by David MacKay, UIT Cambridge Ltd, February 20, 2009, 978-0954452933
David MacKay is a physics professor at Cambridge. He wrote this book
to help the world, and
he is giving it away free. A paper version is
available. I created a text only Kindle version, which is "ok" to
read. If you want a copy, you can buy it on Amazon for $.99 or email
Climate change is about numbers, not adjectives. MacKay puts numbers
behind everything: from cell phone charges to tidal energy. I learned
more about energy production and consumption through this book than
any other source.
MacKay has great sense of humor. He uses it to great effect, because
it lightens up all the numbers in this book. He goes to great lenghts
to make the book readable by non-numeric people. If you want the
calculations, you go to the back of the book, where he provides the
equations in gory detail. I made it through most of the technical
[k190] This heated debate is fundamentally about numbers. How much
energy could each source deliver, at what economic and social cost,
and with what risks? But actual numbers are rarely mentioned.
[k198] If all the ineffective ideas for solving the energy crisis were
laid end to end, they would reach to the moon and back. . . . I
[k199] We are inundated with a flood of crazy innumerate
codswallop. The BBC doles out advice on how we can do our bit to save
the planet -- for example "switch off your mobile phone charger when
it's not in use;" if anyone objects that mobile phone chargers are not
actually our number one form of energy consumption, the mantra "every
little helps" is wheeled out. Every little helps? A more realistic
mantra is: if everyone does a little, we'll achieve only a little.
[k219] In a climate where people don't understand the numbers,
newspapers, campaigners, companies, and politicians can get away with
murder. We need simple numbers, and we need the numbers to be
comprehensible, comparable, and memorable.
[k243] The climate problem is mostly an energy problem.
[k297] From 1769 to 2006, world annual coal production increased
800-fold. Coal production is still increasing today.
[k426] I don't want to feed you my own conclusions. Convictions are
stronger if they are self-generated, rather than taught. Understanding
is a creative process.
[k724] Throughout the book, my aim is not only to work out numbers
indicating our current energy consumption and conceivable sustainable
production, but also to make clear what these numbers depend
on. Understanding what the numbers depend on is essential if we are to
choose sensible policies to change any of the numbers.
[k731] The main thread of the book (from page 2 to page 250) is
intended to be accessible to everyone who can add, multiply, and
divide. It is especially aimed at our dear elected and unelected
representatives, the Members of Parliament.
[k805] The proof of the pudding is, this approximation got us within
30% of the correct answer. Welcome to guerrilla physics.
[k824] Maybe 10%? Then we conclude: if we covered the windiest 10% of
the country with windmills (delivering 2 W/m2), we would be able to
generate 20 kWh/d per person, which ishalf of the power used by
driving an average fossil-fuel car 50 km per day.
[k828] The windmills that would be required to provide the UK with 20
kWh/d per person amount to 50 times the entire wind hardware of
Denmark; 7 times all the wind farms of Germany; and double the entire
fleet of all wind turbines in the world.
[k867] Let's make clear what this means. Flying once per year has an
energy cost slightly bigger than leaving a 1 kW electric fire on,
non-stop, 24 hours a day, all year.
[k929] 3. Solar biomass: using trees, bacteria, algae, corn, soy
beans, or oilseed to make energy fuels, chemicals, or building
materials. 4. Food: the same as solar biomass, except we shovel the
plants into humans or other animals.
[k964] Incidentally, the present cost of installing such photovoltaic
panels is about four times the cost of installing solar thermal
panels, but they deliver only half as much energy, albeit high-grade
energy (electricity). So I'd advise a family thinking of going solar
to investigate the solar thermal option first.
[k1308] The actual power from hydroelectricity in the UK today is 0.2
kWh/d per person, so this 1.5 kWh/d per person would require a
seven-fold increase in hydroelectric power.
[k1416] Offshore wind is tough to pull off because of the corrosive
effects of sea water. At the big Danish wind farm, Horns Reef, all 80
turbines had to be dismantled and repaired after only 18 months'
exposure to the sea air.
[k1430] Something I'd like you to notice about this race, though, is
this contrast: how easy it is to toss a bigger log on the consumption
fire, and howdifficult it is to grow the production stack. As I write
this paragraph, I'm feeling a little cold, so I step over to my
thermostat and turn it up. It's so simple for me to consume an extra
30 kWh per day. But squeezing an extra 30 kWh per day per person from
renewables requires an industrialization of the environment so large
it is hard to imagine.
[k1461] Do windmills kill "huge numbers" of birds? Wind farms recently
got adverse publicity from Norway, where the wind turbines on Smola, a
set of islands off the north-west coast, killed 9 white-tailed eagles
in 10 months. I share the concern of BirdLife International for the
welfare of rare birds. But I think, as always, it's important to do
the numbers. It's been estimated that 30 000 birds per year are killed
by wind turbines in Denmark, where windmills generate 9% of the
electricity. Horror! Ban windmills! We also learn, moreover, that
traffic kills one million birds per year in Denmark.
Thirty-times-greater horror! Thirty-times-greater incentive to ban
cars! And in Britain, 55 million birds per year are killed bycats
(figure 10.6). Going on emotions alone, I would like to live in a
country with virtually no cars, virtually no windmills, and with
plenty of cats and birds (with the cats that prey on birds perhaps
being preyed upon by Norwegian whitetailed eagles, to even things
up). But what I really hope is that decisions about cars and windmills
are made by careful rational thought, not by emotions alone. Maybe we
do need the windmills!
[k1553] I don't think so. Obsessively switching off the phone-charger
is like bailing the Titanic with a teaspoon. Do switch it off, but
please be aware how tiny a gesture it is. Let me put it this way: All
the energy saved in switching off your charger for one day is used up
in one second of car-driving. The energy saved in switching off the
charger for one year is equal to the energy in a single hot bath.
[k1720] To work out the power required to maintain the meat-eater's
animals as they mature and wait for the chop, we need to know for how
long the animals are around, consuming energy. Chicken, pork, or beef?
Chicken, sir? Every chicken you eat was clucking around being a
chicken for roughly 50 days.
I don't like the switching from kg to lb.
[k1726] To condense all these ideas down to a single number, let's
assume you eat half a pound (227 g) per day of meat, made up of equal
quantities of chicken, pork, and beef. This meat habit requires the
perpetual sustenance of 8 pounds of chicken meat, 70 pounds of pork
meat, and 170 pounds of cow meat. That's a total of 110 kg of meat,
or 170 kg of animal (since about two thirds of the animal gets turned
into meat). And if the 170 kg of animal has similar power requirements
to a human (whose 65 kg burns 3 kWh/d) then the power required to fuel
the meat habit is 3 kWh/d 170 kgx 65 kg =~ 8 kWh/d.
[k1752] The energy cost of Tiddles, Fido, and Shadowfax
Animal companions! Are you the servant of a dog, a cat, or a horse?
[k1763] To figure out whether driving a car or walking uses less
energy, we need to know the transport efficiency of each mode. For the
typical car of Chapter 3, the energy cost was 80 kWh per 100
km. Walking uses a net energy of 3.6 kWh per 100 km -- 22 times
less. So if you live entirely on food whose footprint is greater than
22 kWh per kWh then, yes, the energy cost of getting you from A to B
in a fossil-fuel-powered vehicle is less than if you go under your own
steam. But if you have a typical diet (6 kWh per kWh) then "it's
better to drive than to walk" is a myth. Walking uses one quarter as
[k1798] Walking has a CO2 footprint of 42 g/km; cycling, 30 g/km. For
comparison, driving an average car emits 183 g/km.
This is abrilliant example of the law of large numbers and
stellar forces. The little bit that the earth slows down causes the
oceans to move. Stop and think about that power requirement.
[k1836] Tidal energy is sometimes called lunar energy, since it's
mainly thanks to the moon that the water sloshes around so. Much of
the tidal energy, however, is really coming from the rotational energy
of the spinning earth. The earth is very gradually slowing down.
Lacking physics accumen has its benefits for me. When someone
doesn't publish a computable result it's probably because the results
stink. More importantly I think all energy problems distill in fiscal
values, dollars. If someone could make money off of tides (even
semi-plausibly, i.e., enough to fool investors) they would be doing it
[k1869] One way to extract tidal energy would be to build tide farms,
just like wind farms. The first such underwater windmill, or
"tidal-stream" generator, to be connected to the grid was a "300 kW"
turbine, installed in 2003 near the northerly city of Hammerfest,
Norway. Detailed power production results have not been published, and
no-one has yet built a tide farm with more than one turbine, so we're
going to have to rely on physics and guesswork to predict how much
power tide farms could produce.
[k1890] The current proposals for the barrage will generate power in
one direction only. This reduces the power delivered by another
50%. The engineers' reports on the proposed Severn barrage say that,
generating on the ebb alone, it would contribute 0.8 kWh/d per person
on average. The barrage would also provide protection from flooding
valued at about GBP 120M per year.
[k1914] Totting everything up, the barrage, the lagoons, and the tidal
stream farms could deliver something like 11 kWh/d per person (figure
[k1929] False. The natural tides already slow down the earth's
rotation. The natural rotational energy loss is roughly 3 TW
(Shepherd, 2003). Thanks to natural tidal friction, each century, the
day gets longer by 2.3 milliseconds.
[k1949] One of the main sinks of energy in the "developed" world is
the creation of stuff. In its natural life cycle, stuff passes through
three stages. First, a new-born stuff is displayed in shiny packaging
on a shelf in a shop. At this stage, stuff is called "goods." As soon
as the stuff is taken home and sheds its packaging, it undergoes a
transformation from "goods" to its second form, "clutter." The clutter
lives with its owner for a period of months or years. During this
period, the clutter is largely ignored by its owner, who is off at the
shops buying more goods. Eventually, by a miracle of modern alchemy,
the clutter is transformed into its final form, rubbish. To the
untrained eye, it can be difficult to distinguish this "rubbish" from
the highly desirable "good" that it used to be. Nonetheless, at this
stage the discerning owner pays the dustman to transport the stuff
[k1974] Let's assume you have a coke habit: you drink five cans of
multinational chemicals per day, and throw the aluminium cans
away. [...] So a five-a-day habit wastes energy at a rate of 3 kWh/d.
[k1985] The energy cost of making a rechargeable nickel-cadmium AA
battery, storing 0.001 kWh of electrical energy and having a mass of
25 g, is 1.4 kWh (phases R and P). If the energy cost of disposable
batteries is similar, throwing away two AA batteries per month uses
about 0.1 kWh/d.
[k2003] What about a car, and a road? Some of us own the former, but
we usually share the latter. A new car's embodied energy is 76 000 kWh
-- so if you get one every 15 years, that's an average energy cost of
14 kWh per day.
[k2156] In the UK, the population density is 5 times greater, so
wide-scale geothermal power of this sustainable-forever variety could
offer at most 2 kWh per person per day.
[k2161] In "enhanced geothermal extraction" from hot dry rocks (figure
16.5), we first drill down to a depth of 5 or 10 km, and fracture the
rocks by pumping in water. (This step may create earthquakes, which
don't go down well with the locals.)
[k2185] 2006) describing the USA's hot dry rock resource. Another more
speculative approach, researched by Sandia National Laboratories in
the 1970s, is to drill all the way down to magma at temperatures of
600--1300 degrees C, perhaps 15 km deep, and get power there. The
websitewww.magma-power.com reckons that the heat in pools of magma
under the US would cover US energy consumption for 500 or 5000 years,
and that it could be extracted economically.
[k2208] If again we assume that 6% of this expenditure went to energy
at a cost of 5c per kWh, we find that the energy cost of having
nuclear weapons was 26 000 kWh per American, or 1.4 kWh per day per
American (shared among 250 million Americans over 51 years). What
energy would have been delivered to the lucky recipients, had all
those nuclear weapons been used? The energies of the biggest
thermonuclear weapons developed by the USA and USSR are measured in
megatons of TNT. A ton of TNT is 1200 kWh.
[k2214] If dropped on a city of one million, a megaton bomb makes an
energy donation of 1200 kWh per person, equivalent to 120 litres of
petrol per person. The total energy of the USA's nuclear arsenal today
is 2400 megatons, contained in 10 000 warheads. In the good old days
when folks really took defence seriously, the arsenal's energy was 20
000 megatons. These bombs, if used, would have delivered an energy of
about 100 000 kWh per American. That's equivalent to 7 kWh per day per
person for a duration of 40 years -- similar to all the electrical
energy supplied to America by nuclear power.
[k2226] "Trident creates jobs." Well, so does relining our schools
with asbestos, but that doesn't mean we should do it!
[k2398] For any renewable facility to make a contribution comparable
to our current consumption, it has to be country-sized. To get a big
contribution from wind, we used wind farms with the area of Wales. To
get a big contribution from solar photovoltaics, we required half the
area of Wales. To get a big contribution from waves, we imagined wave
farms covering 500 km of coastline. To make energy crops with a big
contribution, we took 75% of the whole country. To sustain Britain's
lifestyle on its renewables alone would be very difficult. A
renewable-based energy solution will necessarily be large and
[k2440] 66,000? Wow, what a lot of homes! Switch off the chargers!
66,000 sounds a lot, but the sensible thing to compare it with is the
total number of homes that we're imagining would participate in this
feat of conservation, namely 25 million homes. 66 000 is just one
quarter of one percent of 25 million. So while the statement quoted
above is true, I think a calmer way to put it is: If you leave your
mobile phone charger plugged in, it uses one quarter of one percent of
your home's electricity. And if everyone does it? If everyone leaves
their mobile phone charger plugged in, those chargers will use one
quarter of one percent of their homes' electricity. The "if-everyone"
multiplying machine is a bad thing because it deflects people's
attention towards 25 million minnows instead of 25 million sharks.
[k2520] In a standard fossil-fuel car, for example, only 25% is used
for pushing, and roughly 75% of the energy is lost in making the
engine and radiator hot.
[k2535] Figure 20.3 shows a multi-passenger vehicle that is at least
25 times more energy-efficient than a standard petrol car: a bicycle.
[k2538] Figure 20.4 shows another possible replacement for the petrol
car: a train, with an energy-cost, if full, of 1.6 kWh per 100
passenger-km. In contrast to the eco-car and the bicycle, trains
manage to achieve outstanding efficiency without travelling slowly,
and without having a low weight per person. Trains make up for their
high speed and heavy frame by exploiting the principle of small
frontal area per person.
[k2548] But whoops, now we've broached an ugly topic -- the prospect
of sharing a vehicle with "all those horrible people." Well, squish
aboard, and let's ask: How much could consumption be reduced by a
switch from personal gas-guzzlers to excellent integrated public
[k2559] Vancouver's trolleybuses consume 270 kWh per vehicle-km, and
have an average speed of 15 km/h. If the trolleybus has 40 passengers
on board, then its passenger transport cost is 7 kWh per 100 p-km.
[k2568] In 2006--7, the total energy cost of all London's underground
trains, including lighting, lifts, depots, and workshops, was 15 kWh
per 100 pkm -- five times better than our baseline car. In 2006--7 the
energy cost of all London buses was 32 kWh per 100 p-km.
[k2595] The energy consumption of individual cars can be reduced. The
wide range of energy efficiencies of cars for sale proves this. In a
single showroom in 2006 you could buy a Honda Civic 1.4 that uses
roughly 44 kWh per 100 km, or a Honda NSX 3.2 that uses 116 kWh per
100 km (figure 20.9). The fact that people merrily buy from this wide
range is also proof that we need extra incentives and legislation to
encourage the blithe consumer to choose more energy-efficient cars.
[k2607] People today choose their cars to make fashion
statements. With strong efficiency legislation, there could still be a
wide choice of fashions; they'd all just happen to be
energy-efficient. You could choose any colour, as long as it was
[k2611] While we wait for the voters and politicians to agree to
legislate for efficient cars, what other options are available?
We could pray!
[k2616] Where excellent cycling facilities are provided, people will
use them, as evidenced by the infinite number of cycles sitting
outside the Enschede railway station (figure 20.13).
I like the idea of a tax based on the amount of road you consume,
not the length of the drive.
[k2630] Take a trunk road on the verge of congestion, where the
desired speed is 60 mph. The safe distance from one car to the next at
60 mph is 77 m. If we assume there's one car every 80 m and that each
car contains 1.6 people, then vacuuming up 40 people into a single
coach frees up two kilometres of road!
[k2667] Whereas the average new car in the UK emits 168 g, the hybrid
Prius emits about 100 g of CO2 per km, as do several other non-hybrid
vehicles -- the VW Polo blue motion emits 99 g/km, and there's a Smart
car that emits 88 g/km. The Lexus RX 400h is the second hybrid,
advertised with the slogan "LOW POLLUTION. ZERO GUILT." But its CO2
emissions are 192 g/km -- worse than the average UK car! The
advertising standards authority ruled that this advertisement breached
the advertising codes on Truthfulness, Comparisons and Environmental
[k2674] A 30% reduction in fossil-fuel consumption is impressive, but
it's not enough by this book's standards. Our opening assumption was
that we want to get off fossil fuels, or at least to reduce fossil
fuel use by 90%. Can this goal be achieved without reverting to
[k2692] I've looked up the performance figures for lots of electric
vehicles -- they're listed in this chapter's end-notes -- and they
seem to be consistent with this summary: electric vehicles can deliver
transport at an energy cost of roughly 15 kWh per 100 km. That's five
times better than our baseline fossil-car, and significantly better
than any hybrid cars. Hurray! To achieve economical transport, we
don't have to huddle together in public transport -- we can still
hurtle around, enjoying all the pleasures and freedoms of solo travel,
thanks to electric vehicles.
[k2808] Then I looked at the numbers. The sad truth is that ocean
liners use more energy per passenger-km than jumbo jets.
[k3024] The thermostat (accompanied by woolly jumpers) is hard to
beat, when it comes to value-for-money technology. You turn it down,
and your building uses less energy. Magic! In Britain, for every
degree that you turn the thermostat down, the heat loss decreases by
about 10%. Turning the thermostat down from 20 degrees C to 15 degrees
C would nearly halve the heat loss. Thanks energy-saving technology
has side-effects. Some humans call turning the thermostat down a
lifestyle change, and are not happy with it. I'
[k3292] I do hope that this sort of smart-metering activity will make
a difference. In the future cartoon-Britain of 2050, however, I've
assumed that all such electricity savings are cancelled out by the
miracle of growth. Growth is one of the tenets of our society: people
are going to be wealthier, and thus able to play with more
gadgets. The demand for ever-moresuperlative computer games forces
computers' power consumption to increase. Last decade's computers used
to be thought pretty neat, but now they are found useless, and must be
replaced by faster, hotter machines.
[k3435] If we used all the mineable uranium (plus the depleted uranium
stockpiles) in 60-times-more-efficient fast breeder reactors, the
power would be 33 kWh per day per person.
[k3453] If fast reactors are 60 times more efficient, the same
extraction of ocean uranium could deliver 420 kWh per day per
person. At last, a sustainable figure that beats current consumption!
-- but only with the joint help of two technologies that are
respectively scarcely-developed and unfashionable: ocean extraction of
uranium, and fast breeder reactors.
[k3501] Let's imagine generating 22 kWh per day per person of nuclear
power -- equivalent to 55 GW (roughly the same as France's nuclear
power), which could be delivered by 55 nuclear power stations, each
occupying one square kilometre. That's about 0.02% of the area of the
country. Wind farms delivering the same average power would require
500 times as much land: 10% of the country. If the nuclear power
stations were placed in pairs around the coast (length about 3000 km,
at 5 km resolution), then there'd be two every 100 km. Thus while the
area required is modest, the fraction of coastline gobbled by these
power stations would be about 2% (2 kilometres in every 100).
[k3508] The nuclear industry sold everyone in the UK 4 kWh/d for about
25 years, so the nuclear decommissioning authority's cost is 2.3
p/kWh. That's a hefty subsidy -- though not, it must be said, as hefty
as the subsidy currently given to offshore wind (7 p/kWh).
Accountability is not something we can make happen, but we can
calculate the cost of errors in lives, land, and money. All systems
are imperfect, which is what this book is about so I don't think you
can talk about economics only when it is convenient. What is the cost
of large windmills in terms of lives lost constructing them? People
regularly fall off of oil rigs or die of cancer due to leaks from
toxic chemicals from refineries and fossil fuel devices.
[k3526] If we let private companies build new reactors, how can we
ensure that higher safety standards are adhered to? I don't know.
[k3531] Indeed, according to a paper published in the journal Science,
people in America living near coal-fired power stations are exposed to
higher radiation doses than those living near nuclear power plants.
[k3535] So if we got our electricity from sources with a death rate of
1 death per GWy, that would mean the British electricity supply system
was killing 45 people per year. For comparison, 3000 people die per
year on Britain's roads. So, if you arenot campaigning for the
abolition of roads, you may deduce that " death per GWy" is a death
rate that, while sad, you might be content to live with. Obviously, 0.
[k3541] The death rates vary a lot from country to country. In China,
for example, the death rate in coal mines, per ton of coal delivered,
is 50 times that of most nations.
[k3790] In the DESERTEC plans, the prime areas to exploit are coastal
areas, because concentrating solar power stations that are near to the
sea can deliver desalinated water as a by-product -- valuable for
human use, and for agriculture.
This is already done with propane tanks and ice blocks (not to
mention highly caloric foods) at filling stations in the US.
[k4064] Some people say, "Horrors! How could I trust the filling
station to look after my batteries for me? What if they gave me a duff
one?" Well, you could equally well ask today "What if the filling
station gave me petrol laced with water?"
[k4124] If 30 million electric vehicles were willing, in times of
national electricity shortage, to run their chargers in reverse and
put power back into the grid, then, at 2 kW per vehicle, we'd have a
potential power source of 60 GW -- similar to the capacity of all the
power stations in the country. Even if only one third of the vehicles
were connected and available at one time, they'd still amount to a
potential source of 20 GW of power.
[k4794] The average American uses 250 kWh/d per day. Can we
hit that target with renewables?
Seems like the height of the windmills affects this number. If
you stagger the windmills vertically they can be packed more densely
[k5367] How densely could such windmills be packed? Too close and the
upwind ones will cast wind-shadows on the downwind ones. Experts say
that windmills can't be spaced closer than 5 times their diameter
without losing significant power.
[k5424] Perhaps the worst windmills in the world are a set in Tsukuba
City, Japan, which actually consume more power than they
generate. Their installers were so embarrassed by the stationary
turbines that they imported power to make them spin so that they
looked like they were working!
[k5681] This cartoon also applies without modification to
submarines. The gross transport cost (in kWh per ton-km) of an airship
is just the same as the gross transport cost of a submarine of
identical length and speed. The submarine will contain 1000 times more
mass, since water is 1000 times denser than air; and it will cost 1000
times more to move it along. The only difference between the two will
be the advertising revenue.
[k5735] Bioethanol from sugar cane Where sugar cane can be produced
(e.g., Brazil) production is 80 tons per hectare per year, which
yields about 17 600 l of ethanol. Bioethanol has an energy density of
6 kWh per litre, so this process has a power per unit area of 1.2
W/m2. Bioethanol from corn in the USA The power per unit area of
bioethanol from corn is astonishingly low. Just for fun, let's report
the numbers first in archaic units. 1 acre produces 122 bushels of
corn per year, which makes 122x 2.6 US gallons of ethanol, which at 84
000 BTU per gallon means a power per unit area of just 0.02 W/m2 --
and we haven't taken into account any of the energy losses in