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The Green World from Solar Energy
[278th]Scinece Story
2009년 12월 18일 (금) 20:24:58 Kim Min-jeong, Editor-in-Chief yacuza3104@pusan.ac.kr

 

The Green World from Solar Energy

 

   

The principle of solar cell

          Early this year, a surge of bicycles to keep the environment and people healthy overwhelmed the Korean peninsula. Lee Myeong-bak, President of Korea, made bike roads to encourage people to ride bikes in each city. Busan administration has also made efforts to build up a walking culture. Thus, now the environment is a hot potato. One type of power which makes Korea a low carbon and green growth country is solar generation. Then, what is solar generation?
          On a sunny day, we can’t open our eyes when look at the sky around the sun. The reason is the light is so bright. How much energy does the sun gives to the Earth? The earth receives the energy of 1,353J per square meter from the sun in only 1 second. This is equal to the amount of 1.35kW/m2*s. Considering the loss of energy from the refraction and reflection by the atmosphere, the earth receives the energy of 800 ~ 1000W/m2*s. So, we can calculate the amount of solar energy in all of space of the earth during 1 year. That is 795,000*1012kWh. It is an amazing number, because the energy used by human during 1 year is 82.83*1012kWh. The solar energy is about 10,000 times more than the energy used by humans. Therefore, if we can use only 0.01% of solar energy, we can live without concerning about the energy.
          Like this, the sun emits huge energy. However, humans cannot use this energy easily. In other words, solar energy is disposable. How can we use this energy?
          In 1839, Alexandre Edmond Becquerel (1820-1891), French Physicist, discovered that the current will be produced when exposing a material to a light at first. After, Albert Einstein (1879~1955), a theoretical physicist, erected this phenomenon as the photoelectric effect. Let’s try to know what the photoelectric effect is and how it produces a current.
          The photoelectric effect is the phenomenon producing a current by the light. The light exhibits properties of both waves and particles. It is called wave-particle duality. The property of waves is diffraction, interference, and refraction. For example, if you put in half a chopstick in water, you can see it like bending. This phenomenon is refraction. It proves that light has waves. However, particles of light move like a thrown ball. According to the atom model of Niels Hendrik David Bohr (1885~1962), Danish physicist, an atom is composed of protons, neutrons, and electrons. The nucleus is composed of protons and neutrons. Electrons orbit the nuclear, because the electric attraction exists between the nucleus and electrons. We can imagine that a weight suspended from a thread is turning. If we hit the weight enough to cut the thread off, the weight will be free. Like this, if the light has a strong energy hit the electron, it will free the electron. This phenomenon is the photoelectric effect, and it means that light has the property of particles.
          This effect is the starting point of solar generation, because we get a current from the sunlight. People though that we can produce a refined current. The sunlight hits electrons in one material, and another material which has sufficient electrons is attached to first material to first material. So, we can produce a current from sunlight. This is the concept of a solar cell.
          Nowadays, companies are developing solar cells having an efficiency over 20% through related research. The price has also decreased, although it is more expansive than electricity. Can you imagine a beautiful world without being concerned about energy through the development of the solar cell?

By Kim Min-jeong, Editor-in-Chief
yacuza3104@pusan.ac.kr

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