Advanced societies require sources of external energy for transportation, heating, ventilation, production of goods, and comfort. As the world's population rapidly increases and the available supplies of economically, technologically, and environmentally extractable hydrocarbons diminishes, it is imperative that nations begin to seriously invest in developing alternative energy sources and strategies. Increased efficiency and conservation of presently known hydrocarbon reserves will help postpone the depletion of this resource, but it will eventually run out or become exceedingly expensive. To maintain levels of comfort and production in the world's civilizations, acceleration of the research and development of sustainable energy-harvesting techniques is necessary.
Primary energy sources are those that contain energy in a form (high potential) that enables them to be converted directly to lower forms of energy that are directly usable by people. These include fossil fuels, nuclear energy, and renewable resources such as biofuels, geothermal energy, hydroelectricity, solar power, tidal power, and wind power. Fossil fuels will eventually be depleted, cause significant pollution, disrupt the environment in their extraction, and emit greenhouse gases. Nuclear fuels are limited in abundance since the known resources of uranium will be depleted in dozens (uranium 235) to thousands (uranium 238) of years, and the generation of nuclear power, albeit efficient and clean, is plagued with the problem of how to dispose of the radioactive wastes. There are alternative energy sources that are renewable, clean, and efficient.
Biomass fuels involve using garbage, corn, or other vegetables to generate electricity. When garbage decomposes it generates methane that can be captured and then burned to produce electricity. Burning garbage can generate energy and alleviate land-use stress from landfills, but it also generates air pollution similar to that of burning fossil fuels. Biofuel such as vegetable oil is produced from sunlight and carbon dioxide (CO2) by plants. It can be modified to burn like diesel fuel and is safer than gasoline since it has a higher flash point. However, the amount of plant matter required to generate biofuels is large and competes with land use for farming to feed people and livestock, driving up food prices. It also takes a significant amount of fuel to plant, fertilize, and grow biofuel stock, so some argue that there is no net gain in the biofuel economy.
Geothermal energy taps heat resources that are close to the surface in some regions of Earth, such as near volcanic centers. Less efficient geothermal sources are present in most places. Two wells are drilled in the ground; water is injected into one, and it becomes heated by the hot rocks at depth. The water is then extracted, or naturally shoots up as steam, from the other well. The energy from the steam can drive turbines to create electricity, and the heat from the water can be used as an energy source for things like home heating. Geother-mal energy is cheap and generally clean, but is most efficient in specific locations where the underlying geology places hot material close to the surface.
Hydroelectricity uses the gravitational potential energy of a river by means of a dam, flume, or tunnel, using the pressure from water at high elevation to pass through a turbine or waterwheel to drive specific temperature and pressure, organic-rich beds known as source rocks become compacted, and the organic material undergoes chemical reactions to form hydrocarbons including oil and gas. These fluids and gases have a lower density than surrounding rocks and a lower density than water, so they tend to migrate upward until they escape at the surface or are trapped between impermeable layers, where they may form a petroleum reservoir.
oil traps are of many varieties, divided into mainly structural and stratigraphic types. structural traps include anticlines, where the beds of rocks are folded into an upward arching dome. In these types of traps, petroleum in a permeable layer that is confined between impermeable layers (such as a sandstone bed between shale layers) may migrate up to the top of the anticlinal dome, where it becomes trapped. If a fault cuts across beds, it may form a barrier or it may act as a conduit for oil to escape, depending on the physical properties of the rock in the fault zone. In many cases faults juxtapose an oil-bearing permeable unit against an impermeable horizon, forming a structural trap. salt domes in many places form diapirs that pierce through oil-bearing stratigraphic horizons. They typically cause an upwarping of the rock beds around the dome, forming a sort of anticlinal trap that in many regions has yielded large volumes of petroleum. stratigraphic traps are found mainly where two impermeable layers such as shales are found above and below a lens-shaped sandstone unit that pinches out laterally to form a wedge-shaped trap. These conditions are commonly met along passive margins, where transgressions and regressions of the sea cause sand electric generators or mills. Hydroelectric plants are clean, in many cases water can be stored to be used at peak demand, and there are many undeveloped places with high potential to generate new hydroelectric power. However, construction of dams on rivers seriously affects the river dynamics and ecology, so the future of hydroelectricity may lie mostly in situations where underground tunnels can be made that utilize the gravitational potential energy, but do not seriously disrupt the river environment.
Solar power uses solar cells to convert sunlight into electricity, utilizing the most steady source of energy in the solar system. Sunlight can heat water or air in solar panels, create steam using parabolic mirrors, or be used in a more passive way, utilizing the light entering windows to heat buildings. Solar power is most efficient in places where the solar radiation is the highest. Places like the sunny desert southwestern United States are much more suited for solar power than the Pacific Northwest, which is shrouded in clouds many days of the year. Solar panels operate at different efficiencies, depending on the sunlight conditions and their construction. Assuming a 20 percent efficiency, all of the energy needs of the United States could be met if an area the size of Arizona were covered with solar panels. Solar energy requires a complementary energy storage system, since it is not available at night or during cloudy weather.
Tidal power can be harnessed by building impoundment dams that capture water at high tide and slowly release the water through turbines during low tide. Water turbines can also be located in areas with strong tidal currents, with most of the infrastructure located underwater. These turbines can be connected to electrical generators or to gas compressors, which then store the energy as compressed gas that can be slowly released to drive turbines as needed to generate electricity.
Wind power captures the energy of the wind by placing large wind turbines in persistently windy locations. The wind turns the blades of the turbines that cause the rotation of magnets that in turn generate electricity. Some locations are prone to steady and strong winds, and these locations can be the sites of wind farms where many tall towers with large blades are set up to harness the wind's power. This source of energy is clean, produces no chemical or air pollution, and is renewable. The blades of the turbines are high off the ground, so wind farms on land can function along with the primary use of the land, such as grazing or farm ing. Wind farms can also be placed offshore in appropriate locations; however, they can interfere with radar systems so can pose a risk to national security if placed inappropriately. Additionally, the wind is not always predictable or reliable, so wind power needs to have a storage system or be built in conjunction with other energy systems. Some communities consider wind farms to be an eyesore, and some are said to generate low-frequency noise that affects some people and animals.
The world's supply of cheap hydrocarbon reserves is running out. Examining the future trends in energy use, it is clear that many different types of renewable energy sources need to be integrated in an intelligent system that responds to local and national needs and continues to provide the energy needed for civilization's comforts and development.
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