viernes, junio 13, 2008

An Energy Lesson

Energy = the ability to do work

About half a million years ago human beings learned to make fire. By collecting and burning wood they were able to warm themselves, cook food and manufacture primitive implements. Thousands of years later the Egyptians discovered the principle of the sail. Later still came the invention of the water wheel. All these activities utilise various forms of energy - biological, chemical, solar and hydraulic.

Living standards

Energy, 'the ability to do work', is essential for meeting basic human needs, extending life expectancy and providing a rising living standard.

We have progressed over many thousands of years from a primitive life, which depended for energy on the food that could be gathered, to the hunters who had more food and used fire for heating and cooking, to the early farmers who used domesticated animals as a source of energy to do work.

We took our first steps in the use of mechanical energy with the harnessing of wind and water power. Later, the industrial revolution, based on coal and steam power, laid the foundations for today's technological society, with significant developments such as the internal combustion engine and the large-scale generation of electricity.

Population

Together with this increasing energy consumption, it has been possible for the world to sustain an ever increasing population. At present, however, three quarters of world energy production is consumed by the one quarter of the world's population living in the industrialised countries.

Continuing rapid growth is foreseen in the near future, with the world's population rising from the present 6 billion to about 8 billion over the next 25 years, and perhaps 10 billion later in the century. Most of the population growth will be in the developing countries, which is where more than three quarters of the world's people already live.

Such a population increase will have a dramatic impact on energy demand, at least doubling it by 2050, even if the developed countries adopt more effective energy conservation policies so that their energy consumption does not increase at all over that period.

Energy

can be considered in two categories - primary and secondary.

  • Primary energy is energy in the form of natural resources, such as wood, coal, oil, natural gas, natural uranium, wind, hydro power, and sunlight.
  • Secondary energy is the more useable forms to which primary energy may be converted, such as electricity and petrol.

Primary energy can be renewable or non-renewable:

  • Renewable energy sources include solar, wind and wave energy, biomass (wood or crops such as sugar), geothermal energy and hydro power.
  • Non-renewable energy sources include the fossil fuels - coal, oil and natural gas, which together provide over 80% of our energy today, plus uranium.

The availability of energy

There is no shortage of primary energy. The sun pours an abundance on to our planet each day. We see this energy in a variety of forms, ranging from solar radiation, through wind and waves, to trees and vegetation which convert the sun's rays into plant biomass. In addition, there is an enormous amount of energy in the materials of the earth's crust, the fossil fuels also storing energy from the sun. Uranium is an energy source which has been locked into the earth since before the solar system was formed, billions of years ago.

The challenge today is to move away from our heavy dependence on fossil fuels and utilise non-carbon energy resources more fully. Concerns about global warming are a major reason for this.

Fossil fuels

have served us well. Coal was the first to be widely used industrially and to increase people's standard of living. Oil is a convenient source of energy. Because of its easy availability and low price, it played an important role in the economic development of many countries during the past century. It remains vital for much transport. Natural gas is widely used alongside coal and oil, as a very versatile fuel.

But the question of "Why Uranium?" puts the focus on energy sources which are suitable for electricity. Generating electricity already accounts for 40% of primary energy use, and at 2.7% per year, demand for it is growing twice as fast as for total energy worldwide.

Where should this come from? To put the choices into perspective, let us look briefly at the potential and limitations of each source of electric power, beginning with 'renewables'.

Hydro-electric

generating facilities have the attraction of providing electricity without polluting the atmosphere. They harness the energy of falling water, which can occur naturally, but more often has to be engineered by the construction of large dams with lakes behind them. The advantages of hrdro-electricity have long been appreciated and today it provides 18% of the world's power. In many countries most of the suitable dam sites have already been used, thus limiting further major development of this source.

Other renewable energy sources have more potential for increased use, but also have characteristics which limit their ability to play a major role in meeting electricity needs, bearing in mind that much of the demand is for continuous, reliable supply:

Solar energy

has considerable logical and popular appeal. However, for electricity generation solar power has limited potential, as it is too diffuse and too intermittent. First, solar input is interrupted by night and by cloud cover, which means that solar electric generation plant can typically only be used to a small proportion of its capacity. Also, there is a low intensity of incoming radiation and converting this to high-grade electricity is still relatively inefficient (less than 20%), though this has been the subject of much research over several decades.

On a small scale (and at relatively high cost) it is possible to store electricity. On a large scale any solar electric generation has to be worked in with other sources of electricity with full back-up. While it is true that sunlight itself is free, the capital, energy and materials costs of conversion, maintenance and storage are extremely high. The main role of solar energy in the future will be that of direct heating.

Wind

like the sun, is 'free' and is increasingly harnessed for electricity. About 20,000 megawatts capacity is now installed around the world. However, in meeting most electricity demand, similar back-up issues arise as for solar. It is not always available when needed, and some means is required to provide substitute capacity for windless periods. Nevertheless, costs have come down, and contracts for electricity from some new US plants are as low as for conventional sources.

Geothermal

energy comes from natural heat below the earth's surface. Where hot underground steam can be tapped and brought to the surface it may be used to generate electricity. Such geothermal sources have potential in certain parts of the world, and some 8000 MWe of capacity is operating. There are also prospects in other areas for pumping water underground to very hot regions of the earth's crust and using the steam thus produced for electricity generation.

Biomass

Most forests and agricultural crops are technically capable of being converted into some form of energy, even if the primary purpose of the crop is to provide food. There are also some 'energy farms', where crops are produced solely for energy production. Such farms however compete with other crops for water, fertiliser and land use, thus requiring some choice between fuel and food. Biomass does provide a useful and growing source of energy, especially for rural communities in third world countries, and organic waste and water plants can be used to produce methane or 'biogas'. Nevertheless, it is only likely to play a very small role overall.

Thus as we head into a new century, the only energy resources available for economic large-scale electricity generation are likely to be gas, coal and nuclear.

Oil

has generally become too expensive to use for electricity and it has the great advantage of being a portable fuel suitable for transport. Wherever possible it is conserved for special uses, such as transport and in the petrochemical industry.

Gas

can be seen in the same way as oil, as being too valuable to squander for uses such as large-scale electricity generation. But after the oil price shocks of the 1970s, increased exploration efforts revealed huge deposits of natural gas in many parts of the world and today these are extensively used for power stations. The main virtue of gas however is that it can be reticulated safely and cheaply to domestic and industrial users and burned there to provide heat very efficiently. It is also a valuable chemical feedstock.

Coal

is abundant and world production is about 3.5 billion tonnes per year, most of this being used for electricity. It dominates the scene, and produces 38% of all electricity worldwide, while uranium produces 16%. In OECD countries the figures are closer together: 38% and 24% respectively.

Uranium

is also abundant, and technologies exist which can extend its use 60-fold if demand requires it. World mine production is about 35,000 tonnes per year, but a lot of the market is being supplied from secondary sources such as stockpiles, including material from dismantled nuclear weapons. Practically all of it is used for electricity.

Economics

The difference in fuel requirements between coal fired and nuclear power stations also affects their economics. The cost of fuel for a nuclear power station is very much less than for an equivalent coal fired power station, usually sufficient to offset the much higher capital cost of constructing a nuclear reactor. Consequently, in practical terms, electricity from nuclear reactors in many regions is competitive with electricity produced from coal, even after providing for management and disposal of radioactive wastes and the decommissioning of reactors.

As gas prices rise and coal faces the prospect of economic constraints on its emissions, nuclear energy looks increasingly attractive.

Electricity generation - the future fuel mix

For most countries the questions that need to be answered are: What are our likely electricity requirements? What forms of generation are available to us? Which combination will affordably provide our needs with maximum security, and the least harm to our population and environment?

In mid 2001, there were 31 countries of varying size, political persuasion and degree of industrial development, which included nuclear power in their energy mix and were operating nuclear reactors. Over 16% of the world's electricity is being produced by more than 440 reactors, with 30 more under construction. Belgium, China, France, Germany, Hungary, India, Japan, Russia, Switzerland, UK and USA are just some of the countries with major nuclear energy programs.

In 2000 there was as much electricity produced from nuclear energy as from all sources worldwide in 1961 (2438 billion kilowatt-hours).

No country would want to be too dependent on a single energy source. For many it is therefore not a question of coal or nuclear for their main supply of electricity, but a combination of both, with as much help as possible from renewable sources, and back-up from gas.

To quote an Indian physicist, the late Dr Homi Bhabha,"No energy is more expensive than no energy".

To Investigate or Consider:

  • How important is it to provide for all the world's population to enjoy living standards comparable with those in developed or western countries today?
  • What is the role of energy in providing for high standards of living? Is it more or less important with high population densities?
  • Since 1960 the proportion of electricity in total energy use has almost doubled. Why is this?
  • There is a view that increasing the proportion of electricity in total energy used is the most effective form of energy conservation. Why might this be?
  • What factors are likley to affect the price of fossil fuels over the next 20 years?
  • What will be the effect of increased prices for them, especially oil?
  • What are the different waste management strategies for spent nuclear fuel in UK, France and Japan on the one hand and USA, Sweden and Switzerland on the other?
  • What are your answers to the three questions in the fourth last paragraph in the main text above?

SOURCE>

Of course, left aside of this article learn about the current crisis food with a direct relation in the production of "bio fuel" based on natural "green" oil.

Next chapter.