a) The construction of wind energy farm is costly.
b) The continuous whistling and whirling is irritating.
c) The location of wind energy farms affects the route of migratory birds.
d) It can be located only in vast open areas where the minimum velocity for a windmill to function is 15 km/hr.

Biomass: Biomass is defined as living matter or its residues.  Biomass includes all new plant growth,  agricultural and forest residues,  biodegradable organic affluents from industries and carbonaceous wastes.  
BioEnergy: The energy obtained from the biomass is called bioenergy.  
Biogas: It is a mixture of gases produced by anaerobic degradation of biomass in the presence Of water but in absence of oxygen.  
Anaerobic Degradation: Anaerobic microorganisms decompose the biomass which contains carbon compounds through a series of reactions into a mixture of gases called biogas. 
Composition of Biogas: It is mainly composed of 75 % methane, 25 % carbon dioxide and traces of other gases.  
Working of a Biogas Plant: The cow dung and other wastes are mixed with water in equal proportions in the mixing tank to  Prepare the slurry. This slurry enters the digester upto the cylindrical level through inlet chamber. The slurry takes around 50  - 60 days to start function. During this period, the slurry undergoes anaerobic degradation in presence of water, but in absence of air due to the closed dome. Now, the biogas starts collecting in the dome. When more and more biogas is collected, it develops a pressure on the slurry in the dome forcing the spent slurry to move into overflow tank through the outlet chamber. From the overflow tank, the spent slurry is removed and used as manure. This is because the spent slurry is rich in nitrogen and phosphorus compounds. When the slurry began to function, more fresh slurry is added regularly to produce more biogas. This biogas formed is then supplied to village homes through a network of pipes for cooking purpose through the gas outlet. The large scale of using the bio-wastes and sewage materials for producing biogas can provide a safe and efficient method of waste disposal apart from supplying energy and manure.

a) using smokeless devices.
b) Afforestation.

The glass windows have the property to pass through it only radiations which have wavelength near to the visible light or shorter wavelength. It does not allow infrared radiations of higher wavelength. Since the sun sends infrared radiations of lower wavelength, these pass through the glass windows, get trapped inside the car as heat. The heat or infrared radiations of higher wavelength do not pass out the car and thus heat gets trapped in the car for longer time.

Biomass energy and water energy. Biomass can be managed by replacing trees and water on Earth can be used again and again.

When burning of biomass is not involved in production of energy, then there is no chance of pollution. Wind energy, hydel energy, solar energy, etc. are pollution free.

a) They are non-renewable
b) They produce air pollutants on burning.

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.

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.

a) It should be able to do large amount of work for each unit of mass or volume.
b) It should be easily accessible.
c) It should be easily transported.
d) It should be economical.

Nuclear energy has three advantages:
(a) It has very high efficiency, small amount of nuclear fuel can produce large amount of heat energy which can be controlled and used .
(b) It does not release any harmful gases like S02' CO2, N02 etc. in the air which may cause acid rain or green house effect.
(c) Once the reaction is initiated it can go on automatically for decades unless we want to stop it.

Before the beginning of the Industrial revolution, wind and water energy were used for serving many purposes but the ways of their use were not efficient. Windmills were used to powerful flour mills. The flow of water was used for transporting wooden logs. Now-a-days, both wind energy and water energy are being harnessed to produce electricity which means a better and more efficient use of these forms of energy.

A good fuel should have many desirable characteristics Some of them are as follows:
a) It should produce a high amount of energy for each unit of mass or volume.
b) It should be easily available and should be easy to transport.
c) It should be economical.

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.

In a process called nuclear fission, the nucleus of a heavy atom (such as uranium, plutonium or thorium), when bombarded with low-energy neutrons, can be split into lighter nuclei with a release of tremendous amount of energy if the mass of the original nucleus is just a little more than the sum of the masses of the individual products.

The released energy can be used to produce steam and further generate electricity. The major hazard of nuclear power generation is the storage and disposal of spent or used fuels. Improper nuclear-waste storage and disposal result in environmental contamination. Further, there is a risk of accidental leakage of nuclear radiation. The high cost of installation of a nuclear power plant, high risk of environmental contamination and limited availability of uranium makes large-scale use of nuclear energy prohibitive. The only viable way to dispose off radioactive waste is to bury it deep underground. "The nuclear waste also should be guarded against any misuse.

Environmental consequences of increasing demand for energy are as follows:
a) Use of fossil fuels is increasing air pollution which is not good for our health.
b) Air pollution is causing much damage to the ecosystem.
c) Greenhouse effect has resulted in global warming which is manifesting itself in strange changes in the weather pattern around the world.
d) Too much exploitation of fossil fuels is going to create a situation when there would be not fossil fuel.
Steps to reduce energy consumption:
a) Judicious use of energy is the only way.
b) Use public transport instead of private modes of transport.
c) Use bicycle whenever possible.
d) Walk for short distance commute.
e) Avoid unnecessary use of modern gadgets which consume lot of energy.
f) Get a solar water heater installed for winter.