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Renewable energy sources/ Non-conventional energy sources:
The increasing energy demands have compelled countries all over the world to think of a policy on energy and look into the possibility of having an energy system with no or very limited environmental impacts. The deposits of coal and oil will exhaust one day. The energy crisis has shown that for sustainable development in the energy sector, we must replace them with non-polluting renewable sources and conserve them. Efforts are being made to develop new sources of energy. These are called renewable sources of energy and include solar energy, wind energy, ocean energy, geothermal energy, urban waste, agricultural waste, energy plantations etc. These are non-polluting, environmentally clean and socially relevant. Moreover, no nation can afford to depend on only one form of energy there has to be a mix of various forms of energy.
Non-renewable energy sources/ Conventional energy sources: The resources which have accumulated in nature over a long span of time and cannot be quickly replenished when exhausted are known as Non-renewable energy sources e.g. Coal, Petroleum, Natural gas, and nuclear fuels like uranium and thorium Advantages of Renewable sources of Energy:
1. Renewable energy is available in abundant quantity and is free to use.
2. Renewable energy has low or zero carbon emissions, therefore they are considered green and eco-friendly.
3. Renewable energy develops self-reliance and minimizes the reliance on any third country for the supply of energy.
4. Renewable sources can cost less than consuming the local electricity supply.

Advantages of Non-renewable sources of Energy:
1. Non-renewable sources of energy are cheaper and easy to use.
2. Non-renewable sources release a great amount of energy from the small amount of resource use (uranium).
Disadvantages of Non-renewable sources of Energy:
1. Non-renewable sources of energy are limited and will end one day. Thus, their prices will keep rising and will not be accessible and available for everyone.
2. Their use is not eco-friendly as they release toxic gases that are creating serious environmental changes.
Disadvantages of Renewable sources of Energy:
Though renewable energy has many benefits and advantages it also has certain limitations, such as
1. High cost of initial investment to set up the plant. 2. Non-availability (Solar light only when days are sunny)
3. Loss of biodiversity and forest along with modification of local environment (Dam for hydroelectric energy).

1)Solar Energy The Sun is considered to be the ultimate source of energy for all other forms of energy either directly or indirectly. Advantages:
1. The energy produced by the sun is a renewable source of energy. The power source of the sun is absolutely free.
2. It produces electricity which doesn’t cause pollution of the environment.
3. It can be used in remote and isolated areas where there is no power supply.
4. Most solar energy systems have a lifespan of about 30 to 40 years.

Disadvantages:
1. Solar energy can be harnessed only during the daytime or when it is a sunny day. Cloudy skies reduce its effectiveness. 2.Solar energy can be unreliable at times. 3. The amount of sunlight reaching the Earth’s surface varies with location, time of day, time of year and other weather conditions. 4.Transmission remains a barrier that has to be breached. 5. Installation cost is high as: a.Solar panels, solar cells as well as collectors are comparatively expensive to manufacture. b. It uses a special grade of Silicon which is expensive. c. Since silver is used for connecting the cells together it is more expensive. d. The current produced is DC and converting it to AC increases the cost.

2. Wind Energy The high-speed moving winds due as a result of their motion possess a lot of energy in them in the form of kinetic energy. Sun is the main driving force for the wind. Wind energy can be captured by making use of windmills. The force of the striking wind is the main driving force that helps the blades of the windmill to rotate continuously. The revolving blades can be utilised to drive a number of machines like electric generators, flour mills and water pumps. Nowadays a large number of windmills are being installed in clusters known as wind farms that feed power to the utility grid by producing a large amount of electricity.  Advantages:
 1. The wind is free of cost and can be captured efficiently with the help of modern technology.
2. Wind energy could also be used to produce hydrogen by electrolysis of water.
3. It can be used in remote and isolated areas where there is no power supply.

Disadvantages:
1. The main disadvantage of wind power is down to the wind’s unreliability factor.
2. A minimum wind speed of 15 km/hr i.e. 4.2 m/s is required to rotate the wind turbine. 3.The installer has to face nature’s problems because the wind doesn’t blow all the time i.e. it is not always predictable, therefore, electricity needs to be stored until it is used. There is also the requirement for backup systems.
Hydroelectric Energy

Hydropower is defined as “The electricity that is generated from the energy of falling water and running water that can be utilised for various useful purposes. Hydropower has been used in our country since ancient times for various purposes such as irrigation and the operation of various mechanical devices, such as watermills, sawmills, textile mills, dock cranes, domestic lifts, powerhouses and paint making. Hydroelectricity is considered to be the most widely used and accounts for nearly 16 % of global electricity generation. Advantages:
1. Hydroelectricity is a clean source of energy.
2. The water can also be utilised for irrigation purposes.
3. The water can also be utilised as a source of drinking water provides drinking water to people living, particularly in the desert of Rajasthan and Gujarat.
4. It is absolutely non-polluting, has a long life, and has very low operating and maintenance costs, unaffected by inflation.

Disadvantages: 1.The construction of Dams requires a huge investment of money and they need to be constructed to a very high standard. 2.The natural environment gets destroyed as a result of large-scale flooding.

Tidal Energy
The rise and fall of water in the oceans are referred to as high tide and low tide. In order to rotate the turbine, there is a requirement of several meters difference between the high and low tide. This difference in the tides can be exploited to harness tidal energy by constructing a tidal barrage. The seawater will flow into the reservoir of the barrage during the high tide turning the turbine and producing electricity by rotating the generators. When the sea level is low during the low tide sea water which was stored in the barrage reservoir flows out into the sea turning the turbine and producing electricity by rotating the generators.

Non-renewable energy resources:
Fossil Fuels: Fossil fuels principally comprise hydrocarbons. Fossil fuels involve deposits of once-living organisms. This may take centuries to form. Fossil fuels for energy provision are of three types: Coal, Oil and Natural gas. Coal:
Coal was formed during the Carboniferous age around 255-350 million years ago, in hot damp regions of the earth. The plants and animals that occurred during this period, along the banks of rivers and swamps, getting buried alive or after their death in the soil and due to heat accompanied by pressures gradually got converted into peat and coal over millions of years of period. The vegetation which was partially decomposed and deeply buried in sedimentary environments got slowly transformed into solid, brittle, carbonaceous rocks commonly known as coal. Peat is known as the precursor of coal. It is a soft organic material that consists of partly decayed plants and deposited mineral matter in some cases. When subjected to high pressure and heat peat becomes coal. 

natural gas Natural gas, a fossil gift from nature, is composed of methane (95%) with small amounts of ethane and propane. Natural gas deposits are accompanied by oil deposits or they may also occur independently. Among fossil fuels, it is the cleanest source of energy. Natural gas can easily be transported through pipelines. It burns without smoke and has a high calorific value. It can be used as a source of energy for domestic as well as industrial purposes. It can also be used for power generation and as a raw material for petrochemical industries and fertilizer plants.LPG (Liquefied Petroleum Gas):
It is widely used as a domestic fuel for cooking and has its main content as odourless butane to which other gases like propane and ethyl mercaptan are added to give a foul smell in order to identify leakage. It is produced by converting petroleum into liquid form under pressure. Indane and Bharat Petroleum are the chief distributing agencies of LPG. CNG (Compressed Natural Gas): CNG is used as a substitute for petrol and diesel in vehicles. Delhi Transport Corporation (DTC) has totally switched over to CNG where buses, as well as auto-rickshaws, run on CNG. It has reduced levels of pollution in the city. CNG is a cleaner fuel than diesel, used currently in many cities and long-distance transport across the country. It contains mostly methane, compressed to 80 atmospheres. CNG also works out cheaper (one-third) than diesel in long run because of its stable price.

NUCLEAR ENERGY
Known for its high destructive value, as evidenced by nuclear weapons, non-renewable nuclear power can also be harnessed to produce energy of commercial value. Nuclear energy can be generated either by:
(i) Nuclear fission in which the nucleus of certain isotopes with a large mass number is split into lighter nuclei on the bombardment of neutrons in order to release a huge amount of energy through a chain reaction. In order to control the rate of fission, only one neutron released is allowed to strike for splitting another nucleus. Uranium-235 nuclei are most commonly used in nuclear reactors.ii) Nuclear fusion on the other hand is a process in which a heavier nucleus is formed from the two isotopes of a lighter element releasing enormous energy in the process. In order to fuse these nuclei extremely high temperatures of nearly 1 billion degree celsius is required. The heat energy produced as a result of either of the processes is used to produce steam which runs the electric turbine. Components of a Nuclear Reactor:
1. Moderator: Heavy water, Graphite, Deuterium, Paraffin
When fast-moving neutrons collide head-on with the protons of moderator substances, their energies are interchanged and thus the neutrons are slowed down. Such neutrons are called thermal neutrons which cause the fission of U235 in the fuel.
2. Control Rods: Boron or Cadmium rods
3. Coolant: A substance which is used to remove the heat produced and transfer it from the
core of the nuclear reactor to the surrounding is called coolant.
4. Shielding: Protected with concrete walls 2-25m thick so that radiations emitted during nuclear reactions may not produce harmful effects on the persons working in the reactors.\
5. Nuclear Fuel: Uranium 235 (U235).

Advantages: 1. Emits very few greenhouse gases and hence does not contribute to global warming.
2. Readily available technology. 3. Generates a high quantity of electricity from a very small amount of nuclear fuel. Disadvantages: 1. High installation cost due to radiation containment and procedures.2. Needs a centralized power source with a large infrastructure? 3.High known and unknown risks.

NATIONAL SOLAR MISSION
All UG Courses
 The National Solar Mission is among the eighth key National missions which comprises India’s National Action Plan on Climate Change (NAPCC). NAPCC was launched on 30th June 2008 and identified the development of solar energy technologies in the country as a National Mission. In order to promote ecologically sustainable growth and meet the challenge of India’s energy security, the national solar mission was launched by the Government of India and State Governments as a major initiative. The Government of India approved National Solar Mission on January 11, 2010. As far as India is concerned undoubtedly, solar energy has got tremendous potential to reduce reliance on non-renewable and depleting energy sources as sunshine is available in great intensity and for a longer duration per day. Besides, it can also permit the decentralized distribution of energy for empowering people at the grassroots level. Environmental impact:
1. Solar energy is environmentally friendly as it has zero emissions while generating electricity or heat. It produces electricity which doesn’t cause pollution of the environment.2.The energy produced by the sun is a renewable source of energy. The power source of the sun is absolutely free. 3.It can be used in remote and isolated areas where there is no power supply. 4. Most solar energy systems have a lifespan of about 30 to 40 years.