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The whole world runs on energy. The earth spins around its axis and travels in its orbit about the sun; volcanoes and earthquakes rock its surface, winds blow, waves crash on the beaches. Energy was required to catalyse the beginning of life and since then, energy is needed to preserve it. Moreover, people use the earth's resources to produce useable forms of energy in order to survive, communicate, travel and also to make life more comfortable.
There are two main categories of energy sources: (a) Renewable, such as the sun, geothermal, tidal and wind energy, which are readily available in nature and (b) non-renewable or finite sources such as fossil (fossil fuels are derived from living organisms which have been fossilised by being subjected to geological forces over very long periods of time), nuclear and chemical sources, whose energy is released by human intervention. Human consumption presently relies mainly on finite energy sources, which provide more than 90% of the total energy used.
The world-wide demand for energy is rapidly increasing every year. With the highly populated developing countries such as China and India joining the lifestyle and technology of the western world, the global demand for electricity is predicted to increase by 265% by the year 2025. At the same time the fossil fuel resources are getting very close to being exhausted as their rate of production (in the case of fossil fuels it is millions of years) is much lower than the rate of consumption. Moreover, the environment is suffering from life threatening pollution: The earth's temperature is increasing as a consequence of the greenhouse effect and the depletion of the ozone layer allows ultraviolet radiation to go through the atmosphere which, among other effects, has serious consequences on human health. As a result the weather conditions become more and more diverse, climate zones move towards the poles or to higher altitudes and living species disappear. At this rate, life on earth is soon going to be unbearable and people will become the victims of their search for comfort.
The difficulty and cost of safely disposing radioactive material and toxic waste, makes the use of nuclear and chemical energy a questionable solution. Therefore, renewable sources of energy need to be considered seriously for two main reasons: a) to meet the world-wide energy demand and b) to protect the environment from the destructive burning of fossil and other fuels.
The energy output of the sun derives from nuclear fusion reactions occurring at its core and is transferred to the surface of the sun by convection and radiation. The intensity of solar radiation in free space at the average distance of the earth from the sun is defined as the solar constant (=1353 W/m2). This power can be converted directly to usable electric energy by photovoltaic conversion in a solar cell.
The solar cell is an important candidate for an alternative terrestrial energy source as a means of converting solar energy into usable electricity. It has great potential as a sustainable, low cost and non-polluting source of energy.
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