Energy

In Brazil, the largest amount of power generated comes from hydropower plants (approximately 95%). In rural and more distant from hydroelectric plants, have been using energy produced in power plants and small scale electricity generated from wind power.
In this article we give an overview of alternative sources of energy: hydro, thermal, nuclear, geothermal, wind, tidal and photovoltaic power.
Hydropower
In power plants, electric power has as its primary source of energy from falling water impounded at a certain height. The potential energy that water has in the upper reservoir is transformed into kinetic energy, which causes the turbine blades rotate, driving the shaft of the generator, producing electricity.
Used hydropower in Brazil on a large scale due to large bodies of water exist.
Currently being discussed alternative sources for producing electricity, because the lack of rain is causing a major deficit in electricity supply. The largest hydroelectric plant in Brazil is the Itaipu (Foz de Iguaçu) which has a capacity of 12,600 MW (Fig. 1).
 
  Figure 1 - Itaipu Hydroelectric plant on the border of Brazil with Paraguay
Thermal energy
Power plants in electric power is obtained by burning fuels such as coal, oil, oil products and, currently, sugar cane (biomass).
The production of electrical energy is accomplished by burning the fuel that heats water, turning it into steam. This vapor is driven by a high pressure pipe and spins the turbine blades, which shaft is coupled to the generator. Then the steam is cooled back to liquid state and water is recycled to again be vaporized.
Several steps must be taken such as the gases from the combustion of fuel must be filtered, preventing pollution of the local atmosphere, the heated water must be cooled to be returned to the rivers because many aquatic species can not withstand high temperatures.
In Brazil this is the second type of power source being used, and now with the crisis we are living in is the one that tends to expand.
Nuclear energy
This type of energy is derived from the fission of the atom's nucleus enriched uranium, releasing a large amount of energy.
Enriched uranium - what is this? We know that the atom consists of a nucleus are located where two types of particles: protons that have positive charge and neutrons have no charge.
In the nucleus, there is a region called electrosphere, where the electrons have negative charges. Atoms of the same chemical element that have the same number of protons and different numbers of neutrons are called isotopes. Uranium has two isotopes, 235U and 238U. The 235U is the only one able to undergo fission. In nature you can only find 0.7% of such isotropic.To be used as fuel in a plant, it is necessary to enrich natural uranium. One method is to "filter" the uranium through very thin membranes. The 235U is lighter and first passes through the membrane than the 238U. This has to be repeated several times and is a very expensive and complex. Few countries have this technology to industrial scale.
 
Figure 2 - Diagram of a reactor Nuclear uranium plant is placed in metal cylinders in the reactor core that consists of a moderator material (usually graphite) to slow down the neutrons emitted by uranium decay, allowing the chain reactions. Cooling the reactor core is performed through liquid or gas circulating through pipes, from the inside. This removed heat is transferred to a second pipe where water circulates. By heating the water turns to steam (the temperature reaches 320oC) that will move the turbine blades which will reach the generator, producing electricity (Fig. 2). After the steam is liquefied and returned to the pipe, where it is again heated and vaporized.
In Brazil, is working to Angra 2 nuclear plant and the production of electric energy is in small quantities that it can not supply the entire city of Rio de Janeiro. At the governmental level is under discussion the construction of the Angra 3 nuclear plant because of energy shortage in the country.
The United States leads the production of nuclear energy and the countries France, Sweden, Finland and Belgium 50% of the electricity consumed comes from nuclear plants.

Geothermal Energy
  
 
Geothermal energy is energy produced from underground molten rock (magma) that heats the water in the subsoil. In Iceland, a country that is located far north, near the Arctic Circle, with intense volcanism, where the hot water and steam rises to the surface (fig-geysers. 3) or are in shallow water, has a lot of usable geothermal energy and electric power is generated from this.
  
  Figure 3-Geiseres Power plants take advantage of this energy to produce hot water and steam. The steam drives turbines that generate nearly 3 million joules of energy per second and the hot water runs through pipes to reach homes.
In the United States of America for such plants in California and Nevada. In El Salvador, 30% of the electricity consumed comes from geothermal energy.
Wind Energy
The windmills are our old acquaintances, and use the energy of wind, ie wind, not to generate electricity, but to do work such as pumping water and grinding grain. In Persia in the fifth century, were already used windmills to pump water for irrigation.
Wind energy is produced by converting the kinetic energy of wind into electrical energy. The energy conversion is carried out through a turbine which consists of an electric generator coupled to a shaft which rotates through the impact of wind turbine blades.
  The horizontal wind turbine (the vertical is no longer used), is essentially formed by a combination of two or three blades, with efficient airfoils, driven primarily by forces of lift, driving generators that operate at variable speed to ensure a high efficiencyconversion (Fig. 4). The installation of wind turbines has an interest in places where the average annual speed of winds exceeding 3.6 m / s.
There are currently more than 20,000 wind turbines in large scale operation in the world (mainly U.S.). In Europe, it is expected to generate 10% of electricity from wind by the year 2030.

Figure 4 - View of field equipment to modern energy utilization of winds (wind). Brazil produces and exports equipment for wind farms, but they are still little used. Here we highlight the Camelinho Plants (1MW in MG), Mucuripe (1.2 MW) and Prainha (10 MW) in Ceará, and Fernando de Noronha Pernambuco.
Tidal power Tidal energy is obtained similarly to hydropower.
 It builds a dam, forming a reservoir near the sea. When the tide is high, the water fills the reservoir, passing through the turbine and producing electricity, and at low tide and the reservoir is depleted water leaving the reservoir, passes through the turbine again, in reverse, producing electrical energy ( Fig. 5). This font is also used in Japan and England. In Brazil we have wide range of tides, for example, in St. Louis at the Bay of San Marcos (6.8 m), but the topography of the coastal economically unfeasible to build reservoirs.

Figure 5 - Box of concrete where, in the up and fall of tides, sea water passes which energy is harnessed to generate electricity.
Photovoltaics
 

Figure 6 - solar photovoltaic panel that uses energy from sunlight to sustain public phone isolated location in Australia. Photovoltaic power is supplied to panels containing photovoltaic cells or solar that under the impact of the sun generate electricity. The energy generated by the panels is stored in battery banks, to be used in periods of low radiation and at night (Fig. 6). Direct conversion of solar energy into electricity in solar cells is accomplished through the photovoltaic effect, which consists in generating an electrical potential difference through radiation. The photovoltaic effect occurs when photons (energy that the sun carries) focus on atoms (in the case of silicon atoms), causing the emission of electrons, generating electric current. This process does not depend on the amount of heat, however, the efficiency of solar cell falls when its temperature increases.
The use of photovoltaic panels to convert solar energy into electricity is feasible for small installations in remote or difficult to access. It is used to power electronic devices on existing rockets, satellites and spacecraft.
The system of co-generation photovoltaics is also a solution, a photovoltaic power source is connected in parallel with a local source of electricity. This system of co-voltaic generation is being implemented in the Netherlands in a residential complex of 5,000 homes, with a capacity of 1 MW of photovoltaic power generation.The United States, Japan and Germany are indicative promote the use of photovoltaics in urban centers. In Ciudad Universitaria - USP - São Paulo, there is a building that uses this type of power source.
In Brazil is already used on a significant scale, the solar collector that uses solar energy to heat water and not to generate electricity.