Two reasons for the need to harness non-conventional sources of energy are as follows:

(a) Conventional sources are going to be exhausted in near future.

(b) Burning of fossil fuels causes environmental pollution.

Two ways of harnessing energy from ocean are as follows:
 (a) Tidal energy
 (b) Ocean thermal energy

(i) Use of smokeless appliances.
(ii) Afforestation

Plane mirror reflects the sunlight in the solar cooker and thus increases the intensity of solar energy. Glass sheet prevents heat from escaping the solar cooker. In other words, the glass sheet produces greenhouse effect.

(i) Solar cells have no moving parts
(ii) Requires little maintenance
(iii) They can be set up in remote areas

Biomass is a fuel that is obtained from organic materials. Following are some methods of harnessing biomass:
(a) Using firewood as fuel
(b) Using cow dung cakes as fuel
(c) Production of gobar gas

Because of it being erratic, energy cannot be harnessed continuously. Large areas are required for wind farms.

Nuclear energy is harnessed in nuclear power plants. It contains a nuclear reactor, a boiler and a turbine.
• The nuclear reactor is the place where nuclear fission is carried out. Nuclear fission produces a huge amount of energy.
• Energy produced during nuclear fission is utilized to boil water, so that steam can be generated.
• Steam is utilized to turn the turbines to produce electricity.
The following figure shows the working of a nuclear power plant.