Solar Energy – A renewable and emission-free power source (Part I)
By: Marina Thurau
The need for alternative sources of energy which are green and earth-friendly has been a subject of concern to many scientists, researchers and policy makers for a long time. Fortunately, some inroads have been made, like wind, tidal and wave power, biogas and solar power but they have not been harnessed to the extent of minimizing the traditional dependency on oil and hydrothermal power generation. For instance, in Africa where the Sun is shines everyday, the use of energy from the sun can be of immense benefit to the populace and that will bring a huge amount of development and improvement in the lives of the people.
In the following article, therefore, we will have a special look at the use of the energy provided by the sun and how to utilize it through modern technology called solar-thermal and photovoltaic energy.
The sun, the central star in our solar system, has produced energy through a process in its core called nuclear fusion for the past 4.5 billion years. This energy supplies all the life processes and life circles on earth with light and warmth and keeps them moving (water, wind, nutrition, energy cycles etc.). If our sun would just stopped shining today, life on earth, as we know it, cannot exist anymore. After eight minutes, that is the time the light of the sun needs to reach the surface of the earth, our planet would turn into a freezing cold mass of matter drifting in the endless and dark expanse of space.
According to scientists, the sun has used nearly the first half of its hydrogen supply, one of the main components of this star, and part of the nuclear fusion, producing enormous amounts of energy besides helium and smaller fractions of other chemical elements like oxygen, carbon dioxide, nitrogen, neon, iron etc,. This nuclear fusion is a very complex process in the core of the sun where gravity pulls all of the mass inward and creates such an intense pressure, that it forces atoms of hydrogen to convert to helium, which generates energy. This energy is carried by particles of light (so-called photons) through the sun´s spherical shell (the radiative zone) to the top layer of the solar interior (the convection zone). The boiling motions of the gases (convection) in this zone transfer the energy to the sun´s surface. This process can take more than a million years.
The good news is that scientists estimate that the sun’s nuclear fusion will continue for about another five billion years. Until then we will have a good chance of using the sun´s power for our own purposes. It is therefore important to upgrade our current knowledge and technologies on how to utilize this great potential of renewable energy. This means understanding the electromagnetic radiation, which is released by the sun, and the process of transforming this radiation into electrical power. The electromagnetic radiation emitted from the sun´s surface spreads in all directions and only some part of it reaches the earth’s surface.
This radiation consists of self-sustaining oscillating electric and magnetic fields at right angles to each other and to the direction of propagation and carries energy through a medium, including empty space, where it travels at the speed of light – because it is light. The spectrum of electromagnetic radiation ranges from Radio waves, Microwaves, Infrared, Visible light, Ultraviolet, X-rays to Gamma rays depending on its specific wavelength. We are also aware that light has a split personality. Sometimes it behaves like a wave, and at other times it is best regarded as particle-like. When this happens, we refer to it as a package of energy called a photon. If the sun emits electromagnetic radiation, we imply that photons are created and conversely, when radiation is absorbed by matter (for example our Photovoltaic material), photons are consumed.
The principle of this consumption of photons and the transformation into electrical energy was first discovered in 1839 by the French physicist, Alexandre Edmond Becquerel. But it took another 66 years to explain the photoelectric effect properly and completely. This was done by Albert Einstein, who for this excellent work was awarded the Nobel Prize for Physics in 1921. Another half a century later (1954), some physicists and the semiconductor industry were able to invent the first photovoltaic cell – a silicon cell. This gave the impulse for further and ongoing research for more efficient and better materials and technologies.
Nowadays, we differentiate between two systems/ technologies using solar power: solar-thermal energy (STE) and photovoltaic (PV). STE is a technology for harnessing solar energy for thermal energy. The heat from the sun’s rays is collected, concentrated and used to heat a fluid or gas. This heated fluid is used to run a heat engine, which turns a generator to produce electricity. PV, on the other hand, directly converts sunlight into electricity.
In part two of this article, we will have a closer look at the two different technologies, their advantages and disadvantages and their applications in our daily lives.
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