ENERGY FROM THE SUN:



Most of the energy we use can be traced back to the Sun:
  • Fossil fuels are stores of energy that came from the Sun millions years ago.
  • Radiation [light and heat] from the Sun can be absorbed by solar panels to provide hot water. Sunlight can also be absorbed arrays of solar cells [photocells] to generate electricity. In some countries, you may see these on the roofs of houses. 
  • The wind is caused when air is heated by the Sun. Warm air rises; cool air flows into replace it. This moving air can be used to generate electricity using wind turbines.
  • Most hydroelectric power come ultimately from the Sun. The Sun's rays cause water to evaporate from the oceans and land surface. This water vapour in the atmosphere eventually forms clouds at high altitudes. Rain falls on high ground, and can then be trapped behind a dam. This is the familiar water cycle. Without energy from the Sun, there would be no water cycle and much less hydroelectric power.                                                                       
However, we make use of a small amount of energy that does not come from sunlight. Here are three examples:
  • A small amount of hydroelectric power does not depend on the Sun's energy. Instead, it is generated from the tides. The Moon and the Sun both contribute  to the oceans' tides. Their gravitational pull causes the level of the ocean's surface t rise and fall every twelve-and-a-bit hours. At high tide, water can be trapped behind a dam. Later, at lower tides, it can be released to drive turbines and generators. Because this depends on gravity, and not the Sun's heat and light, we can rely on tidal power even at night and when the sun is hidden by the clouds.
  • Nuclear power makes use of nuclear fuels - mostly uranium - mined from underground. Uranium is a slightly radioactive element, which has been in the ground ever since the Earth formed, together with the rest of the solar system, 4.5 billion years ago. So uranium did not gets its energy from the sun.
  • Geothermal energy also depends on the presence of radioactive substance inside the Earth. These have been there since the Earth formed; they have been continuously releasing their store of energy ever since.
 The source of the Sun's energy
The Sun releases vast amount of energy, but it is not burning fuel in the same way as we have seen for fossil. The Sun consists largely of hydrogen, but there is no oxygen to burn this gas. Instead, energy is released in the Sun by the process of nuclear fusion. In nuclear fusion, two energetic hydrogen atoms collide and fuse [join up] to form an atom of helium.
          Nuclear fusion require very high temperature and pressures. The temperature inside the Sun is close to 15 million degrees. The pressure is also very high, so that hydrogen atoms are forced very close together, allowing them to fuse. 
          Scientists and engineers would like to be able to make fusion happen in a similar way here on Earth. Experimental reactors have been built, but it is very tricky to create the necessary conditions for fusion to happen in a controlled way. Perhaps, one day, fusion will prove a safe, clean way of producing a reliable electricity supply.

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