G. Steinberg-Yfrach, J. L. Rigaud, E. N.
Durantini, A. L. Moore, D. Gust, T. A.
Moore, Nature 1998,392, 479 – 482.
[40] It is estimated that millions of people in
poor countries suffer from severe respi-
ratory problems arising from indoor air
pollution generated by improperly vent-
ed stoves fueled with biomass.
[41] International Energy Agency, Biofuels
for transport—An international perspec-
tive,2004, can be found under http://
www.iea.org/textbase/nppdf/free/2004/
biofuels2004.pdf
[42] K. S. Kheshgi, R. C. Prince, G. Marland,
Annu. Rev. Environ. Resour. 2000,25,
199 – 244.
[43] For a recent assessment on energy
return on energy investment for bioe-
thanol see R. Hammerschlag, Environ.
Sci. Technol. 2006,40, 1744 – 1750.
[44] J. Hill, E. Nelson, D. Tilman, S. Polasky,
D. Tiffany, Proc. Natl. Acad. Sci. USA
2006,103, 11 206 – 11 210.
[45] G. Hess, Chem. Eng. News 2006,84-
(March 6), 50 – 56.
[46] European Wind Energy Association and
The European Commission, 2003,Wind
Energy, the Facts. An Analysis of Wind
Energy in the EU-25, can be found under
http://www.ewea.org/index.php?id =91
[47] Note that a substantially smaller area,
150000 km2, covered with 10 %-efficient
photovoltaic panels would in principle
cover the current world total energy
demand.
[48] See http://www.enwave.com/enwave/
[49] S. G. Chalk, J. Romm, M. Jacoby, Chem.
Eng. News 2005,83(August 22), 30 – 35.
[50] N. Armaroli, V. Balzani, Energia Oggi e
Domani, Bononia University Press, Bo-
logna, 2004.
[51] R. Coontz, B. Hanson, Science 2004,305,
957.
[52] U. Bossel, The Hydrogen Illusion,2004
can be found under http://www.efcf.com/
reports/
[53] H. Akimoto, Science 2003,302, 1716 –
1719.
[54] See http://www.esttp.org/cms/front_
content.php
[55] International Energy Agency, Key
World Energy Statistics,2005 can be
found under http://www.iea.org/dbtw-
wpd/Textbase/nppdf/free/2005/
key2005.pdf
[56] US Energy Information Administration
Database, which can be found under
http://www.eia.doe.gov/
[57] D. Kennedy, C. Norman, Science 2005,
309, 75.
[58] R. E. Smalley, MRS Bull. 2005,30, 412 –
417.
[59] R. W. Kates, Annu. Rev. Energ. Environ.
2001,26, 1 – 26.
[60] T. Princen, The Logic of Sufficiency,
MIT Press, Cambridge, MA, 2005.
[61] European Commission, Annex to the
Green Paper—A European Strategy for
Sustainable, Competitive and Secure En-
ergy,2006.
[62] See http://www.un.org/millenniumgoals/
[63] D. King, Nature 2004,430, 311 – 316.
[64] A reviewer has criticized this essay
stating that “It does illustrate the idea
that scientists should not be allowed to
write about economics or public policy:
they know a few of the words, but none
of the music”. We wonder which words
and music the economists and politicians
know who insist on the need to increase
the gross domestic product (GDP) of
developed countries when it is known
that this does not make people happier
(see, for example, D. Kahneman et al. ,
Science 2006,312, 1908 – 1910) and with-
out considering that increasing GDP
means increasing the consumption of
resources, mostly taken form poorer
countries, and accumulation of waste
that is immediately distributed to the
whole world (e.g. carbon dioxide) or
later directed to poor countries (e.g.
electronic waste). The mounting con-
cern about the massive environmental
degradation and related social unrest of
the so-called worlds factory, China,
should prompt deep reflections in this
regard.
[65] J. Johnson, Chem. Eng. News 2003,
81(October 6), 20 – 23.
[66] See, for example, http://www.olla-proj-
ect.org
[67] R. R. Ernst, Angew. Chem. 2003,115,
4572 – 4578; Angew. Chem. Int. Ed.
2003,42, 4434 – 4439.
Essays
66 www.angewandte.org 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim Angew. Chem. Int. Ed. 2007,46,52–66
