Introduction
History of the Energy System
Human Energy Needs
Science Notes
Energy Transformation
Measuring Matter, Force, & Energy
Energy Accounting & Balance
Fundamental Forces of Nature
Energy and Chemical Stability
Chemical Formations
Chemistry of Fossil Fuels
Energy Use, Efficiency, and the Future
Energy Sources, Technologies, & Impacts
Exercises
Internet Links
Other Resources
Energy System PDF
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Energy Sources, Technologies, and Impacts

Historical, geographical, and political contexts have led to the adoption of different fuels and related technologies to produce energy. As described in the history section, we have progressed from using above ground, easily accessible sources of energy, such as wood and direct solar energy, to fuels such as coal and oil that require large infrastructures and energy to mine and process before extracting energy from them. Table 9 at the end of this section outlines different energy sources and the information relevant to the environmental impact of these sources.

As described before, over 95% of the world's energy requirement is currently met by fossil fuels -- coal, oil, and natural gas. In various technologies, they release energy by the process of combustion. Major byproducts are carbon dioxide and various residuals such as fly ash. The environmental problems relating to fossil fuel use are described in detail in the Atmospheric System. Environmental pollution, especially air, global climate change, and resource depletion are the greatest drawbacks of heavy fossil fuel use. Another problem (particularly for the U.S.) is dependence on foreign resources. Development of oil in the Atlantic has been a response to the U.S. need for fuel independence. Alaskan oil exploration involves destruction of pristine land and unique natural habitats.

Coal burning, while a simple technology, has numerous side effects in addition to carbon dioxide emission noted above. Coal occurs in combination with sulfur in many places. High sulfur coal, when burned, produces sulfur dioxide, which is the source of acid rain. Countries like the U.S. regulate the amount of sulfur that can be in coal used for power production; therefore high sulfur coal must be cleaned before it can be burned. Coal burning also produces large amounts of particulates in the form of fly or bottom ash, which must be disposed of or recycled.

Currently, coal power plants with the encouragement of government and to the liking of environmental groups, are developing ways to burn coal and reduce the large amount of coal byproducts. Coal-gasification is one such technology. Coal is pulverized, mixed with water and then combined with gases such as nitrogen and oxygen. The gaseous mixture is then heated and a synthetic gas is produced as the particulates or ash falls to the bottom of the burner. As the gas cools, sulfur particulates are separated and used to make sulfuric acid. This is an example of getting more than one product from a fuel source. The gas is then used to produce steam that spins turbines and generates electricity.

The energy in the bonds within the nucleus may be released through nuclear fission or nuclear fusion reactions. The technology used to produce nuclear power is based on nuclear fission. The fuel for fission reactions are heavy nuclei, particularly uranium, thorium, and plutonium (a material that no longer occurs in nature, but of which the U.S. and states of the former Soviet Union have enormous supplies because of the bomb programs). The U.S. led the world in nuclear power production, producing about 728 billion kilowatt-hours. France ranked second, with 375 billion kilowatt-hours, and Japan was third, at about 309 billion kilowatt-hours produced.1 In 1999, the nuclear share of total electricity generation for France was 75%, for Japan was 33%, and for the U.S. was 20%.2 Nuclear energy is often considered the desirable alternative to coal, because it does not release carbon dioxide. The materials involved in nuclear power are, however, heavily radioactive varying from uranium, the starting material, to the various byproducts during all phases of the energy production cycle, and the last byproduct, generally termed "radioactive waste." These byproducts are "radioactive," that is, they emit particles of radiation and high-energy electromagnetic radiation, such as gamma rays. This quality makes the materials dangerous. People and other parts of nature exposed to this radiation can suffer serious long-term damage. Many of the radioactive materials are also very long-lived, continuing to emit radiation for hundreds of years or more. Nuclear fission power technologies have been designed with numerous safeguards and extreme caution as to be "safe." However, if the global economy were to depend predominantly on nuclear power, radioactive material transport over air, land, and water could pose a very large exposure risk. Radioactive waste disposal is also a challenging problem, as it has to be kept isolated for thousands to millions of years!

Nuclear fusion is the reaction responsible for the production of energy in the sun. Hydrogen is the main fuel for energy source. In fact, the sun is a huge nuclear fusion reactor. But the extreme high temperature and pressure needed for fusion to take place has been a formidable obstacle to designing fusion systems on any usable scale. Nuclear fusion would not produce many radioactive wastes like fission but will produce radioactive tritium (an isotope of hydrogen) for which we would have to design safeguards.

Hydropower, wind, direct solar radiation, and geothermal power are all renewable resources. Of these, hydropower is the best developed. Starting with water wheels that converted the kinetic energy of running water into various kinds of motion, to vast projects like the Hoover Dam, the technology for conversion of hydropower to electricity has long been explored. While it produces no byproducts, hydroelectric power requires waterfalls or dams with a large volume of flow. In the case of dams built for hydropower, the devastation of land and distinctive ecological niches can be large. The conflict between development of cheap hydroelectricity, preservation of habitat, and economic interests are encapsulated in the example of the endangerment of salmon in the Pacific Northwest, due to extensive dam building on the Columbia River. Hydropower can also come from hot water springs, where the kinetic energy of water comes from the heat at the Earth's core.

The Sun and Energy
Except for nuclear energy, geothermal energy from the Earth's hot core, and energy from running water accelerated by the Earth's gravitation naturally (waterfalls) or artificially (dams), all other energy on the Earth comes from the sun. The sun's energy also plays a principal role in hydropower by driving the water cycle. The nature of solar radiation -- electromagnetic energy from the sun -- is described in detail in the Atmospheric System.

On average, one square meter on the side of the Earth facing the sun receives 1400 W (Joules per second). In a 24-hour period the total amount of energy reaching the upper atmosphere is 14.4 million calories. One-third of it is reflected back into space by cloud cover, and the rest, traveling through the atmosphere, powers the wind and water cycle, and drives the Earth's climate. The total sunshine entering our atmosphere every year is equivalent to 500,000 billion barrels of oil or 800,000 billion metric tons of coal! On a bright sunny day in the northern latitudes, when the sun is at the highest point, about 1000 Watts/ m2 reaches the ground. On cloudy days, it can be as low as 200 Watts/m2.

The main problem with solar energy for high levels of use comes from the fact that it is so diffuse and spread out, and has to be collected over large areas. In effect, this is what the foliage of plants does, storing some of the energy through photosynthesis. It is important to note that only a small fraction of the solar spectrum -- in the violet and some in the red region -- is used for photosynthesis. Sunlight has a large quantity of energy in the green and yellow regions, most of which is reflected by the leaves. However, it is the capture of energy through photosynthesis, combined with elements like carbon, oxygen, and hydrogen from the Earth and its atmosphere, which results in biomass immediately. This biomass eventually results in a favorite fuel of today (coal) after millions of years of "processing" by the Earth. Oil and natural gas are similarly produced from organisms buried for millions of years under rock foundations. Ancient humans used the gentle, spread out solar energy and biomass for drying, cooking, and heating. Today's needs demand much larger quantities concentrated in space and time. This tendency promotes rapid depletion of the solar "capital" invested into coal formation over millions of years.

One of the less thoughtful energy uses in our convenience-dominated society is the use of "high-quality" and concentrated energy even when "low-quality" spread-out energy would suffice. A good example is our use of fossil fuel energy driven clothes dryers, even in the summer when clothes could just dry on a clothesline from direct solar energy. In the ideal use of energy, we would distinguish between the needs requiring high or low "quality" energy. Using energy at the appropriate level and from renewable resources is what is referred to by Amory Lovins as a "soft energy path." One soft technology philosophy argues that we adapt our life styles to suit the energy available to us.

Figure 23 is derived from the proceedings of UNERG, the United Nations Conference on New and Renewable Sources of Energy held in Nairobi, Kenya, in 1981. The figure shows the different grades of energy derived from direct solar energy. Passive collectors are static and collect heat energy that falls on them. Active collection involves mechanisms for storing and/or following the direction of the sun's rays to receive the maximum energy. Many ancient civilizations, including the Egyptians, Pueblo and Anastasi Indians, and Greeks, built their houses to take maximum advantage of the sun's apparent movement in the sky. However, as more technological energy systems developed, building with the sun's position in mind became a lost art, especially in industrialized countries.

Figure 21: Solar energy collection options.

Photon collection refers to collecting the energy through natural or artificial chemicals -- in the form of biomass (firewood, animal dung, and waste materials) or in water or chemicals such as certain salts, which hold the heat.

To convert solar radiation into electricity, we use photovoltaic cells. Photovoltaic cells are based on the phenomenon of photoelectricity -- that light can release electrons from certain materials. Using these materials, light can be converted directly into electricity. This phenomenon was discovered in the late 1800's by George May in Ireland. Rudolf Hertz in Germany produced the first photoelectric cell soon thereafter using the element selenium and Albert Einstein explained the physics of photoelectricity in 1905. However, the first practical solar cells were only developed in the 1950's by the Bell Telephone Company. The early version of the cell cost thousands of dollars per watt of electricity yielded. The first large scale testing occurred in space on the NASA satellite Vanguard in 1958.

The conversion efficiency (amount of electrical energy output per input of light energy) of the largest photoelectric cells is still below 20%. This means we have to collect sunlight over a large area for any useful application. For example, if the conversion efficiency is 15%, we need a 6.5 square feet of photovoltaic material to power a 100-watt light bulb.

Solar technologies have made the largest inroads in space applications. Collection of solar energy by satellites for Earth's applications have been long considered. The basic idea is that if the collection were in a geosynchronous orbit around the Earth (35,890 km or about 22,500 miles above the equator), we could capture the energy before so much of it was absorbed by clouds and the atmosphere. Various technical difficulties have essentially halted this SPS (Solar Power Satellite) project.

If we followed a philosophy of ecologically friendly design, the best use of solar would be in the passive or active collection, rather than the conversion to electricity. However, as a society, we have chosen to use electricity as the form of energy for almost all applications and a large source of our environmental problems -- pollution, resource depletion, habitat loss -- lies in this societal choice.

Wind is derived from solar energy moving large masses of air. The two basic phenomena that are responsible for wind patterns are a large global circulation and local effects. Cool polar air is drawn towards the tropics to replace lighter, warmer air that rises and moves towards the poles. This creates areas of high and low pressure and circulation patterns are set up differently in the northern and southern hemispheres because of the Earth's rotation. This sets up the global patterns, such as the trade winds. Locally, the circulation depends upon whether the air is over land or water. Air over oceans and large bodies of water is cooler than that over land, and cooler air is drawn toward the land as the warmed air rises. Together these two patterns produce movements of enormous complexity.

The wind represents kinetic energy of air arising from the thermal energy of sunlight. A large part of this energy is lost in various functional forces, and only a small portion can be captured by windmills. High tech windmill designs have been developed by various aircraft companies, because of their expertise in wind dynamics.

In summary, the sun it still our most valuable source, powering most of our energy sources. Our survival may depend upon a wise and judicious use of the numerous, versatile sources the sun provides.

Life Cycle of Electricity Generation
Electricity is a form of energy that has become the core of our industrial societies. The ease with which it can be transported, stored, controlled, and used has changed the fabric of society. This section looks at the generation of electricity from various common fuel sources.

Electrical energy is the combined potential and kinetic energy of electrons in materials. Materials that have electrons that are mobile, rather than being confined to orbits around the atomic nucleus, can conduct electricity. Metals are prime examples of conductors. A discovery by Michael Faraday of England in 1831 is the cornerstone of our large-scale electricity generation. Faraday discovered that when a conductor moves in a magnetic field, an electric current is produced in the conductor. This Faraday's Law, and the fact that we can make large magnets is the basis of an electric generator. If we can use an energy source to move a conducting coil of wire that is placed in a magnetic field, the current produced in the wire can then be transported to deliver electric energy. Figures 24.A-D demonstrate the sequence of electric power production and distribution from four sources: running water, coal, nuclear fission, and wind.

Figure 24.A-D: Electricity Generation Methods

A power plant consists essentially of a huge generator -- a gigantic coil of wire capable of rotating in the space between the poles of an enormous horseshoe magnet. The motion of the coil is caused by a shaft connecting it to a turbine, whose rotation spins the coil. In all power plants then, the energy obtained from the sources has to cause the turbines to turn, which then rotates the coil. This energy is delivered directly to the turbines by the falling water in a hydroelectric power plant, and by the wind in a wind farm. In the case of coal and nuclear fission, the primary energy is used to transform water into steam or high-pressure water, which then drives the turbines. Figures 24.A-D illustrate the steps prior to this, and show the similarity of the final steps of electricity distribution for all sources.

The current from the coil is then carried to the final place of use through transmission and distribution lines. Some of the energy is lost along the wires. To minimize this loss, the electricity is transmitted at very high voltages (thousands of volts) along transmission lines and the voltage "stepped down" near the location of use using transformers. Electricity is then carried over smaller distribution lines to homes and businesses for use. The huge steel towers typical of transmission lines are a familiar sight, as are the distribution lines -- the smaller wires near buildings attached to "telephone poles." Transformers are the ceramic structures on local distribution line poles.

Impacts of Energy Production and Use
Energy production and use produce some of the most lasting and significant environmental effects. Some of these are discussed in detail in the Atmospheric System. Each source of energy brings with it some impacts. Here we summarize the overall nature of the impacts.

Fossil fuels cause some of the largest impacts. In order for a typical 500-Megawatt plant to produce about 158 Terawatt-hours (tera = 1012) of electricity per year, it takes 1.5 million tons of coal and 0.15 million tons of limestone. It produces emissions to the air of 1 million tons of carbon as carbon dioxide, plus 10000 tons of ash and 193000 tons of scrubber sludge -- both of which contain large quantities of sulfur. (check numbers) Global climate change, resulting from atmosphere increases in CO2, is described in detail in the Atmospheric System. Even seemingly slight temperature changes can cause changes in weather patterns, climate, melting of polar ice caps, and sea-level rise.

Figure 25: Industry Emissions, in thousands of short tons.
Source: Energy Information Agency

Gasoline combustion releases pollutants that, under certain conditions, give rise to photochemical smog and high levels of atmospheric ozone. Impacts from oil drilling include destruction of ecosystems. The many impacts of extensive fossil fuel use is discussed in detail in the Atmospheric System.

From the mining and processing of the fuels to the production stage, nuclear power requires the handling of radioactive material. The potential for accidental release of these materials and exposure to people, and the problem of long-term disposal of radioactive wastes, are the main environmental concerns of nuclear power.

Hydroelectric power causes disturbances in ecosystems from dams and large land use. A striking example of the loss of biodiversity is the rapidly declining populations in the remaining species of salmon in the Pacific Northwest. (See exercise: Salmon Management in the Pacific Northwest.)The Three Gorges Dam project currently underway in China requires the displacement of one million people, in addition to the devastation of land and ecosystems. But the People's Republic of China has made rapid industrialization a national priority, and this requires an enormous development of power production systems.

Alternative energy sources, such a wind and solar energy, also have large land use implications.

Energy Source
Force of Origin
Energy production
Usage
Environmental Impact
Oil, Petroleum Electromagnetic forces in atomic bonds Non renewable · 38% of world's consumption in 2000
· Easily transported
· Large portion in transportation industry
Refining and consuming produce air, water, and solid waste pollutants
Natural Gas Electromagnetic forces in atomic bonds Non renewable · 20% of world's consumption in 2000
· Flexible for use in industries, transportation, power generation
Produces fewer pollutants than oil and coal, and less CO2
Coal Electromagnetic forces in atomic bonds Non renewable Primary resource for electricity Produces CO2 and other air, water and solid waste pollutants
Biomass: Wood and organic waste including societal waste Electromagnetic forces in atomic bonds

· Renewable
· In terms of timber, it is easily harvested and abundant in certain areas; but it takes a long time to grow a tree.

Low energy potential relative to other resources · Burning emits CO2 and other pollutants
· Possible toxic byproducts from societal waste
· Loss of habitat when trees harvested, unless sustainable tree farms
Hydro-electric Gravitational force of water · Renewable
· Clean resource with high efficiency
· Influenced by climate and geography
Low economic cost, though high start up costs Destruction of farmlands, dislocation of people, loss of habitat, alteration of stream flows
Solar Power (photo-voltaics) Electromagnetic energy from the sun

· Renewable
· High economic cost particularly in terms of start-up
· Dependent on climate and geographical location
· Need a storage system for the energy to ensure reliability
· Not advanced enough for global use

· Technology is already in use for remote applications and non-centralized uses where it is economically competitive with alternatives
· Unlimited resource that is clean, efficient, safe, and renewable
Large land use
Solar Power - (solar thermal) Electromagnetic energy from the sun

· Renewable
· Central-thermal systems to convert solar energy directly to heat
· More competitive economically than photovoltaics
· Dependent on climate and geographical location

· Solar energy technology not advanced enough for global use
· Many industrial plants use solar
Geo-thermal Gravitational pressure and nuclear reactions in the Earth's core · Extracts heat from underground masses of hot rock.
· Technology is still undeveloped.
· Can be geographically dependent
· Consumption is localized
· Efficient
Disrupts natural geyser activity
Wind Power Gravitational & electromagnetic energy from the sun · Renewable
· Unlimited resource that is a very clean process, no pollutants
· Economic cost comparable to current technologies
· System must be designed to operate reliably at variable rotor speeds
· Technology not advanced enough for global societal us

· Aesthetic issues
· N
eeds lots of land
· Possible impacts on birds and their migration patterns
· Some noise pollution

Nuclear Fission Strong nuclear forces in nuclear bonds · Non renewable resource U-235 (uranium)
· Highly technological infrastructure necessary for safe operation
· Production of nuclear energy has a high cost due in part to regulations
· High water usage for cooling
Currently accounts for 10-12% of the world's electricity · Byproduct is highly radioactive and highly toxic
· Produces radioactive wastes that have a long lifetime
· Disposal solution complex technically and politically
· Safety issues in terms of operating a facility with the potential to release radiation to the atmosphere
· Public perception problem in terms of radiation, etc.
Nuclear Fusion Weak nuclear force · Technology is not yet viable and requires research investment
· Technology still not developed enough to make this a viable source
Possibility high for water pollution because of radioactive tritium

Table 9: Energy Sources and related information.

[1] Energy Information Administration, International Energy Annual 1999, DOE/EIA-0219(99) (Washington, DC, January 2001.)

[2] Energy Information Administration, International Energy Outlook 2001, DOE/EIA-0484(2001) (Washington, DC, March 2001.)

 

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  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.