Sources of Energy

India's energy transition — from fossil fuel dependence to 500 GW of renewable energy by 2030 — is among the most consequential policy stories of this decade. UPSC GS3 questions on energy security, renewable energy, nuclear power, and climate commitments require a solid understanding of how each energy source works, its advantages and disadvantages, and where India's programme stands. This chapter provides the scientific foundation; the UPSC connect sections bring it to policy.

PART 1 — Quick Reference Tables

Characteristics of a Good Fuel

Fossil Fuels — Formation and Problems

Non-Conventional Energy Sources — Summary

PART 2 — Detailed Notes

1. Conventional Energy Sources

Fossil fuels: Formed over millions of years from buried organic matter. They are energy-dense, easy to transport and store, and power the global economy — but they are finite and their combustion is the primary driver of climate change.

Coal: India has the 4th largest coal reserves globally. Coal accounts for ~70% of India's electricity generation. India is both the 3rd largest producer and 2nd largest importer of coal. Thermal power plants burn coal to boil water → steam → turbine → generator. Thermal efficiency: ~33–40% (most energy lost as heat).

Petroleum (crude oil) and Natural Gas: India imports ~85% of its crude oil requirements — making energy import dependency a major strategic and economic vulnerability. The Ministry of Petroleum and Natural Gas manages India's energy security. OPEC (Organization of the Petroleum Exporting Countries) pricing decisions directly affect India's current account deficit and inflation.

Hydroelectric power: Kinetic and potential energy of flowing water. Water stored in reservoirs at height (potential energy) is released through turbines. India has 46.9 GW of installed hydroelectric capacity (2024). Large dams have faced controversy — Tehri Dam, Sardar Sarovar (Narmada) — due to displacement of communities, submersion of forests, and environmental impacts.

2. Solar Energy

Photovoltaic (PV) cells: The photovoltaic effect (Becquerel, 1839; practical application by Bell Labs, 1954) converts light directly to electricity. When photons hit a semiconductor (silicon), they knock electrons loose, creating a current. Solar cells are made of silicon wafers with a p-n junction.

Solar thermal systems:

• Solar cookers: Use mirrors to concentrate sunlight onto a black cooking pot. Can reach temperatures up to 140°C. No fuel cost; no air pollution.
• Solar water heaters: Collectors on rooftops absorb sunlight to heat water. Common in domestic and industrial use.
• Concentrating Solar Power (CSP): Large mirrors focus sunlight onto a receiver to generate steam and run a turbine. More efficient than PV for utility-scale power; can include thermal storage (molten salt) to provide power at night.

India's Solar Programme: India's installed solar capacity was approximately 81 GW as of March 2024 and is the world's 4th largest solar market. The Jawaharlal Nehru National Solar Mission (JNNSM) — now part of the National Action Plan on Climate Change (NAPCC) — set the trajectory. India aims for 500 GW from non-fossil fuel sources by 2030 (NDC target).

PM-KUSUM (Pradhan Mantri Kisan Urja Suraksha evam Utthaan Mahabhiyan): Scheme to solarise agriculture — install solar pumps for irrigation and solar panels on agricultural land (agri-voltaics). Three components:

• Component A: Decentralised solar plants (up to 2 MW) on barren agricultural land
• Component B: Standalone off-grid solar pumps for farmers
• Component C: Grid-connected solar pumps and solarisation of existing pumps

3. Wind Energy

Wind energy is converted to electricity by wind turbines. Modern turbines are 80–150 metres tall with blades up to 80 metres long, capturing maximum wind at height. Horizontal axis wind turbines (HAWT) are the standard commercial type.

Wind farms — clusters of wind turbines — are sited where average wind speeds exceed 6 m/s. India has ideal conditions in Tamil Nadu (Muppandal, one of Asia's largest wind farms), Gujarat, Rajasthan, Andhra Pradesh, Karnataka, and Maharashtra. India has ~47 GW of installed wind capacity (2024), 4th largest globally.

Offshore wind: Wind speeds are higher and more consistent at sea. India's first offshore wind tender (off Gujarat and Tamil Nadu coasts) aims to develop 1 GW initially. Potential: 127 GW off Indian coast (NIWE estimate).

4. Biomass Energy

Biomass includes all organic material derived from living or recently living organisms: agricultural residues (paddy straw, sugarcane bagasse), wood, animal dung, municipal solid waste, algae.

Direct combustion: Wood and crop residue burning. Major source of indoor air pollution in rural India — 3.8 million premature deaths globally per year linked to household air pollution (WHO). Pradhan Mantri Ujjwala Yojana (PMUY) distributes LPG connections to below-poverty-line households to replace solid biomass cooking fuels.

Biogas: Produced by anaerobic decomposition (fermentation without oxygen) of organic matter by methanogenic bacteria.

Biogas composition: ~55–65% methane (CH4), ~35–45% CO2, traces of H2S. The digester is sealed; dung/waste fed in → bacteria break down organic matter → methane produced → used for cooking or electricity.

By-product: slurry (digested effluent) — an excellent fertiliser, richer in nitrogen and phosphorus than undigested dung.

India has over 5 million domestic biogas plants. Gobar-Dhan (Galvanizing Organic Bio-Agro Resources Dhan) scheme promotes waste-to-energy from cattle dung and agricultural waste.

Biofuels:

• Ethanol: Fermentation of sugar or starch crops (sugarcane, maize). India's Ethanol Blending Programme (EBP) — 20% ethanol blending in petrol by 2025 (E20 target). Reduces import dependency; provides income to sugarcane farmers.
• Biodiesel: Transesterification of vegetable oils or animal fats. India focuses on non-edible oils (Jatropha) to avoid food-fuel competition.

5. Tidal, Wave and Geothermal Energy

Tidal energy: Twice daily tides (caused by gravitational pull of moon and sun on Earth's oceans) can be harnessed using tidal barrages (build a dam across an estuary; water flows through turbines as tide rises and falls) or tidal stream generators (like underwater wind turbines). India's potential sites: Gulf of Kutch (Gujarat), Gulf of Khambhat, Sunderbans. No commercial plant yet.

Wave energy: Kinetic energy of ocean surface waves. Converted to electricity by oscillating water column devices, point absorbers, or overtopping devices. India's coastline offers significant potential but technology is still pre-commercial globally.

Geothermal energy: Earth's internal heat (from radioactive decay in the core and residual heat from planetary formation). High-temperature hydrothermal systems can run steam turbines directly. Lower-temperature systems use heat pumps. India's potential: Puga Valley (Ladakh/J&K), Tattapani (Chhattisgarh), Manikaran (Himachal Pradesh). ONGC and GSI have surveyed these sites; no commercial plants yet.

6. Nuclear Energy

Nuclear fission: Splitting of heavy nuclei (Uranium-235, Plutonium-239) by neutron bombardment. Releases enormous energy (1 kg of U-235 = energy from ~3,000 tonnes of coal). The fission reaction releases neutrons → chain reaction.

Nuclear reactor components:

• Fuel: Uranium-235 (natural U contains 0.7% U-235; enriched for most reactors) or Thorium (India's Three-Stage Nuclear Programme uses thorium — India has world's largest thorium reserves: ~25% of global)
• Moderator: Slows neutrons to increase fission probability. Heavy water (D2O) in Indian PHWRs; ordinary water in PWRs; graphite in some designs.
• Control rods: Made of neutron-absorbing materials (boron, cadmium, hafnium). Inserted/withdrawn to control reaction rate.
• Coolant: Transfers heat from reactor core to steam generator. Heavy water or light water in most designs.
• Shielding: Concrete and steel barriers to contain radiation.
• Containment building: Last line of safety; surrounds reactor vessel.

India's Three-Stage Nuclear Programme (devised by Homi J. Bhabha):

• Stage 1: PHWRs (Pressurised Heavy Water Reactors) using natural uranium → produce Pu-239 as by-product
• Stage 2: Fast Breeder Reactors (FBRs) using Pu-239 + thorium → produce U-233; Prototype FBR (PFBR) at Kalpakkam
• Stage 3: Advanced Heavy Water Reactors (AHWRs) using U-233 and thorium — the final stage exploiting India's vast thorium reserves

Nuclear fusion: Merging light nuclei (e.g., deuterium + tritium → helium + neutron + energy). The sun's energy source. Would provide virtually unlimited clean energy — deuterium from seawater; no radioactive waste products. Challenge: achieving and sustaining the extreme temperatures (~100 million °C) needed to overcome electrostatic repulsion between nuclei. ITER (International Thermonuclear Experimental Reactor) in France — a 35-nation project including India — aims to demonstrate fusion feasibility. Commercial fusion power: unlikely before 2050.

🎯 UPSC Connect: India's National Hydrogen Mission

National Green Hydrogen Mission (2023): India aims to become a global hub for green hydrogen production — using renewable electricity to electrolyse water (2H2O → 2H2 + O2). Hydrogen is used in fertiliser production (replacing natural gas), steel manufacturing (replacing coking coal), and potentially as a transport fuel.

Targets: 5 million metric tonnes of green hydrogen production per year by 2030; 125 GW of dedicated renewable energy capacity; ₹19,744 crore government outlay.

Green hydrogen can decarbonise sectors that are hard to electrify (heavy industry, long-distance freight, aviation, shipping).

PART 3 — Frameworks & Analysis

Framework: India's Energy Mix and Transition

Framework: Comparing Energy Sources — UPSC Matrix

Exam Strategy

Prelims traps:

• India has the world's largest thorium reserves — this is why India's three-stage nuclear programme culminates in thorium utilisation.
• ITER (fusion) is in Cadarache, France — India is a partner nation.
• Biogas is primarily methane (CH4), not hydrogen or CO2.
• PM-KUSUM is specifically for agricultural solar pumps and solar power on farmland — not urban rooftop solar (that is PM Surya Ghar Muft Bijli Yojana, formerly Rooftop Solar Programme).
• India's renewable energy target is 500 GW non-fossil by 2030 — this includes nuclear and large hydro, not just solar and wind.

Mains frameworks:

• Energy transition: fossil fuel dependence → climate imperative → renewable ramp-up → grid integration challenge → storage solutions
• Nuclear energy: Homi Bhabha's three-stage vision → India-US Civil Nuclear Deal (2008) → NSG waiver → current capacity → expansion plans
• Energy poverty: access to clean cooking fuel → Ujjwala Yojana → shifting from biomass → health co-benefits

Previous Year Questions

Q1 (Prelims 2023): With reference to India's solar energy sector, consider the following statements about the PM-KUSUM scheme… (Tests specific provisions and targets of PM-KUSUM)

Q2 (Prelims 2021): Consider the following statements about nuclear power generation in India: [about three-stage programme, thorium, PFBR] (Tests India's three-stage nuclear programme and thorium strategy)

Q3 (Mains GS3 2023): The National Green Hydrogen Mission has been described as India's transformational initiative for energy transition. Discuss its significance, targets, and challenges. Science of electrolysis → green hydrogen → industrial decarbonisation → India's mission

Q4 (Mains GS3 2020): Why is India's ambitious renewable energy target facing headwinds? Examine the challenges and suggest measures to accelerate India's renewable energy transition. Science of solar/wind → intermittency challenge → grid integration → storage → policy incentives