Basics of Energy & Environment is a high-yield, cross-disciplinary section of ESE (IES) Paper I, common to all engineering branches. This module spans conventional energy sources (fossil fuels, nuclear), renewable energy (solar, wind, hydro, and others), energy efficiency and conservation, environmental pollution (air, water, solid waste), climate change and global agreements, and Indian environmental legislation — with every formula, standard number, and numeric fact carried over, plus worked examples and diagrams for each topic.
After studying this chapter you will be able to:
This module has no strict subject prerequisite, but it connects closely with Environmental Engineering (pollution control, EIA) and Project Management (sustainability planning). Once you've worked through the chapters below, head to the Energy & Environment hub page to generate practice tests, or explore Study Material for other subjects.
| Fuel | Calorific Value (approx.) | Key Issues |
|---|---|---|
| Coal | 25–35 MJ/kg | Highest CO₂ per unit energy; SOₓ, NOₓ, particulates; India has ~7% world reserves |
| Petroleum (crude oil) | 42–44 MJ/kg | Transport fuel dominant; finite reserves; oil spills |
| Natural gas (methane) | 50–55 MJ/kg | Cleanest fossil fuel; lower CO₂; methane leakage risk |
Fission: heavy nucleus (U-235, Pu-239) splits into lighter nuclei + 2–3 neutrons + energy.
Calorific values comparison (coal < oil < natural gas) and nuclear energy basics (fission vs fusion, India's thorium reserves) are tested. India's installed nuclear capacity and PHWR type are factual questions.
Coal (25–35 MJ/kg) < Petroleum (42–44 MJ/kg) < Natural gas (50–55 MJ/kg)
\(E = mc^2\); 1 kg U-235 fission ≈ 83 TJ ≈ 2700 tonnes of coal
PWR, BWR, PHWR (CANDU/RAPS — India's standard reactor type)
~25% of world supply; basis for India's three-stage nuclear/thorium cycle programme
Given: Rank coal, petroleum, and natural gas in increasing order of calorific value.
Solution: Coal has the lowest calorific value (25–35 MJ/kg), followed by petroleum (42–44 MJ/kg), with natural gas having the highest (50–55 MJ/kg) — making it the cleanest-burning fossil fuel per unit of energy released.
Answer: Coal < Petroleum < Natural gas.
Given: Which type of nuclear reactor is most commonly used in India, and what fuel does it use?
Solution: India predominantly uses Pressurised Heavy Water Reactors (PHWRs), based on the CANDU design, exemplified by plants like RAPS (Rajasthan Atomic Power Station). PHWRs use natural (unenriched) uranium as fuel with heavy water as both moderator and coolant.
Answer: PHWR (CANDU-type), using natural uranium.
Given: Why does India's long-term nuclear programme rely on a thorium cycle rather than continuing indefinitely with uranium?
Solution: India holds approximately 25% of the world's thorium reserves but comparatively limited uranium reserves. The three-stage nuclear programme is designed to progressively convert this abundant thorium into usable nuclear fuel, ensuring long-term energy self-sufficiency.
Answer: Because India has abundant thorium (~25% of world reserves) but limited uranium, making thorium the strategic long-term fuel choice.
Fig. 1.1 — Calorific values of coal, petroleum, and natural gas, in ascending order.
| Technology | Principle | Application |
|---|---|---|
| Photovoltaic (PV) | Photoelectric effect; semiconductor converts sunlight → electricity | Rooftop, grid-scale solar farms |
| Solar thermal (CSP) | Concentrated mirrors heat fluid → steam → turbine | Large utility power plants |
| Solar water heater | Flat plate or evacuated tube collector; heats water directly | Domestic and industrial hot water |
India has the 4th largest wind power capacity in the world; Tamil Nadu, Gujarat, and Rajasthan are leading states.
India is the 4th largest hydropower producer; Bhakra–Nangal and Sardar Sarovar are major projects.
| Source | Key Facts |
|---|---|
| Biomass | Combustion or biogas (anaerobic digestion → CH₄); carbon-neutral if sustainably managed |
| Geothermal | Earth's heat; Puga valley (Ladakh) potential in India; high capital cost |
| Tidal | Gulf of Kutch and Gulf of Khambhat (India) — 7,000 MW potential; high capital cost |
| Wave | Offshore wave energy; still largely experimental |
| Hydrogen | Green hydrogen from electrolysis using renewables; National Green Hydrogen Mission (India 2023) |
Betz limit (59.3%) for wind turbines, the hydropower formula, and India's state-wise renewable energy leadership are frequently asked. India's 2030 renewable energy targets (500 GW non-fossil capacity) reflect in policy questions.
\(P = \tfrac{1}{2} \rho A V^3\); \(\rho = 1.225\text{ kg/m}^3\)
\(\dfrac{16}{27} \approx 59.3\%\) (theoretical max); practical turbines: 35–45%
\(P = \rho g Q H \eta\); \(\eta \approx 0.85\text{–}0.90\)
4th largest wind power capacity; 4th largest hydropower producer
Given: A wind turbine has a rotor swept area of 5000 m² and operates in wind of velocity 10 m/s. Using air density \(\rho = 1.225\text{ kg/m}^3\), estimate the theoretical power available in the wind.
Solution: \(P = \tfrac{1}{2} \rho A V^3 = 0.5 \times 1.225 \times 5000 \times 10^3 = 3{,}062{,}500\text{ W} \approx 3.06\text{ MW}\).
Answer: Approximately 3.06 MW (theoretical, before Betz limit and turbine losses).
Given: Using the result from Example 1 (3.06 MW theoretical wind power), what is the maximum power a turbine could theoretically extract, per the Betz limit?
Solution: Maximum extractable power = \(3.06 \times 0.593 \approx 1.81\text{ MW}\), since no turbine can exceed the Betz limit of 59.3% efficiency regardless of design.
Answer: Approximately 1.81 MW (Betz limit maximum).
Given: A hydropower plant has a discharge of 50 m³/s, a net head of 40 m, and an overall efficiency of 0.87. Taking \(g = 9.81\text{ m/s}^2\) and water density \(\rho = 1000\text{ kg/m}^3\), find the power output.
Solution: \(P = \rho g Q H \eta = 1000 \times 9.81 \times 50 \times 40 \times 0.87 \approx 17{,}066{,}000\text{ W} \approx 17.07\text{ MW}\).
Answer: Approximately 17.07 MW.
Fig. 2.1 — The Betz limit (59.3% theoretical maximum) versus the practical efficiency achieved by real wind turbines (35–45%).
Energy audit: systematic examination of energy flows to identify savings opportunities. Types: (1) Walk-through (preliminary); (2) Detailed (investment grade).
| Sector | Key Measures |
|---|---|
| Industry | Variable frequency drives (VFDs); waste heat recovery; cogeneration (CHP); LED lighting |
| Buildings | Energy-efficient windows (double glazing); insulation; HVAC optimisation; green building rating (GRIHA, LEED) |
| Transport | Electric vehicles; fuel-efficient engines; modal shift to rail/public transport |
| Agriculture | Energy-efficient pumps; drip irrigation (reduces pumping); solar pumps |
The Energy Conservation Act, 2001 and BEE (Bureau of Energy Efficiency) are directly asked. Cogeneration = simultaneous production of electricity and useful heat — efficiency up to 80% vs ~35% for power alone.
\(SEC = \dfrac{\text{Energy consumed}}{\text{Unit of production}}\)
Walk-through (preliminary) vs Detailed (investment grade)
Up to 80% (combined heat+power) vs ~35% for electricity generation alone
Energy Conservation Act, 2001; BEE (apex body, Ministry of Power)
Given: A factory wants a quick, low-cost preliminary assessment of its energy use before committing to a full investment-grade study. Which audit type should it commission first?
Solution: A walk-through audit is the preliminary, lower-cost assessment used to identify obvious inefficiencies before a detailed (investment-grade) audit is commissioned for deeper analysis.
Answer: Walk-through audit.
Given: A plant currently generates electricity alone at 35% efficiency. If it switches to a cogeneration (CHP) system operating at 80% overall efficiency, by how many percentage points does efficiency improve?
Solution: Improvement = \(80\% - 35\% = 45\) percentage points, since cogeneration captures and uses the waste heat that would otherwise be lost in electricity-only generation.
Answer: 45 percentage points.
Given: Which act established the Bureau of Energy Efficiency (BEE) and mandates energy audits for designated consumers in India?
Solution: The Energy Conservation Act, 2001 established BEE as the apex body under the Ministry of Power, and mandates periodic energy audits for large ("designated") energy consumers.
Answer: The Energy Conservation Act, 2001.
Fig. 3.1 — Cogeneration (combined heat and power, ~80% efficiency) versus electricity-only generation (~35% efficiency).
| Pollutant | Primary Source | Effect |
|---|---|---|
| SO₂ | Coal combustion, smelting | Acid rain; respiratory damage |
| NOₓ | Combustion (thermal, vehicles) | Smog; acid rain; ozone formation |
| CO | Incomplete combustion | Haemoglobin binding; toxic |
| PM2.5 | Combustion, construction dust | Deep lung penetration; cardiovascular disease |
| VOCs | Solvents, vehicles, industry | Ground-level ozone precursor |
| CO₂, CH₄, N₂O | Fossil fuels, agriculture, waste | Greenhouse effect; climate change |
BOD (Biochemical Oxygen Demand): oxygen required to decompose organic matter over 5 days at 20°C.
Municipal Solid Waste (MSW): the 4Rs — Reduce, Reuse, Recycle, Recover. Solid Waste Management Rules, 2016 (India): source segregation mandatory (wet, dry, hazardous).
Landfill (sanitary): lined cells, leachate collection, gas extraction. Composting: biodegradable fraction → manure. Waste-to-energy (WtE): incineration or RDF; calorific value of MSW ≈ 1500–2000 kcal/kg.
The BOD vs COD distinction (BOD = biological; COD ≥ BOD; COD includes non-biodegradable matter) is a very common question. The oxygen sag curve's point of minimum DO — the critical point — is tested both conceptually and numerically.
Clean water: < 2 mg/L. Sewage: 150–300 mg/L. Measured over 5 days at 20°C.
COD ≥ BOD always, since COD includes non-biodegradable organic matter
Saturation ≈ 9 mg/L at 20°C; fish require > 4 mg/L to survive
≈ 1500–2000 kcal/kg (relevant for waste-to-energy feasibility)
Given: A wastewater sample has a BOD of 120 mg/L. Would you expect its COD to be higher, lower, or equal to 120 mg/L?
Solution: COD is always greater than or equal to BOD, because COD measures total oxidisable matter (including non-biodegradable compounds via chemical oxidation), while BOD only measures the biodegradable fraction consumed by microorganisms over 5 days.
Answer: Higher — COD ≥ BOD always.
Given: A river downstream of a sewage discharge point shows a Dissolved Oxygen level of 3 mg/L. Is this water suitable for fish survival?
Solution: Fish generally require a DO level greater than 4 mg/L to survive. At 3 mg/L, the water is below this threshold and would stress or kill fish populations — this point likely corresponds to the critical point on the oxygen sag curve near the sewage discharge.
Answer: No — 3 mg/L is below the 4 mg/L threshold required for fish survival.
Given: A power plant burning coal releases a gas that combines with atmospheric moisture to form acid rain. Which pollutant is this, and what is its primary source?
Solution: This describes SO₂ (sulphur dioxide), primarily emitted from coal combustion and smelting operations, which reacts with atmospheric water vapour to form sulphuric acid, causing acid rain.
Answer: SO₂, primarily from coal combustion and smelting.
Fig. 4.1 — The oxygen sag curve: dissolved oxygen falls after sewage discharge, reaches a critical point, then recovers downstream through natural reaeration.
Natural greenhouse effect: CO₂, H₂O, CH₄, N₂O, O₃ absorb outgoing infrared radiation, warming Earth's surface by ~33°C. Enhanced (anthropogenic) greenhouse effect: excess GHG from fossil fuels raises global temperature.
| Agreement | Year | Key Provision |
|---|---|---|
| Kyoto Protocol | 1997 | First binding GHG reduction targets for developed (Annex I) countries |
| Paris Agreement | 2015 | Limit warming to 1.5–2°C above pre-industrial; NDCs (Nationally Determined Contributions) |
| Montreal Protocol | 1987 | Phase-out of ozone-depleting CFCs; most successful international environmental treaty |
| Stockholm Convention | 2001 | Persistent Organic Pollutants (POPs) elimination |
| Basel Convention | 1989 | Control of transboundary movement of hazardous waste |
Stratospheric ozone (O₃) absorbs harmful UV-B radiation (280–315 nm). CFCs (chlorofluorocarbons): chlorine radical chain reaction destroys O₃.
\(CO_2 = 1\) · \(CH_4 = 28\) · \(N_2O = 265\) · HFCs = 1,000–10,000 · \(SF_6 = 23{,}500\)
Warms Earth's surface by ~33°C — without it, Earth would be far colder
Dobson Units (DU); normal ≈ 300 DU; ozone hole < 220 DU
Montreal (1987) · Basel (1989) · Kyoto (1997) · Stockholm (2001) · Paris (2015)
Given: If 1 tonne of CH₄ is released, how many tonnes of CO₂-equivalent emissions does this represent, using its 100-year GWP?
Solution: CO₂-equivalent = mass × GWP = \(1 \times 28 = 28\) tonnes of CO₂-equivalent, since CH₄ has a GWP of 28 relative to CO₂'s reference value of 1.
Answer: 28 tonnes CO₂-equivalent.
Given: A student mixes up the Montreal Protocol and the Kyoto Protocol, assuming both address the same issue. What is the key distinction?
Solution: The Montreal Protocol (1987) specifically addresses ozone-depleting substances (CFCs), aiming to protect the stratospheric ozone layer. The Kyoto Protocol (1997) addresses climate change, setting binding greenhouse gas reduction targets for developed countries — a different environmental problem entirely, even though both are UN-led international treaties.
Answer: Montreal Protocol = ozone layer protection; Kyoto Protocol = climate change (GHG reduction).
Given: A region measures 210 Dobson Units of ozone. Is this considered part of an "ozone hole"?
Solution: Since normal ozone levels are approximately 300 DU, and an "ozone hole" is defined as levels below 220 DU, a reading of 210 DU falls below this threshold and would be classified as within an ozone hole.
Answer: Yes — 210 DU is below the 220 DU ozone-hole threshold.
Fig. 5.1 — Global Warming Potential of CO₂, CH₄, N₂O, and SF₆ relative to CO₂'s reference value of 1 (bar heights illustrative, not to linear scale given SF₆'s extreme value).
| Act | Year | Scope |
|---|---|---|
| Water (Prevention and Control of Pollution) Act | 1974 | CPCB and SPCBs established; effluent discharge standards |
| Air (Prevention and Control of Pollution) Act | 1981 | Ambient air quality standards; stack emission norms |
| Environment (Protection) Act (EPA) | 1986 | Umbrella legislation; EIA notification; hazardous waste rules |
| Forest Conservation Act | 1980 | No diversion of forest land without Central Government approval |
| Wildlife Protection Act | 1972 | Protection of wild animals, birds, plants; National Parks, Sanctuaries |
| National Green Tribunal Act | 2010 | NGT established; fast-track disposal of environmental disputes |
EIA process (India, EPA 1986, EIA Notification 2006):
Wildlife (1972) · Water (1974) · Forest Conservation (1980) · Air (1981) · EPA (1986) · NGT (2010)
Umbrella environmental legislation; enables EIA notification and hazardous waste rules
CPCB (Central) and SPCBs (State) established under the Water Act, 1974
Screening → Scoping → Baseline data → Impact prediction → Mitigation → EMP → Public hearing → EAC appraisal → Decision
Given: Which single Indian act is considered the overarching "umbrella" environmental law, under which the EIA notification and hazardous waste rules were later issued?
Solution: The Environment (Protection) Act, 1986 (EPA) is the umbrella legislation, enacted after the Bhopal Gas Tragedy (1984), under which numerous subordinate rules and notifications (including the EIA Notification) have since been issued.
Answer: The Environment (Protection) Act, 1986.
Given: In India's EIA process, which step comes immediately after "Scoping" and before "Impact prediction and evaluation"?
Solution: Following the 9-step EIA sequence (Screening → Scoping → Baseline data collection → Impact prediction...), "Baseline data collection" — establishing the existing environmental status — comes immediately after Scoping and before Impact prediction.
Answer: Baseline data collection.
Given: Which act established the Central Pollution Control Board (CPCB) and State Pollution Control Boards (SPCBs) in India?
Solution: The Water (Prevention and Control of Pollution) Act, 1974 established both the CPCB (at the central level) and SPCBs (at the state level), along with effluent discharge standards.
Answer: The Water (Prevention and Control of Pollution) Act, 1974.
Fig. 6.1 — The nine-step Environmental Impact Assessment process, from Screening to the final Environmental Clearance decision.
59.3% = 16/27
\(P = \rho g Q H \eta\)
< 2 mg/L; sewage 150–300 mg/L
COD ≥ BOD always
28 (over 100 years)
265
1987 — CFCs / ozone layer
2015 — 1.5–2°C warming limit
1986 — umbrella environment law
2010
Dobson Units (DU); normal ≈ 300 DU
Coal < Petroleum < Natural gas
~25% of world reserves
Up to 80% vs ~35% electricity-only
≈ 9 mg/L at 20°C; fish need > 4 mg/L
1974 — established CPCB and SPCBs
| Topic | Paper I Focus |
|---|---|
| Conventional Energy | Calorific value comparisons; nuclear reactor types and India's thorium strategy |
| Renewable Energy | Betz limit and wind/hydro power formula numericals; India's renewable rankings |
| Energy Efficiency | BEE/Energy Conservation Act facts; cogeneration efficiency comparison |
| Environmental Pollution | Pollutant-source-effect matching; BOD/COD/DO numericals and oxygen sag curve |
| Climate Change | GWP value recall; treaty-year-provision matching; ozone Dobson Unit facts |
| Environmental Legislation | Act-year-scope matching; EIA 9-step sequencing |
Q1. A wind turbine has 4,000,000 W of theoretical wind power available. Applying the Betz limit (59.3%), what is the maximum extractable power?
Q2. A sample has a BOD of 180 mg/L. Is this closer to clean water (<2 mg/L) or raw sewage (150–300 mg/L)?
Q3. 2 tonnes of N₂O are released. Using its 100-year GWP of 265, what is the CO₂-equivalent?
Q4. The Montreal Protocol (1987) and the Kyoto Protocol (1997) were signed 10 years apart. Which one addresses ozone depletion, and which addresses climate change?
Q5. India's EPA was enacted in 1986 and the NGT Act in 2010. How many years apart were these two milestones in Indian environmental law?