UPSC CSE Prelims
Renewable Energy Sources Previous Year Questions (PYQs)

Detailed Explanation:

Alternative powertrain vehicles are vehicles that do not rely on conventional petrol or diesel internal combustion engines as their primary source of propulsion.

• Statement I is Correct: Battery Electric Vehicles (BEVs) run entirely on electricity stored in batteries.

• Statement II is Correct: Hydrogen Fuel Cell Vehicles (FCEVs) generate electricity from hydrogen using fuel cells.

• Statement III is Correct: Fuel Cell Electric Hybrid Vehicles (FCEHVs) combine fuel cells, batteries, and electric motors.

• Therefore, all three are considered alternative powertrain vehicles, making Option C the correct answer.

Vehicle-wise Analysis

Alternative Powertrain Vehicles

What are Alternative Powertrains?

These are vehicle propulsion systems that use alternatives to conventional petrol or diesel engines.

Major Types

Important Facts

• BEVs produce zero tailpipe emissions.

• FCEVs emit only water vapor as a by-product.

• Hydrogen-based vehicles are considered important for long-range and heavy-duty transport.

• Alternative powertrains help reduce dependence on fossil fuels and lower carbon emissions.

Detailed Explanation:

In most Lithium-ion Electric Vehicle (EV) batteries, the cathode is made using combinations of Lithium, Cobalt, and Nickel.

• Statement I (Cobalt) ✅ Correct – Used in cathodes such as NMC and LCO batteries.

• Statement II (Graphite) ❌ Incorrect – Graphite is generally used in the anode, not the cathode.

• Statement III (Lithium) ✅ Correct – A key component of all lithium-ion battery cathodes.

• Statement IV (Nickel) ✅ Correct – Commonly used in NMC and NCA cathode chemistries.

• Therefore, only three elements (Cobalt, Lithium, and Nickel) usually make up battery cathodes, making Option C the correct answer.

Element-wise Analysis

EV Battery Components

Common Cathode Chemistries

• LCO – Lithium Cobalt Oxide

• NMC – Nickel Manganese Cobalt

• NCA – Nickel Cobalt Aluminum

• LFP – Lithium Iron Phosphate

Important Facts

• Cathode materials largely determine a battery's energy density and cost.

• Graphite remains the most widely used anode material in EV batteries.

• Demand for Lithium, Nickel, and Cobalt has increased significantly due to the global EV transition.

Detailed Explanation:

Correct Answer: ✅ Option 4 (All Four)

Distributed Energy Resources (DERs) are small-scale energy generation, storage, or management systems located close to consumers rather than large centralized power plants. They help improve grid reliability, energy efficiency, and renewable energy integration.

✅ Battery Storage – Correct: Stores electricity locally and supplies power when needed, making it a key DER.

✅ Biomass Generators – Correct: Small-scale biomass-based power plants can generate electricity near consumption points.

✅ Fuel Cells – Correct: Fuel cells produce electricity in a decentralized manner and are widely recognized as DERs.

✅ Rooftop Solar Photovoltaic Units – Correct: One of the most common DERs, generating electricity directly at homes, offices, and industries.

Short Notes: Distributed Energy Resources (DERs)

• DERs are small-scale energy resources located near end-users.

• Include both energy generation and energy storage technologies.

• Common examples: rooftop solar, battery storage, fuel cells, biomass plants.

• Reduce transmission and distribution losses.

• Improve grid resilience and reliability.

• Support integration of renewable energy sources.

• Can operate independently or alongside the main grid.

• Important for the development of smart grids and decentralized energy systems.

Detailed Explanation:

Answer: Option 3 — 1 and 3

This question compares traditional sodium lamps with modern LED lamps used in street lighting. Statement 1 correctly identifies that sodium lamps emit light omnidirectionally (360 degrees), while LEDs are directional, reducing light wastage. Statement 3 correctly notes that sodium lamps produce nearly monochromatic yellow light, whereas LEDs offer better color rendering and spectrum diversity.

✅ Statement 1 – Correct: Sodium lamps emit light in all directions (360 degrees), while LED lamps are directional and focus light where needed, improving efficiency.
❌ Statement 2 – Incorrect: LED lamps have a significantly longer lifespan (50,000-100,000 hours) compared to sodium lamps (15,000-24,000 hours).
✅ Statement 3 – Correct: Sodium lamps produce monochromatic yellow-orange light (narrow spectrum), while LED lamps offer a broad spectrum with better color rendering index (CRI) for street lighting.

📝 Short Notes: Street Lighting Technologies

Detailed Explanation:

Answer: Option 2 — 2 and 3 only

❌ Statement 1 – Incorrect: Algae-based biofuel production is not restricted to seas. Algae can be cultivated on land using open ponds, closed photobioreactors, or wastewater treatment systems. Continental production is technically feasible and widely practiced.

✅ Statement 2 – Correct: Setting up algae biofuel facilities requires advanced biotechnology, sophisticated engineering for photobioreactors, precise cultivation control systems, and extraction technology. This high-tech infrastructure poses significant challenges for developing countries with limited technical expertise and capital.

✅ Statement 3 – Correct: Large-scale algae cultivation facilities need extensive land/water resources, significant energy inputs, and water usage. These requirements can trigger ecological concerns (biodiversity impact, water depletion) and social issues (land acquisition, displacement of communities, competition with food production).