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−→4H2O+4e−
At cathode:
O2+2H2O+4e−→4OH−O_2 + 2H_2O + 4e^- \rightarrow 4OH^-O2+2H2O+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−→H2O+CO2+2e−
Cathode:
12O2+CO2+2e−→CO32−\frac{1}{2}O_2 + CO_2 + 2e^- \rightarrow CO_3^{2-}21O2+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.
