Introduction
Energy is usually defined as the ability to do work. This is an anthropocentric and utilitarian perspective of energy; however, it is a useful definition for engineering where the aim of machines is to convert energy to work. As a more general description, we would say that energy is a fundamental entity whose availability and flow are required for all phenomena, natural or artificial.
An understanding of how energy is generated and measured is central to our decisions concerning the use and conservation of energy. Large-scale production of energy evolved over centuries but grew radically in the last 400 years and especially since the Industrial Revolution. A century of development and commercialization of electric power technology has ensured an easy supply, and continuous measurement.
Energy is derived in usable forms from numerous sources, such as flowing water, fossil fuels (e.g., coal and natural gas), uranium, and the sun. Electricity is a widely used form of energy. Any of these sources can be used to generate electricity. Liquid fuels such as gasoline and diesel derived from fossil fuels are a widely used source of energy. These fuels form the basis of our easy transportation. A complete understanding of the complexities of the energy systems within the natural environment requires knowledge of some basic physics and chemistry. This is discussed later in this unit in the sections under "Science Notes."
Energy Systems
An energy system may be thought of as an interrelated network of energy sources and stores of energy, connected by transmission and distribution of that energy to where it is needed. The transformation from stores of energy in food to work, and subsequent dissipation of energy is an example of such a system. The starting point of all energy in this "food chain" or "energy chain" (considering only the vegetable and cereal part of our food) is the sun.
Figure 1: Natural Energy System.
In Figure 1, each of the arrows shows transformation or transmission of energy -- that is, the energy changes form or is moved from one place to another. Plants and humans are the agents shown that store and/or transform the energy.
This natural energy system is part of a larger system that includes nutrients from the soil as input, other energy for cooking as input, etc. Figure 1 is drawn to show the parts of transformation of this initial solar energy up to its final dissipation and one storage system (fossil fuels). A complete concept map would show all the other factors. The numerous energy systems in nature include the food chain, the climate and ocean systems, and the cycles of various materials such as water, carbon, and nitrogen.
Most of the energy systems currently in use, both natural and man-made, originate in the Earth-Sun relationship. The fossil fuels we use today are stores of solar energy. Photosynthesis is an example of solar radiant energy transformed into stores of chemical energy that plants and animals (including humans) use to maintain themselves. The conversion of solar radiant energy through photosynthesis is a fundamental natural energy system. The food chain is an example of a natural, solar-based energy system that has sustained human life on Earth. Often we take for granted that energy will always be available for us to use. We fail to recognize the complexities of the energy systems that drive these environmental phenomena and sustain life on Earth. We are intricate parts of the system as end users, completing the dissipation of energy to forms that are so spread out that it is impossible to use that energy again.
Fossil fuels (coal, oil, gas) result from a transformation of plant and animal material over millions of years. The solar energy originally stored in the plant or animal is eventually converted into energy stored in carbon and hydrogen bonds of the fossil fuel. The fuels that took millions of years to make are being used at an enormously rapid rate. Figure 2 is a representation of the use of fossil fuels over time, including an estimation of how long they might last.
Figure 2: Fossil Fuel Timeline.
Source: Clark, Mary E. Ariadne's Thread. St. Martin's Press, New York, 1989.
Reprinted with permission of Macmillan Ltd..
Fossil fuels and fuels like uranium are "spent" once they are used to obtain energy. These are called non-renewable sources of energy. Although new plants can be planted that eventually turn to coal, the process takes millions of years and that is why coal and other fossil fuels are considered non-renewable. Solar and wind energy arrive or circulate air on the Earth everyday. These sources are called renewable.
Wood and trees used as fuel are called renewable, because they can be replanted. However, when we use them so that the rate of use far exceeds the rate of replenishment (trees take time to grow), referring to these sources as "renewable" can be a misnomer!
Energy use in each human activity has grown exponentially since the early days of human civilization. For example, technological capabilities enable us to travel more and process more food. Figure 3 shows the amount of energy (in calories) we spend for each calorie of food we get. It shows that technologies have mechanized and made large production systems of cultivation and fishing. These systems involve large expenditures of energy, as seen in Figure 3. The figure shows that for wet rice production in Asian countries, it takes between 0.02 and 0.1 calories of energy to produce 1 calorie worth of rice as food. Large-scale food production consumes enormous amounts of energy. For example, it takes over 2 calories of energy input to produce 1 calorie worth of eggs in large-scale farms, and it takes 10-15 calories of input for every calorie worth of beef produced in the U.S.. Note how the intensity of energy consumption for U.S. food production has grown almost ten-fold in the 20th century! Add to this the fact that for every calorie of energy our body gets, we have to take in over 5 calories worth of food!
Figure 3: Summary of the energy required for various types of food production.
Source: Clark, Mary E. Ariadne's Thread. St. Martin's Press, New York, 1989.
Reprinted with permission of Macmillan Ltd..
Table 1 shows that as we become more industrialized, each human consumes more calories daily as well. This, along with population increase, has resulted in an enormous increase in the daily calories consumed by humans.
Economic systems / Years Ago / Maximum global population* (approx.) / Daily calories/ person† / Global daily calories consumed byhuman population
Hunter-gathering (before cooking) / 1,000,000 to 500,000 / 1 million / 3000 / 3 x 109
Hunter-gathering (after cooking) / 500,000 to 10,000 / 10 million / 8000 / 8 x 1010
Early agriculture / 10,000 to 2000 / 300 million / 15,000 / 4.5 x 1012
Middle Ages / 1000 / 500 million / ~ 8 x 1012
Europe 10%
Rest 90% / 23,000
15,000
Today / 0 / 5000 million / 2.8 x 1014
North America
Eur, USSR, Japan
Third World / 5%
18%
77% / 314,000
157,000
15,000+
Notes:
*R. Leakey and R. Lewin, Origins (New York: E.P. Dutton, 1977) p. 143; J. Weeks, Population: An Introduction to Concepts and Issues, 2nd edn(Belmont, CA: Wadsworth, 1981) p. 46
†Harrison Brown, The Human Future Revisited (New York: W.W. Norton, 1978) pp. 30-3, with per capita figures for industrialized nations upgraded from 1970 to 1980 levels.
Table 1: Per capita and global energy consumption for different types of human economies.
Source: Clark, Mary E. Ariadne's Thread. St. Martin's Press, New York, 1989. p. 102.
Reprinted with permission of Macmillan Ltd..
History of the Energy System
In the Beginning: Pre-Industrialization
The muscle power of human beings and animals was the first application of energy by humans and the food chain was the energy system in use. Humans have long "designed" energy systems with the goal of producing the most work possible with the least amount of human effort to generate the energy.
Pre-Industrial society depended primarily on muscle power and biomass for their energy needs. Biomass consisted primarily of wood or peat and its energy delivery had a low efficiency. Amory Lovins, an expert on energy, states, "Most of the energy generated by wood or peat went up in the chimneys rather than into the room or cooking pot of pre-industrial societies."
Animal power in the form of horse mills, wind power in the form of windmills, and water power with the use of a water wheel were major energy sources harnessed until the 19th century; especially for "industrial uses." Wood and charcoal were the main fuels for cooking, heating, and other domestic uses, but coal and oil were available as well. "In the Middle East crude oils have been known for millennia from natural seepage and pools, but they were used only rarely as fuels, and more frequently as protective coatings."[1] Coal has its origin in "the lithification of peats produced by accumulations of dead plant matter in wetlands. Difference in original vegetation and, more importantly, in magnitudes of durations of transforming temperatures and pressures, have produced a large variety of coals."[2] As early as the 13th century, coal pits were mined and coal energy was used specifically for the forcing and smelting of metals. In the 1600's, England experienced an energy crisis due to a shortage of wood and began using coal as a substitute fuel source for domestic purposes. Even in the 1700's, wood was the major fuel source in colonial America.
The Industrial Revolution
The quest for more powerful energy sources was propelled by the inventions and discoveries of the Industrial Revolution. As sophisticated mechanical inventions were made, a large reliable and seemingly inexhaustible source of energy became necessary for industrial uses, and transportation. The need for large quantities of accessible, dependable, and transportable energy encouraged the exploration of energy sources. The inventions of the Industrial Revolution provided the equipment to further mine or drill the already visible deposits of coal and oil.
Steam power was developed in the 1600's in conjunction with coal mining to help pump water out of the mines. It had been known since ancient times that heat could be used to produce steam, which could then do mechanical work. However, it was only in the late eighteenth century that commercially successful steam engines were invented. The first commercially successful steam engine was invented by Thomas Savery (1650-1715), an English military engineer. In 1712, this engine was refined by Thomas Newcomen (1663-1729), another Englishman. The Newcomen engine was widely used in Britain and Europe throughout the eighteenth century, but had very low energy efficiency.
A greatly improved steam engine was designed and built in 1763 by James Watt who was asked to repair a Newcomen engine. Watt built and then sold or rented his engines to mining companies, charging them for the "power" in the rate of work the engine produced. Today, the unit for power is called a Watt.
The sun was also studied as an energy source in the 18th century. In 1767, the first solar thermal collector was developed by the Swiss scientist Horace de Saussure. Solar thermal power was used in the American west as an energy source for cooking until oil and natural gas became a more reliable way to generate energy. For simple cooking solar energy was absorbed by black cast iron pots. Solar thermal collectors were also used in the form of hot boxes to cook food.
In 1839, Alexandre Becquerel discovered that an electric current could be generated when certain elements were exposed to light. The scientific explanation of this phenomenon by Albert Einstein, called photoelectricity (light-induced electricity), came much later in 1905. Photoelectricity is the basis of the photovoltaic cells, now used to convert light into electricity. Despite the century and a half since it discovery, photovoltaic means of generating electricity have not been developed with enough vigor for it to become a major source of electricity. This is because the material technology for photovoltaic panels developed slowly. As coal and other fossil fuels were easier to use, and available in plenty, not much effort has gone into photovoltaic research.
Until the early 1800's our understanding of the science of energy was not well developed. The theory at that time was the caloric theory, which said that heat is a substance called "caloric" that flowed from hotter to colder bodies. In the 1840's the English physicist James Prescott Joule did a long series of experiments that showed that heat is a form of energy. Joule found the relationship between a unit of mechanical energy and a unit of heat. This helped Joule finalize what chemists and natural philosophers had come to believe--that the total energy in the universe is constant, although energy is continuously changing forms.
The study and invention of the heat engine and steam power established and confirmed the Laws of Thermodynamics. From 1840-1880, Joule, Lord Kelvin, and James Clark Maxwell in England; Sadi Carnot and Rudolf Clausius in France; and Ludwig Boltzmann in Austria formulated a theory of heat engines, laying the foundations of Thermodynamics, literally the science of "motion from heat." (Thermo=heat and dynamics=motion).
In 1820, the advances in mechanical and materials engineering made the railroad the most efficient and fastest means of transportation. Coal and wood were used as the primary fuel source for the steam engine. The locomotive also changed society's perception of travel and transportation.
Wind energy was developed on a large scale in the United States as an energy source for farms and railroad stations, using tall windmills to pump water from underground wells. There were specific design developments that made these windmills more efficient, although they still generated relatively little power. The height of these windmills helped to ensure they caught the wind and a tailfin generally kept the fan facing the wind.
Another result of the Industrial Revolution was an energy distribution infrastructure built into cities that promoted domestic convenience. As early as 1816, natural gas was piped into cities for domestic uses such as cooking, home illumination, and street lighting. The steam engine was used to pump water into homes and sewage away from homes. The city was undergirded with networks that usually began with water pipes and gas lines and gradually expanded to include sewers, electrical conduits, and telephone lines.[3]
In 1859, when petroleum was drilled in Titusville, Pennsylvania, an apparently plentiful energy source began to replace coal. Oil was distilled into kerosene (referred to as coal oil) and used as a lamp oil. It replaced dwindling supplies of whale oil used for lamps. There were many reasons oil became a more desirable fuel source than coal: it was easy to obtain and transport; it emitted less particulate pollution than coal; it replaced scarce whale oil as a fuel for lamps; and coal had become an unreliable fuel source because of the labor issues surrounding the mining of coal. Miners were striking for safer work environments and more money, which affected the amount of coal available to the consumer.
But the most significant use of crude oil was as the liquid fuel for the internal combustion engine, designed in 1861 by Nikolaus August Otto. The internal combustion engine became one of the most influential inventions of the Industrial Revolution. Although this engine is low in efficiency, it could produce enough work to move a large metal vehicle far distances. The fuel of the internal combustion engine was also easier to use than, for example, shoveling coal into a furnace to power a locomotive. This was the beginning of the use of liquid fuel to advance transportation.
In 1879, Thomas Edison invented the incandescent light bulb -- a major step in the human use of storable energy leading eventually to large-scale electrification. Electricity is similar to a liquid fuel in that it can be transported easily (although not efficiently) from one place to another. One of Edison's goals was to make electricity affordable for all homes. Edison began with the distribution of electricity through a direct current (DC). This meant that electrons would flow one way through a wire to bring electricity to a home; however, a good portion of the energy was lost as the electrons moved through the wire. This loss of energy using direct current to move electricity meant that power plants had to be built close to the homes the plant serviced and was eventually considered impractical.
Nikola Tesla, an inventor employed by Edison, discovered that electrons would alternate or travel back and forth on a wire and travel longer distances with less energy loss. This was called alternating current (AC) and had an advantage because AC could be more easily generated. Edison had so much money invested in his DC power plants that he discredited Tesla's alternate current as dangerous -- thus beginning a "war of the currents." Tesla eventually joined forces with George Westinghouse and began developing power plants using alternating current (AC).