Predicted Question Paper for AKTU KOE074 (Next Exam) 2025

SECTION A – 2 MARKS (≈100 WORDS EACH)

1. Describe the photovoltaic effect.

The photovoltaic effect is the basic principle by which solar cells convert sunlight directly into electrical energy. When sunlight falls on a semiconductor material such as silicon, photons from light transfer their energy to electrons. These electrons gain enough energy to break free from their atomic bonds, creating electron–hole pairs. Due to the built-in electric field at the p-n junction of the solar cell, electrons move towards the n-side and holes towards the p-side, generating a flow of electric current. This conversion of light energy into electrical energy is called the photovoltaic effect.

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2. List the main properties of polycrystalline silicon solar cells.

Polycrystalline silicon solar cells are made from silicon crystals melted together, forming multiple grains. These cells have a bluish appearance due to light reflection from crystal boundaries. They are less expensive to manufacture compared to monocrystalline cells and require less energy during production. Their efficiency typically ranges from 13% to 17%, which is slightly lower than monocrystalline cells. Polycrystalline cells have good durability, long life, and moderate temperature tolerance, making them suitable for large-scale commercial and residential solar power applications.

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3. Calculate the angle of declination for 7th of May in a leap year.

The angle of declination (δ) is calculated using the formula:
δ = 23.45° × sin [360/365 × (284 + n)]
For 7th May in a leap year, the day number n = 128.
Substituting values:
δ = 23.45 × sin [360/365 × (284 + 128)]
δ ≈ 23.45 × sin (406.7°)
δ ≈ +16° (approximately).
Thus, the declination angle on 7th May is around +16 degrees, indicating the sun is north of the equator.

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4. Define solar insolation and solar irradiance.

Solar insolation refers to the total amount of solar energy received on a given surface area over a specific period of time, usually measured in kWh/m² per day. It indicates the total energy available for solar power generation. Solar irradiance, on the other hand, is the rate at which solar energy falls on a surface at a given moment, measured in watts per square meter (W/m²). While irradiance represents instantaneous power, insolation represents cumulative energy received over time.

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5. Write a note on solar radiation and its benefits.

Solar radiation is the electromagnetic energy emitted by the sun and received by the Earth in the form of heat and light. It is the primary source of energy for all renewable solar technologies. Solar radiation can be converted into electricity using photovoltaic systems or into heat using solar thermal systems. The benefits of solar radiation include its abundance, renewability, and non-polluting nature. It reduces dependence on fossil fuels, lowers greenhouse gas emissions, and provides sustainable energy for electricity generation, heating, cooking, and industrial applications.

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6. Write the chemical reaction taking place in an alkaline fuel cell.

In an alkaline fuel cell, hydrogen and oxygen react in the presence of an alkaline electrolyte, usually potassium hydroxide (KOH), to produce electricity.
At the anode:
2H₂ + 4OH⁻ → 4H₂O + 4e⁻
At the cathode:
O₂ + 2H₂O + 4e⁻ → 4OH⁻
Overall reaction:
2H₂ + O₂ → 2H₂O + Electrical Energy
This reaction produces water, heat, and electrical energy with high efficiency.

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7. What is the Seebeck effect?

The Seebeck effect is the phenomenon in which an electric voltage is generated when two dissimilar conductors or semiconductors are joined together and maintained at different temperatures. Due to the temperature difference, charge carriers move from the hot junction to the cold junction, creating an electromotive force. This effect forms the basic principle of thermoelectric generators, which convert heat energy directly into electrical energy. The magnitude of the voltage depends on the temperature difference and the materials used.

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8. State the Peltier effect.

The Peltier effect is the reverse of the Seebeck effect. It states that when an electric current passes through a junction of two dissimilar conductors or semiconductors, heat is either absorbed or released at the junction. Depending on the direction of current flow, one junction becomes cold while the other becomes hot. The Peltier effect is used in thermoelectric cooling devices, such as electronic coolers and portable refrigeration systems, because it allows temperature control without moving parts.

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9. List two advantages of anaerobic digestion.

Anaerobic digestion has several advantages. First, it produces biogas, which is a clean and renewable source of energy that can be used for cooking, heating, or electricity generation. Second, it helps in effective waste management by converting organic waste such as animal dung, agricultural residue, and food waste into useful energy. Additionally, the leftover slurry acts as an excellent organic fertilizer, improving soil fertility and reducing the need for chemical fertilizers.

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10. State two merits of tidal power generation.

Tidal power generation has significant advantages. First, it is a renewable and predictable source of energy because tides occur regularly due to gravitational forces of the moon and sun. Second, tidal power plants produce electricity without emitting greenhouse gases, making them environmentally friendly. Additionally, tidal energy systems have long operational life and low operating costs after installation, contributing to sustainable power generation in coastal regions.

4. Explain the factors considered in site selection for a wind farm. What are the advantages of wind energy conversion systems?

(10 Marks)

Introduction

Wind energy is one of the fastest growing renewable energy sources in the world. The efficiency and economic viability of a wind energy conversion system (WECS) largely depend on proper site selection. A well-selected site ensures maximum power generation, minimum losses, and long-term sustainability of the wind farm.

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Factors Considered in Site Selection for a Wind Farm

1. Wind Speed and Wind Power Density

The most important factor is the availability of sufficient wind speed throughout the year. Wind power density (measured in W/m²) should be high enough to justify installation. A minimum average wind speed of 5–6 m/s at hub height is generally required for commercial wind farms.

2. Wind Direction and Consistency

Consistent wind direction reduces turbulence and improves turbine efficiency. Sites with uniform wind flow allow better turbine alignment and reduce mechanical stress.

3. Topography of the Site

Hilly areas, ridges, coastal regions, and open plains are ideal locations because they experience higher wind speeds due to reduced surface obstruction. Obstacles like buildings, trees, and hills can cause turbulence and energy loss.

4. Land Availability and Cost

Large land areas are required for spacing between turbines to avoid wake effects. The land should be easily available at reasonable cost and should not conflict with agricultural or residential use.

5. Accessibility and Infrastructure

The site must be accessible for transportation of turbine components and maintenance equipment. Availability of roads, cranes, and construction facilities is essential.

6. Grid Connectivity

Proximity to transmission lines and substations is necessary to reduce power transmission losses and installation costs. Remote locations without grid access increase project cost.

7. Environmental and Social Impact

Environmental factors such as noise, bird migration routes, and visual impact must be considered. The site should comply with environmental regulations and cause minimal disturbance to local communities.

8. Climatic Conditions

Extreme weather conditions like cyclones, lightning, or heavy icing can damage turbines. Therefore, climatic stability is an important consideration.

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Advantages of Wind Energy Conversion Systems

1. Renewable and Sustainable

Wind energy is inexhaustible and naturally replenished, making it a long-term solution to energy needs.

2. Environment-Friendly

Wind energy produces no greenhouse gases or air pollutants, reducing carbon emissions and environmental degradation.

3. No Fuel Cost

Wind is free, eliminating fuel procurement and transportation costs.

4. Low Operating and Maintenance Cost

Once installed, wind turbines require minimal maintenance and have long operational life.

5. Suitable for Remote and Rural Areas

Wind energy can be used for decentralized power generation, promoting rural electrification.

6. Energy Security

Reduces dependence on fossil fuel imports and enhances national energy security.

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Conclusion

Proper site selection is crucial for the success of a wind farm. Factors such as wind availability, land, infrastructure, and environmental impact determine the efficiency of wind energy systems. Wind energy conversion systems offer clean, renewable, and cost-effective power, making them an essential component of sustainable energy development.

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5. Explain the availability of raw materials and the conversion process in a biogas plant. Discuss how energy is extracted from biomass.

(10 Marks)

Introduction

Biomass energy plays a significant role in renewable energy generation, especially in rural and agricultural regions. A biogas plant converts organic waste into biogas through biological processes. Biogas is a clean, renewable fuel that helps in waste management and energy production.

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Availability of Raw Materials for Biogas Plant

Biogas plants use organic and biodegradable materials that are easily available, particularly in rural areas. Common raw materials include:

• Animal dung (cow, buffalo, pig dung)

• Agricultural residues (crop waste, straw, husk)

• Kitchen waste (food scraps, vegetable waste)

• Sewage and municipal waste

• Industrial organic waste

India has abundant biomass resources due to its large agricultural base and livestock population, ensuring continuous raw material availability.

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Conversion Process in a Biogas Plant

Biogas production occurs through anaerobic digestion, a biological process carried out in the absence of oxygen. It involves four main stages:

1. Hydrolysis

Complex organic materials such as carbohydrates, fats, and proteins are broken down into simpler compounds like sugars, amino acids, and fatty acids.

2. Acidogenesis

The simpler compounds are converted into volatile fatty acids, alcohols, hydrogen, and carbon dioxide by acid-forming bacteria.

3. Acetogenesis

The acids and alcohols are further converted into acetic acid, hydrogen, and carbon dioxide.

4. Methanogenesis

Methanogenic bacteria convert acetic acid and hydrogen into methane (CH₄) and carbon dioxide (CO₂). Methane is the main energy component of biogas.

Biogas typically contains 55–65% methane, 30–40% carbon dioxide, and traces of other gases.

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Energy Extraction from Biomass

Energy from biomass can be extracted using various methods:

1. Combustion

Direct burning of biomass to produce heat, which can be used for cooking, heating, or steam generation.

2. Anaerobic Digestion

Biogas produced is used for cooking, heating, or electricity generation through gas engines or turbines.

3. Gasification

Biomass is converted into producer gas (CO, H₂, CH₄), which can be used as fuel.

4. Pyrolysis

Thermal decomposition of biomass in the absence of oxygen to produce bio-oil, gas, and char.

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Conclusion

Biogas plants efficiently convert organic waste into useful energy while reducing pollution. Biomass energy extraction methods such as combustion, digestion, and gasification make biomass a versatile and sustainable energy source. Biogas technology supports rural development, waste management, and clean energy generation.

Section C: Questions with Internal Choice (10 marks each)

(a) Describe the main elements of a photovoltaic (PV) system and their functions. Provide a suitable block diagram.

(10 Marks)

Introduction

A photovoltaic (PV) system converts solar energy directly into electrical energy using the photovoltaic effect. PV systems are widely used for residential, commercial, and grid-connected power generation due to their clean and renewable nature.

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Main Elements of a Photovoltaic (PV) System

1. Solar PV Modules (Solar Panels)

Solar panels are the heart of a PV system. They consist of multiple solar cells made of semiconductor materials such as silicon. When sunlight falls on the cells, electrons are released, generating DC electricity.

Function:
Convert solar radiation into direct current (DC) electrical energy.

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2. Mounting Structure

The mounting structure supports and holds the PV panels at an optimal tilt and orientation to receive maximum sunlight throughout the day.

Function:
Provides mechanical support and proper alignment of solar panels.

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3. Charge Controller

The charge controller regulates the voltage and current from the solar panels to the battery.

Function:

• Prevents overcharging of batteries

• Protects batteries from deep discharge

• Improves battery life

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4. Battery Bank

Batteries store excess electricity generated during the daytime for use at night or during cloudy periods.

Function:
Stores electrical energy and provides power when sunlight is unavailable.

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5. Inverter

The inverter converts DC electricity generated by solar panels or stored in batteries into AC electricity suitable for household or grid use.

Function:
Converts DC power to AC power.

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6. Load

The load refers to electrical appliances or equipment that consume power, such as lights, fans, motors, and electronic devices.

Function:
Utilizes electrical energy for useful work.

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7. Grid (Optional – Grid-Connected System)

In grid-connected PV systems, excess electricity is fed into the utility grid.

Function:
Balances power demand and allows net metering.

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Block Diagram of a PV System

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Conclusion

A photovoltaic system consists of solar panels, charge controller, batteries, inverter, and load. Each component plays a vital role in efficient energy generation and utilization. PV systems are environmentally friendly, reliable, and suitable for both standalone and grid-connected applications.

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(b) Discuss the configuration and operation of a solar thermal power plant, illustrating the process flow with a suitable diagram.

(10 Marks)

Introduction

A solar thermal power plant generates electricity by converting solar energy into heat, which is then used to produce steam and drive a turbine. Unlike PV systems, solar thermal plants operate on conventional power generation principles.

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Configuration of a Solar Thermal Power Plant

The main components are:

1. Solar Collector

Solar collectors concentrate sunlight to produce high temperatures. Common collectors include:

• Parabolic trough collectors

• Solar power towers

• Parabolic dish collectors

Function:
Collect and concentrate solar radiation.

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2. Heat Transfer Fluid (HTF)

Fluids such as molten salt, oil, or water absorb heat from solar collectors.

Function:
Transfer heat from collectors to the boiler or heat exchanger.

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3. Heat Exchanger / Boiler

The absorbed heat is transferred to water in the boiler to generate steam.

Function:
Produces high-pressure steam.

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4. Steam Turbine

High-pressure steam rotates the turbine blades.

Function:
Converts thermal energy into mechanical energy.

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5. Generator

The turbine is coupled with a generator.

Function:
Converts mechanical energy into electrical energy.

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6. Condenser

After passing through the turbine, steam is condensed back into water.

Function:
Recycles water for reuse.

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7. Cooling System

Removes excess heat from the condenser.

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Operation of Solar Thermal Power Plant

1. Sunlight is focused onto solar collectors.

2. Heat transfer fluid absorbs thermal energy.

3. The heated fluid produces steam in the boiler.

4. Steam rotates the turbine.

5. The generator produces electricity.

6. Steam is condensed and reused.

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Process Flow Diagram

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Conclusion

Solar thermal power plants effectively convert solar energy into electricity using thermal processes. They are suitable for large-scale power generation and can include thermal energy storage systems to provide power even after sunset.

Section D – Questions with Internal Choice

(10 × 1 = 10)

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(a) Classify the various types of solar thermal collectors. Explain the construction and working of a flat-plate collector, and mention its main advantages.

(10 Marks)

Introduction

Solar thermal collectors are devices used to collect solar radiation and convert it into thermal energy. This heat energy is then used for various applications such as water heating, space heating, drying, and power generation. Based on design and operating temperature, solar thermal collectors are classified into different types.

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Classification of Solar Thermal Collectors

Solar thermal collectors are broadly classified into:

1. Non-Concentrating Collectors

These collectors do not focus sunlight and have the same area for collection and absorption.

• Flat Plate Collectors (FPC)

• Evacuated Tube Collectors (ETC)

2. Concentrating Collectors

These collectors use mirrors or lenses to concentrate solar radiation onto a small area.

• Parabolic Trough Collector

• Parabolic Dish Collector

• Central Receiver (Solar Power Tower)

• Fresnel Reflector

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Flat-Plate Solar Collector (FPC)

Construction of Flat-Plate Collector

A flat-plate collector consists of the following main components:

1. Absorber Plate
   Made of copper or aluminum and coated with black or selective coating to absorb maximum solar radiation.

2. Transparent Cover (Glazing)
   Usually made of glass or plastic, placed above the absorber plate to allow sunlight in while reducing heat loss.

3. Heat Removal Tubes
   Copper tubes are attached to the absorber plate through which working fluid (water or antifreeze) flows.

4. Insulation
   Provided at the bottom and sides using materials like glass wool or polyurethane foam to minimize heat loss.

5. Casing
   An outer metallic box that encloses and protects all components.

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Working of Flat-Plate Collector

When solar radiation falls on the transparent cover, it passes through and strikes the absorber plate. The absorber plate absorbs the radiation and converts it into heat. This heat is transferred to the fluid flowing through the tubes attached to the absorber plate. The heated fluid is then circulated either naturally (thermosiphon) or by a pump to the storage tank for use.

The transparent cover reduces convective and radiative heat losses, while insulation minimizes conduction losses.

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Block Diagram (Description)

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Advantages of Flat-Plate Collectors

1. Simple construction and easy maintenance

2. Low initial and operating cost

3. Can utilize both direct and diffuse solar radiation

4. Suitable for low to medium temperature applications (up to 100°C)

5. Long service life and reliable performance

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Conclusion

Flat-plate collectors are the most widely used solar thermal collectors for domestic and industrial heating applications. Their simple design, low cost, and effective heat collection make them ideal for water heating and space heating systems.

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(b) Explain the operation of a solar pond power plant with the help of a schematic diagram. State the role of cooling towers in this system.

(10 Marks)

Introduction

A solar pond power plant is a unique solar thermal system that collects and stores solar energy in a large body of saline water. It serves both as a solar collector and thermal energy storage system. Solar ponds are particularly useful for power generation and industrial heating applications.

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Principle of Solar Pond

The working principle of a solar pond is based on salt concentration gradient, which prevents convection and allows heat to be stored at the bottom of the pond.

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Structure of a Solar Pond

A solar pond is divided into three distinct layers:

1. Upper Convective Zone (UCZ)

• Low salt concentration

• Temperature close to ambient

• Loses heat to the atmosphere

2. Non-Convective Zone (NCZ)

• Increasing salt concentration with depth

• Acts as an insulating layer

• Prevents heat loss by convection

3. Lower Convective Zone (LCZ)

• High salt concentration

• Stores thermal energy

• Temperature can reach 70–90°C

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Operation of Solar Pond Power Plant

1. Solar radiation penetrates the pond and heats the lower convective zone.

2. Due to high salt concentration, hot water at the bottom does not rise.

3. Heat is stored in the LCZ.

4. Hot brine is pumped to a heat exchanger.

5. Heat exchanger produces steam or heats a working fluid.

6. The turbine rotates, driving a generator to produce electricity.

7. After heat extraction, the cooled fluid is returned to the pond.

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Schematic Diagram (Description)

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Role of Cooling Towers in Solar Pond System

Cooling towers play a crucial role in maintaining efficiency of the solar pond power plant:

1. They cool the working fluid after passing through the turbine.

2. Help condense steam back into liquid form.

3. Maintain temperature balance in the system.

4. Improve overall thermal efficiency.

5. Enable reuse of working fluid, reducing water consumption.

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Advantages of Solar Pond Power Plant

• Integrated heat collection and storage

• Operates even during night and cloudy days

• Low maintenance cost

• Suitable for remote and arid regions

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Conclusion

Solar pond power plants are efficient systems for low-temperature power generation and thermal applications. The salt gradient mechanism allows effective heat storage, while cooling towers ensure smooth and continuous plant operation.

Section E – Questions with Internal Choice

(10 × 1 = 10)

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(a) Explain the principle and working of different types of geothermal power plants (dry steam, flash steam, binary). Discuss recent technical developments in geothermal energy.

(10 Marks)

Introduction

Geothermal energy is a renewable source of energy derived from the natural heat stored within the Earth. This heat originates from radioactive decay of minerals and residual heat from Earth’s formation. Geothermal power plants convert this thermal energy into electrical energy in an efficient and environmentally friendly manner.

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Principle of Geothermal Power Generation

The basic principle of geothermal power generation is to utilize underground reservoirs of hot water or steam to drive a turbine connected to an electric generator. The Earth’s internal heat is continuously replenished, making geothermal energy a sustainable resource.

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Types of Geothermal Power Plants

1. Dry Steam Power Plant

Working

• Dry steam plants use natural steam directly from geothermal reservoirs.

• Steam is piped directly from underground wells to the turbine.

• The turbine rotates and drives the generator.

• Exhaust steam is condensed and reinjected into the ground.

Features

• Oldest and simplest type

• Requires high-temperature dry steam reservoirs (above 150°C)

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2. Flash Steam Power Plant

Working

• Hot water at high pressure (above 180°C) is extracted from underground.

• When pressure is reduced, a portion of the hot water “flashes” into steam.

• The steam drives the turbine.

• Remaining water is reinjected into the reservoir.

Features

• Most commonly used geothermal power plant

• Higher efficiency than dry steam plants

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3. Binary Cycle Power Plant

Working

• Uses moderate-temperature geothermal water (85–170°C).

• Geothermal fluid heats a secondary working fluid (isobutane or pentane).

• The secondary fluid vaporizes and drives the turbine.

• Closed-loop system with no direct emissions.

Features

• Environmentally safest

• Suitable for low-temperature resources

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Schematic Diagram (Description)

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Recent Technical Developments in Geothermal Energy

1. Enhanced Geothermal Systems (EGS)
   Artificial reservoirs created by fracturing hot dry rocks.

2. Advanced Drilling Technologies
   Directional and deep drilling reduce cost and improve access.

3. Hybrid Systems
   Combination of geothermal with solar or biomass energy.

4. Binary Cycle Improvements
   Use of advanced organic fluids to increase efficiency.

5. Supercritical Geothermal Systems
   Utilize supercritical water for very high efficiency.

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Advantages of Geothermal Power

• Renewable and sustainable

• Low greenhouse gas emissions

• Reliable base-load power

• Small land footprint

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Conclusion

Geothermal power plants provide a clean, reliable, and sustainable source of electricity. With advancements such as EGS and binary cycle technology, geothermal energy has immense potential to contribute to future global energy needs.

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(b) Explain the working of a molten carbonate fuel cell (MCFC) using a suitable diagram. Include the various chemical reactions involved.

(10 Marks)

Introduction

A Molten Carbonate Fuel Cell (MCFC) is a high-temperature fuel cell that converts chemical energy of fuel directly into electrical energy through electrochemical reactions. It operates at temperatures around 650°C and is suitable for large-scale power generation.

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Principle of MCFC

MCFC works on the principle of electrochemical oxidation of fuel (hydrogen) using molten carbonate salts as the electrolyte. The high operating temperature allows internal reforming of fuels and improves efficiency.

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Construction of MCFC

The main components of MCFC are:

1. Anode – Porous nickel alloy

2. Cathode – Nickel oxide

3. Electrolyte – Molten mixture of lithium and potassium carbonate

4. External Circuit – For current flow

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Working of Molten Carbonate Fuel Cell

1. Hydrogen fuel is supplied to the anode.

2. Oxygen and carbon dioxide are supplied to the cathode.

3. Electrochemical reactions occur at both electrodes.

4. Electrons flow through the external circuit producing electricity.

5. Heat generated can be used for cogeneration.

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Electrochemical Reactions in MCFC

At Anode

$$H_2 + CO_3^{2-} \rightarrow H_2O + CO_2 + 2e^-$$

At Cathode

$$\frac{1}{2}O_2 + CO_2 + 2e^- \rightarrow CO_3^{2-}$$

Overall Reaction

$$H_2 + \frac{1}{2}O_2 \rightarrow H_2O + \text{Electrical Energy + Heat}$$

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Schematic Diagram (Description)

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Advantages of MCFC

1. High electrical efficiency (up to 60%)

2. Can use multiple fuels (H₂, CO, natural gas)

3. Low emissions

4. Suitable for combined heat and power (CHP)

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Disadvantages

• High operating temperature

• Material corrosion issues

• High initial cost

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Applications

• Utility-scale power plants

• Industrial cogeneration

• Distributed power generation

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Conclusion

Molten carbonate fuel cells are highly efficient and environmentally friendly energy systems suitable for large-scale power generation. Despite technical challenges, ongoing research and material improvements make MCFC a promising technology for future clean energy solutions.

Section F – Questions with Internal Choice

(10 × 1 = 10)

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(a) What is the basic principle of wind energy conversion? Describe the methods used to mitigate the fluctuating nature of power generation in wind turbines.

(10 Marks)

Introduction

Wind energy is one of the fastest-growing renewable energy sources in the world. Wind energy conversion systems (WECS) convert the kinetic energy of moving air into electrical energy. However, wind speed is highly variable, leading to fluctuations in power output. Therefore, understanding the principle of wind energy conversion and methods to mitigate power fluctuation is essential.

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Basic Principle of Wind Energy Conversion

The fundamental principle of wind energy conversion is based on the conversion of kinetic energy of wind into mechanical energy and then into electrical energy.

When wind flows through the swept area of a wind turbine rotor, part of its kinetic energy is captured by the blades, causing them to rotate. This mechanical rotation drives a generator that produces electricity.

The power available in wind is given by:

$$P = \frac{1}{2} \rho A V^3$$

Where:

• $\rho$ = air density

• $A$ = swept area of rotor

• $V$ = wind velocity

This equation shows that wind power is highly sensitive to wind speed, which explains the fluctuating nature of wind energy.

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Working of Wind Energy Conversion System

1. Wind strikes turbine blades causing rotation.

2. Rotor transmits mechanical energy to the shaft.

3. Gearbox increases rotational speed.

4. Generator converts mechanical energy into electrical energy.

5. Power electronics condition the output for grid connection.

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Schematic Diagram (Description)

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Methods to Mitigate Fluctuating Power Generation

1. Pitch Control Mechanism

Blade angle is adjusted according to wind speed to regulate power output and prevent overloading.

2. Variable Speed Operation

Turbines operate at variable rotor speeds to maximize energy capture and smooth power output.

3. Energy Storage Systems

Batteries, flywheels, and pumped hydro storage store excess energy and supply it during low wind conditions.

4. Power Electronic Converters

Converters smooth output voltage and frequency, ensuring grid stability.

5. Hybrid Wind Systems

Wind energy is combined with solar or diesel generators to ensure continuous power supply.

6. Wind Farm Aggregation

Multiple turbines spread over a large area reduce overall output variability.

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Advantages of Wind Energy Conversion

• Clean and renewable

• No fuel cost

• Low operating cost

• Scalable technology

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Conclusion

Wind energy conversion systems efficiently harness wind power, but wind variability causes output fluctuations. Through advanced control systems, energy storage, and hybrid configurations, these fluctuations can be effectively minimized, ensuring reliable and stable power generation.

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(b) Explain the principle of thermoelectric power generation. Discuss the performance characteristics and limitations of thermoelectric power generators.

(10 Marks)

Introduction

Thermoelectric power generation is a direct energy conversion process that converts heat energy into electrical energy using thermoelectric materials. It is based on temperature difference rather than mechanical motion, making it a solid-state and highly reliable power generation method.

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Principle of Thermoelectric Power Generation

Thermoelectric power generation works on the Seebeck effect. When two dissimilar conductive materials are joined and their junctions are maintained at different temperatures, an electromotive force (EMF) is generated.

The magnitude of generated voltage is proportional to the temperature difference between the hot and cold junctions.

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Working of Thermoelectric Generator (TEG)

1. Heat is supplied to the hot junction.

2. The cold junction is maintained at a lower temperature.

3. Charge carriers move from hot to cold side.

4. Voltage is generated across the terminals.

5. Electrical power is delivered to the load.

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Schematic Diagram (Description)

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Performance Characteristics of Thermoelectric Generators

1. Seebeck Coefficient

Higher Seebeck coefficient increases voltage output.

2. Electrical Conductivity

High electrical conductivity improves power output.

3. Thermal Conductivity

Low thermal conductivity is desirable to maintain temperature difference.

4. Figure of Merit (ZT)

$$ZT = \frac{S^2 \sigma T}{k}$$

Where:

• S = Seebeck coefficient

• σ = electrical conductivity

• k = thermal conductivity

Higher ZT indicates better performance.

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Limitations of Thermoelectric Power Generators

1. Low conversion efficiency (5–8%)

2. High material cost

3. Limited power output

4. Heat dissipation challenges

5. Material degradation at high temperatures

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Applications

• Spacecraft power systems

• Waste heat recovery

• Remote power generation

• Sensors and portable devices

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Conclusion

Thermoelectric power generation offers a simple, reliable, and maintenance-free method of converting heat into electricity. Despite low efficiency, advancements in material science and nanotechnology are improving performance, making thermoelectric generators increasingly attractive for niche applications.

Section G – Questions with Internal Choice

(10 × 1 = 10)

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(a) Illustrate the factors affecting biogas production. Write a short note on the working of any one type of biogas plant (Floating Drum Digester).

(10 Marks)

Introduction

Biogas is a renewable and eco-friendly source of energy produced through anaerobic digestion of organic materials such as animal dung, agricultural waste, and kitchen waste. The biogas produced mainly consists of methane (CH₄), carbon dioxide (CO₂), and small amounts of other gases. The rate and efficiency of biogas production depend on several physical, chemical, and biological factors.

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Factors Affecting Biogas Production

1. Temperature

• Microorganisms are highly sensitive to temperature.

• Optimum temperature range: 30–40°C (mesophilic range).

• Low temperature reduces gas production rate.

2. pH Value

• Ideal pH range is 6.8–7.5.

• Acidic or alkaline conditions inhibit bacterial activity.

3. Carbon to Nitrogen (C/N) Ratio

• Optimal C/N ratio is 20:1 to 30:1.

• Excess carbon slows digestion; excess nitrogen leads to ammonia toxicity.

4. Retention Time

• Time the substrate remains in the digester.

• Longer retention increases gas yield.

5. Nature of Raw Material

• Animal dung, food waste, crop residues, and sewage sludge.

• Easily biodegradable materials produce more biogas.

6. Moisture Content

• Proper water content is necessary for bacterial growth.

7. Mixing and Loading Rate

• Uniform mixing ensures proper digestion.

• Overloading reduces efficiency.

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Floating Drum Biogas Plant

Construction

A floating drum biogas plant consists of:

1. Digester Tank – Underground chamber where anaerobic digestion occurs.

2. Inlet Tank – For feeding slurry.

3. Gas Holder (Drum) – Made of steel, floats on slurry.

4. Outlet Tank – For spent slurry removal.

5. Gas Outlet Pipe – Supplies biogas to appliances.

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Working of Floating Drum Biogas Plant

• Organic waste mixed with water is fed into the digester.

• In the absence of oxygen, anaerobic bacteria break down organic matter.

• Biogas accumulates in the floating drum.

• As gas volume increases, the drum rises.

• Gas is drawn through a pipeline for cooking or lighting.

• Digested slurry flows out and is used as organic manure.

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Schematic Diagram (Description)

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Advantages of Floating Drum Plant

• Constant gas pressure

• Easy gas volume indication

• Simple operation

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Conclusion

Biogas production depends on several controllable factors. Floating drum biogas plants are efficient, easy to operate, and suitable for rural households, providing clean energy and high-quality organic manure.

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(b) Explain the principle and working of an Ocean Thermal Energy Conversion (OTEC) power plant. Discuss its efficiency and environmental impacts.

(10 Marks)

Introduction

Ocean Thermal Energy Conversion (OTEC) is a renewable energy technology that utilizes the temperature difference between warm surface seawater and cold deep seawater to generate electricity. OTEC systems are particularly suitable for tropical regions where temperature differences exceed 20°C.

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Principle of OTEC

The working principle of OTEC is based on the Rankine cycle. Warm surface water is used to vaporize a working fluid, while cold deep water is used to condense it, producing continuous power generation.

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Types of OTEC Systems

• Closed Cycle OTEC

• Open Cycle OTEC

• Hybrid Cycle OTEC

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Working of Closed Cycle OTEC Power Plant

1. Warm surface seawater heats a low-boiling-point working fluid (ammonia).

2. The fluid vaporizes and drives a turbine.

3. The turbine rotates a generator producing electricity.

4. Cold deep seawater condenses the vapor back to liquid.

5. The working fluid is recycled in a closed loop.

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Schematic Diagram (Description)

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Efficiency of OTEC Power Plant

• Overall efficiency is low (2–4%) due to small temperature difference.

• Continuous operation possible day and night.

• Suitable for base-load power generation.

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Environmental Impacts

Positive Impacts

• Renewable and sustainable

• No greenhouse gas emissions

• Provides desalinated water (open cycle)

Negative Impacts

• Disturbance to marine ecosystems

• Discharge of nutrient-rich cold water

• High installation and maintenance cost

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Conclusion

OTEC power plants offer a clean and continuous energy source for tropical coastal regions. Despite low efficiency, technological advancements may enhance its commercial viability while minimizing environmental impacts.