(SEM VII) THEORY EXAMINATION 2023-24 RENEWABLE ENERGY RESOURCES

KOE074 – RENEWABLE ENERGY RESOURCES

B.Tech (SEM VII) – Theory Examination
Time: 3 Hours | Max Marks: 100

SECTION A

(Attempt all questions in brief – 2 × 10 = 20 marks)

a. Describe photovoltaic effect.

The photovoltaic effect is the phenomenon by which electrical energy is generated when sunlight falls on a semiconductor material. Photons excite electrons, creating electron–hole pairs and producing a voltage across the p–n junction.

b. Write down the properties of polycrystalline silicon cell.

Polycrystalline silicon cells are made from multiple silicon crystals. They have moderate efficiency, lower manufacturing cost than monocrystalline cells, good mechanical strength, and slightly lower performance due to grain boundaries.

c. Calculate angle of declination for 7th of May of a leap year.

Day number for 7th May (leap year):
January (31) + February (29) + March (31) + April (30) + 7 = 128

δ=23.45sin⁡(360366(284+128))\delta = 23.45 \sin\left(\frac{360}{366}(284 + 128)\right)δ=23.45sin(366360​(284+128)) δ=23.45sin⁡(404.6∘)≈+16.5∘\delta = 23.45 \sin(404.6^\circ) \approx +16.5^\circδ=23.45sin(404.6∘)≈+16.5∘ 

d. Define solar insolation and solar irradiance.

Solar irradiance: Instantaneous solar power received per unit area (W/m²).

Solar insolation: Total solar energy received per unit area over a given time (kWh/m²/day).

e. Comment on solar radiation and its benefits.

Solar radiation is the energy emitted by the sun in the form of electromagnetic waves. Benefits include clean energy generation, reduction of greenhouse gases, renewable supply, and low operating cost.

f. Write the chemical reaction taking place in alkaline fuel cell.

At anode:

2H2+4OH−→4H2O+4e−2H_2 + 4OH^- \rightarrow 4H_2O + 4e^-2H2​+4OH−→4H2​O+4e−

At cathode:

O2+2H2O+4e−→4OH−O_2 + 2H_2O + 4e^- \rightarrow 4OH^-O2​+2H2​O+4e−→4OH− 

g. What is Seebeck effect?

Seebeck effect is the generation of an electric voltage when two dissimilar conductors are joined and maintained at different temperatures.

h. State Peltier Effect.

Peltier effect is the absorption or release of heat when an electric current passes through a junction of two different conductors.

i. List two advantages of anaerobic digestion.

Produces renewable biogas                          Reduces organic waste and pollution

j. Write the merits of tidal power generation.

Renewable and predictable energy               No fuel cost and low emissions

SECTION B

(Attempt any three – answers provided for ALL)

2(a). Main features of renewable and non-renewable energy sources

Renewable energy sources:
Solar, wind, biomass, tidal, geothermal. They are naturally replenished, eco-friendly, and sustainable but may suffer from intermittency.

Non-renewable energy sources:
Coal, oil, natural gas, nuclear fuels. They provide reliable power but cause pollution, resource depletion, and environmental damage.

2(b). Central receiver tower and temperature range

A central receiver tower system uses a field of heliostats (mirrors) to focus sunlight onto a receiver mounted on a tower. The concentrated solar energy heats a working fluid like molten salt.

Temperature range:
Typically 500°C to 1000°C, suitable for high-efficiency power generation.

2(c). Closed-cycle MHD generating system

In a closed-cycle MHD system, an inert gas (like helium) mixed with seeding material flows through a magnetic field. The moving conductive gas generates electricity without mechanical turbines.

Advantages:                                              High efficiency

No moving parts                                        Faster response

2(d). Site selection for wind farms and advantages

Site selection factors:                                 High average wind speed

Low turbulence                                             Proper terrain

Grid connectivity                                           Environmental impact

Advantages of wind energy conversion system:

Renewable and clean                                    Low operating cost

Suitable for rural and remote areas

2(e). Availability and conversion of biogas and biomass energy

Biogas is produced from organic waste through anaerobic digestion. Biomass energy is converted into useful energy via combustion, gasification, or fermentation.

Energy conversion:
Biomass → Biogas → Heat / Electricity

SECTION C

3(a). Main elements of a PV system

A photovoltaic system consists of:            Solar panels

Charge controller                                       Battery bank

Inverter                                                       Load

Solar panels convert sunlight into DC power, which is stored or converted into AC for use.

3(b). Solar thermal power plant and process

A solar thermal power plant uses mirrors to concentrate sunlight and produce heat. The heat generates steam, which drives a turbine connected to a generator.

Steps:
Solar collection → Heat transfer → Steam generation → Turbine → Electricity

4(a). Classification of solar thermal collectors and flat plate collector

Types of collectors:                                     Flat plate collectors

Evacuated tube collectors                             Concentrating collectors

Flat plate collector:
Consists of absorber plate, transparent cover, insulation, and fluid tubes.

Advantages:                                                  Simple construction

Low cost                                                          Suitable for low-temperature applications

4(b). Solar pond-based electric power plant

A solar pond stores solar energy in its lower layer due to salt gradient. The stored heat is used to generate steam, which runs a turbine. Cooling towers help condense exhaust steam.

5(a). Working of geothermal power plants and technical developments

Geothermal plants use heat from Earth’s interior to produce steam and generate electricity.

Types:                                                              Dry steam

Flash steam                                                       Binary cycle

Technical developments:                                Enhanced geothermal systems (EGS)

Improved drilling techniques                            Better heat exchangers

5(b). Molten carbonate fuel cell (MCFC)

MCFC operates at high temperatures (~650°C) using molten carbonate electrolyte.

Reactions:
Anode:

H2+CO32−→H2O+CO2+2e−H_2 + CO_3^{2-} \rightarrow H_2O + CO_2 + 2e^-H2​+CO32−​→H2​O+CO2​+2e−

Cathode:

12O2+CO2+2e−→CO32−\frac{1}{2}O_2 + CO_2 + 2e^- \rightarrow CO_3^{2-}21​O2​+CO2​+2e−→CO32−​ 

6(a). Principle of wind energy conversion and fluctuation control

Principle:
Kinetic energy of wind is converted into mechanical energy by turbine blades and then into electrical energy.

Methods to overcome fluctuation:               Energy storage systems

Hybrid power systems                                      Pitch control and power electronics

6(b). Performance and limitations of thermoelectric power generator

Performance:
Direct conversion of heat to electricity, low maintenance.

Limitations:                                                    Low efficiency

High cost                                                          Limited power output

7(a). Factors affecting biogas generation and biogas plant

Factors:                                                           Temperature

pH value                                                           C/N ratio

Retention time

Floating drum biogas plant:
Gas is stored in a movable drum that rises and falls with gas production.

7(b). OTEC power plant: principle, working, efficiency, and environmental effects

Principle:
Uses temperature difference between warm surface water and cold deep sea water.

Working:
Warm water vaporizes working fluid → turbine → condenser → cycle repeats.

Efficiency: Low (2–4%)

Environmental effects:
Minimal pollution, but may affect marine ecosystem locally.