Sources of Energy
Since the invention of the steam engine, humans have relied more and more on nonrenewable sources of energy, especially coal, petroleum, and natural gas; the reserves of which are limited. To a lesser extent, they have made use of renewable resources, such as water power from rivers to produce electricity, which nevertheless comes at a cost to the environment. Thus, one of the greatest challenges of today is how to obtain energy in an economical, safe, and clean way from renewable sources. Besides the importance of availability, the impact that sources of energy produce on the environment counts a great deal. The nonrenewable sources of energy coal, petroleum, and natural gas make up eighty-one percent of the world’s production of energy. Their consumption on such a massive scale contributes to the greenhouse effect.
Coal and Petroleum
Coal and petroleum are the main energy sources in the developed world. They come from ancient organic deposits that have been buried in the bowels of the Earth for hundreds of millions of years. Petroleum’s pure state is called crude oil, which is a mixture of different hydrocarbons of little use. Hence, the oil must first be distilled to separate its components. These resources, which pollute the atmosphere when burned, are available only in limited reserves.
After petroleum, natural gas slowly rose to a position of importance in the global balance of energy sources because of its availability and efficiency. It has a reputation of being the cleanest fossil fuel. Technological advances, especially in the discovery of deposits, have produced an explosion in the reserve statistics in the last 15 years. These developments have been accompanied by an ever-increasing dependency on natural gas in different parts of the planet. Natural gas is known as “the phantom energy” because it is a colorless, odorless fluid that contains between seventy to ninety percent methane, the component that makes it useful as a source of energy.
Gasoline or diesel with added alcohol (ethanol) produced from crops such as corn appears more and more promising as solutions to the problems posed by the eventual exhaustion of the Earth’s coal and petroleum reserves, as well as the high cost of fossil fuels on the global markets. However, this type of energy presents new challenges. One item of environmental concern is the possibility that massive exploitation of biofuels could lead to the replacement of jungles and woodlands with single crop plantations meant only for the production of raw plant materials. Ethanol is the alcohol in the medicine cabinets of our homes. It can be used in its pure form as fuel or combined with gasoline in different proportions. Two common mixtures are E10 and E85, which have 10 percent and 85 percent ethanol, respectively. 70 percent of the world’s ethanol production is accounted for by Brazil and the United States. In Brazil, ethanol is made from sugarcane, and in the USA, it is made from corn.
A biodigester is when anaerobic bacteria (bacteria that does not require oxygen to live) decompose organic material through processes such as rotting and fermentation, they release biogas that can be used as an energy resource for heating and for generating electricity. They also create mud with very high nutritional value, which can be used in agriculture or fish production. This technology appears promising as an energy alternative and laboratory tests have demonstrated that the biodigestion process kills up to eighty-five percent of the harmful pathogenic agents present in the organic waste, pathogens which would otherwise be released into the environment. Biogas contains about fifty-five to seventy percent methane, its energy-producing component.
The Anaerobic Lagoon at the Cal Poly Dairy 25KW Power Plant to the Right Using the Biogas Created
Today another efficient method for obtaining electric energy is through a controlled nuclear reaction. The nuclei of certain atoms, like uranium 235, can be broken apart when bombarded by neutrons. In doing so, they release great amounts of energy and new neutrons that can break down the nuclei of other atoms, generating a chain reaction called nuclear fission.
To achieve the breakdown of the nucleus, the neutrons must collide at a specific speed, which is governed by a moderating substance, such as water, heavy water, or graphite. The purpose of nuclear fission is to create very hot steam to operate turbines and electrical generators. The high temperatures are achieved by using nuclear energy from the reactor. Although this technology has been used for half a century, it continues to be at the center of debate because of the risks it poses to the environment and health and because of the vast amounts of highly toxic waste it creates.
About 20 percent of the world’s electricity is generated by the force of rivers through the use of hydroelectric power plants. The kinetic energy of rivers is transformed into mechanical energy by turbines and then into electrical energy by generators. This technology, which has been used since the nineteenth century, employs a renewable, non-polluting resource, although the technology’s impact on the environment is high. According to the United Nations, two third of the world’s hydroelectric potential is currently being used, especially in North America and Europe.
Aerial view of Hoover Dam Showing Four Intake Towers which Gradually Funnel Water Towards the Powerhouse
The harnessing of solar energy to produce electricity and heat for everyday use is gaining popularity. Applications of this clean, unlimited form of energy range from charging batteries in telecommunications satellites, to public transportation, all the way to the solar households being built in greater numbers throughout the world. Photovoltaic Energy, the energy obtained from sunlight, requires the use of solar or photovoltaic cells. The energy is essentially formed by a thin layer of semiconductor material (silicon, for example), where the photovoltaic effect (the transformation of light into electrical energy) takes place. The sun shines on the cell where energetic photons (sunlight) move (vibrates) electrons and make them jump to the illuminated face of the cell. The negatively charged electrons generate a negative terminal on the illuminated face and leave an empty space in the now positively charged dark face (the positive terminal).
Once the circuit is closed, there is a constant flow of electrons (electric current) from the negative terminal to the positive one. The current is maintained as long as the Sun illuminates the cell.
Another use of sunlight is as a source for heating water as well as for heating homes. In this case, solar collectors are used; unlike photovoltaic cells, the solar collectors do not produce electric energy. The collectors work using the greenhouse effect: It absorbs the heat from the sun and then prevents this heat from being lost. In doing so, it warms a pipe, through which the fluid (water or gas) flows, which in turn heats a water tank. The water from the tank is ready for domestic use of heating.
In recent years one of the most promising renewable energy resources is the use of wind to produce electricity by driving enormous wind turbines (windmill). The turbines convert the wind into electrical energy through the use of simple technology based on mechanical gears. The wind moves the blades of the wind turbine, producing mechanical energy, which is then converted into electrical energy. Eolic power is an inexhaustible, clean, non-polluting source of energy with some disadvantages. The most important disadvantages are our inability to predict precisely the force and direction of the wind and the negative impact that groups of large towers have on the local landscape.
Geothermal energy is another clean and promising source of energy. The first geothermal plant started operating more than One hundred years ago. Geothermal plants generate electricity from the heat that emanates from the Earth’s interior. Geothermal power plants, however, suffer from some limitations, such as the fact that they must be constructed in regions with high volcanic activity. The possibility of this kind of plant becoming defunct due to a reduction in such volcanic activity is always present, along with the obvious dangers of such technology.
Some people consider hydrogen fuel cells the energy source of the future and predict that in the short term it will gain widespread use in place of fossil fuels. Hydrogen fuel cells produce electricity from the energy released during the chemical reaction of combining hydrogen and oxygen. In the cell, hydrogen collects at the anode and oxygen at the cathode. A catalyst separates the hydrogen electrons from their nuclei. Hydrogen nuclei cross the electrolytic layer without their electrons. Freed electrons, which cannot cross the electrolytic layer, flow through the circuit until they reach the cathode, thereby producing electric current.
The by-products of the process are water and heat, the reaction continues as long as fuel is supplied. Among the advantages of hydrogen-based energy are its very low pollution level and its inexhaustibility (it can be recycled and reused.) Disadvantages include the complications inherent in handling pure hydrogen, its costs, and the wide-scale conversion that would be necessary for petroleum-fueled engines and systems.