The Big Picture

Energy is a subject that is central to the understanding of ecology; it is also a commodity that we purchase every day. In fact, energy is central to what we do every day - work. Energy is the ability to do work. When you work, someone pays you for your expended energy. That money is used to buy food, which is itself energy in a different form, to replace the energy that you have burned in working. You also use your money to pay heating and electric bills, fill the gas tank of your car, or buy natural gas to cook your food. Thus, humans are part of the energy flow in the food web, and our monetary system is just a way of representing energy. These commercial sources of energy are derived from energy in various other parts of the ecosystem, including fossil fuels, wood, nuclear power, hydroelectric power, wind power, or geothermal power, but ultimately they all trace back to the sun's energy. In this chapter, the authors explain just what energy is, review the laws of thermodynamics, demonstrate how to calculate energy efficiency, describe various energy units, contrast energy with power, and show how energy consumption is calculated. In addition, they examine the alternative ways of meeting our future energy needs: the "hard path" of building more energy generating capacity and the "soft path" of energy conservation.

Frequently Asked Questions

• Energy is the ability to do work.
• Work is exerting a force over a distance (Work = force x distance)

• 1st Law of Thermodynamics states that energy may be converted from one form to another, but it is never lost from the system.
• 2nd Law of Thermodynamics states that during conversion from one type of energy to another, some energy is converted to heat, and the entropy of the system must increase.
• Heat and entropy are different. The Second Law says that there is always waste heat created. All of the energy in a system is not usable to do work. Entropy is a measure of the amount of unusable energy in a system. (Its units are not energy but energy/temperature.) The waste heat given off increases the amount of unusable energy increasing the entropy.

• Potential Energy - This is stored energy (high quality energy) and can be used to do work.
• It can be stored as:
• Chemical energy - coal, oil, natural gas (fossil fuels)
• Nuclear energy - stored in atomic bonds
• Gravitational energy - water stored behind dams or a vehicle at the top of a hill
• Solar Energy - The sun's energy, which constitutes the electromagnetic spectrum (including heat and visible light). Solar energy is the source of almost all energy used by Earth's biota.
• Kinetic energy - Kinetic energy is energy that an object has due to its state of motion.
• Heat - Energy that flows from a high temperature object to a low temperature object in a system; it can be used for work (low quality energy).

• When work is done or an object is moved, the following sequence normally occurs:
• Potential energy --> Kinetic energy --> Heat
• Low entropy in system ----> High entropy in system
• High quality energy -----> Low quality energy
• Organized (ordered) energy ----> Disorganized (disordered) energy
• It is possible to work backwards here, for heat to cause motion of things and thus create kinetic energy and then potential energy; however when this occurs entropy of the entire system increases at each conversion.

• Entropy is a measure of the amount of energy unavailable to do work in the system. It is the randomness of a system.
• As the molecules of the compounds in which energy is stored are burned, the bonds between the atoms are broken, releasing energy and making the distribution of the molecule's atoms more random. Thus the molecules in candy bar or gasoline, after they are consumed, have higher entropy states than before they are consumed. Both a car that has been pushed downhill and a battery-powered flashlight that is burning have higher entropy states than the car at the top of the hill or the flashlight when it is turned off.
• All the energy in a system eventually ends up in an unusable form. This means that entropy increases over time in all systems.
• Entropy is NOT energy. Its units are not energy but energy/temperature. When all of the energy is heat energy, the system is at the same temperature, and none of the energy is usable. Entropy is maximized.
• This is a one-way path; you can't go back to high quality energy from low quality energy.
• This is why energy cannot be recycled, and why new high-quality energy from the sun is always needed for the Earth's ecosystems.

• Friction is the force that converts kinetic energy into heat energy when work is done. It changes organized motion into disorganized motion.

• There are two kinds of energy efficiency: first-law and second-law efficiency.
• First-law efficiency is the ratio of total energy output (or the work done by the device) to total energy input (the amount of energy used to do work).
• Second-law efficiency is a ratio equal to the minimum amount of energy needed to perform a task divided by the actual energy used to perform the task. The minimum amount of energy is the input energy required under ideal (Carnot efficiency) conditions. Carnot efficiency is the maximum efficiency attainable for a given set of conditions (This type of ideal efficiency was first described by the French engineer Sadi Carnot in 1824).
• Second-law efficiency takes into account the fact that not all energy is available to do work (2nd Law of Thermodynamics).
• Second law efficiencies can often be improved because our actual machines are not ideal Carnot efficiency machines. For example, automobile engines can be redesigned so that we can get more MPG, but still go the same distance at the same speeds. The more closely we approach the ideal efficiency, the more energy we can save.
• An electrical power plant is 33 % efficient in terms of second-law efficiency. That means that for every 3 units of coal burned, 2 units are lost as heat and 1 unit is converted to electricity.

• A heat engine produces work from heat.
• A coal-burning power plant is a heat engine, because it burns coal to heat water, which becomes steam and turns a turbine that generates electricity.
• Many energy-demanding technologies use heat engines to power them, including automobiles and steam engines.
• Heat engines produce a great deal of waste heat, which causes thermal pollution and contributes to global warming.
• Most objects that do work are actually heat engines. One important example is living organisms. They use heat energy released from their food to do work. To see a good example of heat energy in food, burn a potato chip (not the baked kind).

• In 1994, the total energy consumption in the USA was 86 exajoules (an exajoule is approximately 1 quadrillion BTU's)
• The USA uses 25 % of the world's energy with 5 % of the world's population.
• Most of the USA's energy comes from the fossil fuels (coal = 22 exajoules, natural gas = 22 exajoules, and oil = 31 exajoules, 14 exajoules from domestic production and 17 exajoules from net imports) (See Figure 15.4 and Table 15.3).
• The overall first-law energy efficiency for the USA is 50 %. (See Table 15.1) This means that half of all the energy we use to do work is lost into atmosphere as heat (43 exajoules in 1994). This heat loss to the atmosphere is part of the reason why the Earth is gradually warming.

• Energy is measured using the following units:
• 1 joule = 9.481 x 10 ^-4 BTU's = 0.239 cal = force of 1 Newton applied over 1 meter
• 1 calorie = amount of heat needed to raise 1 g (or ml) of H₂O 1 ^oC = 4.18 joules
• 1 Kilocalorie (or Kcal) = 1000 calories (dieters count Kcals, but call them "Calories")
• 1 British Thermal Unit (BTU) = 252 calories = 1055 joules
• 1 quad = 1 quadrillion BTU's = approximately 1 exajoule
• 1 exajoule = 10¹⁸ joules or a billion gigajoules = approximately 1 quad = (9.481 x 10¹⁵) BTU's
• 1 kilowatt-hour = 3,600,000 joules

• Power is the rate of energy use (Energy used/unit time).
• Power is measured using the following units:
• 1 watt = 1 joule/second = 3.413 BTU/hr = 4.34 cal/hr
• 1 kilowatt = 1000 watts
• 1 megawatt = 1000 kilowatts
• 1 gigawatt = 1000 megawatts
• 1 horsepower = 7.457 x 10² watts

• This is a process of using waste heat from large power generating facilities to do useful work.
• For example, the location of a business building next door to a power-generating facility can save on heating costs. This is because the 2 units of heat produced for every 1 unit of electricity produced can be used to heat the building. This saves the business from having to reconvert electricity back into heat, as is frequently done (think of an electric range, electric water heaters, and electric home heat).
• Cogeneration represents an improvement in the overall efficiency of burning fossil fuels, so it creates less thermal pollution and CO₂ release.

• The three areas that have the greatest potential for energy savings are building design, industrial energy use, and automobiles.
• These three energy uses account for 85 % of the current consumption in the USA, so efficiency improvements will have the biggest impacts here.
• Building design - Heating, cooling, and lighting of buildings accounts for about 27 % of all energy use. One way to conserve energy in buildings is to use more passive solar design, i.e., build with most windows facing south, install window overhangs or awnings, use high R-value insulation in walls, double pane glass, etc. (See Chapter 17)
• Industrial energy use - Industrial energy use accounts for 37 % of all energy use. In the 1990's, industrial output has climbed while energy use by industry has stabilized; this means that more goods are produced per unit of energy today than in the 1970's. Industry has become more second-law efficient since the 1970's, due to the use of cogeneration facilities, solar energy, more efficient pumps and motors.
• Automobile design - Highway vehicles accounts for 21 % of all energy use. In 1970, the average car got 14 mpg; today the average is 28 mpg (highway driving in both cases). Cars have become more fuel-efficient, without impairing anyone's ability to drive around. Some cars now get 50 mpg, and it is possible to get 100 mpg in the future.

• There are two choices ahead for energy policy in the USA: The hard path and soft path.
• The hard path means building more power generating capacity to meet an increasing demand for energy by a growing population in the USA. It is "hard" because it means increasing the "hardware" needed to make power. This option will require more money to be spent on increasing capacity.
• The soft path means becoming more energy efficient than we have been. By encouraging conservation and increasing energy efficiency, we can make more goods and provide more services with the same amount of energy. This path is "soft" because it means not building more power plants, but changing the behavior of people and the energy efficiency of machines. This option will save energy and thus save money.

Ecology In Your Backyard

• How can you improve the energy efficiency in your life? Try some of these ideas:
• Do you drive a car when you could ride a bike or walk instead? Both driving and biking produce CO₂, but driving contributes more CO₂ and from a different source (fossil fuels) than biking or walking. (When biking, the CO₂ comes from the food you have eaten, but that carbon came from the atmosphere very recently; the car's CO₂ came from fossil organisms, so it is being reintroduced into the atmosphere after 300 million years of storage in the Earth).
• How is your water heated? Most homes and apartments have electric water heaters, which are wasteful because water must be heated twice: first at the power plant to make steam to turn the generators, then later to make the water hot at your house. A better idea is to use natural gas or solar. Solar is by far the best choice, but installation of a solar hot water heater can cost $5,000. This amount of investment can be recovered in 10 years of fuel bill savings, however.
• What kind of light bulbs do you use? If you use the traditional incandescent bulbs, you are wasting money and contributing to global warming as well. Compare the energy efficiency of fluorescent and incandescent bulbs in Table 15.1 in the text. If everyone switched to compact fluorescent bulbs from incandescent, the amount of energy used and CO₂ released would both decrease. Again, compact fluorescent bulbs cost more initially ($7.00 or more per bulb), but they last much longer and produce the same amount of light as an incandescent, with a lot less energy used.
• Please respond to these questions or send thoughtful examples and comments to:

Hardcopy Links In The Library

• Fickett, A.P. 1990. Efficient use of energy. Scientific American 263 (3): 157-163.
• Lovins, A. B. 1990. The negawatt revolution. Across the Board, September 1990, pp. 18-23.
• Nixon, W. 1991. Energy for the next century. E Magazine, May/June 1991, pp. 31-39.
• White, D.C., C.J. Andrews, and N.W. Stauffer. 1992. The new team: Electricity sources without carbon dioxide. Technology Review, January 1992, pp. 42-50.

Ecolinks On The Web

• http://www.homepower.com/ - Homepower Magazine. The hands-on journal of home-made power. Surf here to find out how some people are living a more energy conservation minded lifestyle "Off the Grid".
• http://sorrel.humboldt.edu/~ccat - Humboldt State University's Campus Center for Appropriate Technology. This site features an on-line tour of a campus building designed with energy-efficiency in mind, from solar hot water heaters to organic gardens.
• http://www.eren.doe.gov/ - US Department of Energy - Energy Efficiency and Renewable Energy (EE) Programs. This website has links to a variety of other websites for a diversity of organizations and agencies that specialize in energy efficiency. You may also email an energy expert here about specific questions that you may have.
• http://www.energy.ca.gov/ - Access Energy, the Internet information service of the California Energy Commission. At this site you can take a energy education tutorial ("Energy Quest"), or learn about energy efficiency. California has made the greatest strides of all the fifty states in promoting energy efficiency and alternative sources of energy. Over the next 20 years, California's population is expected to increase from nearly 30 million in 1990 to more than 43 million in 2011. As a result of this addition of nearly 4 million households, energy demand will increase by 29 percent. Energy efficiency is expected to provide three-quarters of the increased electricity needs. Since 1977, building and appliance efficiency programs administered by the California Energy Commission have saved more than $11 billion in energy costs. By 2011, savings in the electricity supply system, natural gas market competition and new construction and transportation sectors, can grow to more than $43 billion - a significant source of funds for other economic activities within the state.
• http://www.eia.doe.gov/neic/press37.html - US Department of Energy Report on Compact Fluorescent Lighting Technology. Potential Residential Energy Savings Substantial With Compact Fluorescent Lighting Technology - read about how much energy and money you can save with compact fluorescent bulbs.
• http://fcn.state.fl.us/fdi/fdi-home.htm - The Florida Design Initiative. This is a group of architects based at Florida A&M University in Tallahassee, FL that are out to change the standard housing and building designs in Florida and elsewhere to more energy efficient standard construction practices.
• http://www.acadia.net/sunco/ - American SunCo, Inc. Solar Energy Research Development and Consulting company. These people manufacture the SunTracker 8 system of moving photovoltaic panels for more efficient solar electric energy production.
• http://www.ccnr.org/amory_figure_2.html - The Hard and Soft Energy Paths -- according to Amory Lovins. Lovins is a physicist who came up with the terms hard and soft paths. This is an online graphic version of his explanation of the choice in energy policy that we must make. Also check out his keynote address to the Green Energy Conference in Montreal 1989: "The Negawatt Revolution" reproduced in full online here: http://www.ccnr.org/amory.html
• Note: If any of these links are not working, please see if alternative links are available at the Ecolink Update Site.

Ecotest Online

1. The greatest use of energy in the United States is for:

a. Industrial processes

b. Home heating and air conditioning.

c. Automobiles

d. All of these are correct

2. One proven way to avoid shortages of energy in the future and save money at the same time is to:

a. choose the "soft path" over the "hard path" for our future energy policy.

b. use secondary recovery methods to get more oil from old wells.

c. build more small-scale hydroelectric plants.

d. None of these choices will really succeed.

3. Ultimately, all the energy used on earth is derived from:

a. sunlight.

b. abiogenic production of organic compounds.

c. electromagnetism produced by Earth's rotation.

d. nuclear reactions in Earth's core.

4. The United States has 5 % of the world's population and uses ________ % of the world's energy, mostly from non-renewable energy sources.

a. 25

b. 75

c. 10

d. 50

5. When an industrial plant, such as a paper mill, produces steam for heat and electricity on-site, this is termed:

a. dual-fuel operation.

b. cogeneration

c. simultaneous fuel utilization.

d. a power cooperative.

6. The measurement of energy used per unit time is called ____________________.

a. kilocalories

b. kilowatt-hours

c. power

d. first-law efficiency

e. second-law efficiency

7. One _____________ is equal to the heat needed to raise 1 g of water 1 ^oC.

a. joule

b. calorie

c. kilocalorie

d. BTU

e. kilowatt-hour

8. The total energy consumption in the USA in 1994 was _____________________.

a. 31 exajoules

b. 43 exajoules

c. 22 exajoules

d. 14 exajoules

e. 86 exajoules

9. Any process that uses heat to do work is called _________________________.

a. thermodynamically inefficient

b. a heat engine

c. second-law inefficient

d. a frictional force

e. High-quality energy process

10. Which of the following systems has the highest level of entropy?

a. Gasoline in a car's fuel tank

b. Glucose in a candy bar

c. An incandescent light bulb that is illuminating a room

d. A stationary car at the top of a hill.

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