Автор: Пользователь скрыл имя, 09 Марта 2012 в 12:50, реферат
Alternative energy refers to energy sources that have no undesired consequences such for example fossil fuels or nuclear energy. Alternative energy sources are renewable and are thought to be "free" energy sources. They all have lower carbon emissions, compared to conventional energy sources. These include Biomass Energy, Wind Energy, Solar Energy, Geothermal Energy, Hydroelectric Energy sources.
Alternative energy refers to energy sources that have no undesired consequences such for example fossil fuels or nuclear energy. Alternative energy sources are renewable and are thought to be "free" energy sources. They all have lower carbon emissions, compared to conventional energy sources. These include Biomass Energy, Wind Energy, Solar Energy, Geothermal Energy, Hydroelectric Energy sources. Combined with the use of recycling, the use of clean alternative energies such as the home use of solar power systems will help ensure man's survival into the 21st century and beyond..
Alternative energy can also refers to the different and subtle energies of the Universe.The awareness and study of these energies, which are similar to electrical energies that science knows can result in amazing curative and healing energies.
Societies have taken advantage of wind power for thousands of years. The first known use was in 5000 BC when people used sails to navigate the Nile River. Persians had already been using windmills for 400 years by 900 AD in order to pump water and grind grain. Windmills may have even been developed in China before 1 AD, but the earliest written documentation comes from 1219. Cretans were using "literally hundreds of sail-rotor windmills [to] pump water for crops and livestock."
The Earth receives
an incredible supply of solar energy. The sun, an average star,
is a fusion reactor that has been burning over 4 billion years. It provides
enough energy in one minute to supply the world's energy needs for one
year. In one day, it provides more energy than our current population
would consume in 27 years. In fact, "The amount of solar radiation
striking the earth over a three-day period is equivalent to the energy
stored in all fossil energy sources."
Solar energy is a free, inexhaustible resource, yet harnessing it is a relatively new idea. The ability to use solar power for heat was the first discovery. A Swiss scientist, Horace de Saussure, built the first thermal solar collector in 1767, which was later used to heat water and cook food. The first commercial patent for a solar water heater went to Clarence Kemp of the US in 1891. This system was bought by two California executives and installed in one-third of the homes in Pasadena by 1897.
Producing electricity from solar energy was the second discovery. In 1839 a French physicist named Edmund Becquerel realized that the sun's energy could produce a "photovoltaic effect" (photo = light, voltaic = electrical potential). In the 1880s, selenium photovoltaic (PV) cells were developed that could convert light into electricity with 1-2% efficiency ("the efficiency of a solar cell is the percentage of available sunlight converted by the photovoltaic cell into electricity"), but how the conversion happened was not understood. Photovoltaic power therefore "remained a curiosity for many years, since it was very inefficient at turning sunlight into electricity." It was not until Albert Einstein proposed an explanation for the "photoelectric effect" in the early 1900s, for which he won a Nobel Prize, that people began to understand the related photovoltaic effect.
The term "biomass" refers to organic matter that has stored energy through the process of photosynthesis. It exists in one form as plants and may be transferred through the food chain to animals' bodies and their wastes, all of which can be converted for everyday human use through processes such as combustion, which releases the carbon dioxide stored in the plant material. Many of the biomass fuels used today come in the form of wood products, dried vegetation, crop residues, and aquatic plants. Biomass has become one of the most commonly used renewable sources of energy in the last two decades, second only to hydropower in the generation of electricity. It is such a widely utilized source of energy, probably due to its low cost and indigenous nature, that it accounts for almost 15% of the world's total energy supply and as much as 35% in developing countries, mostly for cooking and heating.
Biomass is one of the most plentiful and well-utilised sources of renewable energy in the world. Broadly speaking, it is organic material produced by the photosynthesis of light. The chemical material (organic compounds of carbons) are stored and can then be used to generate energy. The most common biomass used for energy is wood from trees. Wood has been used by humans for producing energy for heating and cooking for a very long time.
Biomass has been converted by partial-pyrolisis to charcoal for thousands of years. Charcoal, in turn has been used for forging metals and for light industry for millenia. Both wood and charcoal formed part of the backbone of the early Industrial Revolution (much northern England, Scotland and Ireland were deforested to produce charcoal) prior to the discovery of coal for energy.
Wood is still used extensively for energy in both household situations, and in industry, particularly in the timber, paper and pulp and other forestry-related industries. Woody biomass accounts for over 10% of the primary energy consumed in Austria, and it accounts for much more of the primary energy consumed in most of the developing world, primarily for cooking and space heating.
It is used to raise steam, which, in turn, is used as a by-product to generate electricity. Considerable research and development work is currently underway to develop smaller gasifiers that would produce electricity on a small-scale. For the moment, however, biomass is used for off-grid electricity generation, but almost exclusively on a large-, industrial-scale.
There are two issues that affect the evaluation of biomass as a viable solution to our energy problem: the effects of the farming and production of biomass and the effects of the factory conversion of biomass into usable energy or electricity. There are as many environmental and economic benefits as there are detriments to each issue, which presents a difficult challenge in evaluating the potential success of biomass as an alternative fuel. For instance, the replacement of coal by biomass could result in "a considerable reduction in net carbon dioxide emissions that contribute to the greenhouse effect." On the other hand, the use of wood and other plant material for fuel may mean deforestation. We are all aware of the problems associated with denuding forests, and widespread clear cutting can lead to groundwater contamination and irreversible erosion patterns that could literally change the structure of the world ecology.
Biomass has to be considered in the search for an alternative source of energy that is abundant in a wide-scale yet non-disruptive manner, since it is capable of being implemented at all levels of society. Although tree plantations have "considerable promise" in supplying an energy source, "actual commercial use of plantation-grown fuels for power generation is limited to a few isolated experiences." Supplying the United States ' current energy needs would require an area of one million square miles. That's roughly one-third of the area of the 48 contiguous states. There is no way that plantations could be implemented at this scale, not to mention that soil exhaustion would eventually occur. Biomass cannot replace our current dependence on coal, oil, and natural gas, but it can complement other renewables such as solar and wind energy.
According to Flavin and Lenssen of the Worldwatch Institute , "If the contribution of biomass to the world energy economy is to grow, technological innovations will be needed, so that biomass can be converted to usable energy in ways that are more efficient, less polluting, and at least as economical as today's practices." When we have enough government support and have allotted enough land for the continuous growth of energy crops for biomass-based energy, we may have a successful form of alternative energy. But "as long as worldwide prices of coal, oil and gas are relatively low, the establishment of plantations dedicated to supplying electric power or other higher forms of energy will occur only where financial subsidies or incentives exist or where other sources of energy are not available." Although it is currently utilized across the globe, biomass energy is clearly not capable of sustaining the world's energy needs on its own.
Energy from the Earth What could be more natural or plentiful? The source of geothermal power is the heat contained inside the Earth; heat so intense that it creates molten magma. There are a few different types of geothermal energy that can be tapped. "Some geothermal systems are formed when hot magma near the surface (1,500 to 10,000 meters deep) directly heats groundwater." The heat generated from these hot spots flows outward toward the surface, manifesting as volcanoes, geysers, and hot springs . Naturally-occurring hot water and steam can be tapped by energy conversion technology to generate electricity or to produce hot water for direct use. "Other geothermal systems are formed even when no magma is nearby as magma heats rocks which in turn heat deeply-circulating groundwater." In order to maximize the energy gleaned from these so-called "hot dry rocks," geothermal facilities will often fracture the hot rocks and pump water into and from them in order to use the heated water to generate electricity.
The concentration of geothermal energy at any given location must be quite high in order to make heat extraction feasible, and not all geothermal sites are created equally. Regions that have well-developed geothermal systems are located in geologically active areas. These regions have continuous, concentrated heat flow to the surface. The western United States has the best geothermal regions in the country, while Iceland , New Zealand , the Philippines , and South America , are some of the more prominent global "hot spots." In Iceland , geothermal energy, caused by the constant movement of geologic plates coupled with the volcanic nature of the island, is used to heat 95% of all homes.
Unfortunately even good geothermal areas are a non-renewable renewable. "The Geysers," the world's largest geothermal facility, is a working model on how not to approach a so-called "renewable" geothermal resource. Built in the 1950s on a steam field in Northern California , the facility was established on the apparent assumption that geothermal resources were infinite at that locatio. However, by the late 1980s, steam decline became noticeable and sustained. Depletion occurred because steam was being extracted faster than it could be naturally replaced. According to a report by Pacific Gas and Electric, "because of declining geothermal steam supplies, the Company's geothermal units at The Geysers Power Plant are forecast to operate at reduced capacities." In response, "plant operators and steam suppliers continually seek new operating strategies to maximize future power generation coupled with daily injection of millions of gallons of reclaimed municipal wastewater." Even though improvements in efficiency and conservation are being implemented and in 1996 The Geysers was still producing enough electricity to supply the power demand of a city like San Francisco , it is projected that the steam field will be defunct in 50 years or so. To prevent this sort of thing from happening elsewhere, geothermal facilities can use a closed-loop system at all times, or the re-injection of water back into the system for constant steam generation, as PG&E is now implementing at The Geysers.
Despite the fact that geothermal energy is abundant renewable, and able to reduce our dependence on imported fuels, the fact remains that fields of sufficient quality to produce economic electricity are rare. In addition, many of those that are known are located in protected wilderness areas that environmentalists want to preserve. Unless research and technology join forces to "harvest" geothermal power through non-traditional means, such as deep-crustal drilling or the acquisition of heat from magma, the tapping of geothermal energy is limited to a handful of locations.
Environmental concerns also taint the issue of geothermal energy. Although no combustion occurs, some applications produce carbon dioxide and hydrogen sulfide emissions, require the cooling of as much as 100,000 gallons of water per megawatt per day, and dispose of toxic waste and dissolved solids.
Another type of geothermal energy being used commercially is Earth energy, extracted through heat pumps. Heat contained in shallow ground is used to directly heat or cool houses since the temperature inside the ground tends to stay at the yearly average. Therefore, in the winter the ground is warmer than the air and can be used to heat a building, and in the summer the ground is cooler than the air and can act as an air conditioner. Researchers know that "no active technology for home cooling is more efficient than the geothermal heat pump." This technique reduces the reliance on other resources and can be utilized anywhere, resulting in significant environmental benefits and reduced energy costs.
Reserves: Geothermal energy is found in many places on the earth.
Its use contributes to the development of important third-world countries
including the Philippines, Indonesia, Mexico, countries of Central and
South America, and countries in eastern Africa and in eastern Europe.
Italy, Iceland, New Zealand, Japan and France, along with the United
States, are developed countries using geothermal energy.
There is a very large geothermal resource base in the U.S. and in the world, much of which can not yet be economically used. In fact, the resource base for the renewable energies- geothermal, solar, biomass and wind -- is much larger than the total resource base in coal, oil, gas, and uranium (nuclear power).
There are also other problems that prevent us from taking full advantage of this form of energy. Even though there are geothermal resources throughout the world, our current technology is not sufficient or economical enough to warrant its widespread use. Funding for energy extraction that involves the penetration of magma is not available because we do not yet know how to prevent a high-temperature, high-pressure blowout. When heat pumps are considered, which tap local sources of heat and can help to reduce a family's electricity bill by about $1 per day, the system is not economically viable. It "may have a payback period in excess of 5 years," which will increase with decreased electricity rates "unless equipment and installation costs drop dramatically." In addition, Earth energy is not "intense" enough to produce power for the electrical distribution grid; it is only sufficient to reduce the draw from the grid.
There are definite obstacles to be overcome before geothermal energy can be easily and economically harnessed for everyday, worldwide use. Case in point: "Construction of new domestic electricity-producing geothermal facilities in the Western United States during 1996 was limited to one site, due to the availability of cheap, plentiful natural-gas-fired electricity in the West."
Moving water is a powerful entity responsible for lighting entire cities, even countries. Thousands of years ago the Greeks used water wheels, which picked up water in buckets around a wheel. The water's weight caused the wheel to turn, converting kinetic energy into mechanical energy for grinding grain and pumping water. In the 1800s the water wheel was often used to power machines such as timber-cutting saws in European and American factories. More importantly, people realized that the force of water falling from a height would turn a turbine connected to a generator to produce electricity. Niagara Falls , a natural waterfall, powered the first hydroelectric plant in 1879.
Man-made waterfalls dams were constructed throughout the 1900s in order to maximize this source of energy. Aside from a plant for electricity production, a hydropower facility consists of a water reservoir enclosed by a dam whose gates can open or close depending on how much water is needed to produce a particular amount of electricity. Once electricity is produced it is transported along huge transmission lines to an electric utility company.
"By the 1940s, the best sites for large dams had been developed." But like most other renewable sources of energy, hydropower could not compete with inexpensive fossil fuels at the time. "It wasn't until the price of oil skyrocketed in the 1970s that people became interested in hydropower again." Today one-fifth of global electricity is generated by falling water.
"Over the past 100 years, the United States has led the world in dam building. Secretary of the Interior Bruce Babbitt recently observed that, 'on average, we have constructed one dam every day since the signing of the Declaration of Independence.'"Of the 75,187 dams in the US , less than 3% are used to produce 10-12% of the nation's electricity. With over 2,000 facilities, the US is the second largest producer of hydropower worldwide, behind Canada . The dams that do not produce electricity are used for irrigation or flood control. Many people believe these pre-existing sites could contribute to the country's power supply in a cost-effective manner if hydroelectric facilities were constructed.
There are several favorable features of hydropower. Anywhere rain falls, there will be rivers. If a particular section of river has the right terrain to form a reservoir, it may be suitable for dam construction. No fossil fuels are required to produce the electricity, and the earth's hydrologic cycle naturally replenishes the "fuel" supply. Therefore no pollution is released into the atmosphere and no waste that requires special containment is produced. Since "water is a naturally recurring domestic product and is not subject to the whims of foreign suppliers," there is no worry of unstable prices, transportation issues, production strikes, or other national security issues.
Hydropower is very convenient because it can respond quickly to fluctuations in demand. A dam's gates can be opened or closed on command, depending on daily use or gradual economic growth in the community. The production of hydroelectricity is often slowed in the nighttime when people use less energy. When a facility is functioning, no water is wasted or released in an altered state; it simply returns unharmed to continue the hydrologic cycle. The reservoir of water resulting from dam construction, which is essentially stored energy, can support fisheries and preserves, and provide various forms of water-based recreation for locals and tourists. Land owned by the hydroelectric company is often open to the public for hiking, hunting, and skiing. Therefore, "hydropower reservoirs contribute to local economies. A study of one medium-sized hydropower project in Wisconsin showed that the recreational value to residents and visitors exceeded $6.5 million annually." Not to mention the economic stimulation provided by employment.
Hydroelectric power is also very efficient and inexpensive. "Modern hydro turbines can convert as much as 90% of the available energy into electricity. The best fossil fuel plants are only about 50% efficient. In the US , hydropower is produced for an average of 0.7 cents per kilowatt-hour (kWh). This is about one-third the cost of using fossil fuel or nuclear and one-sixth the cost of using natural gas," as long as the costs for removing the dam and the silt it traps are not included. Efficiency could be further increased by refurbishing hydroelectric equipment. An improvement of only 1% would supply electricity to an additional 300,000 households.
Hydropower has become "the leading source of renewable energy. It provides more than 97% of all electricity generated by renewable sources worldwide. Other sources including solar, geothermal, wind, and biomass account for less than 3% of renewable electricity production." In the US , 81% of the electricity produced by renewable sources comes from hydropower. "Worldwide, about 20% of all electricity is generated by hydropower." Some regions depend on it more than others. For example, 75% of the electricity produced in New Zealand and over 99% of the electricity produced in Norway come from hydropower.
The use of hydropower "prevents the burning of 22 billion gallons of oil or 120 million tons of coal each year." In other words, "the carbon emissions avoided by the nation's hydroelectric industry are the equivalent of an additional 67 million passenger cars on the road 50 percent more than there are currently." The advantages of hydropower are therefore convincing, but there are some serious drawbacks that are causing people to reconsider its overall benefit.
Since the most feasible sites for dams are in hilly or mountainous areas, the faults that often created the topography pose a great danger to the dams and therefore the land below them for thousands of years after they have become useless for generating power. In fact, dam failures do occur regularly due to these terrain conditions, and the effects are devastating.
When a new dam's reservoir floods the countryside, people who live in the area have to move and relinquish their former lifestyles in order to make way for the project. This is very stressful and often controversial, especially if a community has maintained a particular way of life on the same land for generations. Such is the case in Chile, where the indigenous Pehuenche "are currently fighting construction of the 570MW, US $500,000,000 Ralco Dam on the Biobo River Eight families continue to refuse to negotiate land exchanges with Endesa [the utility company], and wish to remain on their lands." If the project succeeds, a 13-square-mile reservoir would flood the land and force 600 people out of their homes, 400 of whom are Pehuenche "whose ancestral home is the upper Biobo." A total of five dams have been planned, which "would force the relocation of 1,000 Pehuenches, 20% of the survivors of this ancient culture."
The construction of a dam not only affects the people nearby, it can severely alter a river's natural functions. According to American Rivers, a conservation organization, "by diverting water for power, dams remove water needed for healthy in-stream ecosystems. Stretches below dams are often completely de-watered." This may not seem like a significant problem until animal species are studied. Birds that have migrated to a specific riparian environment for generations no longer have enough insects on which to prey when the water level drops. If they have few migration alternatives, that could mean the endangerment of species that once flourished. Fish species such as salmon "depend on steady flows to flush them down river early in their life and guide them upstream years later to spawn. Stagnant reservoir pools disorient migrating fish and significantly increase the duration of their migration." Native populations of fish may decrease or disappear altogether due to temperature changes caused by dams. Slower water flow means warmer temperatures, and bottom-release of cold water means cooler temperatures. Several of hydropower's disadvantages focus on fish. It is easy to forget how important fish and other aquatic life are, some of which reside at the bottom of the food chain.
The environmental changes caused by hydroelectric projects may be obvious to the local biologist, but elude the average person. Most people will more readily notice a smoggy haze developing in an area where a coal plant is operating than a smaller population of a particular bird species where a hydropower facility functions. Such oversights lead people to believe that nothing is wrong.
Hydroelectric companies and organizations often emphasize their "clean" manufacture of electricity and neglect to mention the long-term environmental hazards. "Dams hold back silt, debris, and nutrients." Silt collects behind the dam on the river bottom, accumulating heavy metals and other pollutants. Eventually this renders the dam inoperable, leaving the mess for future generations, who will either have to remove the collected debris or live with a potentially catastrophic mudflow poised to inundate the area below the dam.