The electricity grid is the greatest engineering invention of all time. The grid provides light, heat, cold, mechanical power, computation, and communications to billions of people. A key aspect of the grid is that the generators are separated from the consumers by transmission lines. The electricity is generated in favorable locations – hydroelectric dams in the mountains, solar panels in the desert, wind turbines offshore, and coal plants near cooling water. We can see how electricity has grown in importance from Figure 7.1, which shows the electricity share of primary energy over time. It has increased from 9% in 1950 to 41% in 2017. The non-electrical transportation energy share has also grown, but more slowly, from 14% in 1971 to 20% in 2017. These increases came at the expense of non-electrical stationary energy whose share fell from 65% in 1971 to 39% in 2017. The electricity plot has a noticeable curvature.

For almost all of human history and for almost all people, the most important question each day has been, “Will our family have enough food to eat?” That, is until the Green Revolution. In the 1950s American agronomist Norman Borlaug (Figure 6.1), funded by the Rockefeller Foundation, developed a hybrid that was a cross between a Mexican wheat that was well adapted to a range of conditions and a short, stiff Japanese wheat that could support the weight of extra grains. This allowed farmers to apply more fertilizer without the wheat lodging, that is, falling over. Mexican farmers began growing Borlaug’s dwarf wheats in 1961 and doubled their yield. Since then there has been a spectacular increase in world crop yields. Figure 1.21 showed the history for cereals. Borlaug also argued that increasing crop yield was the best way to reduce deforestation. This has been called the Borlaug hypothesis. We will see in Section 6.5.1 that there is evidence to support his idea.

The resources of oil, gas, and coal are finite. The time will come when their production will fall, never to rise again. Alternatives are our once and future energy supply. So what did people do before fossil fuels? Many of their needs were similar to ours. People required light at night. They wanted to travel and to ship their goods. Farmers needed help plowing their fields. At high latitudes, people must have heat to survive. We will discuss three of their energy sources: horses, whale oil, and wood. Horses carried riders and they pulled plows, like tractors today. Whale oil provided light and wood produced heat. We conclude the chapter with a look at a society with a limited energy supply – the Norse Greenland colony.

Stationary demand is the energy that is not used for transportation. It includes homes, offices, factories, mines, and farms. Stationary demand was 77% of total primary energy demand in 2017, so it is much larger than transportation demand. The share has been stable; it was also 77% in 2000. Figure 8.1 shows the history of world stationary demand. The character of demand differs from supply. Much of demand comes from families and small companies, while energy suppliers are typically large companies. For this reason, we will be plotting demand on a per-person basis. Demand data are not as good as supply data. The demand data series do not go back far in time and there are gaps. Lights, heaters, refrigerators, and air conditioners have had significant efficiency improvements in recent years, but changes in stationary demand are not dramatic. There is nothing in the history of stationary demand comparable in scale to the fracking revolution or the explosive growth of solar PV.

Oil is a liquid mixture of hydrocarbons, usually found in rock. It is also called petroleum (Figure 5.1) The Latin roots of the word “petroleum” mean rock oil. In earlier times it was called rock oil to distinguish it from vegetable oils like rapeseed oil and animal oils like whale oil. Many different molecules may be present in petroleum. Examples are heptane and isooctane, which are used to define the octane scale for gasoline (Figure 5.2). Normal heptane is zero on the octane scale and isooctane is 100. Mixtures with higher octane numbers are more resistant to premature detonation in a spark-ignition engine. The isooctane carbon chain has branches that give it a higher octane number. Oil seeps have been known for thousands of years, and on a small scale, oil was skimmed off the surface of ponds and recovered from wells dug by hand. It was mainly used in medicines, particularly for skin ailments.

Coal is a black rock that burns (Figure 4.1). The surface of coal can be shiny, and in the 1800s it was popular to polish it to make a gemstone called jet. Queen Victoria had a jet mourning necklace. Figure 4.2 shows a representative portion of the chemical structure of coal. It is formed of irregular sheets of linked carbon rings. When coal burns the carbon atoms are oxidized to form carbon dioxide and the hydrogen atoms produce water vapor. There is also sulfur, which produces sulfur dioxide, a major pollutant. Coal reigned as the most important energy source from 1888 through 1956 (Figure 1.4). During this time coal provided double the energy of wood and water (Figure 1.6). Coal-powered locomotives and ships enabled fast long-distance transportation over land and sea for the first time. Coal stoves allowed people to heat their homes comfortably.

Let us begin by describing the sort of energy we are interested in. In this book, our emphasis will be on useful energy, energy that people apply to their purposes, like heat from a wood stove (Figure 1.1) or the energy derived from eating rice (Figure 1.2). Nowadays most of us buy our energy, although some people do split their own firewood. The energy supply is the amount that producers sell, like the 562 million tonnes of oil that flowed from Saudi wells in 2017. The energy demand is the amount that consumers buy, like gasoline for a car and electricity to light a home. Energy sales are an important part of the economy, and for this reason most countries keep good energy statistics, although they often miss the energy that people generate for themselves, like the firewood they split and the electricity from home solar panels (Figure 1.3). For energy statistics, a useful publication is the BP Statistical Review of World Energy, which has been published annually by the oil company since 1951.

For most of human experience, for most people, land transportation meant walking. For raiders like the Mongols and Comanches, it meant horses. In some societies, the better off rode in carriages. With the coming of the steam locomotive in the 1800s, people could ride a train. However, the real agent of deliverance has been the motor car. Steam engines needed a firebox, boiler, and large cylinders and this made them too heavy for a car. The problem was solved by the invention of engines where the fuel burned inside the cylinders. These engines are called internal-combustion engines to distinguish them from the external-combustion steam engines. The most important car engine has been the Otto-cycle, 4-stroke engine invented by Nikolaus Otto in 1876 in Cologne, Germany. In Otto’s engine, fuel mixed with air is first drawn into the cylinder by the motion of the piston. Next the piston compresses the fuel mixture, which is then lit by a flame.