A PIB backgrounder on 4 September 2026 took stock of India's geothermal programme. The National Policy on Geothermal Energy was notified in September 2025, with the Ministry of New and Renewable Energy as nodal ministry. In July 2026 the ONGC Energy Centre commissioned the country's first two geothermal wells at Puga Valley, Ladakh, more than 14,000 feet above sea level — 1,000-metre-deep wells for reservoir evaluation that pave the way for a 1-megawatt demonstration power project, India's first.
One megawatt is small. What makes the topic worth an hour is that it sits on top of the physical geography syllabus: to explain geothermal energy you have to explain the inside of the Earth.
The interior, layer by layer
| Layer | State | Thickness | Composition |
|---|---|---|---|
| Crust | Solid | 5–8 km under oceans; 24–56 km under continents | Silicate rock |
| Mantle | Hot, dense rock; behaves plastically | ~2,900 km — the largest layer | Silicates rich in iron and magnesium |
| Outer core | Liquid | ~2,400 km thick | Molten iron and nickel |
| Inner core | Solid | ~2,400 km wide | Iron and nickel |
Temperature rises with depth: about 3,700 °C at the mantle-core boundary and 5,000–6,000 °C in the core. The heat has two sources — radioactive decay of uranium, thorium and potassium in the interior, and residual heat from the planet's formation.
That heat drives convection currents in the mantle, and those currents drive plate tectonics: earthquakes, volcanoes and mountain building. In tectonically active zones, faults and fractures let hot material rise close to the surface, heating groundwater trapped in permeable rock into reservoirs of hot water and steam. Geothermal energy is that heat, tapped. The chain is worth stating in one line for an answer: radioactive decay → mantle convection → plate boundaries → fractured crust → hot reservoirs → wells.
The average geothermal gradient is roughly 25–30 °C per kilometre of depth; at Puga and similar sites it is far steeper, which is why a 1,000-metre well is useful there and would not be in a stable craton.
How the electricity is made
A geothermal plant is a thermal power station without a furnace. Deep wells bring up hot water or steam; steam drives a turbine coupled to a generator; the used water is condensed and reinjected into the reservoir, which sustains the resource. Three designs exist:
- Dry steam — steam comes straight from the well to the turbine; rare, needs very hot reservoirs.
- Flash steam — high-pressure hot water is depressurised so that part of it flashes to steam.
- Binary cycle — moderate-temperature water heats a secondary fluid with a lower boiling point, which drives the turbine. This is what makes 70–80 °C fluid, as at the Gandhinagar project, usable.
Two properties set geothermal apart from the other renewables. It is weather-independent and available round the clock, giving it a capacity factor close to that of a thermal plant, whereas solar delivers for a fraction of the day. And it supports direct heat use — district heating, greenhouses, aquaculture, space heating and cooling — without generating electricity at all.
Where India's heat is
The Geological Survey of India has mapped 381 hot springs and identified 10 geothermal provinces, with a theoretical prospect of nearly 10.6 GW and 42 sites flagged as promising for power or direct heat.
The ten provinces: Himalayan · Naga-Lushai · Andaman and Nicobar Islands · Son-Narmada-Tapi (SONATA) · West Coast · Cambay Graben · Aravalli · Mahanadi · Godavari · South Indian Cratonic.
Read that list against a tectonic map and it explains itself. The Himalayan province (Puga, Chumathang, Manikaran, Tapoban) sits on the collision zone. Andaman and Nicobar sits on a subduction arc with an active volcano at Barren Island. SONATA, Cambay, Mahanadi and Godavari are rift basins — old fractures in the peninsula that still let heat rise. The West Coast province, with hot springs in Maharashtra's Konkan, follows the faulted margin left when India separated from Madagascar. Geothermal potential is tectonic history written as hot water.
The named field projects show the strategy:
| Site | What it tests |
|---|---|
| Puga Valley, Ladakh | First two wells, July 2026; path to the 1 MW demonstration plant |
| Gandhinagar, Gujarat | Solar-geothermal integration; three wells at 70–80 °C; 50–90 kW generated |
| Ankleshwar, Gujarat | Retrofitting unproductive oil and gas wells for power |
| Tawang, Arunachal Pradesh | Himalayan-province study |
The Ankleshwar idea is the clever one. Abandoned hydrocarbon wells are already drilled, logged and instrumented — the most expensive part of a geothermal project done for free by a previous industry. The Cambay basin is both an oil province and a geothermal province for the same reason: it is a rift.
Beyond conventional reservoirs, Enhanced Geothermal Systems create fractures artificially in hot dry rock and pump water through them, widening the map to places without natural hot springs. MNRE sanctioned five R&D projects in July-August 2025 covering assessment, indigenous technology and field demonstration.
Why it matters to the transition
India's target is Net Zero by 2070. Solar and wind are cheap but intermittent; the grid needs firm renewable power to back them, and the current candidates — storage, hydro, nuclear — are each constrained. Geothermal is a firm, indigenous, low-carbon source, which is why a 1 MW plant in Ladakh is being treated as a milestone rather than a footnote. Globally the leaders are the United States, Indonesia, the Philippines, Türkiye, New Zealand, Kenya and Iceland — nearly all of them on plate boundaries, which is the whole lesson in one list.
🔑 Revision block
- National Policy on Geothermal Energy notified September 2025; nodal ministry MNRE.
- July 2026: ONGC Energy Centre commissioned India's first two geothermal wells at Puga Valley, Ladakh (>14,000 ft; 1,000 m deep) → first 1 MW demonstration plant.
- Interior: crust 5–8 km (oceanic) / 24–56 km (continental) → mantle ~2,900 km → outer core liquid Fe-Ni ~2,400 km → inner core solid Fe-Ni ~2,400 km. Mantle-core boundary ~3,700 °C; core 5,000–6,000 °C. Heat from U, Th, K decay + residual heat.
- Mantle convection → plate tectonics → fractured crust → hot reservoirs. Gradient ~25–30 °C/km.
- Plant types: dry steam, flash steam, binary cycle (binary uses low-temperature fluid). Water reinjected. Round-the-clock, weather-independent; direct heat uses.
- GSI: 381 hot springs, 10 provinces, ~10.6 GW prospect, 42 promising sites.
- Provinces: Himalayan, Naga-Lushai, Andaman & Nicobar, SONATA, West Coast, Cambay Graben, Aravalli, Mahanadi, Godavari, South Indian Cratonic.
- Projects: Gandhinagar (solar-geothermal, 50–90 kW), Ankleshwar (repurposed oil wells), Tawang. Five MNRE R&D projects, July-August 2025. EGS widens the map.
- Net Zero 2070. Global leaders: USA, Indonesia, Philippines, Türkiye, New Zealand, Kenya, Iceland.
🎯 Practice MCQs
Q1. India's first geothermal wells were commissioned at: (a) Manikaran (b) Puga Valley (c) Tattapani (d) Bakreswar → (b), Ladakh, July 2026.
Q2. The Earth's outer core is: (a) solid iron (b) liquid iron and nickel (c) silicate rock (d) molten basalt → (b).
Q3. The largest layer of the Earth by thickness is the: (a) crust (b) mantle (c) outer core (d) inner core → (b), about 2,900 km.
Q4. Heat in the Earth's interior comes chiefly from: (a) solar radiation (b) radioactive decay and residual formation heat (c) tidal friction (d) volcanic eruptions → (b) — uranium, thorium and potassium.
Q5. The nodal ministry for the National Policy on Geothermal Energy is: (a) Ministry of Power (b) Ministry of Earth Sciences (c) Ministry of New and Renewable Energy (d) Ministry of Petroleum → (c).
Q6. A binary-cycle geothermal plant is suited to: (a) dry steam reservoirs (b) moderate-temperature water using a secondary working fluid (c) volcanic vents only (d) offshore sites → (b).
Q7. SONATA, as a geothermal province, stands for: (a) South Narmada Tapi (b) Son-Narmada-Tapi (c) Sonbhadra-Nagpur-Tapi (d) Son-Nagpur-Tawa → (b).
Q8. The number of hot springs mapped by the GSI is: (a) 181 (b) 281 (c) 381 (d) 481 → (c).
Q9. Which geothermal province is associated with an active volcano? (a) Cambay Graben (b) Andaman and Nicobar Islands (c) Aravalli (d) Mahanadi → (b) — Barren Island.
Q10. The chief advantage of geothermal over solar power is: (a) lower cost (b) round-the-clock availability (c) ease of siting (d) no water use → (b).
Q11. The Ankleshwar project tests: (a) solar-geothermal hybrids (b) repurposing unproductive oil and gas wells (c) Himalayan hot springs (d) offshore drilling → (b).
Q12. Continental crust is approximately how thick? (a) 5–8 km (b) 10–15 km (c) 24–56 km (d) 100–150 km → (c) — oceanic crust is 5–8 km.
📋 How this gets asked (PYQ pattern)
Earth-interior and energy questions run in four shapes. The layer item — which layer is liquid, which is thickest, or the crust's thickness under oceans against continents. The source item — where interior heat comes from, with solar radiation as the planted error. The site item — a geothermal or hot-spring location matched to its State. The comparison item — geothermal against solar and wind on availability, or a plant type matched to its reservoir temperature.
The fresh 2026 hook is Puga's first two wells and the 1 MW plant, together with the 381 / 10 / 10.6 GW figures, suited to a data question. A statement pair on round-the-clock availability and the project site is the likeliest two-statement item, with Manikaran offered in place of Puga. As always, we describe the recurring pattern, not any exact past question.
Preparing for CDS or OTA? Geothermal is physical geography and energy policy in one topic — learn the four layers and the ten provinces, and the policy dates attach themselves. Build the base with our notes on economic geography and energy and the CDS/OTA geography hub, follow the daily CDS/OTA current affairs, and prepare with our faculty in the upcoming Cavalier courses in Delhi.
✍️ Written by Aditya Tiwari — Geography & governance faculty at The Cavalier. Reviewed by the Cavalier Faculty Desk. The Cavalier, founded by ex-Army officers, has trained NDA/CDS/SSB aspirants since 2001 (Facebook · YouTube).
Source: PIB backgrounder, 4 September 2026. Earth-science and energy facts cross-verified with independent sources.