Session-2011-12

Name : p.nagarjun.reddy

Class : tenth (10)

Roll no : 26

Topic : renewable sources of

Energy.

Submitted to: sanjay sir

Submitted from: nagarjun

Renewable Energy Sources in India

Wind Energy

Wind power is one of the most efficient alternative energy sources. There has been good deal of development in wind turbine technology over the last decade with many new companies joining the fray. Wind turbines have become larger, efficiencies and availabilities have improved and wind farm concept has become popular. It could be combined with solar, especially for a total self-sustainability project.

The economics of wind energy is already strong, despite the relative immaturity of the industry. The downward trend in wind energy costs is predicted to continue. As the world market in wind turbines continues to boom, wind turbine prices will continue to fall. India now ranks as a “wind superpower” having a net potential of about 45000 MW only from 13 identified states.

Hydro Electric Power

India has a huge hydro power potential, out of which around 20 % has been realized so far. New hydro projects are facing serious resistance from environmentalists. Resettlement of the displaced people with their lands becomes major issue. The rebirth of waterpower had to await the development of the electric generator, further improvement of the hydraulic turbine, and the growing demand for electricity by the turn of the 20th century (see Electric Motors and Generators). Commercial power companies began to install a large number of small hydroelectric plants in the mountain regions near the major population centers, and by 1920 hydroelectric plants accounted for 40 percent of the electric power produced in the United States.

 

Hydroelectric power generation was accelerated by the establishment of the Federal Power Commission in 1920. Although additional hydroelectric plants were being built, the simultaneous development of larger and more cost-efficient steam-power plants made it obvious that only very large and costly hydroelectric installations could compete effectively, and that the federal government would have to assume a major share in their construction. Motivated by the search for the multiple use of water resources, including navigation, flood control, and irrigation, in addition to power production, the Tennessee Valley Authority, or TVA, started government participation in large-scale waterpower development in 1933.

Electricity Generators

 

Most major installations depend on a large water-storage reservoir upstream of the dam where water flow can be controlled and a nearly constant water level can be assured. Water flows through conduits, called penstocks, which are controlled by valves or turbine gates to adjust the flow rate in line with the power demand. The water then enters the turbines and leaves them through the so-called tailrace. The power generators are mounted directly above the turbines on vertical shafts. The design of turbines depends on the available head of water, with so-called Francis-type turbines used for high heads and Kaplan, or propeller turbines, used for low heads.

In contrast to storage-type plants, which depend on the impounding of large amounts of water, a few examples exist where both the water drop and the steady flow rate are high enough to permit so-called run-of-the-river installations; one such is the joint American-Canadian Niagara Falls power project. See Niagara Falls (waterfall).

Small-scale hydroelectric plants, with capacities between 1 kilowatt and 1 megawatt, are being developed in some countries. In many of China's districts, for example, such dams are the main source of electric power. Other developing nations are also showing interest in such projects, which can make good use of available labor. In the United States, interest in small-scale plants increased following passage of the Public Utilities Regulatory Policies Act in 1978, because it states that large utilities must buy power fed into their lines by these small-scale plants.

Nuclear energy

The release of nuclear energy can occur at the low end of the binding energy curve (see accompanying chart) through the fusion of two light nuclei into a heavier one. The energy radiated by stars, including the Sun, arises from such fusion reactions deep in their interiors. At the enormous pressure and at temperatures above 15 million ° C (27 million ° F) existing there, hydrogen nuclei combine according to equation (1) and give rise to most of the energy released by the Sun.

Nuclear fusion was first achieved on earth in the early 1930s by bombarding a target containing deuterium, the mass-2 isotope of hydrogen, with high-energy deuterons in a cyclotron (see Particle Accelerators). To accelerate the deuteron beam a great deal of energy is required, most of which appeared as heat in the target. As a result, no net useful energy was produced. In the 1950s the first large-scale but uncontrolled release of fusion energy was demonstrated in the tests of thermonuclear weapons by the United States, the USSR, the United Kingdom, and France. This was such a brief and uncontrolled release that it could not be used for the production of electric power.

In the fission reactions discussed earlier, the neutron, which has no electric charge, can easily approach and react with a fissionable nucleus—for example, uranium-235. In the typical fusion reaction, however, the reacting nuclei both have a positive electric charge, and the natural repulsion between them, called Coulomb repulsion, must be overcome before they can join. This occurs when the temperature of the reacting gas is sufficiently high—50 to 100 million ° C (90 to 180 million ° F). In a gas of the heavy hydrogen isotopes deuterium and tritium at such temperature, the fusion reaction

Occurs, releasing about 17.6 MeV per fusion event. The energy appears first as kinetic energy of the helium-4 nucleus and the neutron, but is soon transformed into heat in the gas and surrounding materials.

If the density of the gas is sufficient—and at these temperatures the density need be only 10-5 atm, or almost a vacuum—the energetic helium-4 nucleus can transfer its energy to the surrounding hydrogen gas, thereby maintaining the high temperature and allowing subsequent fusion reactions, or a fusion chain reaction, to take place. Under these conditions, “nuclear ignition” is said to have occurred.

Tokamak Fusion Reactor

 

The basic problems in attaining useful nuclear fusion conditions are (1) to heat the gas to these very high temperatures and (2) to confine a sufficient quantity of the reacting nuclei for a long enough time to permit the release of more energy than is needed to heat and confine the gas. A subsequent major problem is the capture of this energy and its conversion to electricity.

At temperatures of even 100,000° C (180,000° F), all the hydrogen atoms are fully ionized. The gas consists of an electrically neutral assemblage of positively charged nuclei and negatively charged free electrons. This state of matter is called plasma.

Plasma hot enough for fusion cannot be contained by ordinary materials. The plasma would cool very rapidly, and the vessel walls would be destroyed by the extreme heat. However, since the plasma consists of charged nuclei and electrons, which move in tight spirals around the lines of force of strong magnetic fields, the plasma can be contained in a properly shaped magnetic field region without reacting with material walls.

In any useful fusion device, the energy output must exceed the energy required to confine and heat the plasma. This condition can be met when the product of confinement time t and plasma density n exceeds about 1014. The relationship tn≥ 1014 is called the Lawson criterion.

Target Chamber of the National Ignition Facility

Numerous schemes for the magnetic confinement of plasma have been tried since 1950 in the United States, Russia, the United Kingdom, Japan, and elsewhere. Thermonuclear reactions have been observed, but the Lawson number rarely exceeded 1012. One device, however—the tokamak, originally suggested in the USSR by Igor Tamm and Andrey Sakharov—began to give encouraging results in the early 1960s.

· The confinement chamber of a tokamak has the shape of a torus, with a minor diameter of about 1 m (about 3.3 ft) and a major diameter of about 3 m (about 9.8 ft). A toroidal (donut-shaped) magnetic field of about 50,000 gauss is established inside this chamber by large electromagnets. A longitudinal current of several million amperes is induced in the plasma by the transformer coils that link the torus. The resulting magnetic field lines, spirals in the torus, stably confine the plasma.

Based on the successful operation of small tokamaks at several laboratories, two large devices were built in the early 1980s, one at Princeton University in the United States and one in the USSR. The enormous magnetic fields in a tokamak subject the plasma to extremely high temperatures and pressures, forcing the atomic nuclei to fuse. As the atomic nuclei are fused together, an extraordinary amount of energy is released. During this fusion process, the temperature in the tokamak reaches three times that of the Sun’s core.

Another possible route to fusion energy is that of inertial confinement. In this concept, the fuel—tritium or deuterium—is contained within a tiny glass sphere that is then bombarded on several sides by a pulsed laser or heavy ion beam. This causes an implosion of the glass sphere, setting off a thermonuclear reaction that ignites the fuel. Several laboratories in the United States and elsewhere are currently pursuing this possibility. In the late 1990s, many researchers concentrated on the use of beams of heavy ions, such as barium ions, rather than lasers to trigger inertial-confinement fusion. Researchers chose heavy ion beams because heavy ion accelerators can produce intense ion pulses at high repetition rates and because heavy ion accelerators are extremely efficient at converting electric power into ion beam energy, thus reducing the amount of input power. Also in comparison to laser beams, ion beams can penetrate the glass sphere and fuel more effectively to heat the fuel.

Progress in fusion research has been promising, but the development of practical systems for creating a stable fusion reaction that produces more power than it consumes will probably take decades to realize. The research is expensive, as well. However, some progress was made in the early 1990s. In 1991, for the first time ever, a significant amount of energy—about 1.7 million watts—was produced from controlled nuclear fusion at the Joint European Torus (JET) Laboratory in England. In December 1993, researchers at Princeton University used the Tokamak Fusion Test Reactor to produce a controlled fusion reaction that output 5.6 million watts of power. However, both the JET and the Tokamak Fusion Test Reactor consumed more energy than they produced during their operation.

BIOMASS

Biomass, contraction for biological mass, the amount of living material provided by a given area of the earth's surface. The term is most familiar from discussions of biomass energy, that is, the fuel energy that can be derived directly or indirectly from biological sources. Biomass energy from wood, crop residues, and dung remains the primary source of energy in developing regions. In a few instances it is also a major source of power, as in Brazil, where sugarcane is converted to ethanol fuel, and in China's Sichuan province, where fuel gas is obtained from dung. Various research projects aim at further development of biomass energy, but economic competition with petroleum has mainly kept such efforts at an early developmental stage.

Biomass fuels work by releasing solar energy. Plants, through photosynthesis, convert solar energy to chemical energy, which fuels plant growth. People, in turn, use this stored solar energy through fuels such as wood, alcohol, and methane that are extracted from the plant life (biomass).

Nuclear energy

Solar Energy, radiation produced by nuclear fusion reactions deep in the Sun’s core (see Nuclear Energy). The Sun provides almost all the heat and light Earth receives and therefore sustains every living being.

Solar energy travels to Earth through space in discrete packets of energy called photons (see Electromagnetic Radiation). On the side of Earth facing the Sun, a square kilometer at the outer edge of our atmosphere receives 1,400 megawatts of solar power every minute, which is about the capacity of the largest electric-generating plant in Nevada. Only half of that amount, however, reaches Earth’s surface. The atmosphere and clouds absorb or scatter the other half of the incoming sunlight. The amount of light that reaches any particular point on the ground depends on the time of day, the day of the year, the amount of cloud cover, and the latitude at that point. The solar intensity varies with the time of day, peaking at solar noon and declining to a minimum at sunset. The total radiation power (1.4 kilowatts per square meter, called the solar constant) varies only slightly, about 0.2 percent every 30 years. Any substantial change would alter or end life on Earth.

GEOTHERMAL ENERGY

The distance from Earth’s surface to its center is about 6,500 km (about 4,000 mi). From Earth’s surface down through the crust, the normal temperature gradient (the increase of temperature with increase of depth) is 10° to 30° C per km (29° to 87°F per mi). Underlying the crust is the mantle, which is made of partially molten rock. Temperatures in the mantle may reach 3700° C (6700° F).

The convective (circulating) motion of this mantle rock drives plate tectonics—the 'drift' of Earth's crustal plates that occurs at a rate of 1 to 5 cm (0.4 to 2 in) per year. Where plates spread apart, molten rock (magma) rises up into the rift (opening), solidifying to form new crust. Where plates collide, one plate is generally forced (subducted) beneath the other. As the subducted plate slides slowly downward into the mantle’s ever-increasing heat, it melts, forming new magma. Plumes of this magma can rise and intrude into the crust, bringing vast quantities of heat relatively close to the surface. If the magma reaches the surface it forms volcanoes, but most of the molten rock stays underground, creating huge subterranean regions of hot rock.

TIDAL ENERGY

The energy of tides has been harnessed to produce electricity. In the summer of 1966, a tidal power plant with a capacity of 240,000 kw went

into operation on the Rance River, an estuary of the English Channel in northwestern France. The incoming tide of the river flows through a dam, driving turbines, and then is trapped behind the dam. When the tide ebbs, the trapped water is released and flows back through the dam, again driving the turbines. Such tidal power plants are most efficient if the difference between high and low tides are great, as in the Rance estuary, where the difference is 8.5 m (28 ft). The highest tides in the world occur in the Bay of Fundy in Canada, where the difference between high and low tide is about 18 m (about 60 ft). The erection of a tidal power plant across Passamaquoddy Bay, an arm of the Bay of Fundy, has long been contemplated; however, the project has not yet been begun.