Sources of Energy – Complete AMU 11 Notes

1) Criteria for a Good Fuel

Not all fuels are created equal. When we choose a fuel for a specific purpose, we evaluate it based on several criteria. A "good" fuel has most of these qualities:

2) Calorific Value — How Much Energy?

Calorific value is the amount of heat energy produced when 1 kg (or 1 unit) of fuel is completely burned. It is measured in kJ/kg (or J/g).

Calorific Value Table — Common Fuels:

3) Classification — Renewable vs Non-Renewable ⭐

This is the MOST IMPORTANT concept in this chapter. You WILL get a question on this in AMU. Memorise the classification perfectly.

4) Fossil Fuels — Coal, Petroleum, Natural Gas

Fossil fuels are the remains of dead plants and animals that were buried under the earth millions of years ago. Under heat and pressure, they transformed into coal, oil, and gas. They are non-renewable because they take millions of years to form.

A. Coal:

• Formed from dead trees and plants buried in swamps (carboniferous period ~300 million years ago)
• As burial depth and pressure increase, the carbon content increases:

B. Petroleum:

• Formed from dead sea organisms (plankton) buried under ocean sediments
• Crude oil is a dark, sticky liquid — a mixture of many hydrocarbons
• It is separated into useful products by fractional distillation in a petroleum refinery

C. Natural Gas:

• Mainly methane (CH₄) — 85-95%
• Found above petroleum deposits (associated gas) or in separate reservoirs (non-associated gas)
• CNG (Compressed Natural Gas): Natural gas compressed to ~200 atm for use as vehicle fuel. Cleaner than petrol/diesel — produces less CO₂, NOₓ, SO₂
• Uses: Home cooking, heating, electricity generation, vehicle fuel (CNG), fertilizer production (Haber process — hydrogen from natural gas)
• India has significant reserves in Mumbai High, Krishna-Godavari basin, Assam, Rajasthan

Disadvantages of Fossil Fuels:

5) Thermal Power Plant

A thermal power plant generates electricity by burning fossil fuels (coal, oil, or natural gas).

Detailed Process:

1. Coal is pulverized to powder and burned in a boiler furnace
2. The heat converts water in the boiler into high-pressure steam (~500°C, ~150 atm)
3. The high-pressure steam strikes the blades of a turbine, causing it to rotate at high speed
4. The turbine shaft is connected to a generator (electromagnetic induction → electricity produced)
5. After passing through the turbine, steam is condensed back to water and returned to the boiler
6. The electricity is stepped up by a transformer and transmitted through power lines

6) Hydro Power Plant

A hydro power plant uses the potential energy of stored water to generate electricity. It is a renewable and clean source of energy.

Process:

1. A dam is built across a river to create a reservoir at a height
2. Water from the reservoir is released through large pipes (penstocks) to the turbine at the bottom
3. The falling water strikes the turbine blades at high speed, causing the turbine to rotate
4. The turbine drives the generator → electricity is produced
5. The water is released back into the river downstream

7) Solar Energy ⭐

The Sun is the ultimate source of almost all energy on Earth. Solar energy is produced by nuclear fusion of hydrogen into helium in the Sun's core (~15 million K). The solar constant is ~1.4 kW/m² — the amount of solar energy reaching Earth's upper atmosphere per square meter.

A. Solar Cooker:

A device that uses sunlight to cook food. It is simple, cheap, and environmentally friendly.

B. Solar Water Heater:

• Uses solar energy to heat water for domestic use (bathing, washing)
• Black-painted copper tubes (absorber) placed in a glass-covered box
• Cold water circulates through the tubes, gets heated, and rises to an insulated storage tank by thermosiphon effect (natural convection)
• Can provide water at 60-80°C even in winter in sunny regions
• Widely used in India — mandatory in many new buildings

C. Solar Cell (Photovoltaic Cell) ⭐:

A solar cell converts sunlight directly into electricity without any moving parts. This is the photovoltaic effect.

8) Wind Energy

Wind energy uses the kinetic energy of moving air to generate electricity. India has the 4th largest wind power capacity in the world.

Process:

1. The wind blows and turns the rotor blades (like a large fan). Modern blades are 50-80 m long
2. The rotor is connected to a gearbox that increases the rotational speed
3. The high-speed shaft drives a generator, producing electricity
4. The electricity is transmitted through cables to the grid

9) Biomass and Biogas

Biomass is organic matter from plants and animals — wood, cow dung, crop residue, agricultural waste, sewage. It can be used directly (burning wood/cow dung cakes) or converted to biogas.

Biogas Plant:

A biogas plant converts organic waste into methane-rich biogas through anaerobic digestion (decomposition in the absence of oxygen).

10) Tidal Energy

Tidal energy harnesses the rise and fall of sea levels due to gravitational forces of the Moon and Sun. Tides are predictable — they occur twice daily.

11) Wave Energy

Wave energy captures the energy of ocean surface waves. One common design is the Oscillating Water Column (OWC).

12) OTEC (Ocean Thermal Energy Conversion)

OTEC uses the temperature difference between warm surface water (25-30°C) and cold deep water (4-7°C) of the ocean to generate electricity.

13) Geothermal Energy

Geothermal energy uses the heat from inside the Earth. At depths of 10-15 km, temperatures reach 300-500°C. In some places (volcanic regions, hot springs, geysers), this heat comes close to the surface.

14) Nuclear Energy (Brief Overview)

Nuclear energy is produced by nuclear fission of heavy atoms like Uranium-235 or Plutonium-239. The nucleus splits into smaller nuclei, releasing enormous energy (E = mc²).

(Nuclear fission and fusion are covered in full detail in the Nuclear Physics chapter.)

15) Environmental Impact — Greenhouse Effect, Global Warming, Acid Rain

Greenhouse Effect:

The greenhouse effect is a natural process where certain gases (CO₂, CH₄, H₂O vapor, N₂O, CFCs) trap heat in the Earth's atmosphere, keeping the planet warm (~15°C average instead of −18°C without it). However, human activities (burning fossil fuels, deforestation, agriculture) are increasing these gases → enhanced greenhouse effect.

Global Warming:

• Earth's average temperature has risen by ~1.2°C since pre-industrial times
• Main causes: CO₂ from fossil fuel burning (75% of emissions), methane from agriculture/landfills, deforestation (trees absorb CO₂)
• Effects: Rising sea levels (melting glaciers + thermal expansion), extreme weather (heatwaves, floods, cyclones), crop failure, species extinction, ocean acidification
• Steps to reduce: Shift to renewable energy, energy conservation, afforestation, electric vehicles, carbon capture technology

Acid Rain:

• SO₂ and NOₓ released from burning fossil fuels (coal, petrol, diesel) react with water vapor and oxygen in the atmosphere → sulfuric acid (H₂SO₄) and nitric acid (HNO₃)
• These acids fall as rain, snow, fog, or dry particles
• Effects: Corrodes buildings (Taj Mahal, marble damage), acidifies lakes/rivers (kills fish), damages crops and forests, leaches nutrients from soil, harmful to human health
• Controls: Use low-sulfur coal, install scrubbers in power plants (remove SO₂), catalytic converters in vehicles (reduce NOₓ)

16) PYQ Battle — AMU Past Questions on Sources of Energy

17) Common Mistakes — DON'T DO THESE!

18) Quick Revision — One-Liner Summary