Alternative energy sources
Biomass energy, or photosynthesis, 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-utilized 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) is 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-pyrolysis to charcoal for thousands of years. Charcoal, in turn has been used for forging metals and for light industry for millennia. Both wood and charcoal formed part of the backbone of the early Industrial Revolution (much of 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 byproduct 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.
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.
Our entire planet is heated by the sun. The sun, technically a star, provides the planet with light, heat, and more recently energy.
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 Dutch were responsible for many refinements of the windmill, primarily for pumping excess water off land that was flooded. As early as 1390, they had connected the mill to "a multi-story tower, with separate floors devoted to grinding grain, removing chaff, storing grain, and (on the bottom) living quarters for the windsmith and his family." Its popularity spread to the point that there were 10,000 windmills in England. But perfecting the windmill's efficiency to the point that it "had all the major features recognized by modern designers as being crucial to the performance of modern wind turbine blades" took almost 500 years. By then, applications ranged from saw-milling timber to processing spices, tobacco, cocoa, paints, and dyes.
The windmill was further refined in the late 19th century in the US; some designs from that period are still in use today. Heavy, inefficient wooden blades were replaced by lighter, faster steel blades around 1870. Over the next century, more than six million small windmills were erected in the US in order to aid in watering livestock and supplying homes with water during the development of the West. The first large windmill to produce electricity was the "American multi-blade design," built in 1888. Its 12-kilowatt capabilities were later superseded by modern 70-100 kilowatt wind turbines.
Wind Energy Sources
Today, people are realizing that wind power is one of the most promising new energy sources that can serve as an alternative to fossil fuel-generated electricity.
With today's technology, wind energy could provide 20% of America's electricity (or about the amount nuclear power provides) with turbines installed on less than 1% of its land area. And within that area, less than 5% of the land would be occupied by wind equipment - the remaining 95% could continue to be used for farming or ranching. By the year 2020, 10 million average American homes may be supplied by wind power, preventing 100 million metric tons of CO2 emissions every year. Lessening our dependence on fossil fuels is critical to the health of all living things, and wind energy can do just that.
The 3 billion kWh of electricity produced by America's wind machines annually displace the energy equivalent of 6.4 million barrels of oil and avoid 1.67 million tons of carbon emissions, as well as sulfur and nitrogen oxide emissions that cause smog and acid rain. In other words, more wind power means less smog, acid rain, and greenhouse gas emissions.
Windmills may have been around for almost 1500 years, but it was not imagined that wind power would become affordable enough to compete with fossil fuels. Indeed it has. In fact, many utility services around the world offer wind-generated electricity at a premium of 2 to 3 cents per kWh. If a household used wind power for 25% of its needs, it would spend only $4 or $5 dollars per month for it and the price is still dropping.
Compare this to 4.8 to 5.5 cents per kWh for coal or 11.1 to 14.5 cents per kWh for nuclear power. Wind energy is therefore cheaper than any other new electric generation except natural gas which emits one pound of greenhouse gases for every kilowatt-hour of electricity it generates. The success of this energy is in part due to the fact that its costs have gone down by more than 80% since the early 1980s. Even lower prices are expected, as industry analysts see the cost dropping by an additional 20 percent to 40 percent by 2005."
Electricity from Wind
Germany, the US, Spain, Denmark, India and Australia are among the world's leading nations in the acquisition of wind energy. Wind generated energy is growing in leaps and bounds.
Wind power is now the world's fastest growing energy source and has also become one of the most rapidly expanding industries, with sales of roughly $3 billion in 2008. Major offshore developments are likely in northern European waters in the early part of the next century.
This will be the next major step for this technology and will result in a dramatic increase in decentralized electricity generation. Offshore wind has the potential to deliver substantial quantities of energy at a price that is cheaper than most of the other renewable energies, as wind speeds are generally higher offshore than on land.
As of 1999, global wind energy capacity topped 10,000 megawatts, which is approximately 16 billion kilowatt-hours of electricity. That's enough to serve over 5 cities the size of Miami, according to the American Wind Energy Association. Five Miamis may not seem significant, but if we make the predicted strides in the near future, wind power could be one of our main sources of electricity. With today's technology, wind energy could provide 20% of America's electricity (or about the amount nuclear power provides) with turbines installed on less than 1% of its land area. And within that area, less than 5% of the land would be occupied by wind equipment the remaining 95% could continue to be used for farming or ranching. By the year 2010, 10 million average American homes may be supplied by wind power, preventing 100 million metric tons of CO 2 emissions every year.
Lessening our dependence on fossil fuels is critical to the health of all living things, and wind energy can do just that. The 3 billion kWh of electricity produced by America's wind machines annually displace the energy equivalent of 6.4 million barrels of oil and avoid 1.67 million tons of carbon emissions, as well as sulfur and nitrogen oxide emissions that cause smog and acid rain. In other words, more wind power means less smog, acid rain, and greenhouse gas emissions.
Geothermal energy is heat contained below the earth's surface. The only type of geothermal energy that has been widely developed is hydrothermal energy, which consists of trapped hot water or steam. However, new technologies are being developed to exploit hot dry rock (accessed by drilling deep into rock), geopressured resources (pressurized brine mixed with methane), and magma.
The various geothermal resource types differ in many respects, but they raise a common set of environmental issues. Air and water pollution are two leading concerns, along with the safe disposal of hazardous waste, siting, and land subsidence. Since these resources would be exploited in a highly centralized fashion, reducing their environmental impacts to an acceptable level should be relatively easy. But it will always be difficult to site plants in scenic or otherwise environmentally sensitive areas.
The method used to convert geothermal steam or hot water to electricity directly affects the amount of waste generated. Closed-loop systems are almost totally benign, since gases or fluids removed from the well are not exposed to the atmosphere and are usually injected back into the ground after giving up their heat. Although this technology is more expensive than conventional open-loop systems, in some cases it may reduce scrubber and solid waste disposal costs enough to provide a significant economic advantage.
Open-loop systems, on the other hand, can generate large amounts of solid wastes as well as noxious fumes. Metals, minerals, and gases leach out into the geothermal steam or hot water as it passes through the rocks. The large amounts of chemicals released when geothermal fields are tapped for commercial production can be hazardous or objectionable to people living and working nearby.
At The Geysers, the largest geothermal development, steam vented at the surface contains hydrogen sulfide (H2S) - accounting for the area's "rotten egg" smell - as well as ammonia, methane, and carbon dioxide. At hydrothermal plants carbon dioxide is expected to make up about 10 percent of the gases trapped in geopressured brines. For each kilowatt- hour of electricity generated, however, the amount of carbon dioxide emitted is still only about 5 percent of the amount emitted by a coal- or oil-fired power plant.
Scrubbers reduce air emissions but produce a watery sludge high in sulfur and vanadium, a heavy metal that can be toxic in high concentrations. Additional sludge is generated when hydrothermal steam is condensed, causing the dissolved solids to precipitate out. This sludge is generally high in silica compounds, chlorides, arsenic, mercury, nickel, and other toxic heavy metals. One costly method of waste disposal involves drying it as thoroughly as possible and shipping it to licensed hazardous waste sites. Research under way at Brookhaven National Laboratory in New York points to the possibility of treating these wastes with microbes designed to recover commercially valuable metals while rendering the waste nontoxic.
Usually the best disposal method is to inject liquid wastes or redissolved solids back into a porous stratum of a geothermal well. This technique is especially important at geopressured power plants because of the sheer volume of wastes they produce each day. Wastes must be injected well below fresh water aquifers to make certain that there is no communication between the usable water and waste-water strata. Leaks in the well casing at shallow depths must also be prevented.
In addition to providing safe waste disposal, injection may also help prevent land subsidence. At Wairakei, New Zealand, where wastes and condensates were not injected for many years, one area has sunk 7.5 meters since 1958. Land subsidence has not been detected at other hydrothermal plants in long-term operation. Since geopressured brines primarily are found along the Gulf of Mexico coast, where natural land subsidence is already a problem, even slight settling could have major implications for flood control and hurricane damage. So far, however, no settling has been detected at any of the three experimental wells under study.
Most geothermal power plants will require a large amount of water for cooling or other purposes. In places where water is in short supply, this need could raise conflicts with other users for water resources.
The development of hydrothermal energy faces a special problem. Many hydrothermal reservoirs are located in or near wilderness areas of great natural beauty such as Yellowstone National Park and the Cascade Mountains. Proposed developments in such areas have aroused intense opposition. If hydrothermal-electric development is to expand much further in the United States, reasonable compromises will have to be reached between environmental groups and industry.
Hydroelectric and coal-fired power plants produce electricity in a similar way. In both cases a power source is used to turn a propeller-like piece called a turbine, which then turns a metal shaft in an electric generator, which is the motor that produces electricity. A coal-fired power plant uses steam to turn the turbine blades - a hydroelectric plant uses falling water to turn the turbine. The results are the same.
Typically, a dam is built on a large river which has a large drop in elevation. The dam stores lots of water behind it in the reservoir. Near the bottom of the dam wall there is the water intake. Gravity causes it to fall through the penstock inside the dam. At the end of the penstock there is a turbine propeller, which is turned by the moving water. The shaft from the turbine goes up into the generator, which produces the power. Power lines are connected to the generator that carry electricity to your home and mine. The water continues past the propeller through the tailrace into the river past the dam.
A hydraulic turbine converts the energy of flowing water into mechanical energy. A hydroelectric generator converts this mechanical energy into electricity. The operation of a generator is based on the principles discovered by Faraday. He found that when a magnet is moved past a conductor, it causes electricity to flow. In a large generator, electromagnets are made by circulating direct current through loops of wire wound around stacks of magnetic steel laminations. These are called field poles, and are mounted on the perimeter of the rotor. The rotor is attached to the turbine shaft, and rotates at a fixed speed. When the rotor turns, it causes the field poles (electromagnets) to move past the conductors mounted in the stator. This, in turn, causes electricity to flow and a voltage to develop at the generator output terminals.
Information courtesy of U.S. Geological Survey and U.S. Army Corps of Engineers.
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