Energy & Environmental Engineering (ES-301) - Unit 1 Short Notes

How unit 1 is examined

This unit covers energy resources, efficiency and conservation, fossil fuels, renewable alternatives (solar, wind, biogas, nuclear, tidal, geothermal), sustainability and storage; alternatives, efficiency and storage carry the marks.

Introduction to energy systems and resources

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Definition. Energy is the capacity to do work, measured in joule (J); an energy system is the chain supply, conversion, distribution and utilisation that delivers useful energy to the consumer.

Key points.

1. Primary resources are found in nature (coal, crude oil, natural gas, uranium, sun, wind, water), while secondary forms such as electricity, petrol and coke are produced from them.
2. Conventional sources (coal, petroleum, natural gas, large hydro, nuclear) are widely used, commercially mature and mostly non-renewable, except hydro.
3. Non-conventional sources (solar, wind, biomass, geothermal, tidal, wave, hydrogen) are renewable, replenished naturally, and generally cleaner but less concentrated.
4. Non-renewable resources are finite and form over millions of years, whereas renewable ones are inexhaustible on a human time scale.
5. Coal and oil supply most of the world's commercial energy, hydro and nuclear supply electricity, and solar, wind and biomass are growing fastest.
6. Energy forms include chemical, thermal, mechanical, electrical, nuclear and radiant, and 1 kWh = 3.6 MJ.

<mark>Energy is the capacity to do work, and an energy system is the supply, conversion, distribution and utilisation chain that delivers it.</mark>

Answer frame. Open by defining energy and energy system; draw the chain supply-conversion-distribution-use as boxes; then list the classification (primary/secondary, renewable/non-renewable, conventional/non-conventional) and one line of use per resource; close that a sustainable mix shifts toward renewables.

Asked: [7 marks] (Dec 2025) Explain the concept of energy systems and discuss major energy resources. What is energy? Write various conventional and non-conventional energy sources.

Introduction to Energy, sustainability & the environment

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Definition. Sustainability means meeting present energy needs without reducing the ability of future generations to meet theirs.

Key points.

1. Every energy source affects the environment through resource extraction, emissions, land use and waste.
2. Burning fossil fuels raises CO$_2$, causing global warming, and SO$_x$ and NO$_x$, causing acid rain and smog.
3. A sustainable system is renewable, efficient, affordable and low in pollution.
4. Energy use rises with population and living standards, so environment and energy planning must go together.

Overview of energy systems, sources, transformations, efficiency, and storage

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Definition. Energy is the capacity to do work; energy efficiency is the ratio of useful energy output to energy input, and energy conservation is reducing energy consumption by using less of a service or using energy more efficiently.

Key points.

1. Energy cannot be created or destroyed but only transformed (first law), and every transformation loses some energy as unusable heat (second law).
2. Typical transformations are chemical to thermal to mechanical to electrical in a thermal plant, and radiant to electrical in a solar cell.
3. Global supply is dominated by coal, oil and gas; India relies mainly on coal for electricity and imports most of its oil, while renewables and nuclear are growing.
4. Efficiency is important because it lowers total fuel use, cost and greenhouse-gas emissions for the same useful output.
5. A coal steam plant converts only about 33-40 percent of fuel energy to electricity, an LED converts far more than an incandescent lamp, and an electric motor is about 90 percent efficient.
6. Energy is stored as chemical (fuel, batteries), potential (pumped hydro), thermal (hot water, molten salt), kinetic (flywheel) and magnetic (superconducting coil) energy to match supply with demand.

Formula. $$\eta = \frac{\text{useful energy output}}{\text{energy input}} \times 100\%$$

Example. A plant burns coal giving 100 MJ of heat and delivers 35 MJ of electricity: $\eta = 35/100 = 0.35$, so efficiency = 35 percent and 65 MJ is lost as heat.

Energy conservation methods.

1. Use efficient appliances such as LEDs and star-rated devices, and switch off unused equipment.
2. Recover waste heat and use cogeneration in industry.
3. Maintain equipment regularly and insulate buildings and pipes.
4. Use variable speed drives and high-efficiency motors.

Efficiency by sector.

<mark>Energy efficiency is the ratio of useful energy output to energy input, and improving it lowers consumption, cost and greenhouse-gas emissions.</mark>

Answer frame. Open with the definition of energy and its conservation law; give the scenario (sources, conventional versus renewable, India coal-based); then efficiency with the formula and a small example; then storage types; close that efficiency is the cheapest way to cut emissions. For the sector question, use the table as three headed paragraphs.

Pitfall: Efficiency has no unit and can never exceed 100 percent.

Asked: [14 marks] (Nov 2022) What is Energy? Discuss the energy scenario giving emphasis on: Sources, efficiency and storage. Asked: [7 marks] (Jun 2023) What is Energy conservation? Write down different methods of energy conservation. Asked: [7 marks] (Dec 2024) Describe the concept of energy efficiency and its importance in reducing energy consumption and greenhouse gas emissions. Asked: [7 marks] (Dec 2024) Discuss the various strategies and technologies used to improve energy efficiency in buildings, industries and transportation sectors.

Fossil fuels (coal, oil, oil-bearing shale and sands, coal gasification) - past, present & future

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Definition. Fossil fuels are hydrocarbon fuels (coal, crude oil, natural gas) formed over millions of years from buried plant and animal remains under heat and pressure.

Key points.

1. Coal formed from buried plants that turned to peat, lignite, bituminous coal and anthracite; oil and gas formed from marine organisms buried in sediment.
2. Coal is used for electricity, steel and cement, oil for transport and petrochemicals, and natural gas for power, cooking and fertiliser.
3. Oil shale and oil sands hold heavy hydrocarbons (kerogen, bitumen) that need heating or mining to extract oil, which is costly and damages land and water.
4. Coal gasification converts coal with steam and limited air or oxygen into syngas (CO and H$_2$), which is cleaner to burn and can make chemicals.
5. In the past fossil fuels drove industrialisation, at present they give over 80 percent of world energy, and in future their share must fall because reserves are finite and pollution is severe.
6. Alternatives are needed because of depletion, price and import dependence, and climate change: solar, wind, hydro, biomass, nuclear and geothermal.

Environmental impacts.

1. Air pollution: SO$_x$, NO$_x$, CO and particulates cause smog and respiratory disease.
2. Water pollution: acid rain acidifies lakes, coal-ash runoff contaminates water, and plant cooling causes thermal pollution.
3. Greenhouse gases (CO$_2$, CH$_4$) drive global warming and ocean acidification.

<mark>Fossil fuels are non-renewable hydrocarbon fuels whose combustion releases CO$_2$, SO$_x$ and NO$_x$, so alternatives are essential.</mark>

Answer frame. For the 14-mark question, define and explain formation, classify uses with limitations, state the need for alternatives, then give one line each on solar, wind, hydro, biomass, nuclear and geothermal (see the next topic); for the impacts question, use three headings air, water, greenhouse gases.

Asked: [14 marks] (Nov 2019) What do you understand by fossil fuels? Also explain alternatives for fossil fuels. Asked: [7 marks] (Dec 2024) Describe in brief about the environmental impacts of fossil fuel combustion and greenhouse gas emissions on air pollution, water pollution.

Remedies & alternatives for fossil fuels - biomass, wind, solar, nuclear, wave, tidal and hydrogen

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Solar energy. Solar energy is radiant energy from the sun, used as heat or converted to electricity.

1. Advantages: inexhaustible, clean, low maintenance and reduces the carbon footprint.
2. Disadvantages: high initial cost, intermittent and weather dependent, needs large land, and needs storage.
3. Applications: water heating, power plants, cooking, calculators, water pumping, rural electrification.

Photovoltaic (PV) cell. A PV cell is a p-n junction semiconductor diode that converts light directly into electricity by the photovoltaic effect.

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Working: photons are absorbed, electron-hole pairs form, the junction field separates them (electrons to n side), and current flows through the external load.

Combined PV/thermal (PV/T). A PV/T collector circulates water or air behind the panel, cooling the cells to raise electrical efficiency while giving useful heat. Research uses nanofluids, nanomaterials and phase change materials; challenges are cost, the electrical-thermal trade-off, degradation and limited commercialisation.

Solar water heater.

Wind energy. Wind kinetic energy turns the rotor, the gearbox raises speed, and the generator produces electricity.

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Biomass and biogas. Biomass is organic matter (wood, crop residue, dung) converted by combustion, gasification or anaerobic digestion; it is renewable, carbon-neutral and uses waste, but needs land and gives low efficiency. In a floating drum (KVIC) plant, dung slurry enters the digester through the inlet, bacteria produce gas, and the drum rises to store it at constant pressure; spent slurry leaves by the outlet. Advantages: constant pressure and visible gas quantity. Disadvantages: high cost and drum corrosion needing repainting.

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Nuclear energy. Nuclear energy is released by fission of uranium-235. Advantages: low operating emissions, high energy density, reliable base load. Disadvantages: radioactive waste, high capital cost, accident risk, proliferation.

Tidal energy. A barrage with sluice gates, basin(s), reversible low-head turbines (bulb or Kaplan) and a generator uses tide height difference.

Geothermal, wave, hydrogen. Geothermal challenges: high drilling cost, site specificity, induced seismicity, heat depletion, corrosive H$_2$S gases. Wave energy drives turbines from sea waves; hydrogen is a clean fuel that burns to water but needs energy to produce and store.

Earth-friendly system. Shift to renewables, raise efficiency, use smart grids and decentralised generation, and cut emissions.

<mark>Renewable alternatives such as solar, wind, biomass, tidal and nuclear reduce fossil fuel use, each with its own cost and reliability limits.</mark>

Answer frame. Open with the need for alternatives; for solar, define then advantages, disadvantages, applications; for PV, draw the cell and explain working; for wind, draw the nacelle and trace energy flow; for biogas, draw the drum plant then pros and cons; close by noting that no single source suffices, so a mix with storage is needed.

Asked: [7 marks] (Dec 2023) What are the challenges for the implementation of Geothermal Energy power generation system? Asked: [7 marks] (Dec 2023) Explain in your words how far is research in the field of combined solar panels (PV and Thermal)? Asked: [7 marks] (Jun 2023) How can our energy system be more Earth-friendly? Asked: [7 marks] (Jun 2023, Dec 2025) State advantage, disadvantages and applications of solar energy. What is solar energy? Discuss the importance and limitations of solar energy. Asked: [7 marks] (Jun 2023) How does a forced circulation solar water heater differ from natural circulation solar water heater? Asked: [7 marks] (Jun 2023) Differentiate between single-basin and double-basin tidal plants. Explain briefly the various components of tidal power plants. Asked: [7 marks] (Jun 2023) What is a photovoltaic cell? Explain briefly with a neat diagram a silicon photovoltaic cell. Asked: [7 marks] (Jun 2023) Explain with a neat sketch the construction and working of wind-electric generating plant. Asked: [7 marks] (Jun 2023) Explain with a neat diagram the construction and working of floating drum type biogas plant. State also its advantages and disadvantages. Asked: [7 marks] (Dec 2024, Dec 2025) State the advantages and disadvantages of using nuclear energy as a source of electricity. Define nuclear energy? State the advantages and disadvantages of using nuclear energy as a source of electricity. Asked: [7 marks] (Dec 2025) Describe renewable energy alternatives to fossil fuels with examples. Asked: [7 marks] (Dec 2025) Discuss the use of biomass energy as non-conventional source of energy. What are the advantages of biomass energy.

Sustainability and environmental trade-offs of different energy systems

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">Medium weight</span>

Definition. Sustainability in energy means supplying reliable, affordable energy while protecting the environment and resources for future generations.

Key points.

1. Fossil systems are cheap and reliable but cause air, water and land damage, greenhouse gases and resource depletion.
2. Hydro and nuclear give low-carbon power but bring displacement, dam ecology impacts, and radioactive waste.
3. Solar and wind are clean in operation but intermittent, land-hungry and need storage and manufacturing materials.
4. Biomass is renewable but competes with food and land, and burning it emits particulates.
5. The trade-off is economic against environmental cost and energy security, so a balanced mix is chosen.
6. To be Earth-friendly: move to solar, wind, hydro and geothermal, raise efficiency in generation, transmission and end use, use smart grids and storage, and decarbonise transport and industry.

<mark>A sustainable energy system balances economic cost, energy security and environmental impact by shifting to renewables and efficiency.</mark>

Answer frame. Open by defining sustainability; then list the trade-off for fossil, hydro, nuclear, renewables; then the four Earth-friendly measures; close with the need to transition.

Asked: [7 marks] (Dec 2023, Dec 2025) How can our energy system be more Earth-friendly? Discuss sustainability and environmental trade-offs of fossil fuel-based energy systems.

Possibilities for energy storage or regeneration (pumped storage hydro, superconductor-based storage, high efficiency batteries)

<span style="display:inline-block;padding:.16em .6em;border:1.5px solid currentColor;border-radius:999px;font-size:.68em;font-weight:700;letter-spacing:.06em;text-transform:uppercase;opacity:.75">High weight</span>

Definition. Energy storage holds energy when supply exceeds demand and releases it when needed, which is essential for variable renewables.

Key points.

1. Storage smooths the intermittency of solar and wind and supports the grid at peak demand.
2. Pumped storage hydro pumps water to an upper reservoir using surplus power, then releases it through turbines at peak time; round-trip efficiency is about 70-85 percent.
3. Pumped storage is mature and large-scale, but needs suitable sites, a large capital cost and land.
4. Superconducting magnetic energy storage (SMES) stores energy in the magnetic field of a superconducting coil at near-zero resistance, with very fast response and high efficiency, but needs cryogenic cooling and is costly.
5. High-efficiency batteries include lithium-ion (high energy density, used in vehicles and grids) and flow batteries (liquid electrolyte, long life, easily scaled).
6. Batteries suit small and medium storage; pumped hydro suits bulk storage; SMES suits short, fast grid support.

Hydro power projects. Water stored behind a dam flows through a penstock to a turbine coupled to a generator. Components: dam, reservoir, intake, penstock, turbine, generator, tailrace. Advantages: renewable, cheap running cost, flood control, irrigation. Limitations: high capital, displacement, silting, dependence on rainfall. Classification: by head (high, medium, low), by load (base, peak), by water use (run-of-river, storage, pumped storage). Site selection: water availability, head, catchment area, geology, and access to transport and load centres.

<mark>Energy storage stores surplus energy for later use, with pumped hydro for bulk storage and batteries for flexible storage.</mark>

Answer frame. Open with the role of storage in renewable integration; then pumped hydro (principle, operation, pros, cons); then batteries; close with a comparison. For hydro projects, give components then types, advantages, limitations.

Asked: [14 marks] (Nov 2019) Write a brief note on hydro power projects. Asked: [7 marks] (Dec 2025) Explain energy storage technologies such as pumped storage and high-efficiency batteries. Asked: [7 marks] (Jun 2023) Give the classification of hydro-electric power plant. What are the criteria of site selection for hydroelectric plant?

Last-minute revision

• Energy is the capacity to do work; unit joule; 1 kWh = 3.6 MJ.
• Efficiency = useful output / input x 100 percent.
• Conventional: coal, oil, gas, hydro, nuclear; non-conventional: solar, wind, biomass, geothermal, tidal.
• Coal gasification gives syngas (CO + H$_2$).
• PV cell: p-n junction, photovoltaic effect, needs anti-reflective coating.
• Natural circulation heater uses thermosiphon; forced uses a pump.
• Floating drum biogas: constant pressure, but costly and corrodes.
• Double-basin tidal plant gives continuous power.
• Nuclear: low emissions but waste and high cost.
• Pumped hydro efficiency is about 70-85 percent.
• SMES stores energy in a magnetic field at cryogenic temperature.

Memory hooks

• SCDU: Supply, Conversion, Distribution, Utilisation.
• Solar disadvantages: "CIS-S": Cost, Intermittent, Space, Storage.
• PV layers top to bottom: Grid, ARC, N, junction, P, Back.
• Batteries small, pumped hydro bulk, SMES fast.

Coverage checklist

• Introduction to energy systems and resources: Q5 (Dec 2025).
• Introduction to Energy, sustainability & the environment: not asked recently.
• Overview of energy systems, sources, transformations, efficiency, and storage: Nov 2022, Jun 2023, Dec 2024 (two).
• Fossil fuels (coal, oil, oil-bearing shale and sands, coal gasification) - past, present & future: Nov 2019, Dec 2024.
• Remedies & alternatives for fossil fuels - biomass, wind, solar, nuclear, wave, tidal and hydrogen: all Jun 2023, Dec 2023, Dec 2024 and Dec 2025 alternative questions.
• Sustainability and environmental trade-offs of different energy systems: Dec 2023, Dec 2025.
• possibilities for energy storage or regeneration (Ex. Pumped storage hydro power projects, superconductor-based energy storages, high efficiency batteries): Nov 2019, Dec 2025, Jun 2023 hydro classification.