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 me.

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 part.

[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 digress.

[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 much energy.

[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 already.

[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 14.10).

[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 away.

[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 intrusive.

[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 transport?

[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 green.

[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 claims. "

[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 bicycles?

[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 horizontally(?).

[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 processing!