Preface to second edition
When the first edition of Renewable Energy appeared in 1979, it was the first textbook and research monograph since the 1920s to deal with the renewable energy sources and systems at a scholarly level. Indeed, it was instrumental in establishing the now universally used term “renewable energy” for a new area of science, which emerged under names such as “regenerative energy” in Germany and “solar energy” in the United States of America. In many countries, renewable energy appeared in planning documents as “supplementary energy,” based on a conviction by administrators that this could never become a major source of energy. My suggestion in the journal Science (Sørensen, 1975b) that renewable energy could potentially become a 100% solution was regarded as absurd by many. Things have changed today, where official energy plans of some countries call for over 50% renewable energy coverage by year 2030 (Danish Department of Environment and Energy, 1996), where the best renewable energy technologies are already economically competitive relative to fossil options, and where increased concern over greenhouse warming effects may well alter the perceived indirect costs of different energy solutions.
The structure of the first edition was determined by the aim of placing renewable energy on the academic agenda. It was my goal to show young scientists, engineers, and future planners that renewable energy was at least as interesting and challenging as nuclear energy, and I tried to do this by showing the depth of problems to be solved using advanced techniques, shying no complication of quantum mechanics or nonlinear mathematics. This was seen as positive by reviewers and colleagues, but may have limited the sales figures for the book! Today, the requirements are quite different: now many universities and polytechnic institutes have renewable energy courses in their curriculum, and the task at hand is to provide good teaching materials for the relevant levels of courses. Therefore, I have thoroughly revised the content and presentation in the second edition. The main sections of each chapter are now suited for introductory level study, with only very general prerequisites. Any topic requiring more background is deferred to special sections marked as ADVANCED topics at the top corner of each page. They can be added individually at the choice of the teacher, or they can be left for further study by the user of the book. My reflections on whether to separate elementary and advanced topics in two volumes or keep them together are as follows. Needing to go back to a topic for more detailed study, it is very convenient to be able to find it in a book that you have already worked with. The style and assumptions are known to you, and first of all, the book is on your shelf and need not be retrieved from somewhere else. Against the single-volume solution speaks the book price for those who find it unlikely that they shall need more than the elementary sections. However, we are all surprised by the growth of our needs, and the price of this second edition is even below that of the first edition, thanks to modern preparation and printing methods.
Another issue is the arrangement of material, which I have basically kept as in the first edition: first describing the origin of renewable energy, then its disposition and availability at different geographical locations on Earth, then the techniques of energy conversion systems and systems suitable for each type of renewable energy, and finally the evaluation of the total system, in terms of economic and environmental impacts. The logic of this sequence is evident, but it means that someone wanting to know only about wind power will have to jump from chapter to chapter. This is made much easier in this edition by the addition, on each bottom left page, of references to previous and following sections dealing with the same form of renewable energy. As in the first edition, extensive references and an index are found at the end. The index also serves as a pointer to specialist words and concepts by giving the page where they are first explained. After the table of contents, a list of units and abbreviations is given.
The content has been revised in those areas where new advances have been made, notably in the sections on energy from biomass and on photovoltaic energy conversion, and in the economic chapter on life-cycle analysis. As in the first edition, emphasis is on basic principles. Fortunately, they do not wear much with time, and several sections needed only a light brush-up, sometimes with some tidying effort to keep the size down. However, new data available today have made it possible to improve many of the illustrations, notably in the area of global energy flows. At the end of each chapter, there are topics for discussion, including new ones. They are basically of two kinds: simple topics for classroom discussion and mini-project ideas that can serve as a basis for problem-oriented work extending from a few days to several months in duration. This is a reflection of the different styles of teaching at different institutions, where small projects are often offered to individuals or groups of students for credit, with the indicated range of time devoted to each problem (and a corresponding difference in depth of investigation).
The Danish Energy Agency supported part of the work upon which the second edition updates are based. The author welcomes comments and suggestions, which may be addressed as indicated below.
Allerød, 1998