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What are biofuels? The short answer is fuels made from biomass instead of fossil sources. For UPSC, the short answer is not enough. India's National Policy on Biofuels, 2018 draws precise lines between bioethanol, biodiesel, advanced biofuels and drop-in fuels, and lists exactly which raw materials may be used for each. Prelims questions are built on those lines.
In Tootler's bank of transcribed papers, 17 General Studies questions between 2008 and 2026 deal with biofuels, bioenergy and the clean fuels around them, spread across 13 different exam years. Seven of them come from 2023 to 2026 alone, as sustainable aviation fuel and green hydrogen have joined ethanol and biodiesel in the paper. This guide explains each kind of fuel from the official definitions and shows the questions UPSC has asked on it.
This guide is part of Tootler's series on environment and ecology for UPSC, which maps all 284 environment questions in Prelims by topic.
What counts as a biofuel in India
The 2018 policy names four categories of biofuels that can be used in transport or stationary applications.
| Category | Definition in the National Policy on Biofuels |
|---|---|
| Bioethanol | Ethanol from biomass: sugar-containing materials such as sugarcane, sugar beet and sweet sorghum; starch-containing materials such as corn, cassava, rotten potatoes and algae; and cellulosic materials such as bagasse, wood waste and agricultural or forestry residues |
| Biodiesel | A methyl or ethyl ester of fatty acids made from non-edible vegetable oils, acid oil, used cooking oil, animal fat or bio-oil |
| Advanced biofuels | Fuels from lignocellulosic feedstocks, non-food crops such as grasses and algae, or industrial waste, with low CO2 emissions, that do not compete with food crops for land |
| Drop-in fuels | Liquid fuels from biomass, agri-residues or wastes such as municipal solid waste and plastic waste that meet Indian standards for petrol, diesel or jet fuel and need no engine changes |
Two words in that table do most of the work in exam questions. "Non-edible" separates biodiesel feedstocks from food oils, and "do not compete with food crops" is what makes a fuel advanced.
First, second and third generation biofuels
The generation labels describe the feedstock. First generation (1G) ethanol is made from sugar or starch, using what the policy calls "first generation" technology. Second generation (2G) ethanol is made from agricultural waste with cellulosic and lignocellulosic content, such as rice and wheat straw, corn cobs, bagasse and woody biomass. The policy lists 2G ethanol, algae-based third generation (3G) biofuels, bio-CNG, bio-methanol and bio-hydrogen among its advanced biofuels, and plans second generation biorefineries to produce them.
The reason for the distinction is the food-versus-fuel problem. A 1G plant competes with food for sugarcane or grain; a 2G plant can run on straw, cobs and other residues. UPSC's 2017 question on algae-based biofuels asked about the practical limits developing countries face in building a 3G industry.
Ethanol feedstocks and the 20% blending target
Ethanol is the fuel UPSC has asked about most often, and the questions keep testing which raw materials qualify. Section 5 of the policy widened the list: alongside molasses and sugarcane juice, it allows sugar beet, sweet sorghum, corn, cassava, rotten potatoes, and "damaged food grains like wheat, broken rice etc. which are unfit for human consumption". In a year of projected oversupply, surplus food grains may also be converted, with the approval of the National Biofuel Coordination Committee. That list is the whole of the 2020 question:
According to India's National Policy on Biofuels, which of the following can be used as raw materials for the production of biofuels? 1. Cassava 2. Damaged wheat grains 3. Groundnut seeds 4. Horse grams 5. Rotten potatoes 6. Sugar beet Select the correct answer using the code given below:
Show answer
(a) 1, 2, 5 and 6 only
From a third-party answer key, not yet checked against UPSC's official key.
The policy originally proposed 20% ethanol blending in petrol and 5% biodiesel blending in diesel by 2030. A 2022 amendment advanced the 20% ethanol target to the ethanol supply year 2025-26, allowed more feedstocks, and permitted biofuel production by units in special economic zones and export-oriented units.
Earlier papers asked the same thing in simpler forms: which crop can be grown for ethanol (2009, 2010), and in 2025, how the two largest producers, Brazil and the United States, compare in output and in their main feedstock.
Biodiesel and the oilseed questions
Biodiesel questions turn on the word "non-edible". The policy lists non-edible oilseeds, used cooking oil, animal tallow, acid oil and algae as biodiesel feedstocks. That is why the 2010 paper asked why Pongamia pinnata, like Jatropha curcas, is considered for biodiesel in India:
Other than Jatropha curcas, why is Pongamia pinnata also considered a good option for the production of bio-diesel in India ? 1. Pongamia pinnata grows naturally in most of the arid regions of India. 2. The seeds of Pongamia pinnata are rich in lipid content of which nearly half is oleic acid. Which of the statements given above is/are correct ?
The other biodiesel questions follow from the same idea: which ministry ran the Biodiesel Mission (2008), and in 2021, whether palm oil can be used to make biodiesel as well as in cosmetics.
Beyond liquid fuels: gasification, microbes and aviation fuel
A smaller group of questions covers other ways of getting energy from biomass. The 2012 paper asked what biomass gasification can use and what its gases can power, and the 2011 paper asked why microbial fuel cells are considered a source of sustainable energy.
The newest addition is sustainable aviation fuel. The US Department of Energy describes it as an alternative jet fuel made from non-petroleum feedstocks that can be blended with conventional jet fuel at levels between 10% and 50%, depending on the feedstock and how it is made. One approved production route, Fischer-Tropsch synthesis, draws on municipal solid waste, agricultural and forest wastes and energy crops. The 2024 question asked which of four materials, from agricultural residues and corn grain to wastewater sludge and wood mill waste, can serve as feedstock:
Consider the following materials: 1. Agricultural residues 2. Corn grain 3. Wastewater treatment sludge 4. Wood mill waste Which of the above can be used as feedstock for producing Sustainable Aviation Fuel?
Show answer
(c) 1, 2, 3 and 4
From a third-party answer key, not yet checked against UPSC's official key.
Where green hydrogen fits
Hydrogen is not a biofuel, but UPSC files it in the same part of the paper, and three recent questions ask about green hydrogen directly (2023 twice and 2026). India's National Green Hydrogen Mission has an initial outlay of ₹19,744 crore, most of it (₹17,490 crore) for the SIGHT programme. It ties green hydrogen to renewable electricity: the mission extends waivers of inter-state transmission charges, banking and faster open access to renewable energy used to produce it.
The 2023 questions asked how green hydrogen can be used, from combustion and blending with natural gas to fuel cells, and which heavy industries it could help decarbonise. The 2026 question moved to how green hydrogen is defined and what the mission aims for. Related clean-energy questions in this group asked about alternative powertrain vehicles (2025), distributed energy resources (2024) and net metering (2016).
How to prepare biofuels for Prelims
Read the National Policy on Biofuels once, carefully, with a pen. Sections 3 and 5 alone answer most of the biofuel questions above: the four categories of fuel and the permitted feedstocks for each. Note the 2022 amendment's new blending date beside the original target, since a question can test either.
For the newer fuels, keep a short note for each with three lines: what it is made from, what it replaces, and which Indian mission or policy supports it. That format covers sustainable aviation fuel and green hydrogen now, and will cover the next fuel UPSC adds.
The climate change guide covers the emissions side of the same story, and the air pollution guide covers the 2019 question on what burning crop residue releases into the air.
Frequently asked questions
What are biofuels?
Biofuels are fuels made from biomass rather than from fossil sources. India's National Policy on Biofuels, 2018 covers bioethanol, biodiesel, advanced biofuels and drop-in fuels, made from materials such as sugarcane, corn, non-edible oilseeds, used cooking oil, agricultural residues and municipal waste, for use in transport or stationary applications.
What is the difference between first and second generation biofuels?
First generation ethanol is made from sugar or starch, such as sugarcane, sugar beet, corn or cassava. Second generation ethanol is made from lignocellulosic material such as rice and wheat straw, corn cobs, bagasse or woody biomass, which does not compete with food crops. India's policy counts 2G ethanol among advanced biofuels.
Can food grains be used to make ethanol in India?
Yes, within limits. The National Policy on Biofuels allows ethanol from damaged food grains such as wheat and broken rice that are unfit for human consumption, and from surplus food grains in years of projected oversupply, with the approval of the National Biofuel Coordination Committee.
What is India's ethanol blending target?
The 2018 policy proposed 20% ethanol blending in petrol by 2030. A 2022 amendment advanced that target to the ethanol supply year 2025-26, allowed more feedstocks, and permitted biofuel production by units in special economic zones and export-oriented units.
What is sustainable aviation fuel?
Sustainable aviation fuel is an alternative jet fuel made from non-petroleum feedstocks. It is blended with conventional jet fuel at levels between 10% and 50%, depending on the feedstock and production process. One approved route, Fischer-Tropsch synthesis, uses inputs such as municipal solid waste, agricultural and forest wastes and energy crops.