Thursday, May 28, 2020

Application of solar energy

As the World is progressing day by day, we have consumed the natural resources at the pace that they are on the verge of extinction. Thus, to satisfy our needs we have transited to renewable natural resources. Renewable natural resources are those that are inexhaustible and can be replenished. Such energy resources are also referred as "Non-Conventional energy resources". Solar energy being one of them. 

The direct use of solar energy initiated 2500 years ago by Greeks. The amount of Sun's radiation received by Earth is enormous. On a global scale, two weeks worth of solar energy is roughly equivalent to the energy stored in all known reserves of coal, oil and natural gas on Earth. 

Active and Passive solar systems
Solar energy may be used directly through passive or active solar systems. Passive solar systems do not require mechanical power whereas active solar systems requires mechanical power. Passive solar systems are often used in architectural designs to take advantages of solar energy through the year. Active solar systems usually takes help of pumps or other apparatus to circulate air, water or other fluids from solar collector to heat sink. Solar collectors are flat panels which are usually placed on the top or roofs to collect solar radiation. Short wave solar radiation enters the glass and is absorbed by black background. Long wave radiation are emitted from black material in solar panels but it cannot run away from the glass. The heat collected is then transferred to heat sink. 

House having solar rooftop.

Solar cell

Another important usage of direct solar energy involves solar cells or photovoltaics. It converts solar energy into electrical energy with the help of photovoltaic effect. In simplest form, they consist of two layers of semuconductors sandwiched together, with a barrier between that allows electrons to flow predominantly in one direction only. 1st generation solar cells were having silicon, 2nd  generation were having amorphous silicon or non silicon material such as cadmium telluride whereas 3rd generation are having solar inks, solar dyes and conducive plastics. The single junction silicon solar cells can produce a maximum open circuit voltage of approcimately 0.5 to 0.6 volts. Solar cells are also utilized as photodetectors (for infrared rays), detecting light and other electromagnetic radiation and also to measure intensity of light.

Solar cell is used in calculators.

Solar tower

Solar power tower are also in use in some regions. It is also known as central tower power plants and heliostat power plants. The tower collects the sun light.Such towers have mirrors (known as heliostat)  which can adjust themselves along with the sun's movement so that maximum amount of radiation can be received. Solar towers collects solar energy as heat but it delivers steam to the turbine which helps to produce electric energy. When steam is available in a sufficient amount,it is stored for the future use.

Solar ponds
Solar ponds are used to generate relatively low temperature of about 68°C. Two types of solar ponds are developed. 

Deep solar pond- Such ponds are have a depth of about 3 meters. The pond is designed to collect heat during the summer builiding up a bottom temperature upto 68°C in the fall. During winter, heat can be extracted from the bottom. The pond has hot water in the bottom by addition of salt, which makes the bottom water heavier. Circulation is restricted by addition of salt so that the dense water remains at the bottom and not mixes with the water above. 

Shallow solar pond-  It has a depth of about 5-10 centimeters. The top is transparent for solar energy to pass on whereas on the bottom there is black material that absorbs energy. The pond is insulated to prevent heat loss to soil and rocks. Thus, such ponds are solar collectors.

Solar distillation
In coastal and desert areas, solar energy is used to carry out distillation of water. In such areas, the water is saline and is not usable for drinking purpose. Therefore, solar energy is used there for carrying out distillation of water. In this method, solar radiation is passed through an air tight glass cover over an basin containing saline water. Solar radiation passes through it and gets absorbed and cause the water to evaporate from brine. Such water vapors gets condensed on the roof and gives purified form of water. Then the purified water is to be collected.

Solar green house
Solar green house is mostly utilized by European countries. A green house consists of transparent material such as glass or plastic to collect the solar radiation. Such radiation is utilized by the plants. Solar radiations can pass through the transparent material but the thermal radiations emitted within the greenhouse cannot escape and thus, maintains a warm temperature. As it has a close boundary, the air gets enriched with carbon dioxide and there is less moisture due to reduced transpiration. All these are advantagenous for the growth of plants.