"Sustainable Energy - without the hot air" by Professor David MacKay

Comments by Prof Mike Ashby FRS

The industrial world is addictively dependent on energy, most of it at present generated by burning fossil fuels. With sufficient affordable energy, its continued growth (meaning its provision of a rising GDP per capita to an increasing large fraction of the worlds population) can continue. But it is now clear that this dependence has consequences of increasingly grave concern. There is the reliance on the uninterrupted functioning of a free market in oil and gas when the sources from which they are drawn are localised and vulnerable to cartel action. There is the effect on climate of the accumulation of atmospheric carbon that is a consequence of their use. And there is the ultimate, inescapable depletion and exhaustion of the resource base from which they are drawn.

One answer, frequently offered, is the replacement of fossil fuels by renewable sources of energy - renewable meaning that they can be drawn upon without depleting a resource that cannot be replaced. There are, ultimately, only three sources of renewable energy: the sun, which drives the winds, wave, hydro, photochemical phenomena; the moon, which drives the tides; and radioactive decay of unstable elements giving geothermal heat from the earth's crust or, when concentrated, nuclear power. All three that offer the possibility of power without atmospheric pollution.

It is accepted that replacing fossil fuel sources with one or a combination of these would be expensive, but that by-passes a more fundamental question: is it even possible? If all were exploited in some balanced combination, would they add up to enough? What would be the consequences for land usage? What diminishment in other amenities would the public have to accept? These are questions that politicians, green campaigners and governments seem to overlook. Failure to answer them undermines the credibility of any plan that relies on renewable energy as a solution.

These are the central questions addressed by Professor MacKay in this illuminating book. It cuts to the heart of the problem, using simple (but inescapable) facts of physics and chemistry to assess the limits to the quantities of energy that renewable sources can provide, and the consequences that tapping them would have. The book is written and structured in ways that make its arguments particularly accessible. The reasoning is developed in two parts. The first a readable analysis of the potential of each renewable source, stacking up their contributions to see how nearly the total approaches our current energy consumption. The second develops the physical reasoning in greater depth, explaining where the numbers in the first part come from.

I will not divulge the conclusions - that would deprive the reader of the stimulus of the progressive argument that Professor MacKay builds, and of the fascination in seeing how simple science can be used to explore issues of global significance. This is an example of order-of-magnitude physics at its best: physics applied to the clarification of issues of central economic, social and environmental importance. Fresh air replacing hot air.

Prof Mike Ashby FRS
Engineering Department, Cambridge.
Author of Materials and the environment

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