Alternative Or Non-Conventional Sources of Energy
We need to exploit new sources of energy and also develop technology to use the known sources of energy more efficiently due to the increasing demand for energy.
The energy obtained from the sun is called solar energy. Energy is produced in the interior of the sun by fusion reactions taking place between the hydrogen atoms which fuse to form helium and in the process release a tremendous amount of energy.
Solar energy devices: The devices which are used for harnessing solar energy are called solar energy devices. Some common solar energy devices are solar cookers, solar water heaters and solar cell.
Principle of working of solar energy devices: The solar energy received on earth is very small and is approximately 1.4 X (47/100) or 0.66 kJ/s. The solar energy devices should therefore be capable of collecting maximum amount of solar energy and also retain it for its utilization.
There are two types of such devices:
- Devices which collect solar energy as heat, for ex, solar heater, solar cooker etc.
- Devices which convert solar energy into electricity, for ex, solar cell.
Principle: These devices collect solar energy in the form of heat over a period of few hours during a sunny day.
Construction: A solar cooker consists of the following:
|An insulated wooden or metal box painted black from inside||The inner walls and bottom of the solar cooker is pointed black to maximize absorption of solar radiations as bLack surfaces absorb much heat. It also helps in reducing heat Losses due to reflection.|
|Thick glass sheet||Glass has o peculiar property that it allows infrared radiations of shorter wavelengths but does not allow infrared radiations of Longer wavelengths to pass through it. This helps the heat to be retained inside the box as the glass cover does not allow the heat to radiate.|
|Plane mirror reflector||It increases the effective area for the collection of the solar energy.|
Working: The food to be cooked is placed inside the solar cooker in a metal container. When the sun’s rays fall on the reflector, it sends these rays to the top of the solar cooker. The rays get trapped inside the cooker due to which the temperature inside the box rises to about 100°C to 140°C in a few hours.
Advantages of solar cooker
- It saves fuel as it harnesses solar energy
- It does not produce any smoke and hence does not cause any pollution.
- Since food gets cooked at a relativeLy lower temperatures, the nutrients in the food are preserved.
- Their maintenance requires nominal expenditure.
limitations of solar cooker:
- It cannot be used for cooking food during night hours.
- Even during the daytime, it can be used only on a sunny day and not on a cloudy day.
- The direction of the reflector has to be changed continuously so that it always faces the sun.
- The box-type solar cooker cannot be used for frying or baking.
- There is a high initial expenditure on its installation.
What kind of mirror; concave, convex or plain would be best suited for use in a solar cooker? Why?
Since the amount of solar energy available on earth’s surface is not high, the sun’s rays have to be reflected towards the solar cooker. Con-cave mirrors are therefore best suited for use in a solar cooker as they are converging mirrors and converge the sun’s rays towards the focus of the mirror, where the food container is kept. Higher temperatures are achieved in a solar cooker by using concave mirrors as reflectors as compared to plane mirrors.
Principle: These devices convert solar energy directly into electricity. They are made up of semiconductors like silicon and selenium.
Construction: Solar cells are made of a number of thin layers of silicon containing impurities and are arranged in such a way that when sunlight is incident on them, a potential difference is produced between the two regions of the wafers. A 2 cm2 single solar cell can produce about 0.7 watt of electricity when exposed to sunlight. Solar cells are also known as photovoltaic cells.
Advantages and uses of solar cells:
- These are used as the main source of energy in all artificial satellites and space probes.
- Solar cells are used as a source of electricity for radio or wireless transmissions and at TV relay stations.
- These are used for street lighting and for operating water pumps and radio and television sets in remote areas.
- These are used for operating calculators, watches, and toys.
Limitations of solar cells:
- The initial cost of installation is quite high.
- The availability of special grade silicon used for making solar cells is limited.
- The technology to obtain silicon in pure form is expensive.
- Since silver is used for connecting the solar cells in a solar panel and silver is quite expensive, it adds to the cost of the solar cell.
- The non-availability of efficient systems to store the electricity generated by solar cells and to make it available when required is another problem.
Solar Panel: When a large number of solar cells are connected together by means of connecting wires made of a good conductor like silver, we can obtain a large amount of electricity. This arrangement is known as a solar panel.
Compare and contrast fossil fuels and the Sun as direct sources of energy.
Comparison between fossil fuels and sun as direct sources of energy is given below:
|1. These are non-renewable sources of energy||1. It is a renewable source is of energy|
|2. The fossil fuels have limited reserves and are depleting very fast due to overuse||2. Sun is a very large and long-lasting source of energy|
|3. Use of Fossil fuels results in air pollution.||3. Solar energy is totally clean does not cause any pollution.|
|4. It is non-expensive||4. These are expensive, though the initial cost is high.|
|5. These have to be is extracted for use||5. It is readily available, though only during daytime|
|6. Can be used any time of the day and year||6. Can be used only during daytime when there is plenty of sunshine.|
Compare and contrast bio-mass and hydroelectricity as sources of energy.
Comparison between bio-mass and hydro-electricity as sources of energy is given below:
|1. Biomass makes use of chemical energy||1. Hydroelectricity makes use of kinetic energy of running or falling water from height|
|2. usage of biomass for energy requirement causes air pollution||2. Hydroelectricity is pollution-free source of energy|
|3. Use of biomass does not cause ecological imbalance.||3. Construction of dams for hydroelectricity causes ecological imbalances.|
|4. Biomass is a relatively more economic source of energy than hydroelectricity.||4. Hydro Electricity is a relatively costly source of energy|
|5. Residue is used as manure||5. No residue is left behind.|
Energy from the Sea
The phenomenon of high and low tide give us tidal energy. The energy of the tides or the tidal energy can be harnessed by constructing a dam across a narrow opening to the sea. The water moves in and out of the openings in the dam during high and low tides which rotate the turbines and in this way electricity is generated.
The main limitations of harnessing tidal energy are:
- There are a very few sites that are suitable for building dams.
- The rise and fall of water during tides is not high enough to generate electricity on a large scale.
Sea Wave Energy
The kinetic energy of huge waves near sea shore is trapped to generate electricity.When winds blow across the surface of the oceans, these get converted into waves which possess a lot of kinetic energy. Wave energy is used for rotation of turbine and production of electricity. Areas with an energy density of 40 MW per km of coastline are considered to be economically viable.
Ocean Thermal Energy (OTE)
The energy available from the ocean due to the difference in temperature between warm surface waters heated by the sun and colder waters found at ocean depths is known as Ocean Thermal energy.
Ocean Thermal Energy Conversion (OTEC) Power Plants: These are devices used to harness the ocean thermal energy. There should be a temperature difference of at least 20°C between surface waters and water at depths up to 2000 m (2 km). The warm surface water is used to boil a liquid like ammonia or CFC which produces vapour which is used to drive turbine of generators. The cold water from the ocean depths is pumped up to convert the vapour again into liquid.
What are the limitations of the energy that can be obtained from the oceans?
The limitations of energy that can be obtained from the ocean are:
- There are very limited locations where dams can be built for harnessing tidal energy-
- Wave energy can be trapped for generating electricity only where waves are very strong, which is quite limited.
- It is very difficult to efficiently exploit the energy from oceans due to commercial reasons.
The heat from inside the earth can be utilized as a source of energy under certain favorable conditions that are created by natural processes. This energy is known as geothermal energy. The places below the surface of the earth where the hot magma collects are known as hot spots. The underground water in contact with these hot spots get converted into steam which is extracted by drilling holes through which pipes are driven in. The steam which comes up at high pressure is utilized to rotate the turbine of generators.
The advantages of geothermal energy are:
- These can be harnessed for 24 hours throughout the year.
- It is clean and environmentally friendly.
- It is cost effective as the cost of producing electricity is half the cost of producing electricity by conventional means.
Nuclear reactions: The reactions in which the nucleus of an atom undergoes a change forming new atoms and releasing a tremendous amount of energy.
Nuclear fission: When the nucleus of a heavy atom (such as uranium, plutonium or thorium), is bombarded with low-energy neutrons it can be split apart into lighter nuclei.
During a fission reaction, a tremendous amount of energy is released if the mass of the original nucLeus is just a little more than the sum of the masses of the individual products.
Example: The fission of an atom of uranium produces 10 million times the energy produced by the combustion of an atom of carbon from coal.
Nuclear Fusion: The process in which nuclei of low atomic numbers combine to form a heavier atomic nucleus is known as nuclear fusion.
Nuclear Reactor: In a nuclear reactor designedfor electric power generation, such nuclear ‘fuel’ can be part of a self-sustaining fission chain reaction that releases energy at a controlled rate. The released energy can be used to produce steam and further generate electricity.
Nuclear reactors are used for generation of electrical power, production of fissile materials and for nuclear research and are based on nuclear fission.
Nuclear hazards and safety measures:
- Nuclear radiation seriously affect human bodies and materials including buildings.
- A lot of radioactive materials are produced in nuclear reactors.
- It should be ensured that there is no leakage in the moderator or cooling water of nuclear plants which can contaminate water bodies and soil.
- The main hazard of nuclear power generation is the storage and disposal of spent or used fuels.
- There is a risk of accidental leakage of nuclear radiations.