Solar Energy

Solar Energy: The earth receives a huge amount of energy from the sun. Each square metre of the earth's uprut atmosphere receives about 1.36 kilojoules (kJ) of solar energy per second. In other words, so energy is incident at the rate of 1.36 kW/m2.

The entire energy incident on the upper atmosphere of the earth does not reach its surface. About 40% of this energy is reflected by the atmosphere into space. Then some of it is absorbed by the gases and particles present in the atmosphere. Finailly, only about 47% of the incident energy reaches the earth's surface. Solar energy sustains life processes on the earth. Plants use it to make food. Traditionally we have been using solar energy for drying clothes and grains, making salt from sea water, etc. Newer uses include solar heating devices and solar cells. Solar heating devices such as solar cookers and solar water heaters use the heat energy that comes with sunlight. Solar cells convert solar energy into electricity.

Advantages Of Solar Energy: The advantages are as follows

(a) It is available everywhere.

(b) It is available in plenty (renewable), and it is free.

Limitations of solar energy : The limitations are as follows

(a) It cannot be used at night.

(b) Devices based on solar energy do not work well on cloudy days.

Solar Heating Devices: A solar heating device uses solar energy to heat things like water and food. To make a solar heating device effective, we have to ensure that the device absorbs a lot of heat from sunlight and does not lose too much of the collected heat. To achieve these, the following measures are taken. Increasing the absorption of heat Everything on which sunlight falls absorbs heat from it. However, black and dark-coloured surfaces absorb heat better than do light-coloured and white surfaces. That is why you feel hotter than usual when you wear dark clothes in summer. In certain types of solar heating devices, the surfaces meant for collecting sunlight are painted black to increase the absorption of heat.

Reducing the loss of heat: A hot object loses heat to it surroundings by conduction, convection and radiation. Different methods are used to reduce the loss of heat in heating devices. In a box-type device, to reduce heat loss by conduction, the walls are made of an insulator, ie, a material that is a poor conductor of heat. The box is made airtight so that the air inside cannot take the heat out of the box. Thus, convection loss is also reduced. Radiation loss is reduced by covering the top of the box with giass. Sunlight passes through the glass and heats the materials inside the box. The heated materials radiate heat, but these get reflected back into the box by the glass. This traps the heat (in the same way it is trapped in a greenhouse).

Increasing the amount of sunlight collected: A reflector such as a plane mirror is used to reflect sunlight into the heating device so that more sunlight enters it

Sample Questions

(More Questions for each concept available in Login)

Question : 1

Which of the following gases are responsible for the Green House effect?
A. $CH_4 ;and; N_2$	B. $CO_2 ;and; N_2$	C. $CH_4 ;and; CO_2$	D. $O_2 ;and; N_2$
Right Option : C
View Explanation

Question : 2

The device used for direct conversion of solar energy into electrical energy is
A. Solar heater		B. Photovoltaic cell
C. Voltaic cell		D. Dynamo
Right Option : B
View Explanation

Question : 3

A glass structure used to protect the plants from cold is known ______________________
A. Solar heater	B. Glass house	C. Green house	D. Warm house
Right Option : C
View Explanation