Energy technology in UPSC Prelims: 18 questions on hydrogen, reactors and biofuels
UPSC asked about energy technology in 8 of the last 11 Prelims papers, and 12 of the 18 questions came from 2023 on. What those questions test, the two traps they keep setting, and a plan built on them.
Energy technology looks like a current affairs topic. Green hydrogen, electric vehicles and sustainable aviation fuel all arrive through the news, so most aspirants prepare them from the news. The past papers suggest a different approach. UPSC rarely asks about a scheme’s budget or a plant’s location. It asks what goes into a technology, what comes out of it, and where its limits lie.
This post looks at the 18 energy technology questions asked from 2016 to 2026 and turns them into a plan.
What the numbers say
Three things stand out.
It has grown fast. The first seven papers, 2016 to 2022, had 6 questions between them. The four papers from 2023 to 2026 had 12. Here is every year:
| Year | Questions |
|---|---|
| 2016 | 1 |
| 2017 | 1 |
| 2018 | 0 |
| 2019 | 1 |
| 2020 | 3 |
| 2021–2022 | 0 |
| 2023 | 3 |
| 2024 | 5 |
| 2025 | 3 |
| 2026 | 1 |
It is not yet a yearly topic. It appeared in 8 of the 11 papers, one short of the 9 we use for the must-do list. The gaps were all early: 2018, 2021 and 2022. Every paper since 2023 has had at least one question.
The format moved to “how many”. Only 4 of the 18 were single-answer questions, and none came after 2024. Six used “How many of the above are correct?”, all from 2023 to 2025. One was a Statement-I and Statement-II pair, and the other 7 gave a list with answer codes like “2 and 3 only”.
What UPSC is really testing
By our count, the 18 questions fall into four groups:
- Hydrogen and fuel cells: 6 questions. H-CNG for buses (2019), the uses of green hydrogen (2023), the industries it can decarbonise (2023), the exhaust of a fuel cell vehicle (2024), alternative powertrain vehicles (2025) and what green hydrogen is (2026).
- Nuclear: 4. ITER (2016), IAEA safeguards (2020), uranium enrichment for power (2023) and radioisotope thermoelectric generators (2024).
- Biofuels and fuels from coal: 4. Algae biofuels (2017), raw materials under the National Policy on Biofuels (2020), sustainable aviation fuel feedstocks (2024) and coal gasification (2025).
- Storage and small-scale power: 4. Solar water pumps (2020), distributed energy resources (2024), pumped-storage hydropower (2024) and the elements in EV battery cathodes (2025).
Hydrogen is the clearest thread. Five of the 6 hydrogen questions came from 2023 on, and green hydrogen alone was asked in 2023 (twice) and 2026.
Batteries came up less often than hydrogen: battery storage was one item in the 2024 list, battery vehicles one item in 2025, and only the 2025 cathode question was about batteries alone.
The two traps UPSC keeps setting
Trap 1: the false statement overstates. H-CNG cuts carbon monoxide; it does not eliminate it. Algae can be grown on land, not in seas only. Solar power runs submersible and piston pumps, not only surface and centrifugal ones. Power reactors do not need uranium enriched to at least 60%. An RTG is not a miniature fission reactor.
By our count, 6 false statements across 5 questions failed this way. Each one claimed too much: an absolute word, an inflated number or a bigger label than the technology deserves. When a statement says only, not, eliminates or at least, test that word first.
The nuclear traps borrow from what students already know. India’s thorium programme is famous, so students linked ITER to thorium. ITER is about fusion. Highly enriched uranium is for weapons and some research reactors, so “60%” sounds plausible. Power reactors use natural uranium, as India’s PHWRs do, or uranium enriched to about 3 to 5%. And IAEA safeguards depend on where the uranium comes from, not who runs the plant.
Trap 2: every item fits, and students hold one back. Green hydrogen can be burnt in engines, blended with natural gas and used in fuel cells. It can help decarbonise fertiliser plants, oil refineries and steel plants. Battery storage, biomass generators, fuel cells and rooftop solar are all distributed energy resources. All four materials in the 2024 list can be made into sustainable aviation fuel.
That is 5 of the 18 questions where every item listed was correct, by our count. In most of them, something on the list looked out of place. Steel seems tied to coal, but hydrogen can replace it. Battery storage does not generate power, but it still counts. Corn grain is food, but corn ethanol can be turned into aviation fuel through the alcohol-to-jet route.
“All of them” is not a safe default, though. Only 3 of the 4 elements usually make up battery cathodes, because graphite goes in the anode. Coal gasification can make ethanol and urea, but not nitroglycerine. And the biofuels policy lists cassava, damaged wheat, rotten potatoes and sugar beet, but not groundnut or horse gram.
How to prepare
1. For each technology, write what goes in and what comes out. A fuel cell takes in hydrogen and oxygen and gives out electricity and water. An RTG takes heat from radioactive decay and turns it into electricity. Coal gasification turns coal into syngas, which can then make ethanol or urea. The questions on fuel cell exhaust, RTGs and coal gasification asked exactly this.
2. Learn hydrogen as a set. Know what makes hydrogen green (splitting water with renewable power), the three ways it can be used, and the three heavy industries it can serve. Add H-CNG: a blend of about 18% hydrogen that cuts emissions but is not cheaper than CNG. Six questions sat here, the most of any group.
3. Separate fission, fusion and decay. Ordinary reactors split atoms (fission). ITER is testing fusion. An RTG uses neither, only the heat of decay. Add one line each on enrichment levels and on why some reactors are under IAEA safeguards.
4. Keep feedstock lists. Note what India’s biofuels policy allows and what it leaves out, and what sustainable aviation fuel can be made from. These questions reward knowing the exact list, not the general idea.
5. Read every limiting word. Underline only, not, eliminates and at least before judging a statement. In this area those words decided 4 questions.
6. Solve the past questions before reading more. Start with the energy technology questions, then see the wider energy, physics and chemistry topic.
What to skip: reactor names, plant locations and installed capacity figures. None of the 18 questions asked for them.
Two questions that show the pattern
2019 · Hydrogen and fuel cells. Four statements on hydrogen-enriched CNG for buses. Two were true: H-CNG reduces carbon dioxide and hydrocarbon emissions, and hydrogen up to one-fifth by volume can be blended in. The false two: it cuts carbon monoxide by about 70% but does not eliminate it, and it is not cheaper than CNG. See the question
2024 · Nuclear. Three statements on radioisotope thermoelectric generators. RTGs power spacecraft such as Voyager and the Curiosity and Perseverance rovers, and they can use plutonium-238, a by-product of weapons programmes. But they are not fission reactors. They turn decay heat into electricity, with no chain reaction. The trap was assuming that anything nuclear must be a reactor. See the question
For another science area where the name of a technique is often the trap, see our post on biotechnology. You can also browse the full list of must-do areas.