UGC NET Environmental Science Unit-V: Energy and Environment Syllabus

What is geothermal energy and its main resource types?

Geothermal energy is heat from the Earth's interior. Resource types: hydrothermal (hot water/steam reservoirs), geopressured, hot dry rock (enhanced geothermal systems), and magma. Used for electricity (dry steam, flash steam, binary cycle plants) and direct heating.

Name the main technologies for harnessing solar energy.

(1) Solar photovoltaic (PV) - direct conversion of sunlight to electricity via semiconductors (photovoltaic effect); (2) Solar thermal - collecting heat for water heating or to drive turbines; and (3) Concentrated Solar Power (CSP) using mirrors/lenses to focus sunlight.

What is the photovoltaic effect?

The photovoltaic effect is the generation of voltage and electric current in a semiconductor (e.g. silicon p-n junction) when exposed to light: absorbed photons excite electrons across the band gap, creating electron-hole pairs that are separated to produce a DC current.

Distinguish nuclear fission from nuclear fusion.

Fission: a heavy nucleus (e.g. U-235) splits into lighter nuclei, releasing energy and neutrons. Fusion: light nuclei (e.g. deuterium + tritium) combine to form a heavier nucleus (helium), releasing energy. Fusion releases more energy per unit mass and powers the Sun.

Write a representative nuclear fission reaction of Uranium-235.

n + U-235 -> (U-236*) -> e.g. Ba-141 + Kr-92 + 3 neutrons + ~200 MeV energy. The released neutrons sustain a chain reaction.

Write the main deuterium-tritium fusion reaction.

D (H-2) + T (H-3) -> He-4 + n (neutron) + 17.6 MeV. This is the most achievable fusion reaction, releasing a high-energy neutron and an alpha particle.

What are the principal nuclear fuels used in reactors?

Uranium-235 (fissile, ~0.7% of natural uranium), Uranium-238 (fertile, converts to Pu-239), Plutonium-239 (fissile, bred from U-238), and Thorium-232 (fertile, converts to fissile U-233). India's three-stage programme emphasizes thorium.

What is the basic operating principle of a nuclear reactor?

A controlled, self-sustaining fission chain reaction releases heat. Control rods absorb neutrons to regulate the rate, a moderator slows neutrons, coolant carries heat to produce steam, and steam drives a turbine-generator. Reactivity is kept critical (k=1).

What is the role of a moderator in a nuclear reactor, and give examples.

A moderator slows fast neutrons to thermal energies so they can efficiently cause fission of U-235. Common moderators: ordinary (light) water, heavy water (D2O), and graphite.

Name common types of nuclear reactors.

Pressurized Water Reactor (PWR), Boiling Water Reactor (BWR), Pressurized Heavy Water Reactor (PHWR/CANDU - used widely in India), Gas-Cooled Reactor (GCR/AGR), Fast Breeder Reactor (FBR), and Light Water Graphite Reactor (RBMK).

What distinguishes a Fast Breeder Reactor (FBR)?

An FBR uses fast (unmoderated) neutrons and produces (breeds) more fissile material than it consumes, e.g. converting fertile U-238 to fissile Pu-239 (or Th-232 to U-233). It uses liquid metal (e.g. sodium) coolant. Central to India's 2nd stage nuclear plan.

List the main methods of producing energy from biomass.

(1) Direct combustion (burning for heat/electricity); (2) Biochemical conversion - anaerobic digestion (biogas) and fermentation (bioethanol); (3) Thermochemical conversion - pyrolysis (bio-oil/char), gasification (producer/syngas), liquefaction; and (4) transesterification of oils to biodiesel.

What is biogas, its main composition, and the process that produces it?

Biogas is produced by anaerobic digestion of organic matter by bacteria. It contains ~50-70% methane (CH4) and ~30-40% carbon dioxide (CO2), with traces of H2S, etc. Used for cooking, lighting and power.

What is gasification of biomass and the gas it yields?

Gasification is partial oxidation of biomass at high temperature (700-1000 C) with limited oxygen/steam to produce 'producer gas' or syngas, a mixture mainly of CO, H2, CH4 and N2/CO2, used as fuel or for power generation.

What are the broad categories of energy resources by renewability?

Renewable (non-conventional): solar, wind, hydro, tidal, geothermal, biomass, OTEC - replenished naturally. Non-renewable (conventional): coal, petroleum, natural gas, and nuclear (uranium) - finite stocks formed over geological time.

Which fuel dominates India's primary energy consumption?

Coal dominates India's primary energy mix (over ~50%, the largest share, mainly for electricity), followed by crude oil and then natural gas. India is heavily import-dependent for crude oil (~80%+ imported).

What is the world's dominant source of primary energy?

Fossil fuels supply ~80% of global primary energy; oil is the single largest (~30-33%), followed by coal (~27%) and natural gas (~24%). Renewables and nuclear make up the remainder.

How does per-capita energy consumption in India compare to the world and developed countries?

India's per-capita energy and electricity consumption is well below the world average and far below developed countries (e.g. USA), reflecting its developing status, despite India being among the largest total energy consumers.

Rank the largest national emitters of total CO2 today.

China is the largest total CO2 emitter, followed by the United States, then India (3rd), the EU and Russia. However, in PER-CAPITA terms the USA and other developed nations emit far more than India.

How do CO2 emissions differ between developed and developing countries in per-capita versus historical terms?

Developed countries have much higher PER-CAPITA emissions and bear the largest HISTORICAL/cumulative responsibility for atmospheric CO2. Developing countries (incl. India) have lower per-capita emissions but rising total emissions due to growth - basis for 'common but differentiated responsibilities'.

What is radiative forcing?

Radiative forcing is the net change in the energy balance (incoming minus outgoing radiation) of the Earth-atmosphere system due to a perturbation (e.g. added greenhouse gases), measured in W/m2. Positive forcing warms the surface; negative forcing cools it.

Define global warming and the enhanced greenhouse effect.

Global warming is the long-term rise in Earth's average surface temperature. The enhanced greenhouse effect is the additional warming caused by anthropogenic greenhouse gases (CO2, CH4, N2O, CFCs, water vapour) that absorb and re-emit outgoing infrared radiation, trapping heat.

Which greenhouse gas contributes most to anthropogenic radiative forcing, and what concept ranks gases by warming potency?

CO2 contributes the most to anthropogenic radiative forcing (largest concentration). Global Warming Potential (GWP) ranks gases relative to CO2 (GWP=1) over a time horizon; e.g. methane ~28-34 (100-yr), N2O ~265-298.

What are the main environmental impacts of large-scale hydropower exploitation?

Submergence of land/forests, displacement of people, loss of biodiversity, blockage of fish migration and sediment flow, downstream ecological changes, induced seismicity (reservoir-induced), and methane emissions from decomposing vegetation in reservoirs.

What are the main impacts of large-scale solar energy exploitation?

Large land requirement and habitat disruption, water use for panel cleaning/CSP cooling, ecological disturbance in deserts, hazardous materials and e-waste from PV manufacturing/disposal (e.g. cadmium), and glare/heat effects.

What are the main environmental impacts of large-scale wind energy exploitation?

Bird and bat mortality from rotor blades, noise pollution, visual/landscape impact, land/habitat fragmentation, electromagnetic interference, and offshore impacts on marine life.

What are the main hazards and impacts of large-scale nuclear energy?

Risk of radioactive accidents (e.g. Chernobyl, Fukushima), long-lived radioactive waste disposal problems, thermal pollution of water bodies, uranium mining impacts, decommissioning costs, and weapons-proliferation concerns.

What two cooling-related pollution problems are common to large thermal, nuclear and some solar (CSP) plants?

Thermal pollution - discharge of heated cooling water raises water-body temperature, lowering dissolved oxygen and harming aquatic life; and high freshwater consumption for cooling.

What is the capacity factor of a power plant?

Capacity factor = actual energy output over a period / (rated capacity x time). It measures how fully a plant's capacity is used. Nuclear and fossil baseload plants have high capacity factors; solar and wind are lower due to intermittency.

Why are solar and wind considered intermittent, and what is the implication for the grid?

Their output varies with weather and time of day/season (sunlight, wind speed) and is not dispatchable on demand. This requires energy storage (batteries, pumped hydro), backup capacity, and grid balancing to ensure reliable supply.