Reviews
Sustainability made simple
Phillip Hayson/Science Photo Library
The mainstream media, on the other
hand, rarely seem to use large num-
bers competently. This book, with its
slogan “numbers not adjectives”, is an
attempt to bridge that gap.
It is not often that a physics book becomes a publishing phenomenon; and
when it does happen, the book is usually about strings or cosmology. But
David MacKay’s Sustainable Energy –
Without the Hot Air is different. It
tackles a down-to-earth but controversial subject in a remarkably even-handed manner; it has been lauded
by a number of national and international publications; and it remains
high in the bestseller lists even though
it is free to download.
Despite the trendy word “
sustainable” in its title, this is avowedly not
a book about climate change, nor is it
a political polemic. Instead, its primary purpose is to give decent numerical estimates of the UK’s future
energy production and consumption
after the oil runs out. Such estimates
are normally only found together in
think-tank reports, where they can
appear surprisingly frail: their underlying physics is seldom revealed, and
it is difficult to judge their validity.
If one accepts a need to balance
current energy consumption with gen-
eration, then conclusions emerge
quite clearly, and the book summa-
rizes these in a straightforward man-
ner. Renewable energy takes up a lot
of land, and, for the UK, only wind
over our coastal seas and solar power
from other people’s deserts can pro-
vide us with significant amounts of it.
Nuclear power may be problematic,
even dangerous, but it could meet
much of our needs; compared with
the alternatives, the volume of waste
it produces is small. On the domestic
side, building insulation needs to be
improved and heating needs to be
electrified, probably by the extensive
use of air-source heat pumps.
MacKay uses an additional unit –
kilowatt-hours per 100 passenger-kilo-
metres – when discussing transport,
and this illuminates his comparison
of the energy demands of different
modes of travel. Here again, the likely
advantages of electrifying as much of
our transport infrastructure as possi-
ble become clear; in the absence of a
persuasive “green” alternative like hy-
drogen cells, no other option offers
the flexibility of electricity. The author
is at pains not to let politics intrude on
his message, and the book concludes
with a range of “energy plans” to suit
all political tastes – except head-in-
the-sand failure to acknowledge that
there is a problem.
However, setting energy policy
aside, the book also works on a deeper
level, bringing the concept of energy
home to physics through “back-of-
the-envelope” calculations. MacKay
shows how a physicist initially ap-
proaches a problem by identifying
processes and constraints, and getting
numerical estimates of them.
Naturally, such estimates need to
be refined, but they make a good
starting point – as many physicists will
know from their own lunchtime conversations. For example, we recall a
discussion about recycling in which we
needed to know the conversion rate
of hydrocarbon fuel mass into energy.
For an immediate rough estimate, we
used the calorie content of butter –
and indeed this same calculation appears alongside a picture of a pat of
butter on page 29 of the book. The
butter-derived figure proves to be
about 20% too low – but since one of
us developed instruments to measure
the moisture content of butter, we are
able to improve the estimate by eliminating this moisture mass (which, of
MacKay, a physicist at Cambridge
University who has just been named
as the UK government’s scientific advisor on energy and climate change,
begins by choosing a single unit for
power consumption: kilowatt-hours
per person per day, rather than the
usual muddle of kilowatt-hours, litres,
BTUs, barrels, tonnes and so on.
Though at first this seems clumsy, it
turns out to be rather effective. Figures mostly fall in the range 1–100, and
results are easily translated into personal terms. With this technical detail
firmly in hand, MacKay then builds
up two stacks: a red stack for energy
consumption and a green stack for sustainable energy generation.
Sunset scenario
What lies ahead for
the UK when its oil
runs out?
Sustainable Energy
– Without the Hot Air
David J C MacKay
2008 UI T Cambridge
£ 19.99/$49.95pb
free to download
384pp
