Energy: A Beginner's Guide

Energy will do anything that can be done in the world.

Johann Wolfgang von Goethe (1749–1832)

Contents

List of Figures

1  Energy in our minds: concepts and measures

2  Energy in the biosphere: how nature works

3  Energy in human history: muscles, tools, and machines

4  Energy in the modern world: fossil-fueled civilization

5  Energy in everyday life: from eating to emailing

6  Energy in the future: trends and unknowns

Further readings and data sources

Index

List of Figures

All figures copyright Vaclav Smil, except where indicated.

Figure 1 James Watt (copyright free)

Figure 2 James Prescott Joule (copyright free)

Figure 3 Energies and their conversions

Figure 4 The Earth’s radiation balance (based on NASA image)

Figure 5 The electromagnetic spectrum

Figure 6 Geotectonic plates

Figure 7 The C 3 /C 2 cycle

Figure 8 Kleiber’s line (plotted from data in Kleiber, M. 1961. The Fire of Life )

Figure 9 Specific BMR

Figure 10 Relative share of BMR in adults (plotted from data in FAO. 1985. Energy and Protein Requirements )

Figure 11 The lifetime progression of specific BMR in men and boys (plotted from data in FAO. 1985. Energy and Protein Requirements )

Figure 12 Population densities of different modes of food provision

Figure 13 A Chinese ox (left) and a French horse (right) harnessed to pump water. Reproduced from Tian gong kai wu (1637) and L’Encyclopedie (1769–1772)

Figure 14 A nineteenth-century clipper (copyright free)

Figure 15 Late eighteenth-century French undershot wheel (reproduced from L’Encyclopedie )

Figure 16 Section through an eighteenth-century French windmill (reproduced from L’Encyclopedie )

Figure 17 A late nineteenth-century windmill on the U.S. Great Plains (reproduced from Wolff, A. R. 1900. The Windmill as Prime Mover )

Figure 18 Global coal, crude oil, and natural gas production, and electricity generation during the twentieth century (plotted from data in UN and BP statistics)

Figure 19 James Watt’s steam engine (left) and detail of separate condenser (right) (reproduced from Farey, J. 1827. A Treatise on Steam Engines )

Figure 20 Section through Parsons’s 1 MW steam turbine. Reproduced from the 1911 (eleventh) edition of Encyclopedia Britannica

Figure 21 The energy balance of a coal-fired electricity generating plant

Figure 22 World and U.S. wind generating capacity (plotted from statistics published in U.S. Energy Information Administration and by the World Wind Association)

Figure 23 Atmospheric CO 2 concentrations (plotted from data available from the Carbon Dioxide Information and Analysis Center)

Figure 24 China’s dietary transition, 1980–2000 (plotted from data in various editions of China Statistical Yearbook )

Figure 25 Improvements of lamp efficacy, 1880-2000 (based on an image at http://americanhistory.si.edu/)

Figure 26 T ō kaid ō line Nozomi train in Ky ō t ō station (photo Vaclav Smil)

Figure 27 Cutaway view of GE90 engine (image courtesy of General Electric)

Figure 28 Boeing 747-8I in Lufthansa service (reproduced from Wikimedia)

Figure 29 Where people need more energy: conditions in this Jakarta slum are replicated in scores of low-income countries (reproduced from Wikipedia)

Figure 30 Comparison of power densities of energy consumption and renewable energy production

Figure 31 Decarbonization of the world’s energy supply (calculated from data in UN and BP statistics)

Figure 32 Brazos wind farm in West Texas with 160 one-megawatt turbines (reproduced from Wikipedia)

1

Energy in our minds: concepts and measures

The word energy is, as are so many abstract terms (from hypothesis to sophrosyne), a Greek compound. Aristotle (384–322 B.C.E.) created the term in his Metaphysics, by joining en (in) and ἐργον (work) to form ἐνέργεια (energeia, actuality, identified with movement) that he connected with entelechia, complete reality. According to Aristotle, every object’s existence is maintained by energeia related to the object’s function. The verb energein thus came to signify motion, action, work, and change. No noteworthy intellectual breakthroughs refined these definitions for nearly two subsequent millennia, as even many founders of modern science had very faulty concepts of energy. Eventually, the term became practically indistinguishable from power and force. In 1748, David Hume (1711–1776) complained, in An Enquiry Concerning Human Understanding, that "There are no ideas, which occur in metaphysics, more obscure and uncertain, than those of power, force, energy or necessary connexion, of which it is every moment necessary for us to treat in all our disquisitions."

In 1807, in a lecture at the Royal Institution, Thomas Young (1773–1829) defined energy as the product of the mass of a body and the square of its velocity, thus offering an inaccurate formula (the mass should be halved) and restricting the term only to kinetic (mechanical) energy. Three decades later the seventh edition of the Encyclopedia Britannica (completed in 1842) offered only a very brief and unscientific entry, describing energy as the power, virtue, or efficacy of a thing. It is also used figuratively, to denote emphasis in speech. Little has changed in popular discourse since that, or indeed since Hume’s, time, except the frequency of the term’s misuse. At the beginning of the twenty-first century energy, its derivative verb (energize) and its adjective (energetic), are used ubiquitously and loosely as qualifiers for any number of animated, zestful, vigorous actions and experiences, and energy is still routinely confused with power and force. Examples abound: a powerful new chairman brings fresh energy to an old company; a crowd is energized by a forceful speaker; pop-culture is America’s soft power.

Devotees of physical fitness go one step further and claim (against all logic and scientific evidence) they are energized after a particularly demanding bout of protracted exercise. What they really want to say is that they feel better afterwards, and we have a perfectly understandable explanation for that: prolonged exercise promotes the release of endorphins (neurotransmitters that reduce the perception of pain and induce euphoria) in the brain and hence may produce a feeling of enhanced well-being. A long run may leave you tired, even exhausted, elated, even euphoric – but never energized, that is with a higher level of stored energy than before you began.

Science of energy: origins and abstracts

Sloppy use of ingrained terms is here to stay, but in informed writing there has been no excuse for ill-defined terms for more than a hundred years. Theoretical energy studies reached a satisfactory (though not perfect) coherence and clarity before the end of the nineteenth century when, after generations of hesitant progress, the great outburst of Western intellectual and inventive activity laid down the firm foundations of modern science and soon afterwards developed many of its more sophisticated concepts. The ground work for these advances began in the seventeenth century, and advanced considerably during the course of the eighteenth, when it was aided by the adoption both of Isaac Newton’s (1642–1727) comprehensive view of physics and by engineering experiments, particularly those associated with James Watt’s (1736–1819) improvements of steam engines (Figure 1; see also Figure 19).

During the early part of the nineteenth century a key contribution to the multifaceted origins of modern understanding of energy were the theoretical deductions of a young French engineer, Sadi Carnot (1796–1832), who set down the universal principles applicable to producing kinetic energy from heat and defined the maximum efficiency of an ideal (reversible) heat engine. Shortly afterwards, Justus von Liebig (1803–1873), one of the founders of modern chemistry and science-based agriculture, offered a basically correct interpretation of human and animal metabolism, by ascribing the generation of carbon dioxide and water to the oxidation of foods or feeds.

Figure 1 James Watt

The formulation of one of the most fundamental laws of modern physics originates in a voyage to Java made in 1840 by a young German physician, Julius Robert Mayer (1814–1878), as ship’s doctor. The blood of patients he bled there (the practice of bleeding as a cure for many ailments persisted well into the nineteenth century) appeared much brighter than the blood of patients in Germany.

Mayer had an explanation ready: blood in the tropics does not have to be as oxidized as blood in temperate regions, because less energy is needed for body metabolism in warm places. But this answer led him to another key question. If less heat is lost in the tropics due to radiation how about the heat lost as a result of physical work (that is, expenditure of mechanical energy) which clearly warms its surroundings, whether done in Europe or tropical Asia? Unless we put forward some mysterious origin, that heat, too, must come from the oxidation of blood – and hence heat and work must be equivalent and convertible at a fixed rate. And so began the formulation of the law of the conservation of energy. In 1842 Mayer published the first quantitative estimate of the equivalence, and three years later extended the idea of energy conservation to all natural phenomena, including electricity, light, and magnetism and gave details of his calculation based on an experiment with gas flow between two insulated cylinders.

The correct value for the equivalence of heat and mechanical energy was found by the English physicist (see Figure 2) James Prescott Joule (1818–1889), after he conducted a large number of careful experiments. Joule used very sensitive thermometers to measure the temperature of water being churned by an assembly of revolving vanes driven by descending weights: this arrangement made it possible to measure fairly accurately the mechanical energy invested in the churning process. In 1847 Joule’s painstaking experiments yielded a result that turned out to be within less than one percent of the actual value. The law of conservation of energy – that energy can be neither created nor destroyed – is now commonly known as the first law of thermodynamics.

In 1850 the German theoretical physicist Rudolf Clausius (1822–1888) published his first paper on the mechanical theory of heat, in which he proved that the maximum performance obtainable from an engine using the Carnot cycle depends solely on the temperatures of the heat reservoirs, not on the nature of the working substance, and that there can never be a positive heat flow from a colder to a hotter body. Clausius continued to refine this fundamental idea and in his 1865 paper he coined the term entropy – from the Greek τρόπος (way) – to measure the degree of disorder in a closed system. Clausius also crisply formulated the second law of thermodynamics: entropy of the universe tends to maximum. In practical terms this means that in a closed system (one without any external supply of energy) the availability of useful energy can only decline. A lump of coal is a high-quality, highly ordered (low entropy) form of energy; its combustion will produce heat, a dispersed, low-quality, disordered (high entropy) form of energy. The sequence is irreversible: diffused heat (and emitted combustion gases) cannot be ever reconstituted as a lump of coal. Heat thus occupies a unique position in the hierarchy of energies: all other forms of energy can be completely converted to it, but its conversion into other forms can never be complete, as only a portion of the initial input ends up in the new form.

Figure 2 James Prescott Joule

The second law of thermodynamics, the universal tendency toward heat death and disorder, became perhaps the grandest of all cosmic generalizations – yet also one of which most non-scientists remain ignorant. This reality was famously captured by C. P. Snow (1905–1980), an English physicist, politician, and novelist, in his 1959 Rede Lecture The Two Cultures and the Scientific Revolution:

A good many times I have been present at gatherings of people who, by the standards of the traditional culture, are thought highly educated and who have with considerable gusto been expressing their incredulity at the illiteracy of scientists. Once or twice I have been provoked and have asked the company how many of them could describe the Second Law of Thermodynamics. The response was cold: it was also negative. Yet I was asking something which is about the scientific equivalent of: Have you read a work of Shakespeare’s?

Despite its supposed universality, the second law appears to be constantly violated by living organisms, whose conception and growth (as individuals) and whose evolution (as species and ecosystems) produces distinctly more ordered, more complex forms of life. But there is really no conflict: the second law applies only to closed systems under thermodynamic equilibrium. The Earth’s biosphere is an open system, which incessantly imports solar energy and uses its photosynthetic conversion to new plant mass as the foundation for greater order and organization (a reduction of entropy).

Finally, the third law of thermodynamics, initially formulated in 1906 as Walther Nernst’s (1864–1941) heat theorem, states that all processes come to a stop (and entropy shows no change) only when the temperature nears absolute zero (–273°C).

The first decade of the twentieth century brought a fundamental extension of the first law of thermodynamics when, in 1905, Albert Einstein (1879–1955) concluded that mass is itself a form of energy. According to perhaps the world’s most famous equation – E = mc² – energy is equal to the product of mass and the square of the speed of light. As a result, just six tonnes of matter contain energy that is equivalent to the world’s annual consumption of commercial energy in 2015 – but this astonishing potential remains just that, as we have no means to unlock the mass energy in limestone or water.

The only time when we commercially convert a relatively large (but still very small) share of mass into energy is in nuclear reactors: the fission (splitting) of the nuclei of one kilogram of uranium-235 releases an amount of energy equivalent to 190 tonnes of crude oil as it diminishes the initial mass by just one gram, or a thousandth of its original mass. In contrast, burning one kilogram of crude oil will diminish the mass of the fuel (and of the oxygen needed for its combustion) by only one ten billionth; too small a reduction to measure.

After less than a century of vigorous scientific effort the understanding of the nature of energy phenomena was virtually complete. But despite this large, and highly complex, body of scientific knowledge, there is no easy way to grasp the fundamental concept, which is intellectually much more elusive than is the understanding of mass or temperature. Richard Feynman (1918-1988), one of the most brilliant physicists of the twentieth century, put it with disarming honesty in his famous 1963 Lectures on Physics:

It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount. It is not that way. However, there are formulas for calculating some numerical quantity... It is an abstract thing in that it does not tell us the mechanism or the reasons for the various formulas.

Difficult as it is, we have to try to make that abstract thing more accessible.

Fundamental concepts: energies, conversions, efficiencies

By far the most common definition of energy is the capacity for doing work but the full implication of this simple statement becomes clear only when you go beyond thinking about work as mechanical exertion– in physics terms, energy transferred through application of force over a distance, in common terms a labor to be performed, be it typing a letter or transplanting rice seedlings – and apply the term in a generic manner to any process that produces a change (of location, speed, temperature, composition) in an affected system (an organism, a machine, a planet). If you were to sit motionless in a quiet room for the next ten minutes, contemplating this statement, you would not have accomplished any work, in the narrow, strictly physical and commonly used, sense of applying force to a mechanical task.

But even as you sit motionless your metabolism is performing a great deal of work, as energy obtained from digested food is used (noting just the four key processes) to power your breathing, importing oxygen and exhaling carbon dioxide, to maintain the core temperature of your body at 37°C, to pump blood and to create the numerous enzymes that control everything from digestion to the transmission of nerve signals. By thinking hard about an abstract concept you do actually use a bit more energy but making all those additional neuronal connections in your brain amounts to an entirely negligible mark-up. Even when you are fast asleep, your brain accounts for about twenty percent of your body’s metabolism and even a taxing mental exercise will raise that share only a little.

Outside a quiet room, the work done by various energies is accomplished in myriad ways. The lightning that slashes through summer skies works in a very different way from a giant harbor crane picking up large steel crates from a pier and stacking them up to a dizzying height on a container ship – and the differences are due to one of the most fundamental physical realities, the existences of multiple forms of energy and their conversions, on space and time scales ranging from galactic to sub-atomic and from evolutionary to ephemeral. Lightning works in a tiny fraction of a second, illuminating and heating the atmosphere and decomposing molecules of nitrogen, that is, converting the electrical energy of cloud-to-cloud or cloud-to-earth discharge to electromagnetic, thermal, and chemical energy. In contrast, the motors of stacking cranes in container ports work around the clock, converting electrical energy into mechanical energy and then into the potential energy of loaded cargo.

Energy is not a single, easily definable entity, but rather an abstract collective concept, adopted by nineteenth-century physicists to cover a variety of natural and anthropogenic (generated by humans) phenomena. Its most commonly encountered forms are heat (thermal energy), motion (kinetic or mechanical energy), light (electromagnetic energy) and the chemical energy of fuels and foodstuffs. Some of their conversions are the very fundamentals of life: during photosynthesis a small share of the electromagnetic energy of light becomes the chemical energy of bacteria and plants, and cooking and heating is done by converting chemical energy in biomass (wood, charcoal, straw) or fossil fuels (coals, oils, gases) to thermal energy (Figure 3). Others are a matter of convenience enjoyed