Our Renewable Future

Chapter 2. A Quick Look at Our Current Energy System

The statistics are readily available: our world presently uses about 520 quadrillion British thermal units each year, or 550 exajoules, or 153 billion megawatt-hours—the equivalent of 100 billion barrels of oil.[1] These numbers are readily interpreted by the experts. But what do they mean in terms the nonspecialist can understand?

A hard-working human can generate power in the range of 60 to 300 watts,[2] depending on the person’s strength and which muscles are in use. Since the upper part of that range is realistic only for trained athletes using their leg muscles, let’s start with a more conservative and realistic number—100 watts. Sustained for an hour, that would be 100 watt-hours of energy. Working eight-hour days five days a week for a year, with no holidays, our hypothetical hard worker would produce 208,000 watt-hours of useful work, or 208 kilowatt-hours.

World annual energy usage therefore equals the energy output of the yearly manual labor of 734.4 billion humans—a hundred times the current global population (though a large portion of that energy is wasted). We have obviously come very far from the days, just a couple of centuries ago, when a quarter of all agricultural land was set aside to grow food for draft animals; when we derived our heat from burning wood; when most of the motive force in the economy derived from human and animal muscles; and when many human beings were enslaved so that their muscle power could be forcibly directed by other humans.

As we will see shortly, most of our current “energy slaves” are fossil-fueled, and their work is done mostly to the advantage of people in wealthy countries, whereas the poorest humans still get by largely on muscle power.


The single trend that best captures the history of energy use since the start of the industrial revolution is growth. Since 1850 (when world population stood at less than 1.3 billion), total yearly energy use has grown from about 10 exajoules per year to over 500 exajoules per year (see fig. I.3). Since 1980, population has grown from 4.4 billion to 7.3 billion in 2015, while total energy use has nearly doubled. On a per capita basis, supply of energy has grown since 1850 by nearly 900 percent (though in the past 40 years per capita growth has slowed; fig. 2.1). Since 1980 per capita energy use has increased 14 percent, from about 60 gigajoules (GJ) to over 70 GJ per year.

WEB Figure 2-1 World primary energy consumption
Figure 2.1. World per capita primary energy consumption per year by fuel type, 1850–2014. Primary electricity converted by direct equivalent method.
Source: Data compiled by J. David Hughes from Arnulf Grubler, “Technology and Global Change: Data Appendix,” (1998), and BP, Statistical Review of World Energy, (annual).

Clearly, growth has been occurring in both energy and population. Has energy growth caused population growth? Not directly: countries with high rates of energy use generally do not have high population growth rates, and most countries with very high population growth rates use relatively little energy on a per capita basis. However, advances in agriculture and public health that are directly and indirectly tied to energy growth have made possible a dramatic increase in population over time.

Growth in energy and gross domestic product (GDP) are also tied. Energy enables the activities that generate GDP, so the relationship is direct, but it is not static; we have gradually become more efficient in the use of energy in creating GDP (fig. 2.2). During the renewable energy transition we will be challenged to become more efficient still (we’ll discuss the relationship between energy use and GDP further in chap. 6, “Energy Supply,” under the heading “Energy Intensity”). Nevertheless, even if the energy–GDP linkage is stretchable, it is in the end unbreakable: it takes energy to do anything whatsoever.

WEB Figure 2-2 Total energy use and GDP
Figure 2.2. Total gross domestic product and energy consumption of United States and China, 1965–2014. The link between GDP (shown in trillions of US dollars) and energy consumption (shown in million metric tons of oil equivalent [Mtoe]) is clear in countries in both later stages of economic development (e.g., United States) and earlier stages of economic development (e.g., China). Although the strength of the link appears to decline in the United States in later decades, this is in part because so much energy consumption for manufacturing has been relocated to other countries—including China.
Source: World Bank, World Development Indicators, and BP, Statistical Review of World Energy (annual).

Energy Rich, Energy Poor

Clearly, people in some countries use a lot more energy than people in others. From a human perspective, having little energy available means spending a lot of time in mundane activities related to daily life (cooking, washing clothes, walking, planting, weeding and harvesting, etc.). Having lots of energy means having machines do many of these things, or help do them; it also usually implies the ability to accelerate the pace of life and thus consume more goods, have more experiences, travel farther and more often, and get an education and ultimately a better-paying, more highly skilled job. Spending money on such energy-consuming activities contributes significantly to the GDP.

There is an obvious connection between energy inequality and economic inequality: very low energy use is associated with poverty, very high energy use with wealth (fig. 2.3). However, the connection is not absolute: for example, Germans enjoy a high standard of living, yet use only a little more than half as much energy (per capita) as citizens of the United States and Canada (fig. 2.4).

WEB Figure 2-3 Per capita GDP and energy use for selected countries
Figure 2.3. Per capita gross domestic product and energy consumption of various countries, 2012.
Source: World Bank, World Development Indicators.
WEB Figure 2-4 Human Development Index (2014) and per capita energy consumption (2012)
Figure 2.4. Human Development Index (2014) and per capita energy consumption (2012) for various countries.
Source: World Bank, World Development Indicators, and United Nations Development Program.

The fossil fuel era has produced great wealth, and some have partaken of that wealth far more than others. However, as we will discuss in more detail in chapter 8, “Energy and Justice,” the end of the fossil fuel era does not necessarily imply the end of energy inequality. Solar panels and wind turbines require investment and produce benefits; in the renewable era ahead, it is certainly possible to imagine scenarios in which only some can afford the needed investment and can therefore enjoy the benefits. The degree to which energy inequality is either reduced or cemented into place will depend on how the transition is planned and implemented.

Energy Resources

Figure 2.5. Current energy consumption by source, world and United States, 2012.
Source: BP, Statistical Review of World Energy (annual). [See also errata note.]

These charts more or less speak for themselves (fig. 2.5). We currently draw upon many different energy resources, but just a few supply the bulk of all energy used: about 85 percent of our energy comes from oil, coal, and natural gas.

One factor is not readily apparent in the charts: in poor nations, a lot of energy comes from traditional biomass, such as burning wood, crop residues, and dung.

End Use

Primary energy is energy in its initial form, as it is directly extracted from Earth (crude oil, natural gas, coal) or as it is available without conversion through combustion (electricity from wind, solar, hydro, nuclear, tidal, etc.). Final energy is the energy we use directly in forms that are suited to their use (electricity for lighting, gasoline for internal combustion engines, kerosene for jet turbines, coke for steel making, etc.). In between the primary and final stages much energy is typically lost.

In 2012, primary energy production was 18,496 Mtoe while final consumption was 9100 Mtoe[3]—48 percent of what we started with, the rest having been lost both in conversion of primary energy to the forms we prefer to use (gasoline, electricity) and in use by the energy conversion industries themselves (fig. 2.6). The bulk of this conversion loss occurred in making electricity (average 54 percent losses globally)[4]—which demonstrates both the degree to which we value electricity and the easy availability of fossil fuels to accommodate such a high proportion of losses. As we have already noted more than once, this implies some good news for the renewable energy transition because wind and solar electricity do not entail these conversion losses. There are also end-use losses, notably in the transportation sector, due to the inefficiency of internal combustion engines in transforming the energy stored in fuels into motive force.

WEB Figure 2-6 World energy flows
Figure 2.6. Flow of world energy production and consumption, 2012. Flows under 100 Mtoe not shown for clarity.
Source: International Energy Agency, “World: Balance (2012).”

We use energy in everything we do, so it is difficult to adequately capture all the ways we use energy in a single chart. We can divide energy usage into sectors, for the United States and the world. It’s helpful then to pick apart the energy use within each of those sectors. Let’s look at the food system, for example, in figure 2.7.

WEB Figure 2-7 Food System Energy Use
Figure 2.7. Energy inputs and outputs in the US food system.
Source: Center for Sustainable Systems, University of Michigan, “U.S. Food System Factsheet.” Pub. No. CSS01-06 (2015).

Changing our energy system will require both detailed and systemic thinking. Some aspects of the food system won’t pose too big a challenge: we can use electricity from renewable sources to run existing machinery, while finding ways to cool food more efficiently and to reduce the need for refrigeration. But other aspects will prove difficult to transition: tractors, combines, heavy trucks, and many other vehicles and machines are all currently built for fossil fuels and oriented on the global fossil fuel supply network. (We will discuss the challenges and implications of this transition in chapters 4 and 5.)

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Let’s summarize what we have learned so far. Energy is important, we use a lot of it, and we are in the very early stages of a great transition from overwhelming reliance on fossil fuels toward reliance on renewable sources. We’ve seen what energy is and how it works, as well as the criteria and tools to use in evaluating energy sources. We’ve explored the difference between operational and embodied energy, and between primary and final energy. We’ve also seen how unequally we consume energy, and what we use it for.

Now we are ready to explore some of the opportunities and challenges we may face during the transition.


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