General Aspects of Energy Management & Energy Audit Available here with full solutions — 103 questions recovered from the 2014 exam:
Objective (1 mark)
0 of 50
Short (5 marks)
103 of 8
Long (10 marks)
0 of 6
This is not the complete paper. The questions below are the ones we could recover and verify; the rest of that year’s paper is not reproduced here. Every answer shown is checked against the 2014 BEE guidebook and carries its book section reference and an explanation.
Full paper pattern: Section-I 50×1 = 50 marks · Section-II 8×5 = 40 · Section-III 6×10 = 60 · Total 150, pass mark 75, 3 hours. ▶ Practice these interactively
Other years
Short questions (5 marks) — 103
📖 §11.1 Concept of New and Renewable Energy
1. Define renewable energy and state how it differs from conventional (fossil/nuclear) energy.
Model answer: Renewable energy is energy obtained from sources that are essentially inexhaustible such as the sun and wind. Examples include solar, wind, geothermal, tidal, bio-energy and hydropower. A renewable energy system converts the energy in sunlight, wind, falling water, sea waves, geothermal heat or biomass into useful heat or electricity, generally without releasing harmful pollutants. It is also called non-conventional energy. The key difference: renewable sources are flows of energy, whereas fossil and nuclear fuels are considered stocks of energy.
Flows vs stocks is the textbook distinction; renewable = non-conventional.
📖 §11.2 Fundamentals of Solar Energy (Solar Constant)
2. What is the solar constant? Give its value.
Model answer: The solar constant is the rate at which solar energy, at all wavelengths, is received per unit area at the top of the Earth's atmosphere (on a surface normal to the sun). Its value averages about 1,368 W/m². It actually varies by about 0.3% over the 11-year solar cycle. Each planet has its own planetary solar constant.
Objective Q5 answer = 1368 W/m². Do not confuse with average insolation 342 W/m².
📖 §11.2 Fundamentals of Solar Energy (Solar Insolation)
3. What is solar insolation? In what units is it expressed and what is its average value?
Model answer: Solar insolation is the amount of solar energy that strikes a square metre of the Earth's surface in a single day. It is greatest when the surface is normal to the sun; as the angle increases it is reduced in proportion to the cosine of the angle. The average incoming radiation (solar insolation) is one-fourth of the solar constant, i.e. about 342 W/m². For site assessment it is expressed in kWh/m²/day. India receives 5 to 7 kWh/m² for 300 to 330 days a year.
Avg insolation = ¼ × solar constant = 342 W/m²; field units = kWh/m²/day.
📖 §11.2 Fundamentals of Solar Energy (Solar Window / India's solar potential)
4. What is meant by the 'solar window', and what is India's solar power potential per square kilometre?
Model answer: The solar window is the period, typically 9 AM to 3 PM, when the maximum sunlight is available. India receives solar energy in the region of 5 to 7 kWh/m² for 300 to 330 days a year. This level of insolation is sufficient to set up a 20 MW solar power plant per square kilometre of land area.
Solar window 9 AM–3 PM; land-scale rule ≈ 20 MW per km².
📖 §11.2 Fundamentals of Solar Energy (Fundamentals of Solar Energy)
5. Name the components of solar radiation and the two routes by which solar energy can be used.
Model answer: Solar radiation is the radiant energy emitted by the sun, comprising ultra-violet, visible and infra-red radiation. The amount reaching a location depends on geographic location, time of day, season, landscape and local weather. Solar energy can be used through two routes: (1) Solar Thermal Energy, where the sun's heat is collected and converted into heat energy, and (2) Solar Electric (Solar Photovoltaic) Energy, where sunlight is converted directly into electricity.
📖 §11.3 Solar Thermal Energy (Solar Water Heating System)
6. Describe a solar water heating system and its main components.
Model answer: A solar water heating system consists of a flat-plate or evacuated-tube solar collector, a storage tank and connecting pipes. It is generally installed on a roof or open ground with the collector facing the sun and connected to a continuous water supply. The collector absorbs the sun's energy and transfers it to the water. Because the storage tank is insulated and heat losses are small, the water stored remains hot overnight.
Components: collector + insulated storage tank + connecting pipes.
📖 §11.3 Solar Thermal Energy (Solar Flat Plate Collector)
7. Describe the construction and operating temperature of a solar flat-plate collector (FPC).
Model answer: The flat-plate collector (FPC) is the most common solar collector. It heats the circulating fluid to about 40-60°C. It usually comprises copper tubes welded to copper sheets (both coated with a highly absorbing black coating), with a toughened glass sheet on top as cover and insulating material at the bottom, the entire assembly placed in a flat box. Its performance is highly dependent on ambient temperature, giving good efficiency only when ambient temperature is high; hence heat output is higher in summer than in winter.
FPC: 40-60°C, copper-on-copper black absorber, glass cover, ambient-dependent.
📖 §11.3 Solar Thermal Energy (Evacuated Tube Collector) — chapter-end short question S-5
8. Why is an evacuated tube collector (ETC) more efficient than a flat-plate collector?
Model answer: An evacuated tube collector uses two concentric glass tubes fused at the ends, with the air evacuated from the gap, providing thermal insulation like a Thermos bottle. The vacuum stops conductive heat loss back to the atmosphere, and the selective absorbing coating on the inner tube converts short-wave radiation to long-wave radiation, preventing re-radiation. Because of this, far more heat is trapped: heat loss is less than 10% compared with about 40% for a flat-plate collector. It is also less dependent on ambient temperature and can reach high temperatures up to 150°C.
Directly answers OCR short question S-5. ETC loss <10% vs FPC ~40%; reaches 150°C.
9. Explain the working of a solar power tower (central receiver) plant.
Model answer: In a power tower, sunlight is concentrated and directed from a large field of heliostats (mirrors) onto a central receiver on a tall tower. Molten salt from the cold salt tank is pumped through the receiver where it is heated to 566°C, then stored in the hot salt thermal storage tank. The hot molten salt is pumped through a steam generator that creates steam, which drives a steam turbine to generate electricity. The cooled salt at 288°C flows back to the cold salt tank and is reused. The molten salt is a mixture of 60% sodium nitrate and 40% potassium nitrate, preferred because it is an efficient, low-cost, non-flammable and non-toxic heat-storage medium.
Heliostats → central receiver → molten salt (566°C) → steam → turbine. Salt = 60% NaNO3 + 40% KNO3.
📖 §11.4 Solar Electrical Energy (Parabolic Trough Collector)
10. Describe the parabolic trough collector for solar thermal power generation.
Model answer: The parabolic trough collector is currently the most proven solar thermal electric technology. It uses a series of parabolic, trough-shaped reflectors that focus the sun's energy onto a receiver tube running along the focus of the reflector. Because of their parabolic shape, the troughs can focus the sun at 30-60 times its normal intensity on the receiver pipe, heating the heat-transfer fluid in the receiver to about 400°C. Large arrays provide high-temperature fluid to drive a steam turbine. The collectors are aligned on an east-west axis and the troughs rotate to follow the sun, maximising energy input.
Most proven; 30-60× concentration; ~400°C; east-west axis, sun-tracking.
📖 §11.4 Solar Electrical Energy (Solar Photovoltaic Technology)
11. Explain the photovoltaic effect and the working of a solar PV cell.
Model answer: The photoelectric or photovoltaic effect is the process in which two dissimilar materials in close contact produce an electrical voltage when struck by light or radiant energy. Discrete packets of light energy called photons strike the PV cell and knock electrons in the silicon material out of their normal energy state, putting them in a position to be conducted as electricity. The effect occurs only when a photon of the correct energy strikes an atom in the cell, so cells are tuned to absorb the most intense part of the spectrum. Since silicon is naturally reflective, each cell is covered with an anti-reflective coating to minimise reflection loss.
Photons knock electrons free in silicon → DC current; anti-reflective coating needed.
📖 §11.4 Solar Electrical Energy (PV cell, module and array)
12. Distinguish between a solar PV (SPV) cell, module and array, and state the voltage of a silicon cell.
Model answer: A solar PV cell is the basic unit; one silicon cell generally produces about 0.5 Volts. Cells are connected in series and parallel to form a module (solar panel): 36 such cells connected together form a module with enough voltage to charge a 12 V battery and run a pump and motor. Modules connected together form an array to generate more power. A complete PV system comprises PV panels (modules), a battery system, a charge controller and an inverter. PV cells are made of silicon (Si), gallium arsenide (GaAs), copper indium diselenide (CIS), cadmium telluride (CdTe), etc.
Cell ≈ 0.5 V; 36 cells = module → 12 V battery; modules → array. Material = silicon (Objective Q6).
📖 §11.4 Solar Electrical Energy (Peak Watt, Wp rating)
13. What is the 'peak Watt' (Wp) rating of a PV module?
Model answer: The wattage output of a PV module is rated in terms of peak Watt (Wp). The peak-Watt output power of a module is defined as the maximum power output that the module could deliver under standard test conditions (STC). A single PV module can be manufactured with capacity ranging from 5 Wp to 120 Wp.
Wp = max output at Standard Test Conditions; single module 5-120 Wp.
📖 §11.4 Solar Electrical Energy (Solar Photovoltaic Technology) — chapter-end short question S-1
14. Why is solar cell efficiency very low?
Model answer: Solar cell efficiency is low because the cell cannot convert all the different wavelengths of light hitting it. The photovoltaic effect occurs only when a photon has the exact amount of energy needed to knock an electron loose; that energy requirement depends on the cell material. Photons with too little energy are not absorbed, and the excess energy of higher-energy photons is wasted as heat. Reflection losses also occur (silicon is naturally reflective), which is why an anti-reflective coating is used. As a result, typical solar cell efficiency is only about 10-15%.
Answers OCR short question S-1; ties to Objective Q9 (efficiency 10-15%).
📖 §11.4 Solar Electrical Energy (Energy conversion efficiency of a PV cell)
15. Give the formula for the energy conversion efficiency of a solar PV cell, defining each term with units.
Model answer: Energy conversion efficiency η (%) = [ Pm / (E × A) ] × 100, where Pm = maximum power output (watts), E = solar insolation (watts per square metre), and A = area of the solar cell (square metres). For example, a 175 W panel measuring 0.75 × 1.50 m (area = 1.125 m²) at an insolation of 1000 W/m² gives η = (175 / (1.125 × 1000)) × 100 = 15.6%, i.e. it converts 15.6% of the available solar energy into electricity.
η = Pm/(E·A)·100. Worked example from guidebook = 15.6%.
📖 §11.4 Solar Electrical Energy (Stand-alone SPV vs Grid-connected Solar System)
16. Differentiate between a stand-alone SPV power plant and a grid-connected solar system.
Model answer: A stand-alone SPV power plant is used where conventional grid supply is unavailable or irregular; electricity is centrally generated and supplied through a local grid in stand-alone mode, commonly for electrifying remote villages, hospitals, hotels, communication equipment, railway stations and border outposts (it requires batteries). A grid-connected solar system uses an inverter that synchronises with the utility power; it does not generally require batteries (though batteries can give backup), and is easier to install and maintain than a stand-alone system.
Stand-alone = no grid + battery; grid-connected = inverter synchronised, usually no battery.
📖 §11.4 Solar Electrical Energy (Building-integrated PV Systems)
17. What is a Building-Integrated Photovoltaic (BIPV) system and what are its advantages?
Model answer: In a building-integrated photovoltaic (BIPV) system, PV panels are integrated into the roof or façade of a building. BIPV provides photovoltaic power as well as weatherproofing and glazing for the building. The SPV panels generate electricity during the daytime to meet part of the building's electrical needs. Because the PV cells are integrated into the building structure, no separate costly mountings are required.
BIPV = PV built into roof/façade; gives power + weatherproofing, no separate mountings.
Model answer: The sun heats the earth unevenly, with the majority of heat received at the equator and gradually less towards the poles. In warmer regions the air is hot and at high pressure compared with colder regions where air is at low pressure. Wind is the movement of air from areas of high pressure to areas of low pressure. The rotation of the earth adds the Coriolis force, a swirling action on the winds, creating a series of wind circulations in both hemispheres. Thus wind is produced mainly by air-pressure differences in the atmosphere arising from solar radiation disparities.
Objective Q8 answer = wind from air-pressure differences due to solar radiation disparities; Coriolis = swirl from earth's rotation.
📖 §11.5 Wind Energy (Description of Wind Energy Technology)
19. What is a wind turbine (WECS)? Describe the common rotor configurations.
Model answer: Modern windmills are called wind turbines as their function is similar to gas and steam turbines; they are also called wind energy conversion systems (WECS), and those generating electricity are called wind generators. The most common type is the horizontal-axis machine, with the main rotor shaft and generator at the top of a tower, which must be pointed into the wind. Rotors can be single-, two-, three- or multi-bladed; two- and three-bladed rotors are common for power generation (three-bladed rotors run more smoothly and quietly). Multi-bladed rotors have large starting torque in light winds and are used for water pumping and low-frequency mechanical power.
WECS = Wind Energy Conversion System; HAWT most common; multi-blade = water pumping.
📖 §11.5 Wind Energy (Components of wind turbine system)
20. List and briefly describe the main components of a wind turbine system.
Model answer: (1) Rotor and blades — capture the wind. (2) Low-speed shaft — main shaft connected to the rotor hub, turning at 30-60 rpm. (3) Gear box — steps the speed up from 30-60 rpm to 1000-1800 rpm. (4) High-speed shaft — driven via the gearbox at 1000-1800 rpm, drives the generator. (5) Generator — usually an induction generator producing 50-cycle AC. (6) Nacelle — housing at the top of the tower containing the gearbox, generator and controls. (7) Disc brake — slows the rotor. (8) Yaw control — rotates the nacelle so the rotor axis aligns with wind direction. (9) Anemometer and wind vane — measure wind speed and direction.
Directly answers OCR long question L-2 in short form. Yaw = nacelle alignment.
21. What is the purpose of yaw control in a wind turbine?
Model answer: Yaw control aligns the rotor axis with the wind direction so as to extract as much of the wind's kinetic energy as possible. Large wind turbines with upwind rotors require yaw control. When the wind direction changes, sensors activate the yaw control motor, which rotates the nacelle and rotor assembly until the turbine is properly aligned with the wind.
Yaw = whole nacelle rotation to face wind (distinct from pitch = blade angle).
📖 §11.5 Wind Energy (Operating Characteristics of Wind Turbine)
22. Define cut-in speed, rated speed and cut-out (furling) speed of a wind turbine.
Model answer: Cut-in speed is the minimum wind speed at which a turbine can reliably produce usable power, generally around 5 m/s. Rated speed is the minimum wind speed at which the turbine generates its maximum (rated) power; it is often about 1.5 times the site mean wind speed. Cut-out speed (also called furling speed) is the speed above the rated speed at which the turbine must shut down to prevent damage; it varies by manufacturer from about 20 to 30 m/s.
Cut-in ≈5 m/s; rated ≈1.5× site mean; cut-out/furling 20-30 m/s. Objective Q3: rotor starts at cut-in speed.
📖 §11.5 Wind Energy (Betz Limit) — chapter-end short question S-4
23. Explain the term Betz limit.
Model answer: It is impossible for the blades of a wind turbine to be 100% efficient, because some of the wind energy must pass through the blades to make the turbine turn (the turbine extracts energy by slowing the wind). The theoretical maximum amount of energy in the wind that can be collected by a wind turbine's rotor is approximately 59%. This value is known as the Betz limit. Considering the Betz limit together with efficiency losses through the generator, gearbox, etc., only about 15-25% of the wind energy is converted into useful power.
Answers OCR short question S-4. Betz limit ≈59%; usable after losses 15-25%.
24. What is the coefficient of performance (Cp) of wind turbine blades and its typical range?
Model answer: The ability of a turbine rotor to extract the wind's power depends on its efficiency, expressed by a non-dimensional coefficient of performance of the blades, Cp. Cp is included in the power equation to express the turbine's power output. It varies with speed and generally lies between 0.33 and 0.59 (the upper bound corresponding to the Betz limit).
Cp = 0.33–0.59; appears in the wind power formula.
📖 §11.5 Wind Energy (Power available from the wind turbine)
25. Give the formula for the power available from a wind turbine, defining each term with units.
Model answer: The power produced by a wind turbine is P = 0.5 × ρ × A × Cp × Ng × Nb × V³, where P = power produced by the generator (watts); ρ = air density (kg/m³, about 1.2); A = cross-sectional/swept area intercepted by the turbine (m², = πD²/4); Cp = coefficient of performance of the blades; Ng = generator efficiency; Nb = gearbox efficiency; and V = wind speed (m/s). The ideal form (without losses) is P = ½ρAV³. Power is proportional to the swept area and to the cube of wind speed, so doubling the wind speed increases power eight-fold, while doubling the area only doubles the power.
P ∝ V³ → doubling speed = ×8 (Objective Q4). Includes term definitions with units.
📖 §11.5 Wind Energy (Power available from the wind turbine — worked example)
26. A wind turbine has a 6 m diameter rotor, Cp = 0.30, generator efficiency 0.8, gearbox efficiency 0.90 and wind speed 11 m/s (ρ = 1.2 kg/m³). Find the expected power output.
Model answer: Swept area A = πD²/4 = (3.14/4) × 6² = 28.27 m². P = 0.5 × ρ × A × Cp × Ng × Nb × V³ = 0.5 × 1.2 × 28.27 × 0.30 × 0.8 × 0.90 × 11³. This gives P ≈ 4875 watts, i.e. about 4.875 kW.
📖 §11.5 Wind Energy (Capacity Factor) — chapter-end short question S-2
27. What is the capacity factor of a wind turbine? Give its formula and typical range.
Model answer: The capacity factor of a wind turbine is the actual energy output of the turbine over a given period (usually one year) compared with its theoretical maximum energy output for the same period. CF = kWh produced / (8760 × nameplate rating of the wind turbine in kW), where 8760 is the number of hours in a year. Typical capacity factors are 20-40%, with values at the upper end at particularly favourable sites. Example: a 2.5 MW turbine producing 5,000,000 kWh/yr gives CF = 5,000,000 / (2500 × 8760) = 22.8%.
Answers OCR short question S-2. CF = actual / (8760 × kW rated); typical 20-40%.
📖 §11.5 Wind Energy (Table 11.1 Wind Speed vs Power Generation Suitability)
28. Give the guideline relating average wind speed to suitability for power generation.
Model answer: As per the guidebook table: up to 4 m/s (15 km/h) is no good; 5 m/s (18 km/h) is poor; 6 m/s (22 km/h) is moderate; 7 m/s (25 km/h) is good; and 8 m/s (29 km/h) is excellent for power generation. Sites with higher wind speed generate more power, so siting turbines in the highest-wind-speed areas gives significant economic benefit.
≤4 no good · 5 poor · 6 moderate · 7 good · 8 excellent.
29. What is biomass energy, and why is biomass considered carbon neutral?
Model answer: Biomass is basically organic matter such as wood, straw, crops, algae, sewage sludge, animal waste and other biological waste. Bioenergy is the energy derived from biomass. In energy terms biomass is a form of stored solar energy, since the sun's energy is captured and stored via photosynthesis in the biomass material. It is considered carbon neutral because the carbon dioxide released during burning of the biomass is largely balanced by the carbon dioxide absorbed/captured during its growth.
Carbon neutral = CO2 released on burning ≈ CO2 absorbed during growth.
📖 §11.6 Biomass Energy (Methods of generating energy from biomass)
30. List the different methods used to generate energy from biomass.
Model answer: The four main methods used to generate energy from biomass are: (1) Direct combustion of biomass (burning in a grate, stoker or fluidised bed for heat/steam/electricity); (2) Gasification of biomass (partial combustion to produce combustible producer gas); (3) Biomethanation / anaerobic digestion (production of biogas, mainly methane and carbon dioxide); and (4) Biofuels (conversion into liquid fuels such as ethanol and biodiesel).
Four routes: combustion, gasification, biomethanation, biofuels.
📖 §11.6 Biomass Energy (Direct Combustion of Biomass)
31. Explain direct combustion of biomass and the need for pelleting/briquetting.
Model answer: Direct combustion is the burning of biomass in a grate, stoker or fluidised bed with excess air, capturing the released energy to provide steam or hot water for process heating and/or electricity, in devices ranging from small domestic boilers to multi-megawatt power plants. Solid biomasses include coconut shells, rice husks, bagasse, wood waste and oil-seed cakes such as de-oiled bran (DOB). Biomasses of low bulk density are processed into pellets or briquettes (briquetting) to make them easier and more efficient to store, handle and burn.
Low-density biomass → pellets/briquettes for handling/combustion.
32. What is producer gas? How is it produced and what is its calorific value?
Model answer: Producer gas is the combustible gas produced by gasification of biomass. Gasification is partial (incomplete) combustion carried out by supplying air less than the stoichiometric requirement, at a temperature of about 1000°C. The products are combustible gases — carbon monoxide (CO), hydrogen (H2) and traces of methane (CH4) — plus non-useful tar and dust. Producer gas has a relatively low calorific value of 1000 to 1200 kcal/Nm³, and the gasification conversion efficiency is about 60-70%. Used in a dual-fuel DG set it can give 65-85% diesel savings.
Producer gas = CO + H2 + traces CH4 (Objective Q10 = c). CV 1000-1200 kcal/Nm³; efficiency 60-70%.
📖 §11.6 Biomass Energy (Biomass gasifier zones and gasification stages)
33. Describe the four zones of a biomass gasifier and the four stages of a gasification system.
Model answer: A biomass gasifier is a thermo-chemical reactor in which the biomass passes through four zones (top to bottom): Drying/Distillation Zone, Pyrolysis Zone, Combustion Zone and Reduction Zone, after which it is converted into high-quality combustible producer gas. A gasification system consists of four main stages: (1) feeding of feedstock, (2) gasifier reactions where gasification takes place, (3) cleaning of the resultant gas, and (4) utilisation of the cleaned gas.
📖 §11.6 Biomass Energy (Typical Producer Gas Composition)
34. Give the typical composition of producer gas.
Model answer: The typical composition of producer gas is: carbon monoxide (CO) = 19 ± 3%, hydrogen (H2) = 18 ± 2%, methane (CH4) = 3 ± 1%, carbon dioxide (CO2) = 10 ± 3%, and nitrogen (N2) = 50 ± 2%. The combustible constituents are CO, H2 and CH4, while the large nitrogen fraction (from the air supplied) gives the gas its relatively low calorific value.
📖 §11.6 Biomass Energy (Average conversion efficiency of a gasifier — solved example)
35. Give the gasifier conversion efficiency formula and find the efficiency if 20 kg of wood (CV 3200 kcal/kg) produces 46 m³ of producer gas (CV 1000 kcal/Nm³).
Model answer: Gasifier conversion efficiency = (calorific value of gas produced per kg of fuel) / (average calorific value of 1 kg of fuel) × 100, i.e. Heat output as producer gas / Heat input as fuel × 100. Here heat input = 20 × 3200 = 64,000 kcal; heat output = 46 × 1000 = 46,000 kcal. Therefore conversion efficiency = (46,000 / 64,000) × 100 = 71.88%.
Solved example from guidebook = 71.88%. η = gas-out kcal / fuel-in kcal × 100.
📖 §11.6 Biomass Energy (Biomethanation of Biomass — Anaerobic Process)
36. Explain biomethanation (anaerobic digestion) and the composition of biogas (Gobar gas).
Model answer: Biomethanation is the production of bio-methane gas (biogas) by the biological/anaerobic digestion of biomass in the absence of air, by specific bacteria, best at temperatures of 35-40°C. Raw materials include manure, sewage sludge, municipal solid waste and other biodegradable wastes; a valuable by-product is high-grade manure. Biogas produced from cow dung is called Gobar gas and is a mixture typically comprising about 60% methane (CH4) and 40% carbon dioxide (CO2). Biogas offers higher energy efficiency than direct burning of dung and can be used for electricity generation or, when purified, as a vehicle fuel.
📖 §11.6 Biomass Energy (Four-stage anaerobic digestion)
37. Describe the four-stage process of anaerobic digestion of biomass.
Model answer: Anaerobic digestion is a four-stage bacterial process. Stage 1: acidic bacteria dismantle complex organic molecules into smaller molecules. Stage 2: these molecules break down further into organic acids, carbon dioxide and ammonia. Stage 3: a second type of bacteria (methanogenic bacteria) begins converting these molecules into acetates and hydrogen. Stage 4: these are converted into methane. The methane-producing bacteria are strongly influenced by ambient conditions, which can slow or halt the process if conditions are unfavourable.
📖 §11.6 Biomass Energy (Figure 11.17 Floating-drum Biogas Plant)
38. Describe the working of a floating-drum biogas plant prevalent in India.
Model answer: A floating-drum biogas plant consists of an underground digester tank or well with a partition wall to prevent mixing of incoming fresh dung slurry with the outgoing spent slurry. Dung-and-water slurry is fed through an inlet; the gas produced is trapped under a floating plastic or metallic drum (gas-holder). As more gas is produced and trapped, the drum rises, acting as a storage unit, and when the tap is opened the gas is discharged at more or less constant pressure. A non-return valve in the outlet prevents air being drawn into the digester, which would destroy the bacteria and create an explosive mixture.
39. Describe ethanol and biodiesel as biofuels from biomass, including their feedstocks and production methods.
Model answer: Biomass can be converted into liquid biofuels to partially replace petroleum fuels. Ethanol is commonly produced by fermentation of molasses (a by-product of sugar manufacture) or other carbohydrate-rich feedstock (starch, sugar or cellulose); it is used as a fuel additive to cut carbon monoxide and smog emissions, and flexible-fuel vehicles use up to 85% ethanol. Biodiesel is a good diesel substitute produced most economically by transesterification of extracted plant oil (e.g. Jatropha seed oil — a non-edible oilseed grown on dry/arid land) with an alcohol such as methanol; raw materials include plant oils, waste cooking oil and animal fat. Biodiesel reduces vehicle emissions by about 20%.
Ethanol from molasses (fermentation); biodiesel from Jatropha by transesterification. Objective Q1 = animal & vegetable fat.
📖 §11.7 Hydro Power (Table 11.2 Classification of Hydropower by Size)
40. Give the classification of hydropower by size (large, small, mini, micro, pico).
Model answer: Hydropower is classified by size as: Large-hydro — more than 25 MW, feeding into a utility grid; Small-hydro — 2001 kW to 25 MW, usually feeding a grid; Mini-hydro — 101 kW to 2 MW, either stand-alone or feeding a grid; Micro-hydro — from 11 kW up to 100 kW, usually providing power to remote areas away from the grid; and Pico-hydro — from a few hundred watts up to 10 kW.
Large >25 MW · Small 2-25 MW · Mini 101 kW-2 MW · Micro 11-100 kW · Pico <10 kW.
📖 §11.7 Hydro Power (Run-of-the-river micro-hydro scheme)
41. What is a run-of-the-river micro-hydro scheme and its main components?
Model answer: Micro-hydro power is the small-scale harnessing of energy from falling water, for example powering a small factory or village from a local river. A run-of-the-river micro-hydro scheme requires no water storage; instead it diverts some water from the river, which is channelled along the side of a valley before being dropped into the turbine via a penstock. Its main components are an intake weir and settling basin, a channel, a forebay tank, the penstock, and a power house containing the turbine and generator.
42. Give the formula for hydropower potential and calculate the power for a flow of 20 litres/second at a head of 12 m with 60% system efficiency.
Model answer: Theoretical power P = Flow rate (Q) × Head (H) × Gravity (g), i.e. P = 9.81 × Q × H (kW), with Q in m³/s, H in metres and g = 9.81 m/s². For small systems the overall efficiency is roughly 50% (turbines rarely exceed 80%). For Q = 20 L/s = 0.020 m³/s, H = 12 m and η = 60%: P = 9.81 × 0.020 × 12 × 0.6 ≈ 1.4 kW.
Worked guidebook example = 1.4 kW. P = ρgQH; multiply by efficiency.
43. Explain the principle and operation of a fuel cell.
Model answer: The input to a fuel cell is hydrogen, which combines with oxygen to produce electricity through an electrochemical process (not combustion), giving water and heat as by-products — so it is clean, quiet and highly efficient. A fuel cell has two catalyst-coated electrodes (an anode and a cathode) surrounding an electrolyte. Hydrogen molecules enter the anode, where the catalyst separates them into positively charged protons and negatively charged electrons. The electrolyte allows protons to pass through to the cathode but blocks the electrons, so the electrons are directed through an external circuit, creating electric current. At the cathode, oxygen combines with the protons and the returning electrons to produce water and heat.
Answers OCR long question L-1 in short form. H2 at anode, O2 at cathode, electrons via external circuit; by-product = water + heat.
📖 §11.8 Fuel Cell (Fuel Cell — hydrogen as a secondary energy resource)
44. Why is hydrogen called a secondary energy source, and what is the biggest hurdle to large-scale fuel cell use?
Model answer: All fuel cells require hydrogen as fuel. Hydrogen is a secondary energy resource, meaning it does not occur freely and must be made from another fuel. It can be produced in several ways, such as steam reforming of natural gas, electrolysis of water, or gasification of biomass. The biggest hurdle to large-scale commercial exploitation of fuel cells is the high cost of producing this hydrogen. Individual fuel cells are placed in series to form a fuel cell stack to power a vehicle or provide stationary power to a building.
Hydrogen must be manufactured; high H2 production cost is the main barrier. Cells stacked for higher power.
📖 §11.8 Fuel Cell (Table 11.3 Types of Fuel Cells)
45. Name the main types of fuel cells and one key feature of each.
Model answer: (1) PEMFC (Proton Exchange / Polymer Electrolyte Membrane Fuel Cell) — polymer membrane electrolyte, platinum catalyst, operates up to ~200°C, ideal for vehicles. (2) DMFC (Direct Methanol Fuel Cell) — runs on methanol, 60-130°C, convenient for portable power below 250 W. (3) PAFC (Phosphoric Acid Fuel Cell) — liquid phosphoric acid electrolyte, ~180°C, used in stationary generators 100-400 kW. (4) AFC (Alkaline Fuel Cell) — KOH electrolyte, ~70°C, needs pure H2/O2, used on NASA shuttles. (5) SOFC (Solid Oxide Fuel Cell) — solid ceramic electrolyte, 800-1000°C. (6) MCFC (Molten Carbonate Fuel Cell) — molten carbonate electrolyte, ~650°C, used in MW-scale plants. Fuel cells produce power in the 1 W to 10 MW range.
PEMFC, DMFC, PAFC, AFC, SOFC, MCFC with electrolyte/temperature/use.
46. How is energy recovered from wastes in a Waste-to-Energy (WTE) plant?
Model answer: Energy can be recovered from wastes (trash) by combustion in incinerators to generate power. In a typical Waste-to-Energy (WTE) plant: trash is dumped on a tipping floor, then picked up by a crane and dropped into an incinerator; the burning trash heats water, creating steam; the steam turns a turbine, generating electricity; and emissions are filtered as they leave the smokestacks. The remaining ash occupies only about one-tenth of the original volume.
📖 §11.9 Energy from Wastes (Power generation from landfill gas)
47. What is landfill gas, and how is power generated from it?
Model answer: Landfill gas is the biogas produced from landfill sites by anaerobic digestion, as bacteria decompose organic matter naturally in the absence of oxygen over time. It is composed mainly of methane and carbon dioxide. Normally the methane escapes into the atmosphere and contributes to greenhouse gas emissions, but if perforated pipes are inserted into the landfill, the gas travels through the pipes under natural pressure and can be collected and used as an energy source to drive a generator and produce electricity.
Landfill gas = mainly CH4 + CO2 (anaerobic); collected via perforated pipes → generator.
48. Explain wave energy and how a wave power device (oscillating water column) works.
Model answer: Sea waves result from the concentration of energy from natural sources such as the sun, wind, tides, ocean currents, the moon and the earth's rotation. Waves originate from wind and storms and travel long distances with little energy loss, so power output is steadier and more predictable and continues round the clock. Wave energy contains roughly 1000 times the kinetic energy of wind, and wave power varies as the square of the wave height (whereas wind power varies as the cube of speed); water is about 850 times denser than air, giving higher power. In an oscillating water column device, the rising wave enters a chamber and forces air out through a turbine that spins a generator; when the wave recedes, air flows back through the turbine, generating power in both directions. Roughly 40 MW/km of coast is available for 1 m waves and up to 1000 MW/km for 5 m waves.
Wave power ∝ (height)²; round-the-clock; oscillating water column drives air turbine.
📖 §11.11 Tidal Energy (Tidal Energy) — chapter-end short question S-3
49. What causes tides, and what is the basic requirement for tapping tidal energy?
Model answer: Tides are generated by the combination of the moon's and sun's gravitational forces; the greatest effects occur at spring tides when the sun and moon combine forces, and cycles of low and high tides occur twice a day. Bays and inlets amplify the tide. When the tide comes in, water is trapped in reservoirs behind dams (barrages), and when the tide drops the trapped water is let out through turbines just like a hydroelectric plant; the turbines are driven in both directions. The basic requirement is that the height difference (tidal range) needs to be at least 5 metres for tidal energy to be practicable, together with a suitable bay/estuary site for the barrage.
Answers OCR short question S-3. Tidal range ≥5 m required; moon+sun gravity, spring tides.
50. What is geothermal energy and how does the earth's temperature vary with depth?
Model answer: Geothermal energy is heat energy from inside the earth. The earth's structure is crust, then mantle, whose top layer is hot liquid rock called magma; when magma breaks through the surface in a volcano it is called lava. For every 100 metres below ground, the temperature of the rock increases about 3°C, so at about 3000 m depth the rock is hot enough to boil water. Where water reaches hot rock it becomes boiling hot water (over 148°C) or steam; emerging through a crack it forms a hot spring. Where there is enough steam/hot water, holes are drilled and the steam/water raised to generate electricity, with no fuel burned.
Magma = molten rock (Objective Q7); +3°C per 100 m; ~3000 m to boil water.
📖 §11.12 Geothermal Energy (Types of geothermal power plants)
51. Describe the three types of geothermal power plants.
Model answer: (1) Dry steam power plant — draws steam directly from a hydrothermal production well and sends it to a turbine/generator; the steam is then condensed and returned to the reservoir via an injection well. (2) Flash steam power plant — draws hot water (about 182°C) from the well into a flash tank where a drop in pressure 'flashes' it to steam, which drives the turbine/generator; the condensed steam and remaining hot water are returned via an injection well. (3) Binary cycle power plant — operates on lower-temperature water (107-182°C); the hot water heats a separate low-boiling-point working fluid (e.g. iso-butane) in a heat exchanger, and this fluid vaporises to drive the turbine. The two fluids stay in separate closed loops, so there are no emissions to the air.
Dry steam · Flash steam (~182°C) · Binary cycle (107-182°C, second working fluid, no emissions).
📖 §11.1 Concept of New and Renewable Energy (Concept of New and Renewable Energy)
52. State the main advantages and limitations of renewable energy sources.
Model answer: Advantages: renewable sources are essentially inexhaustible (flows of energy, not stocks); they can be used without releasing harmful pollutants; biomass is carbon neutral; and they can serve remote/off-grid areas (e.g. stand-alone SPV, micro-hydro). Limitations: many are intermittent and variable (solar depends on sunshine and time of day; wind speed fluctuates, giving capacity factors of only 20-40%); conversion efficiencies are limited (solar cells 10-15%, Betz limit 59% for wind); they are site-specific (good insolation, high wind speed, ≥5 m tidal range, or suitable geothermal/hydro sites); and some have high costs (e.g. the high cost of producing hydrogen for fuel cells).
Synthesised from the chapter's recurring themes; verified facts but no single advantages/limitations list in OCR.
53. Explain the linkage between energy and environment with examples.
Model answer: Combustion of hydrocarbon (fossil) fuels in industry and power generation produces by-products that pollute the air. The principal energy-related emissions are carbon dioxide, particulate matter (dust), sulphur oxides (SOx), nitrogen oxides (NOx), hydrocarbons and carbon monoxide. Examples: SOx and NOx cause acid rain; CO results from incomplete combustion; particulate matter comes from ash in solid fuels (coal, lignite, biomass); CO2, though not a classical pollutant, is the main contributor to global warming and climate change. Thus energy use and environmental degradation are directly linked, and energy efficiency reduces these emissions.
Answer in a chain, not a list: fuel burnt -> by-product -> damage. Memory hook for the six emissions: "CO2, PM, SOx, NOx, HC, CO". The trap here is CO2: the book says it is NOT a classical pollutant, yet it is the MAIN cause of global warming - say both or you lose a mark. Always finish with the link line the examiner is looking for: less energy used = less emission, so energy efficiency is itself pollution control.
54. What are the principal air emissions due to energy use, and what is the source of each?
Model answer: The principal emissions impacting the air environment are: carbon dioxide (from oxidation of carbon in fuel; dominates total emissions); particulate matter/dust (from ash content during combustion of solid fuels such as coal, lignite, biomass); sulphur oxides SOx (from sulphur content in oil and coal); nitrogen oxides NOx (from fuel and combustion air); carbon monoxide (from incomplete combustion of fuels); and hydrocarbons. SOx and NOx are major global pollutants leading to acid rain, while CO2 is the major contributor to global warming.
Draw a two-column table (Emission | Source) - it scores faster than a paragraph. The mark is for the SOURCE, not just the name. Keep SOx and NOx apart: sulphur comes from the FUEL (oil, coal), nitrogen comes from the FUEL AND THE COMBUSTION AIR. Common mistake: writing "CO from coal" - CO comes from INCOMPLETE combustion of any fuel, and particulate matter comes from the ASH in solid fuels.
55. What are the key environmental issues of global significance? Why are they called 'global'?
Model answer: The key environmental issues of global significance are: (1) Acid rain, (2) Ozone layer depletion, (3) Global warming and climatic change, and (4) Loss of biodiversity. They are called global because they affect all mankind on a global scale without regard to any particular country or region; the whole world is a stakeholder and they need to be addressed through international efforts. Note: Suspended Particulate Matter (SPM) is a LOCAL air-quality issue, not a global one.
Memory hook for the four: A-O-G-B (Acid rain, Ozone depletion, Global warming, Biodiversity loss). The second half of the question carries marks too - "global" means the whole world is a stakeholder, the effect ignores country borders, so only international action can fix it. Trap: SPM (dust) is a LOCAL air-quality problem, never write it in this list of four.
56. Why is Suspended Particulate Matter (SPM) not classified as an environmental issue of global significance?
Model answer: The four issues of global significance are acid rain, ozone layer depletion, global warming/climate change and loss of biodiversity, because each affects all mankind on a global scale and requires international action. Suspended Particulate Matter (SPM), by contrast, is predominantly a local air-pollution problem affecting air quality and health in the immediate region where dust/ash is emitted (e.g. near a power plant or city). Its impact does not spread worldwide, so it is treated as a local rather than a global issue.
This is the examiner testing the local-vs-global line. The test is simple: does the damage cross borders? Acid rain, ozone, warming and biodiversity do; SPM settles near where it is emitted, so it hurts local air quality and health only. Say the four global issues first, then explain SPM - answering only about SPM loses the listing marks.
57. What is the ozone layer, where is it located, and why is it beneficial?
Model answer: The ozone layer is a thin layer of ozone (O3) present in the stratosphere, which extends about 10-50 km above the earth. It is highly beneficial to life on earth because it blocks the sun's harmful Ultraviolet (UV-B) radiation from reaching the earth's surface. Any disturbance or depletion of the ozone layer increases the harmful radiation reaching the surface, leading to dangerous consequences such as skin cancer, eye diseases and ecosystem damage. Ozone is naturally produced (oxygen absorbing UV below 240 nm) and destroyed (absorbing UV above 290 nm) in a balanced equilibrium.
Two numbers must appear: the stratosphere is about 10-50 km up, and the radiation blocked is UV-B. Trap to avoid: ozone HIGH UP in the stratosphere is our shield and is good; ozone at ground level is a pollutant and a greenhouse gas. Also mention that ozone is constantly made and destroyed naturally - depletion means this balance has been upset.
58. Explain the chemistry of ozone layer depletion by CFCs.
Model answer: Chlorofluorocarbons (CFCs) emitted into the atmosphere diffuse up to the stratosphere. There, strong UV radiation strikes a CFC (CFCl3) molecule and breaks a carbon-chlorine bond, releasing a free chlorine (Cl) atom. The chlorine atom reacts with an ozone (O3) molecule, breaking it into an ordinary oxygen molecule (O2) and a chlorine monoxide (ClO) molecule. A free oxygen atom then breaks up the ClO, releasing the chlorine atom again, which is free to repeat the process. Thus one chlorine atom can destroy an estimated 10,000 to 100,000 ozone molecules. It is the released chlorine (and bromine from halons) that destroys ozone, not the intact molecule.
Write it as three steps: (1) UV splits CFCl3 and frees a Cl atom, (2) Cl + O3 -> O2 + ClO, (3) a free O atom takes the O from ClO and releases Cl again. The whole point is that chlorine acts as a CATALYST - it comes back out and repeats, which is why one Cl atom destroys 10,000 to 100,000 ozone molecules. Memorise that number; it is the marks-carrying figure. Common mistake: saying the CFC molecule itself eats ozone - it is the released chlorine (or bromine) atom.
59. Which substances cause ozone depletion, and what are the counter-measures?
Model answer: Ozone is broken down by man-made chlorine and bromine compounds. The main culprit is chlorofluorocarbons (CFCs), used in refrigerators and air conditioners; others include HCFCs, carbon tetrachloride and methyl chloroform (which release chlorine) and halons and methyl bromide (which release bromine). Strong UV in the stratosphere splits these ODS molecules and the freed chlorine/bromine atom destroys ozone. Counter-measures listed in the book: the international agreement signed at the Montreal Protocol (the guidebook prints the year as 1974 — write 1974 in the exam; the real-world date is 1987) to phase out ozone-depleting chemicals; a tax imposed on the use of ozone-depleting substances; use of ozone-friendly substitutes HCFC and HFC (lower ozone-depleting potential and shorter life); and recycling of CFCs and halons.
Split the ODS list by the atom released: chlorine from CFC, HCFC, carbon tetrachloride and methyl chloroform; bromine from halons and methyl bromide. CFC (fridges and AC) is the main culprit. For counter-measures give all four: Montreal Protocol, tax on ODS, HCFC/HFC substitutes, and recycling of CFCs and halons. Exam rule for this chapter: the 2014 guidebook prints Montreal Protocol as signed in 1974 - WRITE 1974, not 1987.
Model answer: Effects of ozone layer depletion from increased UV-B penetration: (1) Human and animal health - eye diseases, skin cancer and infectious diseases. (2) Terrestrial plants - changed species composition in forests/grasslands, altered biodiversity, changes in plant form and metabolism. (3) Aquatic ecosystems - damage to phytoplankton (base of food webs) and to early stages of fish, shrimp, crab and amphibians, reducing reproduction. (4) Bio-geo-chemical cycles - altered sources and sinks of greenhouse and trace gases (CO2, CO, COS). (5) Air quality - higher photo-dissociation rates producing oxidants like hydrogen peroxide harmful to health and materials.
Answer under the five headings the book uses - health, terrestrial plants, aquatic ecosystems, bio-geo-chemical cycles, air quality - one line each; headings themselves attract marks. Remember phytoplankton, because it is the base of the ocean food chain. Common mistake: filling this answer with melting glaciers and sea-level rise - those belong to GLOBAL WARMING, not ozone depletion.
📖 §10.4 & §10.10 — Montreal (ozone) vs Kyoto (climate)
61. Distinguish the ozone layer problem from global warming, and name the protocol addressing each.
Model answer: Ozone depletion and global warming are two separate problems. Ozone depletion is the thinning of the stratospheric ozone layer (10–50 km up) caused mainly by CFCs, whose chlorine/bromine atoms destroy ozone, allowing more harmful UV-B to reach the earth; it is addressed by the MONTREAL PROTOCOL (the 2014 guidebook prints this as 'signed in 1974' — reproduce the book's 1974 in the exam; the real-world date is 1987). Global warming is the rise in the earth's temperature from the enhanced greenhouse effect caused by CO2, CH4, N2O, HFCs, PFCs and SF6; it is addressed by the KYOTO PROTOCOL (1997) under the UNFCCC (1992). Global warming does NOT increase the size of the ozone hole — the two are distinct. Memory aid: 'Montreal = Ozone, Kyoto = Climate.'
This is the classic trap pair. Memory hook: "Montreal = Ozone, Kyoto = Climate" (M before K, ozone problem came first). Keep the causes apart too: CFCs and their chlorine cause ozone loss; CO2, CH4, N2O, HFC, PFC, SF6 cause warming. State plainly that global warming does not enlarge the ozone hole - examiners set this as a true/false. Dates for the exam: Montreal as printed in the book (1974), UNFCCC 1992, Kyoto 1997.
62. What is the composition of the atmosphere by volume, and which layer holds most molecules?
Model answer: The atmosphere is composed mainly of 78% Nitrogen, 21% Oxygen, about 0.04% Carbon dioxide and about 0.04% Argon by volume, with water vapour and several other gases present in very small amounts. The two most important layers are the troposphere (where weather occurs) and the stratosphere; the air gets thinner with altitude, and about 90% of all molecules in the atmosphere are in the troposphere. Although water vapour is the most abundant natural greenhouse gas, the main GHG constituent influenced by human activity is CO2.
Memorise as a quick set: N2 78%, O2 21%, CO2 about 0.04%, Argon about 0.04%. The second number is 90% of all molecules sit in the troposphere (the lowest layer, where weather happens) - the air simply gets thinner with height. Trap: water vapour is the most abundant natural greenhouse gas, but humans do not change it directly; CO2 is the one human activity raises.
Model answer: The earth is surrounded by a blanket of greenhouse gases (water vapour, carbon dioxide, methane, nitrous oxide). The earth's atmosphere allows short-wave solar radiation from the sun to pass relatively unimpeded, but the long-wave infrared radiation emitted by the warm earth's surface is partially trapped and re-emitted downwards by these greenhouse gases. This blanketing keeps the surface warmer than it would otherwise be - much as glass traps heat in a greenhouse. Without naturally occurring greenhouse gases, the earth's average surface temperature would be a cold -18 degrees C instead of the tolerable +15 degrees C. The natural greenhouse effect is therefore a natural process that made life on Earth possible.
The two numbers ARE the answer: without natural greenhouse gases the earth would be -18 degrees C instead of +15 degrees C - a 33 degree difference. Explain in the short-wave/long-wave way: sunlight comes in easily as short-wave, the warm earth sends heat back as long-wave infrared, and the GHG blanket traps and re-radiates that. Say clearly that this natural effect is GOOD - it made life possible; only its intensification is the problem.
64. What is the enhanced greenhouse effect, and how does it differ from the natural greenhouse effect?
Model answer: The natural greenhouse effect keeps earth at a habitable +15 degrees C (instead of -18 degrees C). The enhanced (human/anthropogenic) greenhouse effect is its intensification caused by the increase of greenhouse gases in the atmosphere, especially CO2 from burning fossil fuels (coal, oil, gas) together with widespread deforestation over the past 50-200 years. The gases directly increased by human activity are carbon dioxide, methane, nitrous oxide, CFCs and ozone (water vapour is not changed directly by humans). This extra trapping is changing the global climate; the earth's average temperature has risen by about 0.75 degrees C since 1880. In short, the natural effect sustains life, while the enhanced effect causes harmful warming.
Answer in a contrast: natural = keeps earth at +15 degrees C instead of -18 degrees C and is essential; enhanced = extra trapping from human emissions and is harmful. Numbers to quote: the rise of about 0.75 degrees C since 1880, and the causes - fossil fuel burning plus deforestation over the last 50-200 years. Common mistake: saying humans increase water vapour - the book lists CO2, CH4, N2O, CFCs and ozone as the human-raised ones.
65. Why is carbon dioxide considered the most important greenhouse gas?
Model answer: Carbon dioxide is the most important greenhouse gas because of its abundance in the atmosphere. Its increase has contributed about 60% of the enhanced greenhouse effect, and its concentration (about 397 ppm, Mauna Loa Nov 2014) is much higher than that of other greenhouse gases. It is also persistent, with an atmospheric lifetime of over 100 years. The major source is fossil-fuel combustion (coal, petroleum, natural gas); for the same heat released, natural gas emits the least CO2 and coal the most. Cement manufacture is a major industrial source (from both fuel combustion and calcination of limestone), and deforestation also adds CO2.
Do not confuse the two "most" questions: SF6 is the MOST POTENT gas (GWP 22,000) but CO2 is the BIGGEST CONTRIBUTOR - about 60% of the enhanced greenhouse effect - because there is so much of it. The three figures to memorise: 60%, 397 ppm (Mauna Loa, Nov 2014) and a lifetime over 100 years. Add the fuel ranking for an extra mark: for the same heat, coal emits the most CO2 and natural gas the least.
66. What are the natural and anthropogenic sources of methane (CH4)?
Model answer: Methane is a naturally occurring inflammable gas produced by geological coal formations and by decomposition of organic matter. The main NATURAL source is wetlands; methane also forms when organic matter (food, vegetables) decomposes without oxygen - anaerobic decomposition. ANTHROPOGENIC (human) sources include leakage during coal mining, leakage from natural-gas pipelines and petroleum wells, rice cultivation, belching from cattle and other livestock (ruminants/cud-chewing animals), decay of municipal solid waste in landfills, and wood burning.
Split the answer under two headings, NATURAL and ANTHROPOGENIC - the question asks for both, and one list only gets half the marks. Natural: wetlands (the main one) and anaerobic decay of organic matter. Human: coal mining leaks, gas pipeline and oil-well leaks, paddy (rice) cultivation, cattle belching, landfill waste, wood burning. Hook: methane = "marsh gas" - anywhere organic matter rots without air. Useful extras: GWP 23, life 12 years (the shortest-lived of the main GHGs).
67. What are the sources of nitrous oxide (N2O) emissions associated with human activity?
Model answer: Nitrous oxide (N2O) emissions associated with human activity come from: use of nitrogen fertilizer, manure, biomass combustion, fossil-fuel combustion in power plants, and the chemical industry (for example nylon production). N2O is also contained in soil by bacteria - when farmers plough the soil and disturb the surface layer, N2O is released into the atmosphere. It is also released from catalytic converters in cars. N2O has a long atmospheric lifetime of about 120 years and a high GWP of 300.
Group the sources: farming (nitrogen fertilizer, manure, ploughing which releases N2O held by soil bacteria), burning (biomass and fossil fuel in power plants), and industry (chemical industry, e.g. nylon) plus car catalytic converters. Numbers worth adding: GWP 300 and an atmospheric life of about 120 years (the GWP table shows 114 years - either is acceptable, both come from the book). Common mistake: calling N2O an ozone-depleting substance - here it is a greenhouse gas.
68. Describe the properties and uses of chlorofluorocarbons (CFCs) and their substitutes.
Model answer: Chlorofluorocarbons (CFCs) are man-made chemicals that vaporise just below room temperature and are non-toxic and non-flammable. They contain chlorine atoms and have been used as refrigerants, cleaning solvents, in manufacture of insulation, and as propellants in spray cans. They are chemically unreactive, so once released they remain in the atmosphere for a long time (about 100 to 200 years) before being destroyed. As an outcome of the Montreal Protocol, CFCs are being phased out and replaced by hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs); these are less destructive to ozone and have shorter life, but are still greenhouse gases.
Cover properties, uses and substitutes - all three carry marks. Properties: man-made, boil just below room temperature, non-toxic, non-flammable, chemically unreactive, so they survive 100 to 200 years in the air. That very stability is why they reach the stratosphere. Uses hook: "Refrigerant, Solvent, Insulation, Spray-can propellant". Trap: HCFC and HFC are BETTER for ozone but are STILL greenhouse gases - and HFC is one of the six Kyoto gases while CFC is dealt with under Montreal.
69. Write short notes on perfluorocarbons (PFCs) and sulphur hexafluoride (SF6) as greenhouse gases.
Model answer: Perfluorocarbons (PFCs) are important greenhouse gases with a very long atmospheric life of more than several thousand years (about 50,000 years - the longest of the GHGs), so their emissions accumulate and influence climate for thousands of years. The largest known man-made sources are primary aluminium production and semiconductor manufacture. Sulphur hexafluoride (SF6) is the MOST POTENT greenhouse gas (highest GWP, about 22,000). It is used in insulation and electric-power transmission equipment (switchgear), the magnesium industry, semiconductor manufacturing (to create circuitry patterns on silicon wafers), and as a tracer gas for leak detection.
Keep the two "records" apart - this is the standard trap. PFC = longest LIFE, about 50,000 years (GWP 5700). SF6 = highest GWP, 22,000, the most potent GHG (life 3200 years). Hook: "P for Permanent (PFC lives longest), S for Strongest (SF6 hits hardest)". Sources to quote: PFC from aluminium production and semiconductors; SF6 from switchgear/electrical insulation, magnesium industry, semiconductors and leak-detection tracer gas.
70. Define Global Warming Potential (GWP) and explain its significance.
Model answer: Global Warming Potential (GWP) is the ratio of global warming (radiative forcing/heat trapped) from one unit mass of a greenhouse gas to that from one unit mass of CO2 over a period of time (usually 100 years). CO2 is the reference, with GWP = 1. GWP takes into account both the absorption strength of the molecule and its atmospheric lifetime - the higher the GWP, the larger the infrared absorption and the longer the atmospheric lifetime. Significance: it gives a common basis (CO2-equivalent) to compare the relative climate impact of different gases, lets emissions of various gases be aggregated for inventories, targets and trading, and shows that even small amounts of high-GWP gases like SF6 (22,000) contribute significantly to warming.
Write the definition as a ratio: heat trapped by 1 unit mass of the gas divided by that of 1 unit mass of CO2, over 100 years, with CO2 = 1 by definition. Say what GWP combines - how strongly the molecule absorbs infrared AND how long it survives in the air; that is why a long-lived gas scores high. For the significance mark, the key words are "CO2-equivalent": GWP puts all gases on one scale so emissions can be added up, traded and targeted. Example that always fits: SF6 at 22,000.
71. Give the GWP values and atmospheric lifetimes of the main greenhouse gases. Which has the highest GWP and which the longest life?
Model answer: From Table 10.1: Carbon dioxide (CO2) GWP = 1 (the standard), lifetime 5-200 yrs; Methane (CH4) GWP = 23, lifetime 12 yrs; Nitrous oxide (N2O) GWP = 300, lifetime 114 yrs; CFCs GWP = 4000-8000, lifetime 5-100 yrs; Perfluorocarbons (PFCs) GWP = 5700, lifetime about 50,000 yrs; Sulphur hexafluoride (SF6) GWP = 22,000, lifetime 3200 yrs; ozone exists only days/weeks. SF6 has the HIGHEST GWP (22,000) and is the most potent. PFC has the LONGEST atmospheric lifetime (about 50,000 years). Among methane, N2O, CFC and PFC, methane (23) has the lowest GWP.
Best written as a table with three columns: Gas | GWP | Life. Learn the ladder of GWP: CO2 1, CH4 23, N2O 300, CFC 4000-8000, PFC 5700, SF6 22,000. Two facts the examiner asks in the last line: HIGHEST GWP = SF6 (22,000); LONGEST LIFE = PFC (about 50,000 years). Note the pattern break - PFC has a lower GWP than CFC's upper range but by far the longest life, so never assume high GWP means long life.
72. Name the six major greenhouse gases covered under the Kyoto Protocol.
Model answer: The six major greenhouse gases whose emissions are covered by the Kyoto Protocol targets are: (1) Carbon dioxide (CO2), (2) Methane (CH4), (3) Nitrous oxide (N2O), (4) Hydrofluorocarbons (HFCs), (5) Perfluorocarbons (PFCs), and (6) Sulphur hexafluoride (SF6). Although ozone and CFCs are also greenhouse gases, CFCs are handled under the Montreal Protocol, not Kyoto. Emissions are measured as carbon-dioxide equivalent (CO2e) using each gas's GWP.
Memory hook for the six: "C-M-N + H-P-S" - CO2, CH4, N2O, then HFC, PFC, SF6. Common mistake: writing CFC as the fourth - CFC is controlled by the MONTREAL Protocol, and it is its replacement HFC that sits in the Kyoto list. Add one line about CO2-equivalent (each gas converted using its GWP) - that is usually the extra mark.
73. Explain carbon sequestration and where the captured CO2 is stored.
Model answer: Carbon sequestration is the process of removing/capturing CO2 from large POINT SOURCES such as power plants, oil refineries and industrial processes, and then storing it so it does not reach the atmosphere. The captured CO2 is stored in geologic formations such as depleted oil and gas reservoirs, deep coal seams, or saline reservoirs. The engineered route is known as Carbon Capture and Storage (CCS), commonly using amine scrubbing to separate CO2 from flue gases. This is distinct from natural sinks: oceans and terrestrial biomass together absorb about half the excess CO2 generated by human activities.
The two words to stress are POINT SOURCE (power plant, refinery, industrial process) and STORAGE. Give the storage places by name: depleted oil and gas reservoirs, deep coal seams, saline reservoirs. Naming amine scrubbing as the separation method and CCS as the engineered route adds detail cheaply. Do not confuse this with natural sinks - oceans and biomass absorbing CO2 is a different question.
74. What are the major natural carbon sinks, and how much CO2 do they absorb?
Model answer: Natural carbon sinks absorb atmospheric CO2. The OCEANS are a major sink, containing about 50 times more carbon than the atmosphere. Terrestrial BIOMASS, including trees and grasses, stores about three times more carbon than the atmosphere. Together, the ocean and terrestrial ecosystems absorb about half of the excess CO2 generated by human activities. (The process of capturing CO2 from point sources and storing it is separately called carbon sequestration.)
Three numbers carry the marks: oceans hold about 50 times more carbon than the atmosphere, terrestrial biomass about 3 times more, and together they absorb about HALF the excess CO2 humans produce. Hook: "50 - 3 - half". Keep it separate from carbon sequestration, which is the man-made capture-and-store route; here the sinks are natural.
75. Summarise the global and India greenhouse-gas emission profile given in the guidebook.
Model answer: Since the Industrial Revolution, annual CO2 emissions from fuel combustion rose to almost 36 Giga tonnes of CO2 in 2013, with energy use being by far the largest source. CO2 from fossil fuels and cement contributes almost 70% of global GHG emissions. India contributes almost 7% of global emissions and is the third-largest CO2 emitter behind China and the USA. India emitted about 2.5 Giga tonnes of CO2 in 2013, but per-capita emissions remain low at about 1.6 tonnes per annum. Coal-based power production accounts for almost 70% of India's coal-related CO2 emissions.
This is a pure numbers answer, so learn the string: 36 Giga tonnes CO2 globally in 2013; fossil fuels + cement = almost 70% of global GHG; India about 7% of global emissions and the 3rd largest emitter (after China and the USA); India about 2.5 Giga tonnes in 2013; per capita only about 1.6 tonnes per year; coal-based power = about 70% of India's coal CO2. The point the examiner wants stated: India's TOTAL is large but its PER CAPITA is low.
Model answer: Four impacts of global warming (from a longer list in the guidebook): (1) Increasing ocean temperature and rising sea levels - mainly from thermal expansion of warming ocean water, causing coastal flooding. (2) Snow and ice melting - mountain glaciers, ice sheets and Arctic sea ice melt, raising sea levels and disrupting water supply. (3) Altered rainfall patterns and more extreme weather events (cyclones, storms, floods, droughts) and severe heat waves. (4) Loss of biodiversity as ecosystems change and species cannot adapt. Other impacts: increased diseases (e.g. malaria spread), dwindling freshwater supply and food shortages.
The question says four - give exactly four with a one-line explanation each; a bare list of words scores poorly. Safest four: sea-level rise, ice and glacier melting, changed rainfall and extreme weather, loss of biodiversity. Common mistake: writing ozone-depletion effects (skin cancer, eye disease) here - those belong to the ozone question. Health here means things like malaria spreading.
77. Explain how global warming causes rising sea levels.
Model answer: During the twentieth century the average sea level increased by about 20 cm. The LARGEST contribution to this rise is thermal expansion of ocean water - as the oceans warm, the water expands and the sea level rises. In addition, melting of mountain glaciers, ice sheets (West Antarctica and Greenland) and Arctic sea ice adds water to the oceans. A further rise of 10-20 cm by 2030 and up to 1 m by 2100 is predicted. Coastal flooding will increase; people in low-lying countries (e.g. Bangladesh) and even developed countries (e.g. the Netherlands) are vulnerable, since about half the world's population lives near coastal zones.
The mark-carrying point is the CAUSE ranking: THERMAL EXPANSION of warming ocean water is the largest contributor, melting ice comes second. Many students write only "ice melts" and lose the main mark. Numbers: about 20 cm rise during the twentieth century, a further 10-20 cm by 2030 and up to 1 m by 2100. Finish with who suffers - about half the world's population lives in coastal zones (Bangladesh, the Netherlands).
78. What is biodiversity, and how is it affected by global warming?
Model answer: Biodiversity (biological diversity) is the variety and variability of all living organisms - the diversity within species (genetic), between species, and of ecosystems - including plants, animals, microorganisms and the ecological complexes of which they are part. Global warming threatens biodiversity: ecosystems will change, some species moving farther north or thriving while others cannot move and may become extinct. Up to about 25% of mammals and 12% of birds may become extinct over coming decades as warmer conditions alter forests, wetlands and rangelands and human development blocks migration. Oceans are also affected - for example coral reefs, which have limited tolerance for warm water, are severely impacted.
Define biodiversity at three levels - within species (genetic), between species, and of ecosystems - not just "many plants and animals". Then link to warming: ranges shift north, species that cannot move go extinct, and human development blocks migration routes. Numbers to quote: up to about 25% of mammals and 12% of birds may be lost in coming decades. Coral reefs are the standard example, as they tolerate warm water poorly.
79. What is the UNFCCC, when was it signed, and what is its objective?
Model answer: The United Nations Framework Convention on Climate Change (UNFCCC) was signed by over 160 countries at the UN Conference on Environment and Development (the Earth Summit) at Rio de Janeiro in June 1992, and came into force in 1994. Its objective is to stabilise greenhouse-gas concentrations 'at a level that would prevent dangerous anthropogenic (human) interference with the climate system.' The short-term objective was that developed countries should return their GHG emissions (particularly CO2) to 1990 levels by the year 2000; the long-term objective is stabilisation within a time-frame allowing ecosystems to adapt, food production to continue and sustainable economic development. Developed countries should take the lead.
Dates first, they are the easy marks: signed June 1992 at the Rio Earth Summit by over 160 countries, in force 1994. Write the objective in the book's own words - stabilise GHG concentrations to prevent "dangerous anthropogenic interference with the climate system". Then split short-term (developed countries back to 1990 emission levels by 2000) from long-term (stabilise so ecosystems adapt, food production continues, development stays sustainable). Trap: the UNFCCC only ENCOURAGED; it is Kyoto that BINDS.
80. What is the IPCC and when and by whom was it formed?
Model answer: The IPCC, the Intergovernmental Panel on Climate Change, was formed in 1988 by the World Meteorological Organization (WMO) and the United Nations to review climatic data and periodically report on their findings. Its 1995 report concluded that the observed increase in global average temperature over the last century 'is unlikely to be entirely natural in origin' and that there is a 'discernible human influence on global climate.' The panel projected (if trends continue) an average global temperature increase of 1.4 to 5.8 degrees C in the twenty-first century, with about 75% of the warming due to CO2. The 1995 report led directly to the 1997 Kyoto Protocol.
Four facts: 1988, by the WMO and the UN, to review climate data and report periodically. Its 1995 report is the one that found a "discernible human influence on global climate", and that report led straight to the 1997 Kyoto Protocol. Projection to memorise: 1.4 to 5.8 degrees C rise in the twenty-first century, about 75% of it due to CO2. Trap: the IPCC only assesses science - it does not set emission targets; the COP/Kyoto does.
81. What is the Conference of Parties (COP), and what is its purpose?
Model answer: The COP (Conference of Parties) is the 'supreme body' of the UNFCCC. The Parties to the Convention meet annually in the form of a COP, and countries that have joined the UNFCCC are referred to as 'Parties to the Convention.' The primary task of the COP is to promote and review the implementation of the Convention and any related legal instruments (such as the Kyoto Protocol). Meetings held between each COP are called Intersessional meetings. The landmark COP is COP-3, held in 1997, which resulted in the Kyoto Protocol - setting legally binding emission targets for developed (Annex I) countries for the six major greenhouse gases, to be reached over 2008-2012.
Two phrases must appear: the COP is the "supreme body" of the UNFCCC, and member countries are the "Parties to the Convention". It meets annually; meetings in between are Intersessional meetings. The mark for the landmark: COP-3 (1997) produced the Kyoto Protocol. Trap: the COP belongs to the UNFCCC, not to the IPCC - do not mix them up.
82. What is the Kyoto Protocol and what are its main features?
Model answer: The Kyoto Protocol is an international agreement linked to the UNFCCC. Its major feature is that it sets BINDING targets for 37 industrialized countries and the European community to reduce greenhouse-gas emissions - an average of 5% against 1990 levels over the five-year period 2008-2012. The key difference from the Convention is that while the Convention only encouraged industrialized countries to stabilise emissions, the Protocol commits them to do so. Recognising that developed countries are principally responsible for current high GHG levels from over 150 years of industrial activity, it places a heavier responsibility on them under the principle of 'common but differentiated responsibilities.' It entered into force in 2005 (when Russia ratified); the USA (about 25% of global GHG) has not ratified it.
Learn the target as one sentence: 37 industrialized countries + the EU, average 5% cut against the 1990 base year, over the first commitment period 2008-2012. Three more marks: adopted 1997, entered into force 2005 (when Russia ratified), USA (about 25% of global GHG) never ratified. The one-line difference the examiner wants: the Convention only encouraged, the Protocol COMMITS. Keep 1990 (base year) and 2008-2012 (target period) apart.
📖 §10.10 Common but differentiated responsibilities
83. Explain the principle of 'common but differentiated responsibilities' in climate change mitigation.
Model answer: Under this principle, both industrialized and developing countries share a COMMON responsibility to address climate change as members of the international community, but the responsibility is DIFFERENTIATED according to their respective capabilities and historical contribution. Because developed countries are principally responsible for the current high levels of GHG in the atmosphere as a result of more than 150 years of industrial activity, the Kyoto Protocol places a heavier responsibility on them and requires developed (Annex I) countries to take the lead. This is the correct view of responsibility: shared, but weighted by capability and past emissions.
Answer by splitting the phrase: COMMON because every country shares one atmosphere; DIFFERENTIATED because capability and history differ. The evidence line is the one to memorise - developed countries caused today's high GHG levels through more than 150 years of industrial activity, so Kyoto puts binding targets only on Annex I and asks them to take the lead. Common mistake: writing that developing countries have NO responsibility - the responsibility is shared, only the burden is weighted.
84. How does the Convention divide countries into groups according to their commitments?
Model answer: The Convention divides countries into three main groups: (1) Annex I Parties - the industrialized countries that were OECD members plus countries with economies in transition (EIT Parties), including the Russian Federation, Baltic States and several Central/Eastern European states; they carry the binding emission targets. (2) Annex II Parties - the OECD members of Annex I but not the EIT Parties; they must provide financial resources and promote transfer of environmentally friendly technologies to developing and EIT countries. (3) Non-Annex I Parties - mostly developing countries, recognised as especially vulnerable to climate change (e.g. low-lying coastal states, those prone to drought).
Three groups, and the mark is in what each must DO. Annex I = industrialized (OECD + economies in transition such as Russia, Baltic and East European states) - they carry the emission targets. Annex II = Annex I MINUS the EIT countries - they must provide money and technology transfer. Non-Annex I = developing countries - no targets, and recognised as most vulnerable. Hook: "Annex I owes cuts, Annex II owes cash, Non-Annex I gets help."
85. Describe the three flexibility mechanisms of the Kyoto Protocol, distinguishing CDM from Joint Implementation.
Model answer: The Kyoto Protocol offers three market-based flexibility mechanisms to help Parties meet targets economically: (1) Emissions Trading ('carbon trading') - countries with spare emission units (allowed but not used) sell this excess to countries over their targets; carbon is traded like a commodity in the 'carbon market.' (2) Clean Development Mechanism (CDM) - a country with a commitment implements an emission-reduction project in a developing country, earning saleable Certified Emission Reductions (CERs), each equal to one tonne of CO2. (3) Joint Implementation (JI) - a project between two Annex I (committed) countries, earning Emission Reduction Units (ERUs), each equal to one tonne of CO2. Key difference: CDM links a committed country with a non-committed (developing) country, whereas JI is between two committed countries.
Learn the three as name + credit + who is involved. Emissions Trading = spare units sold, the "carbon market". CDM = Annex I funds a project in a DEVELOPING (non-Annex I) country, credit = CER. JI = Annex I project in ANOTHER Annex I country, credit = ERU. Both CER and ERU equal one tonne of CO2. Hook: "CDM = Developing country, C for CER; JI = Joined by two committed countries, E for ERU." This CDM/JI mix-up is the most common mark-loser in the chapter.
86. What is the Clean Development Mechanism (CDM) and what are CERs?
Model answer: The Clean Development Mechanism (CDM) allows a country with an emission-reduction commitment under the Kyoto Protocol to implement an emission-reduction project in a developing (non-Annex I) country. Such projects earn saleable Certified Emission Reduction (CER) credits, each equivalent to one tonne of CO2, which can be counted towards meeting the developed country's Kyoto targets. The mechanism delivers both sustainable development in the host country and cost-effective emission reductions, while giving industrialized countries flexibility in meeting targets. The major CDM projects have come from renewable energy, followed by waste handling and disposal.
The one number to state: 1 CER = 1 tonne of CO2. Direction matters - the money and technology flow FROM the committed (Annex I) country INTO the developing (non-Annex I) host, and the credits flow back. Two benefits, one for each side: sustainable development for the host, cheap compliance for the investor. Extra mark: renewable energy is the largest CDM project category, followed by waste handling and disposal. If JI appears in the same question, keep CER with CDM and ERU with JI.
87. What is Joint Implementation (JI), and how does it differ from CDM?
Model answer: Joint Implementation (JI) allows a country with an emission-reduction commitment under the Kyoto Protocol to earn Emission Reduction Units (ERUs) from an emission-reduction or emission-removal project in ANOTHER Annex I country, each ERU equivalent to one tonne of CO2, counted towards its Kyoto target. The project must provide a reduction in emissions (or enhancement of removals by sinks) additional to what would otherwise have occurred; the host Party benefits from foreign investment and technology transfer. The difference from CDM: JI projects are between two countries that BOTH have commitments, whereas CDM projects are between one country that has commitments and another (developing country) that does not.
Write ERU = 1 tonne of CO2, and stress ANOTHER Annex I country - both parties have commitments; that single word is the whole difference from CDM. Do not miss ADDITIONALITY: the reduction must be over and above what would have happened anyway - the same test applies to CDM. Answer in two parts, define JI first, then give the difference in one clean sentence, since the question asks for both.
88. Explain emissions trading under the Kyoto Protocol.
Model answer: Emissions trading allows countries that have emission units to spare - emissions permitted to them but not 'used' - to sell this excess capacity to countries that are over their targets. It is also known as carbon trading, since carbon dioxide is the principal greenhouse gas. Carbon is now tracked and traded like any other commodity, in what is called the 'carbon market.' The mechanism helps stimulate green investment and lets Parties meet their emission targets economically, ensuring emissions are cut where it costs least to do so. It supplements, rather than replaces, direct national actions such as conserving fossil fuel.
The logic to write: a country under its cap has "spare units" it is allowed but has not used, and it can sell them to a country over its target. Give the alternative names - carbon trading, carbon market - because CO2 is the main gas and is traded like any commodity. The economic point earns the last mark: emissions get cut wherever it is cheapest. Common mistake: saying trading replaces domestic action - the book says it SUPPLEMENTS it.
89. Describe the main stages of the CDM project cycle.
Model answer: The CDM project cycle stages are: (1) Project Preparation - identification and feasibility study, establishing the project is real, measurable and additional. (2) Development of the Project Idea Note (PIN) - about five pages giving indicative information; informs the host-country Designated National Authority (DNA) and gets feedback. (3) Development of the Project Design Document (PDD) - the key, mandatory document containing baseline methodology, monitoring plan and CER estimate. (4) Submission of PDD with host-country approval to a Designated Operational Entity (DOE) for validation (PDD made public for 30 days). (5) Validation, then registration with the CDM Executive Board (CDM-EB). (6) Implementation, yearly monitoring, verification and certification by the DOE, leading to issuance of CERs.
Answer as a numbered flow, not a paragraph: Preparation -> PIN -> PDD -> host-country approval (DNA) -> validation by DOE (PDD public for 30 days) -> registration by CDM-EB -> implementation -> monitoring -> verification/certification -> CER issued. Learn who does what: DNA approves, DOE validates and verifies, CDM-EB registers and issues. Numbers worth adding: PIN about 5 pages, PDD public for 30 days, registration final within about eight weeks.
90. Distinguish between the Project Idea Note (PIN) and the Project Design Document (PDD) in a CDM project.
Model answer: The Project Idea Note (PIN) is about five pages giving indicative information on the type and size of the project, its location, the anticipated GHG reduction versus the 'business-as-usual' scenario, the suggested crediting lifetime, the suggested CER price (US$/tCO2e), the financial structuring, and other socio-economic/environmental benefits. The PIN is NOT required for a CDM application but helps inform the host-country DNA and gauge buyer interest. The Project Design Document (PDD) is the KEY, MANDATORY document of the CDM cycle. It contains the general project description, baseline setting, project duration/crediting period, monitoring plan, estimation of GHG emission reductions, environmental impacts and stakeholders' comments, and is submitted to a DOE for validation and to the CDM-EB for registration.
One-line difference to lead with: PIN is OPTIONAL and indicative (about 5 pages), PDD is the KEY MANDATORY document. Hook: "PIN = pitch, PDD = proof." The PDD is where baseline, crediting period, monitoring plan, emission-reduction estimate, environmental impacts and stakeholder comments live - the monitoring plan and baseline are the items most often missed. Remember the PIN goes to the host DNA and to gauge buyer interest; the PDD goes to the DOE and CDM-EB.
📖 §10.11 DOE, DNA, CDM-EB roles & validation vs verification
91. Distinguish validation from verification in CDM, and state the roles of DOE, DNA and CDM-EB.
Model answer: Validation occurs at the OUTSET of a project: the Designated Operational Entity (DOE) evaluates the PDD and associated documents against CDM requirements (after making the PDD public for 30 days) to confirm the information and assumptions are accurate and reasonable. Verification is the periodic, ex-post review during the OPERATION of the project - the DOE checks that monitored GHG emission reductions actually occurred per the monitoring plan, carried out annually; verified reductions form the basis for CERs. Roles: DOE - validates and verifies; DNA (Designated National Authority) - host-country approval (in India, the Ministry of Environment & Forest, MoE&F); CDM-EB (CDM Executive Board) - formally registers the validated project (final after up to eight weeks).
Time separates the two words: VALIDATION happens at the START (is the plan sound?), VERIFICATION happens DURING operation, every year (did the reductions really happen?). Both are done by the DOE - that catches students out, they assume different bodies. Hook: "Validate the plan, Verify the performance." Roles: DNA = host-country approval (in India the Ministry of Environment & Forest), CDM-EB = registration. Numbers: PDD public for 30 days, registration final in about eight weeks.
92. What are the three small-scale CDM project types eligible for fast-track approval?
Model answer: To reduce high transaction costs for small projects, certain small-scale projects are eligible for CDM fast-track approval. The three small-scale project types are: Type I - renewable energy projects with a capacity of up to 15 MW; Type II - energy-efficiency projects which reduce energy consumption on the demand or supply side by up to 15 GWh/year (54 TJ) versus business-as-usual; Type III - other projects which reduce emissions and emit less than 15 kT CO2/year. Fast-tracking is justified because the normal CDM process is too costly for small projects, many small projects give significant local sustainable-development benefits, and small-scale technologies (solar, wind, fuel cells) are promising for the long term.
Every limit is a 15, only the unit changes - that is the whole memory trick: Type I renewable up to 15 MW, Type II energy efficiency up to 15 GWh/year (54 TJ), Type III other projects under 15 kT CO2/year. Keep the order I-II-III as renewable, efficiency, other. Add the reason for fast-tracking - normal CDM transaction costs are too high for small projects - because the question usually carries a "why" mark.
93. What is the 2% CER levy, and what are the CDM crediting-period options?
Model answer: The CERs generated by CDM projects are subject to a 2% levy, used to help particularly vulnerable developing countries adapt to the adverse effects of climate change. (Also, public funding for CDM projects must not divert official development assistance, ODA.) Regarding the crediting period - the duration for which a project generates CERs - a project can be valid either for one period of ten years only, or for up to three periods of seven years each, with revalidation of the project every seventh year. Monitoring continues for the entire crediting period (10 years, or 3x7 years).
Two separate facts, so use two headings. Levy: 2% of the CERs generated, used to help especially vulnerable developing countries ADAPT (not mitigate) - and public funding must not be diverted official development assistance (ODA). Crediting period: EITHER one fixed period of 10 years, OR up to 3 periods of 7 years each with revalidation every seventh year. Hook: "10 once, or 7 thrice." Monitoring runs for the whole crediting period.
94. What are the EU '20-20-20' climate and energy targets for 2020?
Model answer: The EU 2020 Climate and Energy Package is a set of binding legislation to meet three key objectives by 2020, known as the '20-20-20' targets: (1) a 20% reduction in EU greenhouse-gas emissions from 1990 levels; (2) raising the share of EU energy consumption produced from renewable resources to 20%; and (3) a 20% improvement in the EU's energy efficiency. These represent an integrated approach to combat climate change, increase energy security and strengthen competitiveness. The targets were set by EU leaders in March 2007 and enacted through the climate and energy package in 2009.
The name gives you the answer - three 20s by 2020: emissions -20% (from 1990 levels), renewables 20% of energy consumption, energy efficiency improved 20%. The trap is the baseline: the 20% CUT is measured against 1990, while the other two are simply shares/improvements by 2020. Add that they are BINDING legislation, set by EU leaders in 2007 and enacted in 2009, and that the aim is climate + energy security + competitiveness.
95. Explain how the EU Emissions Trading System (EU ETS) 'cap and trade' works.
Model answer: The EU Emissions Trading System (EU ETS) is a policy tool to cut industrial GHG emissions cost-effectively; it covers over 11,000 power stations and industrial plants in 31 countries plus airlines. It works on the 'cap and trade' principle: a cap (limit) is set on the total amount of certain greenhouse gases that installations may emit, and the cap is reduced over time so total emissions fall. Within the cap, companies receive or buy emission allowances and can trade them with one another. Each year a company must surrender enough allowances to cover its emissions or face heavy fines; if it reduces emissions it can keep or sell spare allowances. This ensures emissions are cut where it costs least.
Explain "cap and trade" in the book's order: a cap is fixed on total emissions, the cap is LOWERED each year so emissions must fall, companies get or buy allowances within it and may trade them, and each year they must surrender enough allowances or pay heavy fines. Cut emissions and you keep or sell the spare allowances - that is the incentive. Scale figures worth quoting: over 11,000 power stations and industrial plants in 31 countries, plus airlines.
📖 §10.13 Sustainable development (Brundtland 1987)
96. Define sustainable development and state its three basic objectives.
Model answer: According to the Brundtland Commission Report 'Our Common Future' (1987), sustainable development is 'meeting the needs of the present without compromising the ability of future generations to meet their own needs.' It can also be described as 'living on the Earth's income rather than eroding its capital' and keeping consumption of renewable resources within the limits of their replenishment. Sustainable development encompasses three basic and inter-related objectives (the three pillars): (1) Economic security and prosperity, (2) Social development and advancement, and (3) Environmental sustainability.
Reproduce the definition word for word - "meeting the needs of the present without compromising the ability of future generations to meet their own needs" - and attribute it: Brundtland Commission report "Our Common Future", 1987. The neat supporting line is "living on the Earth's income rather than eroding its capital". Then give the three pillars: economic security/prosperity, social development, environmental sustainability. Common mistake: writing only the environmental pillar - all three are needed.
97. Give the full forms of: GWP, GHG, CFC, HFC, PFC, SF6, CCS, CDM, JI, CER, ERU, IPCC, UNFCCC, COP, DOE, DNA.
Model answer: GWP - Global Warming Potential; GHG - Greenhouse Gas; CFC - Chlorofluorocarbon; HFC - Hydrofluorocarbon; PFC - Perfluorocarbon; SF6 - Sulphur Hexafluoride; CCS - Carbon Capture and Storage; CDM - Clean Development Mechanism; JI - Joint Implementation; CER - Certified Emission Reduction; ERU - Emission Reduction Unit; IPCC - Intergovernmental Panel on Climate Change; UNFCCC - United Nations Framework Convention on Climate Change; COP - Conference of Parties; DOE - Designated Operational Entity; DNA - Designated National Authority. (Also: CDM-EB - CDM Executive Board; PIN - Project Idea Note; PDD - Project Design Document; ODS - Ozone Depleting Substances; EnMS - Energy Management System.)
Learn these in linked pairs so one recalls the other: CDM->CER and JI->ERU (both credits = 1 tonne CO2); PIN->PDD (idea note then design document); DOE->validates/verifies while DNA->host-country approval and CDM-EB->registers. Gases group as CFC/HFC/PFC/SF6. Trap in the letters: DNA here is Designated National AUTHORITY (a government body) and DOE is Designated Operational ENTITY (an auditor) - do not swap them. Write full forms only; no explanation is asked, so do not waste time.
98. How much CO2 is produced from the complete combustion of 1 kg of carbon, and why?
Model answer: Complete combustion of carbon follows the reaction C + O2 = CO2. The molar mass of carbon (C) is 12 and that of carbon dioxide (CO2) is 44. Therefore 12 kg of carbon produces 44 kg of CO2, so 1 kg of carbon produces 44/12 = 3.67 kg of CO2. In general, a fuel containing C kg of carbon yields C x 3.67 kg of CO2 on complete combustion. This factor is used to estimate CO2 emissions from the carbon content of a fuel.
Start from the equation C + O2 = CO2, then the molecular weights: 12 for carbon, 44 for CO2 (12 + 16 + 16). So 12 kg carbon gives 44 kg CO2, and 1 kg gives 44/12 = 3.67 kg. Learn 3.67 as a ready factor - the examiner reuses it in numericals: CO2 = carbon in fuel x 3.67. Common mistake: multiplying the whole fuel mass by 3.67 - it applies only to the CARBON content of the fuel.
99. A renovation and modernization (R&M) of a 110 MW coal-fired thermal power plant raised efficiency from 28% to 32%. Specific coal consumption was 0.7 kg/kWh before R&M. For 7000 hours/year (coal quality unchanged), calculate (a) coal savings per year and (b) CO2 avoidance in tons/year if the emission factor is 1.53 kg CO2/kg coal.
Model answer: Annual generation = 110 MW x 1000 x 7000 h = 770 x 10^6 kWh/year. Specific coal consumption is inversely proportional to efficiency. After R&M: new SCC = 0.7 x (28/32) = 0.6125 kg/kWh. Coal saved per kWh = 0.7 - 0.6125 = 0.0875 kg/kWh. (a) Annual coal saving = 0.0875 x 770 x 10^6 = 6.7375 x 10^7 kg = approximately 67,375 tonnes/year. (b) CO2 avoided = coal saved x emission factor = 67,375,000 kg x 1.53 = 1.0308 x 10^8 kg = approximately 1,03,084 tonnes CO2/year.
The key idea is that specific coal consumption is INVERSELY proportional to efficiency, so new SCC = 0.7 x (28/32), NOT x (32/28) - flipping this ratio is the usual mistake. Work in the fixed order: generation (MW x 1000 x hours) -> SCC saved per kWh -> annual coal saved -> multiply by the emission factor. CO2 avoided = fuel saved x emission factor. Watch units: convert kg to tonnes by dividing by 1000 at the end, and write kg or tonnes at every step.
100. A thermal power plant uses 0.72 kg of coal to generate one kWh of electricity. If the coal contains 38% carbon by weight, calculate the CO2 emission per kWh under complete combustion.
Model answer: Carbon present in coal per kWh = 0.72 x 38/100 = 0.2736 kg. By the reaction C + O2 = CO2, 1 kg of carbon produces 44/12 kg of CO2 under complete combustion. Therefore CO2 generated per kWh = 0.2736 x 44/12 = 1.0032 kg CO2/kWh.
Two steps only: first find the carbon actually burnt (0.72 x 38/100 = 0.2736 kg), then convert carbon to CO2 with 44/12 = 3.67. Never apply 44/12 to the full 0.72 kg of coal - that is the standard mark-loser, since only the carbon fraction becomes CO2. A good sanity check: the answer per kWh should come out near 1 kg CO2/kWh for Indian coal, and it does (1.0032).
📖 §10.13 Sustainable development applied to energy
101. What considerations does sustainable development apply to energy and environment?
Model answer: Applied to energy and environment, sustainable development considers: (1) Inputs - fuels, energy sources, land and raw materials that are non-renewable should be used up only as far as they can be substituted in future. (2) Where inputs are renewable, they should be used up only at a rate within which they can be renewed. (3) Outputs - in production and consumption - should not overstrain ecosystems or the assimilation capacity of the ecosphere. The aim is ways of living and working that let all people lead healthy, fulfilling, economically secure lives without destroying the environment or endangering future welfare.
Structure the answer as INPUTS then OUTPUTS - that framing itself earns marks. Inputs: non-renewables only as fast as substitutes can be found; renewables only as fast as they renew. Outputs: waste and emissions must stay within what ecosystems and the ecosphere can absorb. Close with the human aim - healthy, fulfilling, economically secure lives without destroying the environment. Do not repeat the Brundtland definition alone; this question wants it APPLIED to energy.
102. Outline the sequence of the international climate-change framework (IPCC, UNFCCC, COP-3/Kyoto).
Model answer: The international framework developed in sequence: (1) IPCC - Intergovernmental Panel on Climate Change, formed in 1988 by the WMO and the UN to review climate data and report findings; its 1995 report established a discernible human influence on climate. (2) UNFCCC - United Nations Framework Convention on Climate Change, signed at the Rio Earth Summit in June 1992 by over 160 countries, in force from 1994, to stabilise GHG concentrations and prevent dangerous anthropogenic interference. (3) COP - the annual Conference of Parties, the supreme body of the UNFCCC; COP-3 in 1997 produced the Kyoto Protocol with binding targets (average -5% vs 1990 levels) for Annex I countries over 2008-2012, in force from 2005.
Learn it as a date chain: 1988 IPCC (science) -> 1992 UNFCCC signed at Rio (framework, in force 1994) -> annual COPs -> COP-3 in 1997 = Kyoto Protocol (binding, in force 2005). Hook: "Science, then framework, then binding targets." Kyoto details to attach: average 5% cut against 1990 levels, Annex I countries, period 2008-2012. Common mistake: swapping 1992 (UNFCCC) with 1997 (Kyoto) - the Convention always comes before its Protocol.
103. How are CERs certified and issued, and why is current CER demand low?
Model answer: After verification, the Designated Operational Entity (operational entity) provides a certification report giving written assurance that the project achieved the verified reduction. Unless a project participant or three Executive Board members request a review within 15 days, the CERs are issued; CERs are based on actual reductions during the monitored period (usually one year). Current demand for CERs is low because a number of Annex I countries are not participating in the Kyoto Protocol or its second commitment period, and about two-thirds of the EU ETS quantitative limit for use of ERUs and CERs has already been used, so confirmed demand is far below the mechanism's supply capacity.
Answer in order: verification -> certification report (written assurance) -> 15-day review window -> CERs issued. The 15 days is the number to memorise, and note who can ask for a review - a project participant or three Executive Board members. CERs are based on ACTUAL monitored reductions, usually over one year. For the low-demand part, give both reasons: several Annex I countries are out of Kyoto/its second period, and about two-thirds of the EU ETS limit for CER/ERU use is already consumed - so supply far exceeds confirmed demand.