Physics: The First Science

Chapter 14 - Energy in Civilization

CHAPTER 14 Energy in Civilization The flow of energy Electric energy: what is it and what does it do for us? DC and AC: transformer and generator Energy storage Batteries Supercapacitors Hydrogen Fuel cells Entropy and the second law of thermodynamics: the limits of energy transformation Thermal energy The second law of thermodynamics Entropy Our addiction to fossil fuels Availability The greenhouse effect The rate of energy increase Other sources of energy Nuclear energy Fusion Solar energy Wind Biomass Energy from rivers, oceans, and the earth The sustainability transition Energy fuels our civilization. We use it to heat our homes and our food. As mechanical energy it turns the motors in our industries and households. It is necessary for transportation and communication. 324 / Energy in Civilization We say that we generate energy, but we know that we can only transform it from one form to another.The source of our energy is overwhelmingly the internal energy of the fossil fuels, coal, oil, and natural gas, whose carbon content consists of the remains of living organisms built up over millions of years.There is also the internal nuclear energy of uranium in our reactors, and the energy radiated to us by the sun. In this chapter we explore the energy transformations that underlie our civilization. We also consider the limitations described by the second law of thermodynamics, and some of the obstacles that accompany our use of energy. 14.1 The flow of energy The flow diagram (courtesy Lawrence Livermore National Laboratory) shows the path of energy in the United States from the sources on the left, to the way we use it on the right. The numbers are estimates for 2008, in quads (Q), or quadrillions (= 1015) of british thermal units (btu), where 1btu = 1055 J. 1Q = 1.055E J or exajoules, each equal to 1018 J. oil: 37.5% coal: 22.6% natural gas: 24.0% nuc: 8.5% hydro: 2.5% biomass: 3.9% other: 1.0% U. S. energy consumption 2008 total: 99.2Q = 104.7EJ Here is a chart that shows the consumption of the various kinds of energy in the United States in 2008. The total amount is 99.2Q or 104.7 EJ. oil: 35.9% coal: 27.4% natural gas: 22.8% nuc: 6.0% hydro: 6.4% biomass and other: 1.5% World energy production 2006 total: 470Q = 496EJ And here is a similar chart for the energy production of the world. (The numbers for both charts are from the US Energy Information Administration.) The most drastic message of these diagrams is that about 86% of the world’s energy comes from fossil fuels. The other side of the message is how little of our energy comes from other sources. We will look at the alternatives, and why the patterns of energy use have been so resistant to change. The second message is that in the United States we use about 21% of the world’s energy, while our population is only 4.6% of the total. 0 50 100 150 200 250 Mcal per day Source: Adapted from a similar figure in Energy and Power (W. H. Freeman and Co., 1971). This figure shows how our appetite for energy has changed with time. At the beginning all that was consumed was the daily food, of about 2000 food calories (or 2 × 106 cal = 2 Mcal or about 8.6 MJ) per day. With hunting the amount of food increased, and wood was burned for heat and cooking. Primitive farming brought the planting of crops and the use of animal energy. In a later age animals were also used for transportation, coal was used for heating, and there were other sources of energy, including wind and water. A large increase came (in what we now call the developed world) at the time of the industrial revolution with the introduction of the steam engine and the widespread use of machinery. Finally we arrive at our own time, with modern modes of transportation and 14.3 DC and AC: transformer and generator / 325 all the gadgetry of modern civilization, when we use (in the United States) about 250,000 food calories per person. 0 500 1000 1500 2000 0 1 2 3 4 5 6 7 World population (109 ) year In the same period of time the number of people has increased dramatically. Already in 1798 Malthus saw that this increase could...