Sustainable Energy: Without the Hot Air

David JC MacKay

UIT Cambridge 2009
A book review by Danny Yee © 2012 http://dannyreviews.com/
Could the United Kingdom get all its energy from sustainable sources? Do supply fluctuations make wind power impractical? Is hydrogen going to replace petrol? Answers to these and many other questions can be found, using some simple science and basic mathematics.

Energy policy is one area where, to quote John McCarthy, "he who refuses to do arithmetic is doomed to talk nonsense". Sustainable Energy is a constructive presentation of some basic energy science and engineering, not a polemical debunking, but its chapter epigraphs give a feel for the confused pronouncements in this area, by scientifically innumerate pundits of all political persuasions.

David MacKay promises us "numbers rather than adjectives" and there are indeed a lot of numbers in Sustainable Energy; he doesn't attempt to be exact, but tries to produce rough "back of the envelope" figures. The main part of the text, however, requires no arithmetic other than simple multiplication and division, with anything more complicated relegated to the appendices. MacKay also goes to some trouble to explain key concepts and to standardise everything on a few common units — kilowatt-hours (kWh) and kWh per person per day or per hundred passenger kilometres, and for national power generation or consumption, gigawatts (GW). The result should be broadly accessible.

Part one alternates between chapters evaluating a source of demand for power — cars, planes, heating and cooling, lighting, food production, making and moving stuff — and chapters evaluating a possible source of sustainable energy — wind, solar, hydro, offshore wind, wave, tide, and geothermal.

With the possible exception of wind, most of the latter are quite limited, especially given economic and social constraints (some ballpark kWh/person/day numbers for the UK): solar photovoltaic farms (3) are expensive, wood (5) and biofuels (2) take up a lot of land, and even the UK's decent tide (4) and wave (3) resources don't amount to that much, given a target of around 50kWh/person/day. (Geothermal power is very limited if used sustainably and for the UK small even if used extractively.)

Part two looks at some ways of getting around this problem.

When it comes to reducing the demand for power, it is not the case that "every little helps": worrying about phone chargers being left plugged in or recycling every scrap of paper is just a distraction from changes that actually matter. In the UK, the big demands for energy come from heating, transport, and making and moving "stuff", and the changes that MacKay considers involve better transport, smarter heating, and more efficient electricity use. (He doesn't address the possibility of "changes in lifestyle", but works on the assumption that we are trying to maintain something like current UK living standards and potentially to extend those to the entire planet.)

There's too much about transport in Sustainable Energy to summarise, so I'll just give three fairly random details. Because of fundamental properties of energy storage technologies, electric cars are a much more practical proposition than hydrogen ones. The only form of transport which can match a bicycle for minimising energy per passenger-kilometre is a fully-laden conventional (not high speed) electric train. Freight shipping is fantastically good for moving heavy goods, but passenger liners are considerably worse than jumbo jets for energy consumption per passenger-kilometre.

MacKay considers three possible additions to the sustainable power sources in part one: whether fossil fuels could be sustainable (even "clean coal" could only ever be a stop-gap given the limited resource); whether nuclear power could be sustainable on a long-term basis (with fast-breeder reactors and extraction of uranium from sea water, potentially for tens of thousands of years); and the possibility of drawing on renewable energy from other countries, most likely from desert solar generation in North Africa.

Wind power can only be scaled to large levels with appropriate storage to smooth out fluctuations: this might involve damming every loch in Scotland to provide pumped storage, but nationwide electric car battery storage is a near perfect match in scale, at least for the shorter-term fluctuations.

Finally, MacKay presents six possible ways of making it all add up, but leaves the reader to construct their own preferred solution. He provides cost estimates for one of his plans and attempts to put the sums involved into broader perspective. (Mostly he doesn't deal with economics as such, only bringing costs in when they are a major constraint.)


End-notes to each chapter provide details and references. And ninety pages of appendices go into more detail about the physics of various forms of transport and power generation. Anyone with school physics should be able to follow this, and it's a fun way to learn or refresh some basic science. The topics covered include the energetics of cars and planes, how building heating works, the sustainability of heat pumps, the mechanics of tidal pools, an attempt to account for the embedded energy in the UK's imports, and so forth.

Some examples and case studies are taken from elsewhere, and there's an attempt at the end to consider extending the broad analysis to Europe and the entire world, but Sustainable Energy is mostly quite specific to the United Kingdom: the focus is on the resources available to it and on the demands it faces, in the context of its inhabitants' consumption and behaviour and its political constraints. The basic physics and engineering, however, are universal and given the lack of similar works hand-tailored for other countries Sustainable Energy deserves a global readership.

Small parts of Sustainable Energy have dated. The best combined heat and power (CHP) fuel cells, for example, now have electrical efficiencies of 60% rather than 35%. But here MacKay's approach of attempting to explain fundamental ideas rather than just giving us answers pays off — his analysis and the chart he provides, plotting electrical versus heat efficiency for different CHP systems, allow us to work out the implications of that improvement for ourselves.

It is attractively and effectively illustrated, with good charts and diagrams and some small but informative colour photographs. And it is clearly, sometimes entertainingly, presented. Sustainable Energy Without the Hot Air is highly recommended to anyone who wants to understand the possibilities for future energy.

Note: before you rush off to buy a copy of Sustainable Energy, be advised that it is freely available as a PDF online. I bought a printed copy anyway because the layout, with diagrams and marginal notes and chapter endnotes, works much better in print.

July 2012

External links:
- buy from Amazon.com or Amazon.co.uk
- information from David JC MacKay
Related reviews:
- books about engineering
- more popular science
%T Sustainable Energy: Without the Hot Air
%A MacKay, David JC
%I UIT Cambridge
%D 2009
%O paperback, index
%G ISBN-13 9780954452933
%P 368pp