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‘Energy is Eternal Delight’ William Blake, 1757–1827, (1994) What do we mean by ‘energy’? What does the concept of ‘sustainability’ entail? And what, for that matter, do we mean by the ‘future’ in this context?
Figure 1.7 William Blake The eighteenth century poet and artist William Blake, quoted above, probably expressed our personal experience of energy as we feel it in our day-to-day lives more accurately than any scientific definition. Indeed, the word energy, when it first appeared in English in the sixteenth century, had no scientific meaning at all. Based on a Greek word coined by Aristotle, it meant forceful or vigorous language. It was not until the early 1800s that the concept of energy in the modern sense was developed by scientists to describe and compare their observations about the behaviour of such diverse phenomena as the transfer of heat, the motion of planets, the operation of machinery and the flow of electricity. Today, the standard scientific definition is that energy is the capacity to do work: that is, to move an object against a resisting force. In everyday language, the word ‘power’ is often used as a synonym for energy – and indeed in this book and its companion volume the two words may occasionally be used in this rather loose way merely as substitutes for each other. But when speaking scientifically, power is defined as the rate of doing work, that is, the rate at which energy is converted from one form to another, or transmitted from one place to another. The main unit of measurement of energy is the joule (J) and the main unit of measurement of power is the watt (W), which is defined as a rate of one joule per second. The twin concepts of energy and power will be discussed in more detail in Chapter 2. The term ‘sustainability’ entered into common currency relatively recently, following the publication of the report Our Common Future by the United Nations’ Brundtland Commission in 1987. The commission defined sustainability, and in particular sustainable development, as ‘development that meets the needs of the present without compromising the ability of future generations to meet their own needs.’ (United Nations, 1987). In the context of energy, sustainability has come to mean the harnessing of those energy sources: • that are not substantially depleted by continued use; • the use of which does not entail the emission of pollutants or other hazards to the environment on a substantial scale; and • the use of which does not involve the perpetuation of substantial health hazards or social injustices. This is, of course, a very broad ideal. Although a few energy sources can come close to fulfilling these conditions, most fall considerably short of the optimum. This means that, in practice, sustainability is a relative rather than an absolute concept. It is not so much that some energy sources are sustainable and others not; it is more that some energy sources, in certain contexts, are more sustainable than others. Determining the relative sustainability of one energy system vis-à-vis another is usually a complex process, involving detailed consideration of the specific processes and technologies proposed, the context in which they are being used and the differing values and interests of the various parties involved. For example, suppose the Government of a country is proposing to construct a large hydro-electric power plant like the one shown in Figure 1.25 in Section 1.3 below. The villagers whose homes would be flooded by the associated reservoir would probably take a different view of the plant’s sustainability to that taken by the city-based planners in the electricity utility proposing its construction, whose homes would be unaffected and whose careers would probably stand to benefit from such a major capital project. When we speak of ‘the future’ in the context of a ‘sustainable future’, what do we mean? Next year? One or two decades hence? The end of the twenty-first century? The end of the third millennium? Forever? Ideally, in view of the Brundtland Report’s injunction that humanity should not compromise the needs of future generations, we should judge the sustainability of all energy systems on an indefinite time scale – far into the very distant future. In practice, however, this might be realistically interpreted as endeavouring to ensure that energy systems become sustainable (or at the very least, much less un-sustainable) over the next century or so – with the additional proviso that, even beyond that time horizon, few substantial difficulties can presently be envisaged. Future generations will be justified in blaming us for creating problems that were foreseeable; but they can hardly hold us responsible for eventualities that none of us could have anticipated. |
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