Fossil fuels, such as coal and oil, are likely to run out within the next 50 years. In contrast to this fact, the world's energy consumption is set to increase with population size. For mankind to live in a technological society, alternative sources of energy are required for the future. These sources will mainly rely on renewable sources such as solar, wind, hydroelectric and geothermal power, although nuclear power will continue to play a major role.
Solar power is energy generated by light from the sun. Special devices called solar panels are used to harness such energy. In basic solar panel devices, light excites electrons in the material to higher energy states, allowing them to conduct and produce electricity. Solar panels are now quite versatile and can be used as tiles on roofs of buildings.
Simple wind power has been used in windmills since the fifth century. Simple windmills work by converting wind power into rotational motion using four or more sails. This rotational motion was once used to grind a substance, such as grain, into smaller parts, such as flour. Today, more sophisticated varieties convert wind power directly into electrical energy. Windmills do not typically produce large amounts of energy, and it's quite common to see "wind farms" with hundreds of units being used to generate a fraction of a city's energy supply.
Hydroelectric power already generates approximately 20 percent of the world's energy. The technology works by using water stored behind a dam. The water flows down through a series of tunnels and turns turbines that generate electricity.
Geothermal energy uses heat, naturally occurring deep beneath the surface of the Earth, to generate heat or electricity. This can typically only be used in parts of the world where there is a high amount of volcanic activity such as the Yellowstone basin in the United States or other countries such as Iceland. The geothermal activity can either be used to directly generate heating for housing or can be used to heat steam and drive turbines.
Nuclear power is the extraction of energy by fission (splitting) or fusion (combining) of atomic nuclei. An atom consists of a nucleus with sub-atomic particles called protons and neutrons, surrounded by a cloud of electrons. Einstein's famous equation E=mc^2 demonstrates that energy and mass are equivalent, and that the energy of the protons and neutrons can be extracted. Today's nuclear reactors work via the process of nuclear fission whereby heavier atoms are split into several smaller parts. The sum of the combined mass is less than the individual constituent parts, and the difference is released as energy. In a nuclear power plant the released energy is used to heat steam. The heated steam turns a turbine, which drives a generator, producing electricity.
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