Sun produces its energy by a reaction called nuclear fusion.
Two conditions which are present inside the sun that are responsible for nuclear fusion to occur are very high temperature and very pressure.

a) It is eco-friendly.
b) It is found abundantly.
c) It converts visible as well as IR rays into electricity.

(a) The energy demands are increasing rapidly due to population explosion and our efforts to improve quality of life by adopting faster means of transport and travel, rapid industrialization and extensive use of energy-fed home appliances.
(b) Fossil fuels are fast depleting.

Hydrogen is a much cleaner energy source than CNG. CNG (compressed natural gas) is derived from biomass and hence burning the CNG causes air pollution; albeit on a much smaller scale than coal and petroleum. Use of hydrogen as energy source does not polluting gases. 

It is one of those sources of energy that do not come directly or indirectly from the solar energy.

Because of growing population, the energy demand is rising. We need to find an alternate source of energy which renewable and environment friendly.

LPG (Liquefied Petroleum Gas) for heating my food, because it is easily available and gives no smoke on burning and also takes less time to do the job.

A good source of energy should be renewable and environment friendly.

(a) The solar cells are costly and hence the energy available from them expensive.
(b) 15 km/h is the minimum wind velocity required to obtain useful energy with a windmill.
(c) Nuclear fission is the process in which a radioactive atom splits up into smaller nuclei when struck with low energy neutrons.

(a) A solar cell is a device which converts solar energy into electricity. It is a sandwich of a silicon-boron layer and a silicon-arsenic layer.
(b) Biogas is an ideal fuel for domestic use because it is a cheap and clean fuel, which does not leave behind any residue.
(c) A nuclear power plant is a device in which controlled chain reaction is used.

Advantages of Solar Cooker
a) They are environment friendly.
b) Use of a solar cooker does not involve recurring expenses on fuel.
Disadvantages of Solar Cooker.
a) Solar cooker is very slow.
b) Solar cooker can work only during summer months and is useless during winters and on cloudy days.
c) Solar cooker can be useful at those places which receive plenty of sunshine. This is useless in colder climates.

i) All fossil are the remains of the prehistoric plants and animals. Th energy of the fossil fuels is in fact that solar energy which was trapped by natural processes a long time ago.
ii) Solar energy also appears in the form of energy of water flowing in rivers as is obvious from the water cycle in nature. It is this energy which generates in hydroelectric power plants.
iii) Biomass energy is also the solar energy absorbed by the plans which convert it into chemical energy through photosynthesis.
iv) Human and animals use bioenergy to carry out their life activities.
v) Solar energy is one of the main factors responsible for the movement of air in the atmosphere leading to wind energy.
vi) Solar energy is used directly in solar.

a) Solar energy can be harnessed by using solar energy devices. These devices either use solar energy directly as heat or convert it into solar energy directly as heat or convert it into electricity. One of the devices is solar cooker.
b) Limitations of solar energy:
i) It is not evenly distributed on the Earth.
ii) It requires costly equipment and infrastructure.
c) Using of solar cells.