Solar Energy :An Introduction
Solar energy is the main source:The energy obtained from the sun is called solar energy .Indirectly or directly all forms of energy originate from the solar energy.So ancient man was worshiing Sun as the source/GOD.
Solar Energy:Nuclear fusion of deuterium is said to power the Sun.The energy that radiates out in all the directions is received to some extent by various planets and other celestial bodies.Besides,heat energy ,ultraviolet, gamma rays and visible light also comes from solar energy.
Sources of harnessing Solar Energy:There are various sources of harnessing solar energy.Direct sources include Solar Cooker ,Solar Water Heater and Solar Cells.Indirect sources include Biomass Production which takes place in the presence of solar energy.
- All the solar heating devices are designed in such a way that they help in collecting as much sun's rays as possible.This is done by using a black painted surface,a glass sheet cover and in some cases also a plane mirror reflector.A black painted surface is used because black surface absorbs more heat rays of the sun than a whiter surface.A glass sheet is used as a cover in solar heating devices because a glass sheet traps more and more of sun's rays by producing greenhouse effect.
Solar Cooker:Solar cookers and water heaters are devices that are used to collect solar energy in the form of heat over a period of 5-7 hours by exposure to sun.
- A solar cooker is made of an insulated metal or a wooden box which is painted all black from inside.There is a thick flax sheet used to cover the box and a plane mirror reflector is attached to the box.When the sun rays fall on the reflector ,it sends them to the top of the solar cooker in the form of a strong beam of sunlight.The rays pass through the glass shield and are absorbed by the inner black surfaces of the cooker as well as the containers in which the food to be cooked is placed.A temperature of about 100-140°C. can be obtained by keeping a solar cooker in sunlight for 2-3 hours.
- Advantages of Solar Cooker:
- Saves fuel .
- Pollution free
- Nutrients of the food are restored.
- Disadvantages of Solar Cooker:
- Cannot be used on cloudy day and during night time.
- Cannot be used for frying.
- Takes longer time for cooking.
Solar Water Heater:It is a device in which water is heated by using solar energy.
- It consists of an insulated box which is painted black from inside and in which copper tubes is fitted in the form of a coil.These copper tubes are painted black from outside so that they may absorb hot rays of the sun more efficiently.The box is covered with glass lid so as to prevent heat loss by convection and radiation.The two ends of the copper tube of solar water heater are joined to the water storage tank.
- A solar water heater can be installed on top of flat roofed buildings.and provide domestic hot water throughout the year in a warm or moderate warm climatic conditions.
Solar cells:Solar cells are devices that convert solar energy directly into electricity.Solar cells are made from elements such as silicon and selenium.
- A typical solar cell of 2 cm square piece of pure silicon can produce 0.7 watt of electricity when exposed to sun.A large number of solar cells are joined together to make a solar panel.
- Advantages of solar cells:
- Little or no maintenance cost.
- Can be set up in remote and sparsely inhabited areas where laying of usual power transmission lines is difficult and expensive.
- Disadvantages of solar cells:
- Low efficiency.
- The special grade silicon needed to make solar cells is expensive.
Uses of Solar Cells:
- solar cells are used for calculators and watches.
- All artificial satellites and space probes mainly depend upon electricity generated by solar cells.
- They are being used to provide electric power to light houses and off shore drilling rig platforms.
- They are used for transmission of radio and television programmes in remote areas.
Advantages of Solar Energy:
- Drying clothes is made easier.
- To obtain salt from sea water by evaporation.
- To get rid of moisture content in food grains.
- To preserve fruits,vegetables,sea foods by sun drying.
Disadvantages of Solar Energy:
- Not available uniformly all the time and at all the places.
- Not available in night.
- Cloud formation may obstruct the reception.
Comparison with Fossil Fuels:
- The sun is a renewable source of energy but fossil fuels are a non-renewable source of energy.
- The sun's energy does not cause any pollution but burning of fossil fuels causes a lot of pollution.
- The sun's energy is available in a diffused form but fossil fuels provide energy in concentrated form.
- A special device is always needed to utilise sun's energy but this is not so in the case of fossil fuels.
- The sun's energy is available only during the day time when sun shines but energy of fossil fuels can be used at all times.