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Traditional Power Production
For most people in the Western world, we take the availability of energy as a birthright. Energy is there at the turn of a key when we step into a car or at the flip of a switch in our homes. When we think of energy within the context of sustainability, we are usually thinking of electrical power production and, increasingly, alternative energy sources for vehicles.
In terms of most sources of electrical power, the energy that we rely on in our homes and at work is produced by converting a fuel source (coal, oil, gas, fissile material) into a heat source which produces steam. Steam is used to turn a turbine which converts mechanical energy into electricity. The turbine consists of a coil of wire, which sits inside a permanent magnet; when the coil is rotated (by mechanical energy), electrical energy is produced.
Since the original energy source is derived from a fossil fuel (or a limited geological resource in the case of a nuclear fuel), there is a finite (though immense) amount of energy that can be produced from the earth's resources. Once these resources are depleted, they can never (on a human timescale) be replaced. This article will explain what is a sustainable energy source and touch on the controversy that can accompany them.
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Sustainable Energy Sources: What are They?
As the name implies, a sustainable energy source is something that can (in principle) be used indefinitely since the energy that is produced from it can be replaced. The ecology movement has dubbed such a source as "green" energy. In terms of electricity production, fossil fuels and nuclear fuels are regarded as being unsustainable, since they represent a limited resource which will, eventually, be completely consumed. So, just what is a sustainable energy source then? It is a source of energy that can be replaced indefinitely; either because it can be produced by growing a crop (biofuels, for instance) or is practically limitless (e.g. the energy of the sun; tidal; hydro; wind or geothermal energy).
Wind, hydro and tidal energy sources are converted into electrical energy in much the same way as the fossil fuels; their mechanical energy is used to turn a turbine. In the case of solar energy, a different principle is behind the production of power. The materials used to make a solar cell incorporate semi-conductors, which produce electricity by the photo-electric effect, releasing electrons through the conversion of part of the solar radiation spectrum which falls onto the solar collector.
Geothermal energy can be tapped by bringing hot water from underground up to the surface. The electrical energy is produced from a thermocouple in this situation.
These power sources are regarded to be "clean" since no pollution is produced once they are in operation (of course, that can't be said of their actual construction and installation). While the sun will one day die, and the geothermal energy of the planet is not a truly renewable resource, within the context of continued survival of the human race, they can be regarded as infinite resources.
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The Sustainabilty Controversy
Given that plants can be grown for the production of biofuels; life on earth is only possible because of the proximity of the sun; the wind and tides are produced by the gravitational pull of the moon and the spin of the earth and the geothermal energy is a consequence of the birth of our planet, why isn't all energy produced sustainably? The reason is that these sources are not very efficient at producing electricity.
If the wind is not blowing, a wind farm's output drops to zero; if the sun doesn't shine, the output of a solar cell drops off and in times of water shortage, even hydroelectric power will fail. A traditional power station can produce energy to meet demand around the clock and year long and, compared to the wind farms, solar collectors or tidal barrages needed to produce a comparable amount of energy, they have a tiny footprint. In terms of biofuels which are produced as an alternative to diesel for internal combustion engines, the controversy lies with the fact that significant areas of arable land are being turned over to the production of crops to make biofuels that could be used to feed hungry people. As with most arguments, neither side has a monopoly on the truth.