Unconventional energy resources

Unconventional energy resources are forms of energy harvested from sources other than those utilized for the majority of human energy needs. The vast majority of energy produced for human consumption comes from the combustion of fossil fuels, which are materials that form from the decomposition and fossilization of organic material. Unconventional energy resources include both new sources for potential energy generation and new ways to utilize existing sources of energy. Unconventional sources of fossil fuels include oil shale and tar sand, hydroenergy, the kinetic energy of ocean waves, biofuel, and nuclear energy.

Unconventional Energy Resources

Fossil fuels are materials generated by the decomposition of organic matter through millions of years. The remains of dead animals and plants become buried under successive levels of sediment and are subjected to increasing pressure from the weight of material overlying them and to increasing heat generated by chemical decomposition and thermal heat from the earth’s core.

Through millions of years this mixture of organic material will give rise to kerogen, a tar-like material that will further develop into petroleum and natural gas with even more temperature and pressure. Further compression at great depths leads to the formation of coal, a type of igneous rock.

Coal, petroleum oil, and natural gas are mined from pockets within the earth and then shipped to facilities in which they are subjected to combustion. Heat produced by the combustion of fossil fuels is then filtered through turbine engines to generate electricity. Between 80 and 90 percent of global consumer energy is derived from the combustion of fossil fuels.

The major drawbacks to fossil fuels include the production of environmental pollutants, such as carbon dioxide and methane, which leads to global warming and other types of ecological damage. Fossil fuels are a limited resource because it takes millions of years for new deposits to form from organic matter.

As conventional supplies of fossil fuels have begun to dwindle, scientists are working to develop new resources for energy development, often called unconventional or alternative energy resources. Some unconventional energy resources are based on finding new ways to obtain fossil fuels, while others focus on renewable energy, which is energy derived from potentially limitless sources.

Unconventional Fossil Fuels

Several methods have been developed to harvest fossil fuels from unconventional sources or to convert less desirable forms of fossil deposits into usable fuels. Although these unconventional deposits are available in large quantities, they are more difficult and expensive to harvest, transport, and process than are conventional deposits.

Oil sands and tar oils. Vast quantities of fossil fuel deposits are mixed with sand and other minerals, often called oil sands or tar oils. Fossilized sediments in tar oils are in the form of bitumen, a thick, semiliquid material often called tar; only 10 percent of tar sand is composed of bitumen. The harvest of this fossil fuel requires vast amounts of raw material. For each barrel of oil, 2 to 4 tons of tar sand and four barrels of water must be used, creating a significant amount of waste. It is estimated that tar-sand processing produces 300 percent more waste than traditional oil production. In addition, harvesting oil sand requires mining, which leads to environmental damage to vast ecological areas.

Oil shales. Fossil fuels also can be harvested from oil shales, which are sedimentary rock deposits that contain solid kerogen. When oil shale is mined, processed, and subjected to intense heat, petroleum oil can be extracted. Oil shale is more complex than conventional oil to process because the rocks must be crushed and heated before oil can be extracted—a process called retorting. Oil shales have been harvested since the 1970s, but it was not until the 2000s and 2010s that the technology became available to access oil shale in larger quantities. By 2023, the US Energy Information Administration estimated that 64 percent of crude oil production in the United States came from oil shale.

Harvesting oil shale has a number of drawbacks in addition to high cost, including significant environmental impact. Harvesting shale requires more raw material than harvesting raw oil and therefore causes higher levels of environmental damage during the mining process. Oil shale harvesting has been linked to increased levels of water pollution and increased levels of carbon dioxide emissions. In addition, though oil shale accounts for trillions of barrels of potential oil, it is a finite resource that will eventually be exhausted if oil consumption continues to increase at its current rates.

Hydroenergy

The movement of water within oceans, rivers, and streams produces kinetic energy that can be harnessed and used to generate electric energy. A number of methods are used to capture hydroenergy, most of which rely on the same basic mechanism—utilizing moving water to rotate turbine engines—which fuels the generation of electric power.

Hydroelectric power. Hydroelectric power was the most common type of hydroenergy used in the early twenty-first century. It accounted for around 19 percent of renewable energy production in 2019. In 2022, hydroelectric power accounted for 31.5 percent of the renewable energy generation but only 6.3 percent of the total electricity generation in the US. To harvest hydroelectricity, engineers construct a dam such that there is a significant difference in elevation between the water on one side of the dam and that on the other. Water is prevented from falling into the lower level by a series of gates. When these gates are opened, water flowing through channels passes over turbines, which spin to generate electric current. At night, when human power consumption is typically at its lowest, water is pumped from the lower basin into the upper basin, thereby preparing the dam to produce more energy for the next day.

Hydroelectric dams provide a renewable energy source, but the installation and operation of dams causes environmental and ecological damage. Because dams alter water depth, they destroy habitat for many types of birds, aquatic mammals, fish, reptiles, and amphibians. In addition, dams block passageways that are used by certain animals for daily or migratory movements.

Tidal energy. Another way to generate hydroenergy is to use the kinetic energy of tidal movement. In bays and estuaries, tidal energy is harvested using a special kind of dam, a tidal barrage, that functions similarly to a hydroelectric dam but utilizes the movement of tidal currents to push water through the turbine channels. Because tidal barrages utilize the motion of tidal currents, they require less energy to operate than do hydroelectric dams. However, barrages pose a similar risk to the environment by blocking travel for many types of species and by altering water depth, which affects the surrounding habitat.

Another method of harnessing tidal energy is to use a series of turbine engines placed just under the surface of the water. Called tidal turbines, these machines are useful in areas where steady, reliable tidal-current levels dominate. Tidal turbines are similar to wind turbines, but because water is more viscous than air and because tidal currents are more constant than air currents, tidal turbines provide a more reliable source of continuous energy. Tidal turbines are more affordable and less complex than tidal barrages, but the technology is still in its infancy, and most tidal turbine programs are in the experimental stage.

Tidal turbines produce little pollution and do not require significant environmental damage during installation, but research indicates that they may disrupt the movements of fish and other aquatic animals. Research is ongoing to investigate the best ways to implement tidal turbine technology with the lowest level of ecological impact.

Wave energy. Another relatively new and still experimental method for capturing hydroenergy involves utilizing the kinetic energy in ocean waves to drive electric generators. As wind passes over the surface of the ocean, it transfers a certain amount of kinetic energy to the water, thus generating waves. The strength of surface waves therefore varies according to meteorologic and atmospheric conditions.

Several different models of wave power are being investigated for commercial potential. One of the most promising techniques involves the use of a long, floating, tube-like structure with hinged joints that allow the structure to flex and bend in response to the undulating motion of ocean waves. As the sections of the tube bend, hydraulic rams between the sections are forced to compress, pushing liquid through a hydraulic turbine and thereby generating electricity.

Experimental evidence suggests that wave-power generators pose a low level of environmental threat because most of the technology is mounted at the surface of the ocean. The primary area of concern for environmental scientists is that the wave generators may cause noise pollution in the aquatic environment. Wave technology is a relatively recent field, and research is ongoing to investigate the potential environmental effects of long-term operation.

Biofuels

Biofuels are alternatives to fossil fuels and are made from living plant matter rather than from fossilized remains. The concept of biofuels was developed in the early twentieth century, but the relative ease of fossil fuel mining and production largely stalled research and development until the end of the century. The two most common biofuels in development are ethanol and biodiesel.

Ethanol. Ethanol is an alcohol that is produced in a similar way to beer or spirits. Carbohydrates from plant matter are fermented through the addition of organic acids; fermentation transforms the carbohydrates into alcohols. Most modern biofuels are made using the sugars and starches from corn, but it also is possible to use the cellulose from plant waste to manufacture ethanol. Alternatively, ethanol can be produced by a process called gasification, in which plant matter is subjected to high heat in an atmosphere devoid of oxygen; this converts the plant matter into synthesis gas, or syngas, a hydrocarbon-rich blend of gases. Syngas can then be utilized in separate processes to create ethanol or other fuels.

Biodiesel. Biodiesel is another type of biofuel made by combining alcohol with vegetable or animal oils. Biodiesel is typically manufactured from ethanol and vegetable oil derived from corn. However, methods exist to create biodiesel using recycled oil, such as used cooking oil. Biodiesel can be used directly in cars manufactured to run on diesel but cannot be used as a sole fuel source for petroleum-burning engines.

Both ethanol and biodiesel are used as additives, which are blended by traditional gasoline to more efficient fuels that lower levels of pollutants in their emissions. Support for biofuel increased rapidly in the 1990s, largely because of the potential for biofuel to create a lucrative new market for agricultural crops. Government subsidies were established to support farmers who dedicated a certain portion of their growing efforts to producing corn for biofuel production. In addition, biofuel can potentially be generated using plant waste and other recycled materials, which could mean a significant reduction in solid waste on a global scale.

One of the primary criticisms of biofuels is that production methods utilize petroleum gas in the manufacturing process, mitigating the ultimate goal of reducing fossil fuel reliance. In addition, biofuels have been used to bolster the corn market, and increased corn production can lead to increased use of nitrogen fertilizers, which also constitute a destructive pollutant. Some estimates indicate that increased nitrogen pollution may be more harmful than the carbon dioxide emissions produced by fossil fuel combustion. In addition, the increased agricultural area needed for corn production can lead to further deforestation, for example, thereby hastening environmental collapse in some ecosystems.

Nuclear power uses energy produced by nuclear fission to generate heat, which is then used to generate electricity. Fission is the process by which the nucleus of an atom is induced to split into smaller nuclei, producing light and heat as a by-product of the reaction.

Nuclear power can come from the fission of uranium, plutonium, and thorium, though most modern nuclear reactors utilize uranium. Uranium is mined from sediments, where it occurs in two varieties, usually blended together within the matrix of sedimentary rock. Uranium-235 can be used for fission, while the more common uranium-238 is not generally appropriate for use as reactor fuel.

To induce fission, samples of uranium are bombarded with a stream of free neutrons. When one of the neutrons strikes an atom of uranium-235, it causes the atom to split, thereby releasing heat. Heat from this reaction is used to convert water into water vapor, which rises with force and spins the blades of large turbine engines to generate electricity. In essence, then, though nuclear fission involves the release of vast amounts of atomic energy, this atomic energy must be converted to kinetic energy before it is used to generate electricity. The basic method of utilizing kinetic energy from rising currents to operate a turbine engine is similar to the method used to generate electricity from fossil fuel combustion.

Approximately 82 percent of the energy produced through nuclear fission is converted to kinetic energy, making nuclear energy a more efficient method of producing energy than combustion. Research indicates that fission of one atom of uranium produces 10 million times more energy than the combustion of an atom of coal. In addition, nuclear fission does not produce carbon dioxide as a by-product; instead, it utilizes atmospheric carbon dioxide to cool the reactor environment, thereby contributing little to atmospheric pollution.

While nuclear power generates little atmospheric pollution, the process produces significant amounts of hazardous waste that pose an environmental and ecological threat. Nuclear reactors around the world together generate between ten and twenty tons of radioactive waste each year. Nuclear waste produces heat and radiation, which can be harmful or lethal to nearby organisms. Nuclear waste also can pollute soil and groundwater, spreading the harmful effects of the radiation over a large area. Safely disposing of the waste is an expensive and dangerous process that involves burying waste in large, cooled concrete storage containers filled with glass particles. These waste disposal containers must be monitored for leaks and to keep the radioactive material safe from tampering.

There are additional concerns regarding nuclear energy—namely, the potential for nuclear waste or nuclear fuel to be stolen and used to manufacture weapons. Given security and monitoring processes, the risk of nuclear theft is extremely low, yet this fear has contributed to negative public opinion toward nuclear power.

In addition, though technology allows for the safe operation of nuclear power plants, the potentially catastrophic effects of a nuclear plant meltdown have further reduced popular support. Because of these drawbacks both in waste and in public opinion, the use of nuclear fission is declining on a global scale, despite nuclear energy being a cleaner, more sustainable, and more affordable way to manufacture energy.

Principal Terms

bitumen: viscous, semiliquid material produced as a by-product of the decay of organic material; typically called tar

fossil fuel: fuel source derived from the fossilized remains of organic matter, including coal, petroleum oil, and natural gas

gasification: process that converts carboniferous material to methane and carbon gases by subjecting the material to extreme heat in an environment that prevents combustion

hydroelectricity: electricity produced by converting the kinetic energy within moving water

kerogen: complex fossilized form of organic matter that forms oil and natural gas

kinetic energy: the energy possessed by an object because of its motion

nuclear fission: the process of inducing the nucleus of an atom to split into lighter nuclei, which produces free neutrons and energy

oil shale: sedimentary rock that contains solid deposits of kerogen as inclusions within the rock matrix

renewable energy: energy source that does not depend on a finite, exhaustible resource

turbine: engine that uses the viscosity and movement of a fluid medium, such as a liquid or gas, to perform mechanical work, turning a rotary mechanism that can be used to generate other types of energy

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