Science and Technology › Energy technology
Hydrogen and bioenergy
Hydrogen and fuels made from biology: green hydrogen and how it is made, stored and used, fuel cells, ethanol blending and its feedstock, biogas, and aviation fuel from biomass. Prelims has asked about the raw materials allowed under the National Policy on Biofuels and how green hydrogen is produced.
UPSC has asked
- Prelims 2025: battery electric and fuel cell vehicles as alternative powertrains
- Prelims 2023: uses of green hydrogen as fuel and in fuel cells
- Prelims 2020: raw materials allowed under the National Policy on Biofuels
Showing 1 of 6 subjects, those that changed from 1 to 15 July 2026.Show all
Biofuels
Prelims and Mains
Every litre of petrol sold in India has been one fifth ethanol since April, when the last unblended pump ran dry. Five months on, the argument is over what the blend saves and what it costs in water, in food and at the fuel gauge.
- Since 1 April 2026 all petrol sold in India must be E20 with a minimum Research Octane Number (RON) of 95, and unblended petrol is no longer sold.
- Ethanol is made by fermenting sugars, whether from sugarcane juice or from the starch of maize and rice, and is blended into petrol.
- Blending began as a pilot in 2001, reached 10 per cent in 2021-22 and 19.2 per cent in 2024-25, and hit 20 per cent in 2025-26.
- A blending mandate fixes the percentage the seller must blend, which creates demand a costlier fuel could not win on price.
- A first-generation biofuel is made from a food crop, so it competes for land, water and the plate.
- Maize supplies about 45 per cent of this year's blending ethanol, rice from the Food Corporation of India 22 per cent and sugarcane juice 16 per cent.
- Government estimates put E20 above petrol in cost while crude is below about $70 a barrel, so buyers lose mileage with no lower price for it.
- The Chief Economic Adviser would hold at E20 until the food versus fuel trade-off has been costed.
- The remedy urged is to count blue water and life-cycle emissions feedstock by feedstock, and to move to second-generation ethanol.
The case for
- About ₹2 lakh crore saved in foreign exchange, the government says
- Carbon monoxide and unburnt hydrocarbon emissions fall
- Cane ethanol cuts life-cycle greenhouse gases by about 50 to 70 per cent against petrol
- Mileage falls about 6 to 7 per cent, not the 30 per cent claimed online
The case against
- One litre of cane ethanol can embody 2,000 to 3,500 litres of water
- Grain ethanol cuts greenhouse gases by only about 20 to 50 per cent
- Maize competes with oilseeds for land, and Food Corporation of India rice goes to fuel while sugar prices rise
E20 in older engines
Ethanol carries its own oxygen into the cylinder, which leans out the mixture of fuel and air the engine was tuned for. A modern engine senses that and adjusts; an older one has nothing to sense it with.
- About 240 million vehicles on Indian roads were built for E5 or E10 rather than for a blend this strong.
- Vehicles built from April 2023 are E20 compatible, and long-run tests on them found no extra wear.
- The exception is the 75 to 80 million pre-Bharat Stage IV carburettor two-wheelers, which run lean and hot and whose rubber seals degrade.
- An E10 option at the pump has been urged for these machines, so that a vehicle built for a weaker blend can still buy one.
What changed
18 Aug 2026
The Hindu, 18 Aug 2026: The E20 fuel debate (opens in a new tab)
17 Aug 2026
6 Aug 2026
20 Jul 2026Update
- Parliament was told no decision has been taken to go beyond 20 per cent, although blends of 22 to 30 per cent were exempted from excise duty in June. Petrol dealers say ethanol's affinity for water is contaminating stock during the monsoon.
The Hindu, 20 Jul 2026 · The Hindu, 13 Jul 2026: Insular incentive (opens in a new tab)
10 Jul 2026Update
- The government accepted that E20 can cut mileage by 3 to 5 per cent in some vehicles, because ethanol has a lower calorific value than petrol, and ruled out selling E10 or pure petrol alongside it on grounds of logistics.
The Indian Express, 10 Jul 2026: Government defends E20 against a public backlash, and rules out going back to pure petrol or E10 (opens in a new tab) · The Indian Express, 9 Jul 2026: Government defends E20 against a public backlash, and rules out going back to pure petrol or E10 (opens in a new tab)
Show history (1 earlier entry)
6 Jul 2026Update
- About 5 million tonnes of broken and damaged rice were diverted to ethanol in a year, supplied to distilleries at roughly ₹23 a kg against an economic cost of about ₹44 to the Food Corporation of India.
Background reading: The Indian Express, 23 Aug 2026: E20 can save India money. Why doesn't the consumer see the benefit? (opens in a new tab)
UPSC has asked
- Prelims 2013: by-products of the sugar industry, bagasse and molasses