Solar powerThe Earth receives 1.5⋅1022 J of solar energy. Over 30% of the solar rays are reflected by clouds and the Earth’s surface, but most of them passes through the atmosphere. By heating the atmosphere, the oceans and the dry land, the Sun causes winds, rains, snow and oceanic currents. However, all of the energy dissipates back to the outer space, keeping the planet in thermal equilibrium. A small part of the solar energy is accumulated in lakes and rivers, some is retained in the living plants and animals. The solar power has unique qualities: it is renewable, environmentally clean, controllable and it exceeds all of the energy used today by several orders of magnitude. Solar power is used for heating of greenhouses, residences, it is accumulated in solar power cells, which convert solar radiation into electric power; spaceships use solar panels or photocells to supply astronauts with power in the outer space. The drawback of solar power is that solar rays dissipate over the surface of the earth and a large surface collecting the solar power is needed.
Wind powerAbout 46% of solar power reaching the earth is absorbed by the oceans, dry land and air. This energy powers winds, waves and oceanic currents, as well as weather patterns. Estimation of wind power on the global scale is in the order of 1022 W, however, high altitude winds are accountable for most of that energy, which is not accessible on the surface level. Power of consistent surface winds is estimated at about 1012 W and can be used by wind turbines and sea-faring vessels. The growth of global wind power production increases by 28%. By 2020, up to 10% of the world’s electricity will be produced by wind farms.
Tidal powerTides are the result of the Moon’s and the Sun’s gravitational pull on the Earth, the Moon’s influence being the stronger by far. The power of the tides is an expression of the planetary rotation power. The height of the tides is not uniform. It rarely exceeds one meter in deep ocean, but can be as high as 20 meters over the continental shelf. Tidal energy is estimated at 0.85⋅1020 J. In France (the Rance river) and in Russia (Kislaya Guba), power plants already generate energy from tidal waves. Generation of power from tidal ways is somewhat problematic. For efficient operation of a tidal power plant, the wave must be at least 5 meters high; also, estuaries and small gulfs locked with levees are needed. However, in most places tides are only about 2 meter high, there being only about 30 places on the planet which are suitable for tidal power generation. The most important of them are: the two adjacent gulfs – Fandi (Canada) and Passamukuoddi (US), the French coast along the English Channel, where the Rance power plant has been operating for many years, the estuaries of river in the Irish sea, the Russian White Sea and the Kimberley Coast in Australia. Tidal power may become more prominent in the future, since it is one of the few power systems which operate without any noticeable impact on the environment.
HydropowerAbout 23% of solar radiation evaporates water, which them precipitates as rain or snow. The energy of this water is a renewable resource. Hydropower has been used in a primitive way thousands of years before the 20th century, when massive dams were constructed to produce electricity. Of all the renewable energy sources, hydropower is the most used. The drawback is that the dams have a limited (and likely not very long) lifetime. The flow of water carries fine suspended clay particles; as soon as the flow slows, this material forms sediments and a reservoir may be completely filled in 50 – 200 years. The largest untapped potential of hydropower can be developed where large quantity of hydropower is available.
Geothermal energyThe temperature raises from 15C to 75C just one kilometer under the Earth surface. In the plane’s core, the temperature likely exceeds 5000C. On average, the energy reaching the surface is in the order of 6.3⋅106 J. Besides, the heat of the planet is powered by radioactive decay of such elements s U238, U235, Th232, K40, which are scattered throughout the planet. Water underground is heated and escape to the surface in the form of steam and hot water, also know as geysers. Geothermal hot water is used in Iceland, Japan, Italy, Indonesia, the Philippines, Russia, the US and New Zealand for heating of houses, swimming pools, greenhouses. However, the use of this energy is low compared to that of electric energy.
Atomic energyAtomic energy can be produced by one of the two processes. The first is synthesis of light elements, such as hydrogen and lithium, resulting in heavier elements. This process occurs in stars and in the hydrogen bomb, but it is very difficult to control; it is hoped that in the future, nuclear fusion will become the primary energy source. The second process is fission of heavy elements, such as uranium or thorium. This is the process of the atomic bomb and of nuclear power plants. Since this reaction can be controlled, nuclear fission is already used for production of electricity in nuclear power plants. The U235 isotope of uranium has a natural fission ability; this isotope accounts for only 0.7% of the total of natural uranium atoms. A U235 chain reaction was first accomplished by Enrico Fermi on 2 December 1942 in one of the most important experiments in the history of the planet Earth. The cost of U235 atoms is high. However, fission of one U235 atom releases 3.2⋅1011 J of energy. Since 1 gram of U235 contains approximately 2.56⋅106 J atoms, fission of 1 gram of uranium generates 8.19⋅1010 J, which is equivalent to energy generated by combustion of 2.7 tons of coal. About 300 power plants now use U235 as fuel. The world leader in the atomic power generation is the US (about 50%), followed by Europe (30%) and Japan (12%). Nuclear power generation raises pressing safety issues, as well as the problem of disposal of radioactive waste.
Fossil fuelAt this time, three kinds of fossil fuels are used: coal, oil and natural gas. They account for about 90% of the world’s power generation. The global deposits of coal are estimated 13800 billion tons with additional potential deposits of about 6650 billion tons. The geography of the deposits is as follows: 43% of the world deposits are in Russia, 29% in North America, 14.5% in Asia, mostly in China, and 5.5% in Europe, with the remaining 8% being scattered around the world. Although coal is not the leading fuel on the global fuel, it is still the prevalent type of fuel in some countries; it is possible that the future shortage of oil and gas will lead to increased coal use. Use of coal has many difficulties. It contains from 0.2% to 7% of sulfur mostly in the form of iron disulfide, ferrous iron sulfate, calcium sulfate and some organic compounds. When coal is burned, oxidized sulfur is released into the atmosphere and causes acidic rain and snow. Another problem is coal mining. Subterranean methods of coal extraction are difficult and even dangerous. Strip mining is more efficient and is safer, but it obviously disrupts soil in large areas. The most widely used source of energy is oil and hydrocarbon gas.