The energy of wind is harnessed by using a windmill.
In order to generate a large amount of electricity, a large number of wind turbines are erected over a big area of land which is called wind energy farm.
ADVANTAGE OF HARNESSING WIND ENERGY
Its use does not cause any pollution.
Wind energy is a renewable source of energy which will never get exhausted.
LIMITATIONS OF HARNESSING WIND ENERGY
Wind energy farms cannot be established everywhere. The wind energy farms can be established only at those places where wind blows for most part of the year.
The minimum wind speed necessary for satisfactory working of a wind generator is about 15 km/h. This is not always so.
The wind energy farms require a large area of land.
The setting up of wind energy farms is very expensive.
The radiating light and heat from the sun can be harnessed to convert to other forms of energy like electrical energy and heat. Energy obtained from the sun is called solar energy.
India receives solar energy for greater part of the year due to its strategic location near the equator.
It has been estimated that India receives solar energy equivalent to more than 5000 trillion kWh (5000 * 1018 kWh) during a year.
Solar power is indefinitely renewable and used to power cookers, water heaters, etc.
SOLAR ENERGY DEVICES
A device which gets heated by using sun’s heat energy is called a solar heating device.
All the solar heating devices are designed in such a way that they help in collecting as much sun’s heat rays as possible.
The solar cooker is a device which is used to cook food by utilizing the heat energy radiated by the sun.
The box-type solar cooker can be used to cook only those food materials which require slow heating.
ADVANTAGES OF A SOLAR COOKER
The use of solar cooker for cooking food saves precious fuels like coal, kerosene and LPG.
The use of solar cooker does not produce smoke due to which it does not pollute air.
When food is cooked in solar cooker, its nutrients do not get destroyed. This is because in a solar cooker, food is cooked at a comparatively lower temperature.
In a solar cooker, up to four food items can be cooked at the same time.
LIMITATIONS OF A SOLAR COOKER
The solar cooker cannot be used to cook food during night time.
If the day-sky is covered with clouds, even then solar cooker cannot be used to cook food.
The direction of reflector of solar cooker has to be changed from time to time to keep it facing the sun.
The box-type solar cooker cannot be used for baking (making chapattis, etc.) or for frying.
SOLAR CELLS OR PHOTOVOLTAIC CELLS
Solar cell is a device which converts solar energy (or sun’s energy) directly into electricity.
The primary disadvantage of solar power which is the absence of sunlight can be overcome by the use of solar cells
A solar cell is usually made from two or more layers of semiconductor like Silicon.
One layer contains positive charge and the other contains negative charge, placed adjacent to each other.
When sunlight, consisting of small packets of energy called photons, falls on the surface of solar cell, it is absorbed by the negative layer of the photovoltaic cell.
The energy of the photon gets transferred to an electron in an atom of the cell making it escape the outer shell of the atom.
The freed electron naturally migrates to the positive layer creating a potential difference between the positive and the negative layer.
So, a current begins to flow in the wires connected to the top and bottom of the solar cell to the external circuit.
The strength of current produced depends on the brightness of the light and the efficiency of solar cell. A potential difference (or voltage) of about 0.5 V is generated between the top and bottom surface of a solar cell.
At present, the best designed solar cells can generate 240 W/m2 in bright sunlight, with a maximum efficiency of about 25%.
A single solar cell can produce only a small amount of electricity. A solar cell panel consists of a large number of solar cells joined together in a definite pattern.
ADVANTAGES OF SOLAR CELLS:
Photovoltaic cells generate clean and green energy as no harmful gases such as Cox, NOxetc are emitted.
They do not produce noise pollution which makes them ideal for application in residential areas.
Solar energy is free and abundant in nature.
Solar panels have no mechanically moving parts except in some highly advanced sunlight tracking mechanical bases. Consequently, the solar panel price for maintenance and repair is negligible.
Operation and maintenance cost of cells are very low except the initial cost i.e., purchase and installation.
Solar panels are easy to set up and can be made accessible in remote locations or sparsely inhabited areas at a lesser cost as compared to conventional transmission lines.
DISADVANTAGES OF PHOTOVOLTAIC CELLS:
Energy from the sun is intermittent and unpredictable and can only be harnessed in the presence of sunlight. Also, the power generated gets reduced during cloudy weather.
Long range transmission of solar energy is inefficient and difficult to carry.
The efficiency of solar panels is low compared to other renewable sources of energy.
Photovoltaic panels are fragile and can be damaged relatively easily. Additional insurance costs are required to ensure a safeguard to the investments.
The current produced is DC in nature and the conversion of DC current to AC current involves the use of additional equipment’s such as inverters.
USES OF SOLAR CELLS
Solar cells are used for providing electricity in artificial satellites and space probes.
Solar cells are used for providing electricity to remote, inaccessible and isolated places where normal electricity transmission lines do not exist.
Solar cells are used for the transmission of radio and television programmes in remote areas.
Solar cells are used for providing electricity to ‘light houses’ situated in the sea and to off-shore oil drilling rig platforms.
Solar cells are used for operating traffic signals, watches, calculators and toys.