UPSC CSE Prelims
Renewable Energy & Green Technologies Previous Year Questions (PYQs)
Showing solved Previous Year Questions for Chapter: Renewable Energy & Green Technologies
Topic Breakdown: Scroll →
Consider the following materials:
- Agricultural residues
- Corn grain
- Wastewater treatment sludge
- Wood mill waste
Which of the above can be used as feedstock for producing Sustainable Aviation Fuel ?
Detailed Explanation:
Answer: Option 3 — 1, 2, 3 and 4
All four materials listed can serve as feedstock for producing Sustainable Aviation Fuel (SAF). Agricultural residues and wood mill waste are lignocellulosic biomass sources that can be converted through thermochemical or biochemical processes. Corn grain provides fermentable sugars for ethanol production, which can be upgraded to SAF. Wastewater treatment sludge, rich in organic matter, can undergo anaerobic digestion to produce biogas, subsequently convertible to SAF.
✅ Statement 1 – Correct: Agricultural residues (crop stalks, husks, leaves) are viable lignocellulosic biomass sources for SAF production through various conversion pathways.
✅ Statement 2 – Correct: Corn grain contains fermentable sugars that can be converted to ethanol and further processed into SAF via alcohol-to-jet fuel pathways.
✅ Statement 3 – Correct: Wastewater treatment sludge is rich in organic matter and can be converted to biogas through anaerobic digestion, which can then be upgraded to SAF.
✅ Statement 4 – Correct: Wood mill waste (sawdust, wood chips, bark) is a lignocellulosic material convertible to SAF through gasification, pyrolysis, or other thermochemical processes.
📝 Short Notes: Sustainable Aviation Fuel (SAF)
- Definition: SAF is a drop-in replacement for conventional jet fuel, produced from sustainable feedstocks, reducing lifecycle carbon emissions by up to 80%.
- Feedstock Categories: Includes agricultural residues, forestry waste, municipal solid waste, industrial waste, algae, and dedicated energy crops.
- Production Pathways: Major technologies include Fischer-Tropsch synthesis, Hydroprocessed Esters and Fatty Acids (HEFA), Alcohol-to-Jet (ATJ), and gasification.
- Certification: SAF must meet ASTM D7566 standards and can be blended with conventional jet fuel up to 50% (some pathways allow 100%).
- Global Initiatives: ICAO's CORSIA scheme, EU's ReFuelEU Aviation, and US SAF Grand Challenge aim to scale SAF production and adoption.
- Indian Context: India is exploring SAF production from agricultural waste, used cooking oil, and other biomass sources to decarbonize aviation sector.
Consider the following heavy industries :
- Fertilizer plants
- Oil refineries
- Steel plants
Green hydrogen is expected to play a significant role in decarbonizing how many of the above industries?
Detailed Explanation:
Answer: Option 3 — All three
Green hydrogen, produced through electrolysis of water using renewable electricity, is expected to play a significant role in decarbonizing all three heavy industries mentioned. It offers a clean alternative to fossil fuels in energy-intensive industrial processes, thereby reducing carbon emissions substantially.
1. Fertilizer plants: Green hydrogen can replace natural gas in ammonia synthesis, which is the primary feedstock for fertilizer production. This eliminates the carbon-intensive steam methane reforming process currently used.
2. Oil refineries: Refineries use hydrogen for hydrocracking and desulfurization processes. Green hydrogen can replace the hydrogen currently produced from fossil fuels, reducing the refinery's carbon footprint.
3. Steel plants: Green hydrogen can replace coal and coke in the direct reduction of iron ore (DRI process), eliminating one of the largest sources of industrial CO₂ emissions. Several pilot projects globally are already testing hydrogen-based steelmaking.
📝 Short Notes: Green Hydrogen and Industrial Decarbonization
- Green Hydrogen: Hydrogen produced via electrolysis of water using electricity from renewable sources (solar, wind, hydro). It is carbon-free if the electricity is 100% renewable.
- Fertilizer Industry: Uses hydrogen to produce ammonia (NH₃) via the Haber-Bosch process. Currently, ~1-2% of global energy and CO₂ emissions come from ammonia production using fossil fuel-derived hydrogen.
- Oil Refining: Refineries consume significant hydrogen for upgrading heavy crude, hydrocracking, and removing sulfur. Green hydrogen can directly substitute fossil-fuel-derived hydrogen.
- Steel Industry: Traditional blast furnace method uses coke (from coal) as a reducing agent. Green hydrogen-based Direct Reduced Iron (DRI) technology can replace this, producing water instead of CO₂.
- National Green Hydrogen Mission (India): Launched in 2023 with ₹19,744 crore outlay to make India a global hub for green hydrogen production and export by 2030.
- Challenges: High production cost, infrastructure development, storage and transportation issues, and scaling up electrolyzer manufacturing capacity.
With reference to green hydrogen, Consider the following statements :
- It can be used directly as a fuel for internal combustion.
- It can be blended with natural gas and used as fuel for heat or power generation.
- It can be used in the hydrogen fuel cell to run vehicles.
How many of the above statements are correct?
Detailed Explanation:
Answer: Option 3 — All three
Green hydrogen, produced from renewable energy sources through electrolysis, is a versatile clean fuel that can be utilized in multiple ways. All three statements regarding its applications are correct.
✅ Statement 1 – Correct: Green hydrogen can be used directly as a fuel in modified internal combustion engines, replacing conventional fossil fuels.
✅ Statement 2 – Correct: Green hydrogen can be blended with natural gas (up to 20% in existing pipelines) and used for heating, power generation, and industrial applications.
✅ Statement 3 – Correct: Green hydrogen is used in hydrogen fuel cells to generate electricity for running electric vehicles, offering zero-emission transportation.
📝 Short Notes: Green Hydrogen
- Definition: Hydrogen produced through electrolysis of water using renewable energy sources (solar, wind, hydro), resulting in zero carbon emissions.
- Production Method: Water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) using electricity from renewable sources in an electrolyzer.
- Color Coding: Green (renewable energy), Grey (fossil fuels without carbon capture), Blue (fossil fuels with carbon capture), Brown/Black (coal).
- Applications: Transportation (fuel cell vehicles), industrial processes (steel, ammonia production), energy storage, power generation, and heating.
- India's Initiatives: National Green Hydrogen Mission (2023) targeting 5 MMT annual production by 2030; focus on making India a global hub for green hydrogen production and export.
- Advantages: Zero emissions at point of use, high energy density, long-term storage capability, and versatile applications across sectors.
- Challenges: High production costs, energy-intensive electrolysis process, storage and transportation infrastructure requirements, and need for renewable energy scale-up.
🧐 Not Sure What to Study Next?
Get a personalised study plan based on your goals, time and revision needs.
Consider the following statements:
- Gujarat has the largest solar park in India.
- Kerala has a fully solar powered International Airport.
- Goa has the largest floating solar photovoltaic project in India.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 2 — 2 only
This question tests factual knowledge about solar power installations in India. Only Statement 2 about Kerala's airport is correct, while the claims about Gujarat and Goa are factually incorrect.
❌ Statement 1 – Incorrect: Bhadla Solar Park in Rajasthan (not Gujarat) is the largest solar park in India with a capacity of 2,245 MW, making it one of the largest in the world.
✅ Statement 2 – Correct: Cochin International Airport in Kerala became the world's first fully solar-powered airport in 2015, generating power through its 46 MW solar plant spread across 45 acres.
❌ Statement 3 – Incorrect: The Omkareshwar Floating Solar Project in Madhya Pradesh (not Goa) is the largest floating solar photovoltaic project in India with a capacity of 600 MW.
📝 Short Notes: Major Solar Power Installations in India
| Project/Installation | Location | Capacity/Details | Significance |
|---|---|---|---|
| Bhadla Solar Park | Rajasthan | 2,245 MW | Largest solar park in India; one of the world's largest |
| Cochin International Airport | Kerala | 46 MW solar plant | World's first fully solar-powered airport (2015) |
| Omkareshwar Floating Solar Project | Madhya Pradesh | 600 MW | Largest floating solar project in India |
| Pavagada Solar Park | Karnataka | 2,050 MW | Second largest solar park in India |
| Rewa Ultra Mega Solar Park | Madhya Pradesh | 750 MW | One of the largest single-site solar plants |
With reference to solar water pumps, consider the following statements:
- Solar power can be used for running surface pumps and not for submersible pumps.
- Solar power can be used for running centrifugal pumps and not the ones with piston.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 4 — Neither 1 nor 2
Solar water pumps are versatile and can power both surface and submersible pumps, as well as both centrifugal and piston pumps. The type of pump (surface/submersible or centrifugal/piston) does not limit the application of solar power, making both statements incorrect.
❌ Statement 1 – Incorrect: Solar power can be used for running both surface pumps and submersible pumps, not just surface pumps.
❌ Statement 2 – Incorrect: Solar power can be used for running both centrifugal pumps and piston pumps, not just centrifugal pumps.
📝 Short Notes: Solar Water Pumping Systems
- Components: A solar water pumping system consists of three main components: photovoltaic (PV) array/solar panels, an electric motor (DC/AC/BLDC), and a pump.
- Types by Motor: Systems are classified as Direct Current (DC), Alternating Current (AC), or Brushless DC (BLDC) based on the motor type.
- Types by Pump Installation: Can use surface pumps (installed above ground) or submersible pumps (installed underwater in wells/borewells).
- Types by Pump Mechanism: Both centrifugal pumps (using rotational energy) and positive displacement pumps like piston pumps can be solar-powered.
- Applications: Ideal for irrigation, drinking water supply, livestock watering, and remote areas without grid electricity.
- Benefits: Clean, energy-efficient, sustainable, low operating costs, minimal maintenance, and environmentally friendly alternative to diesel/electric pumps.
In rural road construction, the use of which of the following is preferred for ensuring environmental sustainability or to reduce carbon footprint?
- Copper slag
- Cold mix asphalt technology
- Geotextiles
- Hot mix asphalt technology
- Portlant cement
Select the correct answer using the code given below:
Detailed Explanation:
Answer: Option 1 — 1, 2 and 3 only
For ensuring environmental sustainability and reducing carbon footprint in rural road construction, copper slag (a by-product reducing natural resource demand), cold mix asphalt (lower temperature processing with reduced emissions), and geotextiles (synthetic materials minimizing excavation and resource use) are preferred. Hot mix asphalt requires high energy consumption, and Portland cement production is carbon-intensive, making them less environmentally sustainable choices.
✅ Statement 1 – Correct: Copper slag, a copper refining by-product, can replace sand in concrete, reducing sand mining and environmental impact.
✅ Statement 2 – Correct: Cold mix asphalt technology operates at lower temperatures, consuming less energy and emitting fewer greenhouse gases compared to hot mix.
✅ Statement 3 – Correct: Geotextiles provide soil stabilization and drainage while reducing the need for excessive excavation and natural resource consumption.
❌ Statement 4 – Incorrect: Hot mix asphalt technology requires high temperatures and thus higher energy consumption, making it less environmentally sustainable.
❌ Statement 5 – Incorrect: Portland cement production is highly energy-intensive and emits significant CO₂, contributing substantially to carbon footprint.
📝 Short Notes: Sustainable Road Construction Materials
| Material/Technology | Environmental Benefits | Carbon Footprint Impact |
|---|---|---|
| Copper Slag | By-product utilization; reduces sand mining; waste recycling | Low - diverts industrial waste |
| Cold Mix Asphalt | Lower production temperature (60-100°C vs 150-180°C); allows recycled materials; can be produced on-site | Reduced by 30-50% compared to hot mix |
| Geotextiles | Reduces excavation depth; improves soil stability; extends road life; reduces gravel/stone requirement | Low - reduces material transport and extraction |
| Hot Mix Asphalt | Good performance but high energy demand | High - requires 150-180°C processing |
| Portland Cement | Limited - energy-intensive production | Very High - 0.8-0.9 kg CO₂ per kg cement |
- Green Road Construction: Focus on using industrial by-products, recycled materials, and low-energy technologies
- Rural Road Context: PMGSY (Pradhan Mantri Gram Sadak Yojana) encourages use of sustainable materials and local resources
- Geotextiles Applications: Separation, filtration, drainage, reinforcement, and erosion control in road construction
- Fly Ash & Slag: Other industrial by-products increasingly used as sustainable alternatives in road construction
With reference to solar power production in India, consider the following statements:
- India is the third largest in the world in the manufacture of silicon wafers used in photovoltaic units.
- The solar power tariffs are determined by the Solar Energy Corporation of India.
Which of the statements given above is/are correct?
Detailed Explanation:
Answer: Option 4 — Neither 1 nor 2
Both statements about solar power production in India are incorrect. India is not among the top three global manufacturers of silicon wafers for photovoltaic units, and SECI does not determine solar power tariffs but facilitates project implementation.
❌ Statement 1 – Incorrect: India does not rank among the top three manufacturers of silicon wafers for photovoltaic units; China, Taiwan, and South Korea dominate this sector with China alone accounting for over 90% of global production.
❌ Statement 2 – Incorrect: The Solar Energy Corporation of India (SECI) does not determine solar power tariffs; tariffs are determined through a competitive bidding process conducted by various implementing agencies, with SECI acting as a facilitator and intermediary.
📝 Short Notes: Solar Power in India
- Solar Energy Corporation of India (SECI): A government-owned enterprise under the Ministry of New and Renewable Energy (MNRE), established in 2011 to facilitate solar energy deployment through competitive bidding, tendering, and project implementation.
- Tariff Determination: Solar power tariffs in India are market-driven and determined through reverse auction mechanisms where developers bid competitively; the lowest bidder wins the contract, ensuring cost-effective power procurement.
- Silicon Wafer Manufacturing: India's domestic solar manufacturing capacity is limited, with heavy reliance on imports (especially from China) for solar cells, modules, and silicon wafers; the government is promoting domestic manufacturing through Production Linked Incentive (PLI) schemes.
- Global Leaders: China dominates global solar manufacturing with over 90% market share in silicon wafers, followed by Taiwan and South Korea; India is focusing on building manufacturing capacity through policies like Atmanirbhar Bharat.
- India's Solar Capacity: India ranks among the top 5 countries globally in installed solar capacity and aims to achieve 500 GW of renewable energy capacity by 2030 as part of its climate commitments.
‘Net metering’ is sometimes seen in the news in the context of promoting the -
Detailed Explanation:
Answer: Option 1 — production and use of solar energy by the households/consumers
Net metering is a billing mechanism that allows households and businesses with solar panel installations to send excess electricity generated during the day back to the power grid. In return, they receive credits on their electricity bills which can be used when they draw power from the grid during night-time or cloudy periods when solar production is low. This system promotes decentralized solar energy generation by making rooftop solar installations economically viable for individual consumers, as they effectively use the grid as a virtual battery without needing expensive physical storage systems.
With reference to ‘fuel cells’ in which hydrogen-rich fuel and oxygen are used to generate electricity. Consider the following statements:
- If pure hydrogen is used as a fuel, the fuel cell emits heat and water as by-products.
- Fuel cells can be used for powering buildings and not for small devices like laptop computers.
- Fuel cells produce electricity in the form of Alternating Current (AC).
Which of the statements given above is/are correct?
Detailed Explanation:
✅ Statement 1 – Correct: Pure hydrogen fuel cells emit only water (H₂O) and heat as by-products when hydrogen reacts with oxygen, making them a zero-emission energy source.
❌ Statement 2 – Incorrect: Fuel cells can power both large-scale applications (buildings, vehicles) and small portable devices (laptops, mobile phones). Micro fuel cells and portable fuel cells are already developed for consumer electronics.
❌ Statement 3 – Incorrect: Fuel cells produce electricity in Direct Current (DC) form, not Alternating Current (AC). An inverter is required to convert DC to AC for grid compatibility.
With reference to bio-toilets used by the Indian Railways, consider the following statements:
- The decomposition of human waste in the bio-toilets is initiated by a fungal inoculum.
- Ammonia and water vapour are the only end products in this decomposition which are released into the atmosphere.
Which of the statements given above is/are correct?
Detailed Explanation:
❌ Statement 1 – Incorrect: Bio-toilets used by Indian Railways employ anaerobic bacteria (not fungi) as the inoculum to decompose human waste in an oxygen-free environment.
❌ Statement 2 – Incorrect: The decomposition produces methane gas, carbon dioxide, treated water (after chlorination), and minimal sludge – not just ammonia and water vapour.
With reference to technologies for solar power production, consider the following statements:
- ‘Photovoltaics’ is a technology that generates electricity by direct conversion of light into electricity, while ‘Solar Thermal’ is a technology that utilizes the Sun’s rays to generate heat which is further used in the electricity generation process.
- Photovoltaics generates Alternating Current (AC), while Solar Thermal generates Direct Current (DC).
- India has a manufacturing base for Solar Thermal technology, but not for Photovoltaics.
Which of the statements given above is/are correct?
Detailed Explanation:
✅ Statement 1 – Correct: Photovoltaics (PV) directly converts light into electricity using semiconductor materials, while Solar Thermal uses concentrated sunlight to generate heat, which drives turbines for electricity generation.
❌ Statement 2 – Incorrect: Photovoltaic systems generate Direct Current (DC), which is converted to AC through inverters. Solar Thermal systems produce AC electricity directly through conventional turbine-generator systems.
❌ Statement 3 – Incorrect: India has a strong manufacturing base for Photovoltaics (companies like Adani Solar, Vikram Solar, Tata Power Solar), while Solar Thermal manufacturing is limited to small-scale applications like water heaters.
Biomass gasification is considered to be one of the sustainable solutions to the power crisis in India. In this context, which of the following statements is/are correct?
- Coconut shells, groundnut shells and rice husk can be used in biomass gasification.
- The combustible gases generated from biomass gasification consist of hydrogen and carbon dioxide only.
- The combustible gases generated from biomass gasification can be used for direct heat generation but not in internal combustion engines.
Detailed Explanation:
✅ Statement 1 – Correct: Coconut shells, groundnut shells, and rice husk are excellent agricultural residues and biomass feedstock for gasification due to their high carbon content and low moisture.
❌ Statement 2 – Incorrect: The syngas (synthesis gas) from biomass gasification primarily contains carbon monoxide (CO), hydrogen (H₂), methane (CH₄), and carbon dioxide (CO₂), not just hydrogen and carbon dioxide.
❌ Statement 3 – Incorrect: Syngas from biomass gasification can be used for both direct heat generation and in internal combustion engines after proper cleaning and cooling to remove tar and particulates.