Electricity: thermal and hydel power

Detail

1. Two ways to make electricity

• Hydel power (hydroelectricity) is electricity made by fast-flowing or falling water. The water spins a turbine (a wheel with blades). The turbine turns a generator, which makes electricity.
• Thermal power is electricity made by burning coal, oil or natural gas.

• The fuel is burnt → water is boiled → high-pressure steam spins a turbine → the generator makes electricity.

• Once it is made, the electricity is exactly the same. A bulb cannot "tell" whether its power came from a dam or a coal plant (NCERT Class 10).

2. India's electricity mix today

Measure	Figure	Date
Total installed capacity	5,13,730 MW	31 Dec 2025 [6]
Fossil-fuel capacity (coal, lignite, gas, diesel)	2,46,942 MW (48.07%)	31 Dec 2025 [6]
Non-fossil capacity (renewables, large hydro, nuclear)	2,66,788 MW (51.93%)	31 Dec 2025 [6]
Coal capacity alone	2,19,610 MW (42.75%)	31 Dec 2025 [6]
Non-fossil capacity	283.46 GW	31 Mar 2026 [7]

• Installed capacity is the most power all the plants could give if they ran at full load. Generation is the electricity they actually produce. The two are different things.
• Coal has less than half the capacity but makes about three-quarters of the electricity.
• Coal plants can run day and night, in every season.
• Solar works only in daytime. Wind and hydro change with the season.

• So each MW of coal produces far more units in a year.

• Coal's share of generation was 73.29% in 2024-25 (up to June 2024) [8]. Coal-based thermal power has fuelled over 74% of India's power generation [9]. (NCERT-based estimate: about three-quarters.)

• Coal power generation fell by 3.69% in 2025-26 compared with the same period a year earlier [6].
• Non-fossil targets:
• India's NDC (Nationally Determined Contribution: a country's climate pledge under the Paris Agreement) set a target of 50% non-fossil capacity by 2030. India reached it in June 2025, five years early [6][7].

• The next target is 500 GW of non-fossil capacity by 2030, announced at COP26 (Glasgow, 2021) [7].

• Coal's share of generation is expected to fall to about 55% by 2030 and 27% by 2047 [9].

3. Thermal power

• Thermal power is non-renewable and polluting, but it is still India's main source.
• Non-renewable: coal, oil and gas take millions of years to form, and burning uses them up.

• Polluting: burning releases CO₂, SO₂ (sulphur dioxide), NOx (nitrogen oxides) and fly ash (the fine ash left after coal burns). Fly ash and air pollution are covered in the notes on manufacturing industries and geographical problems.

• Location logic: coal is heavy and bulky, so it costs a lot to move. Plants are therefore built either at the coalfield or at a port.

Pithead plants (built at the mouth of the mine)

Plant / cluster	State	Coalfield / fuel
Singrauli	Madhya Pradesh–Uttar Pradesh border	Singrauli coalfield (Son valley)
Korba	Chhattisgarh	Korba coalfield (Hasdeo basin, Mahanadi system)
Talcher	Odisha	Talcher coalfield (Brahmani valley)
Neyveli	Tamil Nadu	Lignite (a low-grade brown coal)

• Most pithead clusters lie in the Gondwana coal belt of the Damodar, Son, Mahanadi and Godavari valleys. Gondwana coal is about 200 million years old and makes up most of India's coal. Neyveli is the exception: it burns Tertiary lignite, which is much younger coal.
• Pithead plants save on coal transport. Instead, they send power long distances through transmission lines.

Port-based (coastal) plants

Plant	State	Coast
Mundra	Gujarat (Kachchh district, Gulf of Kachchh)	West coast, Arabian Sea
Krishnapatnam	Andhra Pradesh (Nellore district)	East coast, Bay of Bengal

• These plants burn imported coal. Imported coal has less ash and gives more heat than most Indian coal. It arrives by ship, so these plants have no inland rail cost.
• Trap: these plants depend on world coal prices and on the exchange rate.

4. Hydroelectric power

• How it works (step by step):
• A dam stores water at a height (this height difference is called the head).
• Water rushes down a pipe called a penstock.
• The water spins the turbine and the generator makes electricity.

• The water flows back into the river, so the water itself is not used up.

• Benefits:

• It is renewable, because the water cycle keeps refilling rivers.
• Running it gives almost no smoke or CO₂.

• It can start and stop within minutes, so it is useful at times of peak demand (the hours when the most electricity is used).

• Costs:

• Displacement: people living in the reservoir area lose their homes and land.
• Sediment trapping: the dam holds back silt. Fields downstream lose fertile soil, and the reservoir slowly fills up with silt (siltation).
• Ecological damage: forests are flooded, fish can no longer swim upstream, and the river's natural flow changes.

Multipurpose projects that produce hydel power

A multipurpose project is a single dam scheme that serves many uses: irrigation, power, flood control, drinking water and fisheries. (Dams themselves are covered in the note on water resources.)

Project	River	State(s)
Bhakra Nangal	Sutlej	Himachal Pradesh (Bhakra dam) and Punjab (Nangal)
Damodar Valley Corporation (DVC)	Damodar (tributary of the Hooghly)	Jharkhand–West Bengal; India's first multipurpose river valley authority (1948)
Kopili	Kopili (tributary of the Brahmaputra)	Assam (Dima Hasao district)

Hydro potential and where it lies

• The CEA reassessment study (2017–2023) puts India's exploitable large hydro potential at 1,33,410 MW [4]. CEA is the Central Electricity Authority, India's top technical body for power.
• Most untapped potential lies in the Himalayan rivers of the north and north-east (the Indus, Ganga and Brahmaputra systems). Arunachal Pradesh has the largest share of any state.
• Why the Himalaya? The rivers are fed by snow and glaciers, so they flow all year. They also fall steeply, which gives a large head.
• Why the Peninsula has less: Peninsular rivers depend only on rain, so their flow drops in the dry season. The plateau also has gentler slopes. Most good Peninsular sites (Western Ghats, Krishna, Kaveri) are already in use.
• Large hydro declared renewable (March 2019): before this, only small hydro (up to 25 MW) counted as renewable. Since 2019, large hydro (above 25 MW) also counts towards India's renewable targets, and a separate Hydro Purchase Obligation was created. (A purchase obligation means power-buying companies must buy a fixed share of their power from this source.)

5. Subansiri Lower Hydroelectric Project

• Concept: a run-of-river-type dam project of 2,000 MW (8 units × 250 MW), built by NHPC Limited [2]. A run-of-river project uses the river's natural flow and keeps only a small amount of water stored.
• Location: on the Subansiri river, at the Arunachal Pradesh–Assam border (at Gerukamukh) [2].

• River course: the Subansiri rises in Tibet (China). It flows south-east through Arunachal Pradesh and enters the Assam plains. It joins the Brahmaputra from the north (right bank), near Majuli. It is the Brahmaputra's largest tributary.

• It is India's largest hydro project.

• Status: units began running from 2024 onwards. By the latest Ministry of Power update, 2 of the 8 units have been commissioned and are supplying power. Three more are due shortly, and the remaining units are due in phases in 2026-27 [2].
• When complete, it will give about 7,422 million units (MU) a year [2].
• Why there were years of protests downstream (Assam: Lakhimpur and Dhemaji districts):
• The dam lies in a zone of very high earthquake risk, so people feared for dam safety.
• The river's flow would change sharply day to day, causing sudden floods and dry spells downstream.
• Fisheries and farming on the floodplain would suffer.
• The result was that work stopped from 2011 to 2019, which delayed the project.

6. Pumped storage hydropower (PSP)

• Concept: a pumped storage project has two reservoirs, one upper and one lower. It works like a giant water battery.
• When power is cheap or plentiful (sunny afternoons, windy nights), surplus power pumps water from the lower reservoir up to the upper one.
• At peak demand (evenings), the water flows back down through turbines and makes electricity.

• Result: solar and wind power that comes and goes is stored and used later, which keeps the power grid steady.

• India's potential: CEA has identified 1,76,280 MW of pumped storage potential (reassessment 2017–2023) [4].

• Status (latest Ministry of Power data) [3]:
• 10 PSPs (6.2 GW) are commissioned.
• 8 PSPs (8.5 GW) are under construction.
• 5 PSPs (5.8 GW) have been approved by CEA.

• 46 PSPs (64.8 GW) are under survey and investigation.

• Target: 39 PSPs of 47 GW are being pursued for commissioning by 2029-30 [3][5].

• Ministry of Power guidelines on PSPs (April 2023) [5]:
• They set out several ways to allot PSP sites.
• PSPs are exempted from the free-power and Local Area Development Fund obligations.
• Environmental clearance is made simpler.

• Exhausted (worked-out) coal mines can be used as reservoirs.

• Faster approvals: CEA's time to approve a DPR (Detailed Project Report) has been cut from 125 to 90 days [3][5]. Inter-State Transmission System (ISTS) charges are waived (not charged) for PSPs whose construction is awarded by 30 June 2028 [3].

• Where: many sites are planned in the Western Ghats (Maharashtra, Karnataka), Andhra Pradesh and elsewhere. Steep scarps (cliff-like slopes) give a large height difference between two reservoirs a short distance apart.

7. Essay frame: "Write an essay on hydel power in India" (NCERT Class 12 exercise)

Part	Content
Potential	1,33,410 MW of large hydro potential plus 1,76,280 MW of pumped storage potential (CEA 2017–23) [4]
Distribution	Himalayan rivers: snow-fed, flow all year, steep slopes, mostly untapped (Arunachal Pradesh has the most). Peninsular rivers: rain-fed, flow drops in the dry season, best sites already used
Constraints	Seismicity (earthquake risk: the Himalaya lies in Seismic Zones IV–V); GLOFs (glacial lake outburst floods: a lake held behind loose glacial rock bursts and floods the valley); rehabilitation (resettling displaced people, mostly tribal); inter-state and international rivers (Brahmaputra and Subansiri rise in China; Indus Waters Treaty with Pakistan)
Way forward	Large hydro counted as renewable since 2019; PSPs to store solar and wind power; careful study of dam safety and downstream effects

Prelims Hooks

• Pithead plant–state pairs: Korba–Chhattisgarh; Talcher–Odisha; Neyveli–Tamil Nadu (burns lignite, not Gondwana coal); Singrauli–Madhya Pradesh/Uttar Pradesh border.
• Port-based plants burning imported coal: Mundra (Gujarat, Gulf of Kachchh) and Krishnapatnam (Andhra Pradesh, Nellore).
• Trap: coal is about 43% of installed capacity (Dec 2025) [6] but about 73–74% of generation [8][9]. Capacity share is not the same as generation share.
• India crossed 50% non-fossil installed capacity in June 2025, five years before its NDC deadline. The next target is 500 GW of non-fossil capacity by 2030 [6][7].
• Subansiri Lower: 2,000 MW (8 × 250 MW), built by NHPC, on the Arunachal Pradesh–Assam border, on a north-bank (right-bank) tributary of the Brahmaputra, about 7,422 MU a year [2].
• Large hydro (above 25 MW) declared renewable in 2019. Small hydro (up to 25 MW) was already renewable under MNRE.
• Project–river pairs: Bhakra Nangal–Sutlej; DVC–Damodar; Kopili–Kopili (Assam).
• PSP: pumps water uphill when power is surplus and generates at peak. 6.2 GW commissioned. Identified potential (1,76,280 MW) is larger than large hydro potential (1,33,410 MW) [3][4].
• The 2023 PSP guidelines allow exhausted coal mines to be used as reservoirs [5].
• The state with the largest untapped hydro potential is Arunachal Pradesh, not Himachal Pradesh or Uttarakhand.

Mains Points

• Why coal still leads (GS-III, energy security):
• India has large domestic coal reserves (the Gondwana belt).
• Coal plants give steady, round-the-clock base-load power (the minimum power the grid needs at all times).
• Pithead plants keep fuel costs low.

• The cost is air pollution, fly ash and carbon emissions. The answer is a planned shift: coal's generation share is expected to fall to 55% by 2030 and 27% by 2047 [9].

• Hydel's spatial mismatch (GS-I):

• Potential is concentrated in the north-east Himalaya, far from where most electricity is used.
• This makes long transmission lines necessary.

• It also brings conflict between upstream and downstream areas, as the Subansiri protests in Assam show.

• Constraints on Himalayan hydro (GS-III, disasters): earthquake risk (Seismic Zones IV–V), GLOFs and landslides; displacement of tribal communities; silt filling reservoirs; and rivers shared with China. Solutions include basin-wide cumulative impact assessment (studying the combined effect of all dams on a river), dam-safety monitoring and fair resettlement.

• Pumped storage as the "battery" for the 500 GW target:
• Solar and wind output varies by hour and season.
• PSPs store surplus power and release it at the evening peak.
• Policy support includes the 2023 guidelines, faster DPR approval, ISTS charge waivers and the 47 GW target for 2029-30 [3][5].