# Sustainable Energy - without the hot air

by David JC MacKay (UIT Cambridge Ltd, Cambridge, England, 2009) ISBN 978-0-9544529-3-3 (paperback) ISBN 978-1-906860-01-1 (hardback), 368pp

Reviewed by Peter Schroeder

"In a climate where people don't understand the numbers, newspapers, campaigners, companies, and politicians can get away with murder. We need the numbers to be comprehensible, comparable, and memorable. With numbers in place we are better placed to answer the difficult questions concerning issues." So declares David MacKay, a Fellow of the Royal Society and a professor in the Department of Physics at the University of Cambridge, where he has learned that lesson well. That statement is the underlying theme in this book, a theme that differentiates it from the many other recent books on global warming. With meaningful numbers and facts we are liberated from "a flood of crazy innumerate codswallop." At the moment, where numbers are used they are frequently chosen to impress, to score points in arguments rather than to inform. The aim of this book is to help the reader figure out the numbers and do the arithmetic so that he or she can evaluate policies, and see which proposals add up. This book is about physical limits and not about economics and ethics which, while forming a part of the policy-making process, are more appropriately described by specialists in these fields.

With this introduction it is no surprise that Part 1 of the book's four main Parts is titled "Numbers not adjectives;" it has 17 subsections, dealing with the energy associated with cars, wind, solar etc. Eventually the quantitative information we learn in this Part can be applied to arrive at a quantitative estimate of the maximum energy that a country can use and still be consistent with a maximum 2.0oC rise in temperature in the year 2050. Knowing the maximum allowable energy, one can then consider what combination of energy sources can be used.

Numbers imply units. Basically MacKay has chosen to use the MKS system, with the kilowatt (kW) as the unit of power, and the kilowatt-hour (kWh) as the unit for all forms of energy. Derived units include the kilowatt hour per day (kWh/d), and the kilowatt hour per day per person (kWh/dp). These latter units enable easy comparisons between the various fuels and their use in various countries or regions. Such comparisons are vital to planning and policy making. Where do the basic numbers come from? Some come from good measurements, but some must be reasonable assumptions. This produces uncertainties in the final values, and consequently sometimes these may be factors of 2 or more. This process is similar to back of the envelope calculations encountered in scientific circles, and is subject to change as better information becomes available.

The book is intended to be accessible to anyone who can add, multiply and divide. MacKay adds that "it is especially aimed at our dear elected and unelected representatives, the Members of Parliament." More technical details are in Parts 3 and 4. Any reader with high school qualifications in math, physics, or chemistry should enjoy these chapters. For more non-intrusive reading, many details are put into footnotes at the end of each chapter. A wealth of information and useful data is stored in this book. These along with an extensive bibliography make the book a valuable reference; in fact many will find Part 4 the most valuable aspect of the book.

One of the questions tackled in Part 1 is "Can we live on renewables?" Here MacKay does a detailed study of the situation in the United Kingdom (UK). This may be somewhat frustrating to those living elsewhere, but later in the book he briefly indicates how to extend his methods to Europe, North America and finally to the world. He concludes that for the UK it would be very difficult for non-nuclear renewables alone to provide sufficient energy. The remaining renewables are very diffuse and therefore large country-sized areas are needed to make a substantial difference. The wind farms in the UK, for example, would need to be the area of Wales, which conflicts with cropland and forestry requirements. Furthermore the British public, like the public in the world in general, must learn to reject some of the controversial NIMBY arguments. Europe also could not live on non-nuclear renewables; it would be necessary to expand nuclear energy and/or import energy in the form of solar power from other people's deserts. Similarly he concludes that without solar or nuclear power North America would have insufficient energy, but it is different from Europe in that the solar power could come from its own deserts and would not have to be imported. It is a considerable extrapolation to treat the world, but the conclusion is similar. The non-solar renewables are huge, but not huge enough. More forms of solar power or nuclear power are needed.

The penultimate chapter of Part 2 is titled "The last thing we should talk about." If all else fails the last line of defense may be capturing CO2 from thin air, a subject rarely mentioned among the possibilities. Here, it's enough to note that various methods have been suggested and should be pursued along with all the other possibilities suggested in this book.

Part 2, titled "Making a Difference," accepts the idea that the world's energy problems cannot be solved by renewables alone. MacKay replaces the mantra "Little changes can make a big difference" with "If every one does a little, we'll only achieve a little" and "Every big helps." Major changes are essential. He considers two general lanes of inquiry: reducing demand (better transport, smarter heating, etc.), and increasing supply (efficient electricity use, sustainable fossil fuels, living on other countries' renewables, etc. ). I appreciated his chapter titled "Nuclear?" in this latter category. He leaves it to the reader to answer the question, but at the same time provides estimates that knock down many of the anti-nuclear arguments.

Taking all this into account he suggests five energy plans for the UK, each aimed to appeal to a particular class of people: pro-nuclear, pro-wind, pro-NIMBY, pro-diversity, and pro–economics. No-one will be completely satisfied, but the exercise illustrates that there is a large range of possibilities. Choose your own!

The wealth of information in this book is immense. For example, in Part 3 there are details about where the energy goes in driving a car, the physics of wind power, a simple description of how a plane flies, energy-efficient buildings, and much more. This diversity of ideas and information, along with the achievement of the author's quantitative goals, make this a very welcome book.

Peter Schroeder
Emeritus Professor of Physics
Michigan State University

These contributions haven not been peer-refereed. They represent solely the view(s) of the author(s) and not necessarily the views of APS.