The World Demand for Power
Physics Research Report
The World Demand for Power
Summary
The world's demand for power is currently increasing at an alarming rate. Essentially, this demand is currently being met by a small number of energy sources. These include:
* Fossil Fuels
* Alternative Sources (Hydroelectric and Solar)
* Nuclear Power (Fission)
Nuclear fusion power is also in development and will possibly become one of the main sources once fully developed.
This report looks some of the basic Physics currently behind these energy sources and how further advances may be brought about by understanding the Physics of the process.
Introduction and Fossil fuels role
According to a study undertaken by the World Energy Council, by 2020, Western European oil and gas reserves will have declined to a point at which only Norway is expected to have significant reserves of natural gas and Western Europe may well enter a phase of declining oil production and rising oil import dependency. In 25 years time, Europe's dependence on the external supply of conventional fuels is likely to have increased from the current level of around 50% to around 70%.
There are a number of other factors that must be taken into consideration. In 1990 some 75% of the world's population (those in the developing countries) were responsible for only 33% of the world's energy consumption; by the year 2020 that 75% is likely to have risen to 85% and the energy consumption to around 55% (see chart). Thus there will be greater competition for the fuel resources available
The means we have currently of powering our needs, with coal, oil or gas are generally accepted by the masses. However their reputations and standing have been somewhat damaged in recent times with heightened awareness of their environmental hazards. Yet their ability to achieve their fundamental objective, to produce power is unquestionable. Despite the implication of damaging the planet, Governments generally across the world are also in support of fossil fuels and refuse currently to pursue any of the new methods with any seriousness. Despite this lack of commitment the fact is oil, coal and gas take centuries to produce whilst we are using them at a ridiculous rate. The end of the 'tank', which governments seem to fail to accept exists, must therefore be quickly approaching. Recent prediction indicate we have approximately 40 years, continuing at the current rate of power use, until the oil we have discovered dries up. Gas also has an estimated 40 years whilst coal resources are much greater and are expected to last for another century. Coal has become somewhat redundant though with it proving must dangerous to the atmosphere. The fossil fuel that currently provides the Earth with the majority of its energy is oil, contributing 60%. Due to this heavy reliance on the fossil fuel, which has emerged the most suitable for our needs, oil is great demand. The entire Earth, land and sea, has been searched for oil 'reservoirs' and once found as much oil as possible is extracted.
Oil Extraction
As we have said 'the end of the tank' is approaching. One interesting application of Physics is now being used to defer this time. This occurs in the process of oil extraction to actually extract more from existing resources.
Once located and 'drilled' the reservoirs of oil would traditionally rely upon the pressure naturally created by the gas present under the ground to force it up. As the oil was extracted the pressure in the reservoir that forced the material to the surface would gradually decline.
Eventually the pressure will decline so much that the remaining oil will not migrate through the porous rock to the well. When this point is reached, less than one-third of the oil in an oil field will have been extracted. The equating of the pressure acting on the oil 'pocket' and the outward acting pressure from within the 'pocket' cause this drop in pressure. The pressure acting outwards is caused by a lot of molecules being kept closely together in a confined space. Pressure is calculated using the equation:
p = 1/3 Nmv2/ V
Where p is pressure, N is number of molecules, m is momentum, v2 is the average of the velocities squared and V is the volume in which the molecules are restricted.
Using this equation in our situation the only variable we have on the right hand side is the volume. Once a hole has penetrated the oil reservoir the restricted volume is no longer comparatively small but has become an infinite space. This huge increase in V, the denominator in our equation reduces p to almost zero, which is why the natural pressure within the 'pocket cant be relied upon. Part of the remaining oil can be recovered by using gas or water to push the oil to the well, but even then, one-fourth to one-half the oil is usually left in the reservoir. In an effort to extract this remaining oil, oil companies are now beginning to use chemicals to push the oil to the well, or to use fire or steam in the reservoir to make the oil flow easier. Implementing the use of fire causes the temperature to rise. Raising the temperature will have a beneficial effect due to what is shown in the following equation that links pressure and temperature.
p = NkT / V
Where p is the pressure, N the number of molecules and V the volume in which the molecules are held. This time however T, temperature and k, the Boltzmann constant are introduced.
In this instance of using fire to raise the temperature in the pocket it has the effect on the equation of increasing T. T is the denominator on the right hand side of the equation and with the other variables remaining constant p also increases. This greater pressure aids the process of extraction.
The modern methods of Power
With the help of physics, modern scientists can produce more energy with a tiny radioactive pellet than they can with several tons of coal, gas, or oil.
Since the late 1930's it has been hoped that science ...
This is a preview of the whole essay
In this instance of using fire to raise the temperature in the pocket it has the effect on the equation of increasing T. T is the denominator on the right hand side of the equation and with the other variables remaining constant p also increases. This greater pressure aids the process of extraction.
The modern methods of Power
With the help of physics, modern scientists can produce more energy with a tiny radioactive pellet than they can with several tons of coal, gas, or oil.
Since the late 1930's it has been hoped that science could develop these methods as alternatives to using traditional fossil fuels. One of these alternatives is Nuclear Energy. Nuclear Energy is released in significant amounts in processes that affect atomic nuclei, the dense cores of atoms. It is distinct from the energy of other atomic phenomena such as ordinary chemical reactions, which involve only the orbital electrons of atoms.
Nuclear Fission
One method of releasing nuclear energy is by controlled nuclear fission in devices called reactors, which now operate in many parts of the world. Nuclear Fission is the subdivision of the heavy atomic nucleus of uranium or plutonium, into two fragments of roughly equal mass. This process is accompanied by the release of a large amount of energy.
Nuclear fission was discovered in 1938 by Otto Hahn and Fritz Strassman whilst attempting to produce elements heavier than uranium by bombarding uranium with neutrons. The two German chemists did not realise that they had in fact induced a fission reaction. It has since been established that nuclear fission occurs when a particle such as a neutron strikes the nucleus of a uranium atom. This collision causes it to split into two fission fragments, each of which is composed of a nucleus with roughly half the neutrons and protons of the original nucleus. This fission process releases a large quantity of thermal energy as well as gamma rays and two or more free neutrons. These free neutrons fission other uranium nuclei, which then give off neutrons that split still more nuclei. A series of fissions of this kind constitutes a chain reaction, which yields a continuous supply of nuclear energy. This can be illustrated as follows:
The fission of 235U can be described as:
235U + 1 neutron --> 2 neutrons + 92Kr + 142Ba + ENERGY
When a nucleus fissions, it splits into several smaller fragments. These fragments, or fission products, are about equal to half the original mass. Two or three neutrons are also emitted. The sum of the masses of these fragments is less than the original mass. This mass is a result of the binding energy that holds the protons and neutrons of the nucleus together. This 'missing' mass (about 0.1 percent of the original mass) is converted into energy according to Einstein's equation
E = mc2
Where E is the energy, m is the mass and c is the speed of light.
Hence one mole of Uranium can release approx 200 Mev of energy (nb 1 MeV (million electron volts) = 1.609 x 10 -13 joules)
U235 + n -> fission + 2 or 3 n + 200 MeV
65 MeV
7 MeV
6 MeV
7 MeV
6 MeV
9 MeV
200 MeV
~ kinetic energy of fission products
~ gamma rays
~ kinetic energy of the neutrons
~ energy from fission products
~ gamma rays from fission products
~ anti-neutrinos from fission products
Nuclear Fusion
Another method for obtaining nuclear energy, controlled nuclear fusion, has not been perfected even as we enter into the 21st century despite being conceptualised in 1939. It was Hans A Bethe who suggested that much of the energy output of the Sun and other stars resulted from energy-releasing fusion reactions in which four hydrogen nuclei unite and form one helium nucleus. This theory became closer to reality during the early 1950s with American researchers producing the hydrogen bomb. The process involved inducing fusion reactions in a mixture of the heavy hydrogen isotopes, deuterium and tritium, with the reactions being ignited by the extremely high temperatures created in the fission reaction of the atomic bomb. More recently, scientists have sought to devise a practical method of controlled nuclear fusion, in which deuterium and tritium nuclei would combine to form helium nuclei under controlled high temperatures rather than in the uncontrollable heat of a detonating atomic bomb. Controlled nuclear fusion would provide a relatively inexpensive alternative energy source for electric-power generation and thereby help conserve the world's dwindling supply of oil, natural gas, and coal. Fusion also would be more advantageous than nuclear fission as the primary fuel Deuterium, is far more abundant and cheaper as it is contained in water, than any of the materials required for fission reactions.
The fusion reaction involves light atoms, the hydrogen isotopes deuterium and tritium, fusing to form a helium nucleus, otherwise known as an alpha particle, and releasing neutrons. The reaction results in a slight loss of mass and therefore a release of energy which is transferred to the alpha particle and neutrons This fusion releases 17.6 MeV of energy.
In the sun immense temperatures and pressures overcome the repulsive forces which the particles experience in close proximity to each other. On Earth it is not possible to reproduce these conditions and tokamak, or doughnut shaped reactors can only produce a plasma - the fourth form of matter, in which atoms are stripped of their electrons - with a pressure of 2-3 atmospheres. So fusion has to be achieved by heating the plasma to 100 million degrees. Hotter than the sun and too hot for any material to remain solid. The plasma has to be held in empty space.
The plasma is held in empty space by powerful electromagnetic forces created by currents running through the plasma and through the structure of the reactor. Super-conducting materials will be used to create the forces and the development of suitable compounds, in particular niobium tin (Nb3Sn), has been one of the major advances during the years of work on the design. The development of niobium tin will continue and the potential of another compound, niobium titanium (NbTi) will also be explored. The need for superconducting materials adds a level of complexity to the engineering challenges that would be considerable even without them.
Pressure; density; the controlled removal of helium atoms (effectively the ash of the process); the removal of excess heat; ensuring the alpha particles produced as a result of the fusion reaction remain at the right concentration to maintain the reaction - too many and the reaction will overheat, not enough and it will die; the maintenance of the plasma in empty space; and the absorption of neutrons in the wall surrounding the reactor and the conversion of the neutrons' kinetic energy into useful energy are just some of the challenges that need to be addressed.
To maintain the plasma in optimum conditions requires balancing a whole series of criteria. Push the envelope with any one of the limiting criteria and the plasma could collapse. Too much pressure leads to instabilities in the plasma, it develops a condition known as the neo-classical tearing mode (NTM). This instability can lead to the plasma hitting the wall of the reactor, damaging the wall material. One challenge is to produce more robust materials which can cope better when this happens. Instabilities like NTMs can happen if kinks or errors form in the confining electromagnetic field. The errors need to be of a certain size, referred to as the seed island size. If any part of the superconducting coils warm to a temperature where the material becomes resistive, the field will collapse and the plasma escapes. Maintaining a plasma in steady state is like holding a jelly in empty space without touching it.
"The plasma performance depends on how much pressure you can put in, as the fusion power is proportional to the pressure squared," says Martin O'Brien, a programme manager at Culham, the UK's centre for fusion research. "You want to operate at as high a density as possible. But at high densities the performance can degrade. Experimentally it is hard to go higher than an empirically observed density, the Greenwald Limit. There are a variety of boundaries due to instabilities, and all factors must be optimised."
Pressure is not uniform across a plasma; it tends to reach a maximum at its centre. The shape of the plasma is also very important as it affects how much pressure can be contained. The more like a D rather than an O the plasma cross-section, the greater the pressure. The profile of pressure across the plasma is also important, as is the pressure at the edge, known as the pedestal size.
With Nuclear Fusion still in development and the great threat nuclear power posses to human health, powering the planet in this manner is possibly not the answer. With the fatal consequences of contamination apparent, the cost of ensuring employees of the power stations health as well as the publics makes the whole process far less economical. The cost of disposing of the radioactive material is also an expensive process. As uranium, the radioactive source, has such a large half life it takes centuries to become harmless and therefore must be kept away from humans, buried deep in the Earth. Though providing us with a great source of energy nuclear power has dangerous disadvantages and therefore a better alternative must be strived for.
Both hydroelectricity and solar power provide us with this alternative option.
Alternative Sources - Hydroelectric
Hydroelectricity is produced from generators driven by water turbines that convert the potential energy in falling or fast-flowing water to mechanical energy
In the generation of hydroelectric power, water is collected or stored at a higher elevation and led downward through large pipes or tunnels (penstocks) to a lower elevation. In the course of its passage down the steep pipes, the falling water rotates impulse turbines. The potential energy is first converted into kinetic energy by discharging water through a carefully shaped nozzle. The jet, created by the nozzle, is directed onto curved buckets fixed on the periphery of the runner to extract the falling water's energy and convert it to useful work.
Modern impulse turbines are based on a design patented in 1889 by the American engineer Lester Allen Pelton. The free water jet strikes the turbine buckets tangentially. Each bucket has a high centre ridge so that the flow is divided to leave the runner at both sides. For maximum efficiency the runner tip speed should equal about one-half the striking jet velocity. The efficiency (work produced by the turbine divided by the kinetic energy of the free jet) can exceed 91 percent when operating at 60-80 percent of full load.
The power of a given wheel can be increased by using more than one jet. Vertical-shaft such as in hydropower plants units may have four or more separate jets.
If the electric load on the turbine changes, its power output must be rapidly adjusted to match the demand. This requires a change in the water flow rate to keep the generator speed constant. The flow rate through each nozzle is controlled by a centrally located, carefully shaped spear or needle that slides forward or backward as controlled by a hydraulic servomotor.
Proper needle design assures that the velocity of the water leaving the nozzle remains essentially the same irrespective of the opening, assuring nearly constant efficiencies over much of the operating range. It is not prudent to reduce the water flow suddenly to match a load decrease. This could lead to a destructive pressure surge in the supply pipeline. Such surges can be avoided by adding a temporary spill nozzle that opens while the main nozzle closes or, more commonly, by partially inserting a deflector plate between the jet and the wheel, diverting and dissipating some of the energy while the needle is slowly closed. Once the turbine begins to move it in turn drives generators, which convert the turbines' mechanical energy into electricity. Transformers, a illustration can be found below, change the alternating current produced by the generators into a very high-voltage current that is suitable for long-distance transmission.
The structure that houses the turbines and generators, and into which the pipes or penstocks feed, is called the powerhouse.
Hydroelectric power plants are usually employed in dams that impound rivers, thereby raising the level of the water behind the dam and creating a relatively high 'head' (the distance between the two levels). The potential power that can be derived from a volume of water is directly proportional to the working head, so that a high-head installation requires a smaller volume of water than a low-head installation to produce an equal amount of power. In some dams, the powerhouse is constructed on one flank of the dam; part of the dam itself is used as a spillway over which excess water is discharged in times of flood. Where the river flows in a narrow, steep gorge, the powerhouse may be in the dam itself.
In some areas where electric-power demand varies sharply at different times of the day, pumped-stored hydroelectric stations are used. During off-peak periods, some of the extra power available is used to pump water into a special reservoir. Then, during periods of peak demand when the power required by the system exceeds the base-load value, the water is allowed to flow down again to generate additional electrical energy. Pumped-storage systems are efficient and, in most cases, constitute the most economical way to meet peak loads.
In certain coastal areas, such as the Rance River estuary in Brittany, France, hydroelectric power plants have been constructed to take advantage of the rise and fall of tides. When the tides come in, the water is impounded in special reservoirs. The water trapped in these basins is then released and the tidal flow used to power hydraulic turbines, which in turn drive electric generators.
Hydroelectric power has certain advantages over both fossil fuels and its fellow new energy supplier, nuclear power: it is continually renewable owing to the recurring nature of the hydrologic cycle; and it produces neither thermal nor particulate pollution. Hydroelectric power is of varying importance in different countries. Nations such as Norway, Sweden, Canada, and Switzerland are able to rely heavily on hydroelectricity because they all have mountainous regions that are subject to heavy rainfall and that lie in close proximity to industrialised areas that require large amounts of electricity. These countries have built hydroelectricity-producing dams at many of the favourable sites within their borders. Hydroelectric power is utilised on a relatively large scale by various other countries, including the United States, Russia, China, India, and Brazil, but it contributes a much smaller proportion of these nations' total electric-power production
Alternative Sources - Solar Power
The Sun is an extremely powerful energy source, and solar radiation is by far the largest source of energy received by the Earth, but its intensity at the Earth's surface is actually quite low. This is partly because the Earth's atmosphere and its clouds absorb or scatter as much as 54 percent of all incoming sunlight. Despite this, in the 20th century solar energy became increasingly attractive as an energy source owing to its inexhaustible supply and its non-polluting character, which are in stark contrast to such fossil-fuel sources as coal, oil, and natural gas.
The sunlight that reaches the ground consists of nearly 50 percent visible light, 45 percent infrared radiation, and smaller amounts of ultraviolet light and other forms of electromagnetic radiation. This radiation can be converted either into thermal energy (heat) or into electrical energy, though the former is easier to accomplish. Two main types of devices are used to capture solar energy and convert it to thermal energy: flat-plate collectors and concentrating collectors. Because the intensity of solar radiation at the Earth's surface is so low, both types of collectors must be large in area. Even in sunny parts of the world's temperate regions, for instance, a collector must have a surface area of about 40 square m to gather enough energy to serve one person for one day.
The most widely used flat-plate collectors consist of a blackened metal plate, covered with one or two sheets of glass, that is heated by the sunlight falling on it. This heat is then transferred to air or to water, called carrier fluids, that flows past the back of the plate. The heat may be used directly or it may be transferred to another medium for storage. Flat-plate collectors are commonly used for hot-water heating and house heating. The storage of heat for use at night or during cloudy days is commonly accomplished by using insulated tanks to store the water heated during sunny periods. Such a system can supply a home with hot water drawn from the storage tank or, with the warmed water flowing through tubes in floors and ceilings, it can provide space heating. Flat-plate collectors typically heat carrier fluids to temperatures ranging from 66° to 93° C. The efficiency of such collectors (i.e., the proportion of the energy received that they convert into usable energy) ranges from 20 to 80 percent, depending on the design of the collector.
When higher temperatures are needed, a concentrating, or focusing, collector is used. These devices reflect sunlight from a wide area and concentrate it onto a small blackened receiver, thereby considerably increasing the light's intensity in order to produce high temperatures. The arrays of carefully aligned mirrors used in these so-called solar furnaces can focus enough sunlight to heat a target to temperatures of 2,000° C or more. This heat can be used to study the properties of materials at high temperatures, or it can be used to operate a boiler, which in turn generates steam for a steam-turbine-electric-generator power plant. The solar furnace has become an important tool in high-temperature research. For producing steam, the movable mirrors are so arranged as to concentrate large amounts of solar radiation upon blackened pipes through which water is circulated and thereby heated.
Solar radiation may be converted directly into electricity by photovoltaic cells. In such cells, a small electrical voltage is generated when light strikes the junction between a metal and a semiconductor (such as silicon) or a junction between two different semiconductors. The voltage generated from a single photovoltaic cell is typically only a fraction of a volt. By connecting large numbers of individual cells together, however, as in modern solar batteries, more than one kilowatt of electric power can be generated. The energy efficiency of most present-day photovoltaic cells is only about 7 to 11 percent; i.e., only that fraction of the radiant energy received is converted to electrical energy. And since the intensity of solar radiation is low to begin with, huge and costly assemblies of such cells are required to produce even moderate amounts of power. Consequently, photovoltaic cells that operate on solar light have so far been used mainly for low-power applications--as power sources for calculators and watches, for example. Larger units have been used to provide power for weather and communications satellites.
Solar energy is also used on a small scale for other purposes besides those described above. In some countries, for instance, specially designed solar ovens are employed for cooking, and solar energy is used to produce salt from seawater by evaporation.
The potential for solar energy is enormous, since each day the Earth receives in the form of solar energy about 200,000 times the total world electrical-generating capacity. Unfortunately, though solar energy itself is free, the high cost of its collection, conversion, and storage has limited its exploitation.
Conclusion
Many aspects of Physics are being brought to bear on the problem of providing for the worlds growing energy demands. It is likely that in order to meet this demand both the boundaries and utilisation of Physics will need to be significantly developed.
Reference and evaluation of the sources
Microsoft Encarta - as a reference tool and a product Microsoft Encarta has a targeted audience. The audience and standard at which the content is aimed is higher-level G.C.S.E. Though the 'Physics' incorporated was below the standard needed it did provide however a useful backdrop to the Earths energy problems. Unfortunately Encarta was produced in 1995 and therefore provided predicted figures that have since been altered.
Encyclopaedia Britannica - a more recently produced multimedia reference suite (2000) that provided a broader and deeper knowledge of the relevant physics and general appreciation of global power. Also as an educational tool, the source was not biased towards an argument and relied on fact.
Friends of the Earth Website and Greenpeace web site - obviously these organisations have their own agendas, particularly pro renewable energy and anti fossil fuel / nuclear power. However the factual information provided a good basis for the analysis.
UKAEA About Fusion Website - a good website produced by the UK Atomic Energy Authority, Government Funded and therefore with a bias towards nuclear power
BNFL Website - although a commercial company, and hence pro nuclear power, they have a requirement to be seen to be providing clear factual information.
8
