Energy quality

Energy quality is the contrast between different forms of energy, the different trophic levels in ecological systems and the propensity of energy to convert from one form to another. The concept refers to the empirical experience of the characteristics, or qualia, of different energy forms as they flow and transform. It appeals to our common perception of the heat value, versatility, and environmental performance of different energy forms and the way a small increment in energy flow can sometimes produce a large transformation effect on both energy physical state and energy. For example the transition from a solid state to liquid may only involve a very small addition of energy. Methods of evaluating energy quality are sometimes concerned with developing a system of ranking energy qualities in hierarchical order.If energy A is relatively easier to convert to energy B but energy B is relatively harder to convert to energy A, then the quality of energy A is defined as being higher than that of B. The ranking of energy quality is also defined in a similar way. (T.Ohta 1994, p. 90). Energy quality is the contrast between different forms of energy, the different trophic levels in ecological systems and the propensity of energy to convert from one form to another. The concept refers to the empirical experience of the characteristics, or qualia, of different energy forms as they flow and transform. It appeals to our common perception of the heat value, versatility, and environmental performance of different energy forms and the way a small increment in energy flow can sometimes produce a large transformation effect on both energy physical state and energy. For example the transition from a solid state to liquid may only involve a very small addition of energy. Methods of evaluating energy quality are sometimes concerned with developing a system of ranking energy qualities in hierarchical order. Since before antiquity there has been deep philosophical, aesthetic and scientific interest in the contrast of quality with quantity. In some respects the history of modern and postmodern thought can be characterized by the phenomenological approach to these two concepts. A central question has been whether the many different qualitative aspects of the world can be understood in terms of rational quantities, or whether the qualitative and quantitative are irreconcilable: that is, there is no 'rational quality', or quale ratio. Many scientists and analytic philosophers say they are not, and therefore consider some qualitative phenomena like, for instance, spirituality, and astrology to be unquantifiable, unanalysable by scientific methods, and therefore ungrounded in physical reality. The notion of energy quality therefore has a tendency to be linked with phenomena many scientists consider unquantifiable, or at least incommunicable, and are consequently dismissed out of hand. At the same time many people have also recognised qualitative differences in the way things can be done by different entities (both physical and biological). Humans, for example have qualitatively different capacities than many other mammals, due, in part, to their opposable thumb. In the attempt to formalise some of the qualitative differences, entities were grouped according to distinguishing features or capacities. Different schools of thought used different methods to make distinctions. Some people chose taxonomic and genome structure, while others chose energetic function as the basis of classifications. The former are often associated with biology, while the latter with the trophic food chain analysis of ecology. These can be considered attempts to formalise quantitative, scientific studies of the qualitative differences between entities. The efforts were not isolated to biology and ecology, since engineers were also interested in quantifying the amount of work that qualitatively different sources of energy could provide. According to Ohta (1994, pp. 90–91) the ranking and scientific analysis of energy quality was first proposed in 1851 by William Thomson under the concept of 'availability'. This concept was continued in Germany by Z. Rant, who developed it under the title, 'die Exergie' (the exergy). It was later continued and standardised in Japan. Exergy analysis now forms a common part of many industrial and ecological energy analyses. For example, I.Dincer and Y.A. Cengel (2001, p. 132) state that energy forms of different qualities are now commonly dealt with in steam power engineering industry. Here the 'quality index' is the relation of exergy to the energy content (Ibid.). However energy engineers were aware that the notion of heat quality involved the notion of value – for example A. Thumann wrote, 'The essential quality of heat is not the amount but rather its 'value'' (1984, p. 113) – which brings into play the question of teleology and wider, or ecological-scale goal functions. In an ecological context S.E. Jorgensen and G.Bendoricchio say that exergy is used as a goal function in ecological models, and expresses energy 'with a built-in measure of quality like energy' (2001, p. 392).