1.
INTRODUCTION 2. Transformation NATURAL ENERGY
3. SOLAR ENERGY COLLECTION DIRECT
1 flat plate collectors
2 Collectors concentration
3 Solar Ovens
4 solar receivers
5 solar Cooling
4. PHOTOVOLTAIC ELECTRICITY
5. SOLAR ENERGY IN SPACE
6. STORAGE DEVICES
INTRODUCTION
Sun the star by the gravitational pull of its mass, dominates the planetary system that includes the earth. By the radiation of electromagnetic energy, directly or indirectly provides the energy that sustains life on Earth, because all foods and fuels are derived ultimately from plants using energy from sunlight
solar energy, radiant energy produced in the Sun as a result of nuclear fusion reactions. Reaches the Earth through space in quanta of energy called photons (see electromagnetic radiation, photons), which interact with the atmosphere and land surface. The intensity solar radiation at the outer edge of the atmosphere, considering that the Earth is at its average distance from the sun, called solar constant and its average value is 1.37 × 106 erg/s/cm2, or about 2 cal/min/cm2.
However, this amount is not constant, since it seems to vary by 0.2% over a period of 30 years. The intensity of actual power available at Earth's surface is less than the solar constant due to absorption and scattering of radiation that causes the interaction of photons with the atmosphere.
This solar house in Corrales (New Mexico, United States) a flat-plate solar collector (bottom right) provides power to heat water pumped through the mill. Water is stored in large drums.
The intensity of solar energy available at a given point on Earth depends on a complicated but predictable, the day of the year, time and latitude. In addition, the amount of solar energy can be collected depends on the orientation of the receiver.
NATURAL TRANSFORMATION OF THE SOLAR ENERGY
natural collection of solar energy is produced in the atmosphere, oceans and plants on Earth. The interactions of the sun's energy, oceans and atmosphere, for example, produce winds, used for centuries to turn mills. Modern systems use wind power propellers strong, lightweight, weatherproof and aerodynamic design that, when attached to generators, produce electricity for local and specialist or to feed the grid in a region or community.
Nearly 30% of solar energy reaching the outer edge of the atmosphere is consumed in the water cycle, producing rain and potential energy of the mountain streams and rivers. The energy generated by these moving water passing through modern turbines is called hydropower. See also Dam, Weather, Water supply. Thanks to
process of photosynthesis, solar energy contributes to the growth of plant life (biomass), together with wood and fossil fuels from the geological point of view derived from ancient plants, can be used as fuel. Other fuels such as alcohol and methane can also be extracted from biomass.
addition, the oceans are a natural type of solar energy collection. As a result of its absorption by the oceans and ocean currents, temperature gradients occur. In some places, these vertical variations reach 20 ° C over distances of several hundred meters. When large masses of different temperatures, the thermodynamic principle predict that you can create a power generating cycle that extracts energy from the mass with higher temperature and transfer an amount to the mass with lower temperature (see thermodynamics). The difference between these energies manifests itself as mechanical energy (to drive a turbine, for example), you can connect a generator to produce electricity. These systems, called systems of ocean thermal energy conversion (OTEC), require huge energy exchangers and other devices in the ocean to produce power on the order of megawatts. See also Ocean and Oceanography.
DIRECT ENERGY COLLECTION SOLAR
The active solar heating systems include equipment that uses energy from the sun to heat and cool structures. Passive systems involve design of structures that use solar energy for cooling and heating. For example, in this house, a space solar collector used in winter when the blinds are open and the refrigerator or cooler in summer when closed. Thick concrete walls allow for fluctuations in temperature because they absorb heat in winter and outside in summer. Water tanks provide a thermal mass to store heat during the day and release it at night.
The direct collection of solar energy requires artificial devices called solar collectors designed to collect energy, often after concentrating the rays of the sun's energy, once collected, is used in thermal processes or photoelectric or photovoltaic. In thermal processes, solar energy is used to heat a gas or a liquid which is then stored or distributed. In the photovoltaic process, solar energy is converted into electricity without any intermediate mechanical device. Solar collectors fall into two main types: flat plate and concentrating.
flat plate collectors
In thermal processes collectors flat plate solar radiation intercepted an absorber plate by passing the so-called carrier fluid. This, in liquid or gaseous form is heated to cross the channel by heat transfer from the absorber plate (see Heat, Heat Transfer). The energy transfer from the carrier fluid, divided by the solar energy striking the collector and expressed as a percentage, is called the collector instantaneous efficiency. Flat plate collectors generally have one or more transparent cover plates to try to minimize heat loss from the absorber plate in an effort to maximize efficiency. Are capable of heating carrier fluids up to 82 ° C and get between 40 and 80% efficiency.
flat plate collectors have been used effectively for heating water and heating. Typical systems used for home-room fixed collectors mounted on the roof. In the northern hemisphere are oriented towards the south and in the southern hemisphere toward the North. The optimum angle for mounting the collector depends on latitude. In general, for systems that are used throughout the year, such as producing hot water collectors are inclined (to the horizontal plane) at an angle equal to 15 ° latitude and are oriented 20 ° or 20 ° S latitude N. latitude
addition
plate collectors flat, the typical systems of heating and hot water are formed by circulating pumps, temperature sensors, automatic controllers to activate the pump and a storage device. The fluid can be both air and liquid (water or water mixed with antifreeze), while bedrock or an insulated tank used as a means of storing energy.
The collector plates using the sun's energy to heat a fluid carrier, in turn, provides heat for use in a home. The carrier fluid, water in this case, flows through copper pipes in the solar collector during the process some of the energy absorbed solar. Then moves to a heat exchanger where it heats the water to be used at home. Finally, a bomb once again leads the fluid to the solar collector to repeat the cycle. Collectors
concentration
For applications such as air conditioning and central power generation and heat to meet industry needs large, flat plate collectors do not provide, in general, fluids with temperatures high enough to be effective . Can be used in a first phase, and then the fluid is treated with conventional means of heating. Alternatively, you can use concentrating collectors more complex and costly. These are devices that reflect and concentrate solar energy incident on a small receiving area. As a result of this concentration, the intensity of solar energy and temperature increases of receptor (called 'white') can come to several hundreds or even thousands of degrees Celsius. Concentrators must move to follow the sun if they are to operate effectively, the devices used for this are called heliostats.
solar ovens solar ovens are an important application of high temperature hubs. The largest, located in Odeillo in the French Pyrenees, has 9,600 reflectors with a total surface of about 1,900 m2 to produce temperatures of 4,000 ° C. These ovens are ideal for research, for example, materials research, which require high temperatures in environments free of pollutants.
central Receivers
centralized generation of electricity from solar energy is under development. The concept of central receiver or power tower, an array of reflectors mounted on computer-controlled heliostats reflect and concentrate the sun's rays on a water boiler located on the tower. The generated steam cycles can be used in conventional power plants and generate electricity.
Solar cooling
cold may occur with the use of solar energy as a source of heat in an absorption cooling cycle (see Refrigeration). One of the standard system components by absorption cooling, called generator, you need a heat source. Since, in general, require temperatures above 150 ° C for absorbing devices work effectively, concentrating collectors are more suitable than flat plate.
PHOTOVOLTAIC ELECTRICITY In a photovoltaic cell, light excites electrons between layers of silicon semiconductor materials. This produces electrical currents.
solar cells made from thin wafers of silicon, gallium arsenide or other semiconductor material in the crystalline state, convert radiation directly into electricity. Cells are now available with conversion efficiencies greater than 30%. Through the connection of many of these cells into modules, the cost of photovoltaic electricity has been greatly reduced. The current use of solar cells is limited to low power devices, remote maintenance free, as buoys and spacecraft equipment.
SOLAR ENERGY IN THE SPACE
A futuristic project proposed to produce large-scale power to situate solar modules in orbit around the Earth. They concentrated energy of sunlight become microwave antennas to be issued to land for conversion into electrical energy. To produce as much power as five large nuclear power plants (one billion watts each) would have to be assembled in orbit several square kilometers of collectors, with a weight of more than 4000 t, would need an antenna on the ground of 8 m in diameter. It could build smaller systems for islands remote, but the economy of scale advantages for a single high-capacity system (see Astronautics).
ENERGY STORAGE DEVICES FOR SOLAR
Due to the intermittent nature of solar radiation as energy source during periods of low demand the excess is stored solar energy to cover needs when availability is insufficient. In addition to simple storage systems such as water and rock, can be used, particularly in refrigeration applications, more compact devices that rely on phase changes characteristic of eutectic salts (salts that melt at low temperatures). The batteries can be used to store excess electricity produced by wind or photovoltaic devices (see Drums). A global concept is to deliver power over existing networks and use these as additional sources when solar availability is insufficient. However, the economy and reliability of this project sets limits for this alternative.
0 comments:
Post a Comment