Aktu Renewable Energy Resources KOE-074 Btech Short Question, Notes, Quantum Book Pdf

Learn about the B.Tech AKTU Quantum Book Short Question Notes on Renewable Energy Resources. Learn about the concepts of sustainable energy generation and storage, as well as how to harness the power of renewables.

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Important Questions For Renewable Energy Resources:
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Unit-I: Introduction and Solar Cells (Short Question)

Q1. What are the commercial energy sources ?

Ans. Commercial energy sources are those that are readily available on the market and can be purchased from the producing agency. These sources are in charge of the growth of the industrial, agricultural, and commercial sectors. 

Example: Coal, Oil, Natural gas, Petroleum products, etc. 

Q2. What are the non-commercial energy sources ?

Ans. Non-commercial energy sources are those that are not available for purchase in the commercial sector, and thus are frequently overlooked in energy accounting. 

Example: Firewood, Agro-waste, Animal dung, Solar energy, Wind energy, etc.  

Q3. Give the classification of energy resources.  

Ans. These energy resources can be classified as:

• i. Primary energy resources:
  • a. Conventional energy sources and non-conventional energy sources.
  • b. Renewable and non renewable.  
• ii. Secondary energy resources. 

Q4. What are primary energy resources?

Ans. These resources are obtained from the environment. 

Example: Fossil fuels, Solar energy, Hydro energy, and Tidal energy.

Q5. What are secondary energy resources ? 

Ans. These resources do not occur in nature but are derived from primary energy resources.

Example: Electrical energy from coal burning, H₂ obtained from hydrolysis of H₂O, etc. 

Q6. What are the conventional (non-renewable) energy sources ?

Ans. These are energy sources that are finite, meaning they cannot be replenished once depleted. 

Example: Coal, Petroleum product, Natural gas etc. 

Q7. What do you mean by non-conventional (renewable) energy sources ?  

Ans. These are energy sources that are limitless, meaning they can be utilized to generate energy indefinitely. 

Example: Sun, Water, Animal dung, Agro-waste etc. 

Q8. How can renewable energy technologies be compared ?

Ans. Renewable energy technologies are compared using characteristics linked to socioeconomic and operational factors that come into play when utilizing various energy supplies.  Some of these parameters are as following: 

• 1. Energy content.
• 2. Efficiency of conversion process. 
• 3. Cost associated. 
• 4. Availability and distribution. 
• 5. Environment impact.  

Q9. Are fossil fuels renewable ?  

Ans. No. 

Q10. How many types of renewable energy are there normally said to be? 

Ans. Sources of renewable energy:

• i. Solar energy, 
• ii. Biomass, 
• iii. Biogas, 
• iv. Hydro energy, 
• v. Wind energy, 
• vi. Tidal energy, 
• vii. Ocean thermal energy, 
• vii. Hydrogen energy, 
• ix. Geothermal energy,
• x. Hydrogen energy, and 
• xi. Photovoltaic. 

Q11. Define photovoltaic. 

Ans. Photovoltaics (PV) is the conversion of light into electricity utilising photovoltaic semiconducting materials. Commercially, the photovoltaic effect is used to generate power and as photosensors. 

Q12. What are the advantages of non -conventional energy resources ?  

Ans. Advantages: 

• i. Socially relevant and useful and variety of choices available in practice to shift for renewable energy. 
• ii. The system has long life of 10-15 years or more. 
• iii. Energy cost is very low as the sources are available freely. 
• iv. Can be placed at any remote location. 
• v. Renewable energy cannot deplete unlike fossil fuel and uranium resources.  

Q13. What are the disadvantages of non-conventional energy resources ? 

Ans. Disadvantages: 

• i. Low energy density and need large size plant. 
• ii. Intermittent in operation as they depend on seasonal variation. 
• iii. Conversion efficiency is low. 
• iv. Large land area is required for installing the system to get same power as conventional plants. 

Q14. Write a short note on solar cell. 

Ans. Solar Cell: Solar cells are energy conversion devices that employ the photovoltaic effect to convert sunlight to electricity. A single converter cell is referred to as a solar cell or, more broadly, a photovoltaic cell, and a grouping of such cells meant to maximise electric power generation is referred to as a solar module or solar array. 

Q15. Define solar cell materials ? 

Ans. Solar cells are constructed from a variety of materials. Silicon is the most frequent element used in solar cells. To make thin film solar cells, a variety of compound semiconductors will be used. These materials are CulnSe₂, CaS, CaTe, Cu₂S, InP, GaAs, Zinc Telluride (ZnTe), AISb (Aluminium antimonide). 

Q16. What are the various types of solar cells ? 

Ans. According to type of crystal, the solar cells are of three types: 

• i. Monocrystalline silicon cells (band gap 1.12 eV). 
• ii. Polycrystalline silicon cells (band gap 1.12 eV). 
• iii. Amorphous silicon cells (band gap 1.75 eV). 

Q17. How durable are solar panels ?

Ans. Solar panels have a lifespan in excess of about 20 years. 

Q18. Write a short note on solar photovoltaic. 

                                              OR

How can solar energy be converted into electrical energy. 

Ans. Solar energy can be converted to electricity in two ways: 

• i. Photovoltaic (PV devices) or “solar cells”: Solar cells, often known as photovoltaic cells, convert sunlight directly into electricity. PV systems are frequently employed in distant areas that are not connected to the power grid. 
• ii. Solar Power Plants: Solar power plants generate electricity indirectly by using the heat from solar thermal collectors to heat a fluid, which produces steam that powers a generator. 

Q19. Write a short note on photovoltaic effect.

Ans. Photovoltaic Effect: When a solar cell is illuminated, electron hole pairs are generated and the electric current I is obtained. It is the difference between the solar light generated current I_L and the diode dark current I_j. 

Mathematically:  

Q20. Define fill factor. 

Ans. The fill factor of a solar cell is defined as the ratio of the maximum power unit current and voltage to the light generated current and voltage. 

where, 

J_mp = Current at maximum power unit, 

V_mp = Voltage at maximum power unit, 

J_L = Light generated current, and 

V_oc = Open circuit voltage. 

Q21. What do you understand by maximum efficiency of solar cells ?  

Ans. Maximum efficiency of solar cell is defined as the ratio of maximum electric power output to the incident solar radiation. 

where, 

I_S = incident solar flux, 

I_m = maximum current,

A_C = cells area, and  

V_m = maximum voltage.  

Q22. Explain solar cell array. 

Ans. Solar Cell Array: Solar cells are connected in series to make a solar module or array. They could be tracking or fixed arrays. A tracking array is one that is always mechanically perpendicular to the sun-array line, intercepting the maximum isolation at all times. These arrays must be physically moveable by a proper prime mover and are far more sophisticated than stationary arrays. 

Q23. Explain the classification of array. 

Ans. Array are classified in two type: 

• i. Flat plate arrays, and 
• ii. Concentrating arrays. 

Q24. Write down the applications of solar energy. 

Ans. Applications: 

• i. Solar water heating, 
• ii. Solar heating of buildings, 
• iii. Solar distillation, 
• iv. Solar pumping,
• v. Solar drying of agricultural and animal products, 
• vi. Solar furnaces, 
• vii. Solar cooking, 
• viii. Solar electric power generation, 
• ix. Solar thermal power production, and 
• x. Solar green houses. 

Q25. How can you conserve energy and lower your utility bills? 

Ans. Energy can be conserved by increasing output from a given quantity of input by minimising losses/wastage and optimizing efficiency. By using energy wisely and implementing energy-saving measures at home, you may save money and reduce energy waste while satisfying your demands for convenience and comfort. 

Q26. Discuss the terms energy conservation and energy audit. 

Ans. A. Energy Conservation: Energy conservation entails reducing energy usage while maintaining manufacturing quantity and quality. In other words, higher output for the same energy usage. 

B. Energy Audit: An energy audit is a technical study of a facility that studies the machine/wise/section wise/department wise pattern of energy consumption and aims to balance the overall energy intake correlating with production. 

Q27. What is energy poverty ? Name the five nations which consume the highest energy with suitable data.  

Ans. Energy Poverty: It is a lack of access to modern energy services such as access to electricity for households and clean cooking facilities. 

Nations with Highest Energy Consumption:

• i. China: It consumed a record 113.200 trillion British thermal units (BTU) of primary energy. 
• ii. United States of America: It consumed 89,920 trillion BTU, which accounted for over 17 % of world total. 
• iii. Russia: It consumed 27,740 trillion BTU (5.5% of the world total). 
• iv. India: It consumed 23,610 trillion BTU (4.7% of the world total). 
• v. Japan: It consumed 18,810 trillion BTU (3.7 %) of the world total). 

Q28. Discuss the limitations of solar photovoltaic energy conversion. 

Ans. 1. When photons of light energy from the sun strike the cell, some (30%) of them are reflected (due to the high reflectance of semiconductors). 

2. High quantum efficiency electron-hole pairs are produced by incident active photons. Improved cell design is necessary to achieve 95% absorption. 

3. For greatest efficiency, the semiconductor with the best band gap should be employed. 

Unit-II: Solar Thermal Energy (Short Question)

Q1. Define solar radiation.  

Ans. Solar Radiation: The solar radiations received by the earth’s surface differ depending on location. However, radiation received outside the earth’s atmosphere differs from that received on the earth’s surface due to absorption, reflection, scattering, and attenuation by atmospheric particles and clouds. 

Q2. Define solar constant. What is its standard value ? 

Ans. 1. This is the amount of energy received from the sun in unit time on a unit area perpendicular to sun’s rays at the mean distance from the sun.

2. The standard value of the solar constant based on experimental measurements is 1367 W/m² with an accuracy of ±1.5 %.  

Q3. What do you mean by beam radiation ?

Ans. Direct radiation or beam radiation is solar radiation that has not been absorbed or scattered and reaches the ground straight from the sun.  

Q4. What is diffuse radiation ?

Ans. Diffuse radiation is solar energy that is received from the sun after its direction has been modified due to atmospheric reflection and scattering. 

Q5. Discuss altitude angle (𝛂) or solar altitude. 

Ans. It is the vertical angle formed by the sun’s rays projecting onto the horizontal plane and the direction of the sun’s rays (passing through the point).  

Q6. Define irradiance and albedo.  

Ans. Irradiance: The rate of incident energy per unit area of a surface is known as irradiance. 

Albedo: The planet reflects roughly 30% of total solar radiant energy back into space via cloud reflection, dispersion, and reflection at the earth’s surface. This is referred to as the albedo of the Earth’s atmospheric system. 

Q7. What do you mean by incident angle (θ) ? 

Ans. It is define as the angle between the incident beam radiation and the normal to a plane surface.

Q8. What is zenith angle (θ₂) ?

Ans. It is the vertical angle between the sun’s rays and line perpendicular to the horizontal plane through the point.  

Q9. Define latitude angle (ɸ).  

Ans. The latitude of a location is the angle formed by the radial line connecting the location to the centre of the Earth and its projection on the equatorial plane. 

Q10. What do you mean by declination angle (δ) ?

Ans. The declination is the angle formed by the line connecting the sun’s and Earth’s centres and its projection on the equatorial plane. 

Q11. Define hour angle (ω). 

Ans. It is the angle at which the earth must be rotated to bring a point’s meridian directly in line with the sun’s light. In other words, it is the angular displacement of the sun east or west of the local meridian caused by the earth’s revolution on its axis at 15° each hour. 

ω = 15 (LST – 12)

where,    LST = local solar time. 

Q12. What is surface azimuth angle (𝛾) ?  

Ans. It is the angle between the line due south and the horizontal projection of the normal to the inclined plane surface in the horizontal plane. The angle will be taken as negative for the northern hemisphere (India) and positive for the southern hemisphere (Australia). 

Q13. Discuss solar azimuth angle (𝛾_s). 

Ans. It is the angle in a horizontal plane formed by the line due south and the horizontal plane projection of beam radiation. As a result, it indicates the direction of a vertical rod’s shadow thrown in the horizontal plane. 

Q14. What is day length ?  

Ans. Day Length: The times of dawn and sunset, as well as the length of the day, are determined by the location’s latitude and the month of the year. The sunlight is parallel to the ground surface with a zenith angle of 90° during dawn and dusk. The hour angle pertaining to sunrise or sunset (ω_s) is given below: 

Q15. What do you mean by local apparent time (LAT) ?

Ans. Local Apparent Time (LAT): The time used for calculating the hour angle ω is the local apparent time. It is given by,

LAT = Standard time + Equation of time correction + 4 (Standard time longitude – longitude of location)  

In India, standard time is based on 82.5° E longitude. 

Q16. Write down the advantages of solar energy. 

Ans. Advantages: 

• i. It is reusable source of energy. 
• ii. It is easily and abundantly available. 
• iii. It is eco-friendly i.e., pollution free. 
• iv. It decreases greenhouse gas emissions. 

Q17. Write down the disadvantages of solar energy.

Ans. Disadvantages: 

• i. High capital cost due to requirement of large area. 
• ii. Limited to sun shine hours. 
• iii. Need of tracking due to change in position of sun. 
• iv. There is a need of storage. 

Q18. Define solar collectors.  

Ans. Solar Collectors: Solar collectors are used to capture solar energy and transform it into thermal energy by absorbing it. This thermal energy is then used to heat a collecting fluid, which could be water, oil, or air. 

Q19. What are the different types of solar collectors ?

Ans. Solar collectors are classified in two type: 

• i. Non-concentrating collector or flat plate type solar collector, and 
• ii. Concentrating collector or focusing type solar collector. 

Q20. Define flat plate collector.  

Ans. Flat Plate Collector: It is the most basic design and the most important component of any solar thermal energy system. Both direct and diffuse radiations are received and transformed into useable heat in this collector. 

Q21. What do you mean by fin efficiency factor (F) of flat plate collector? 

Ans. It is defined as the ratio of actual heat transfer rate to heat transfer rate if all fins (plate area) are at base temperature. 

Mathematically:  

Q22. What is collector efficiency factor (F_c) for flat plate collector? 

Ans. If the fin is at local fluid temperature, it is defined as the ratio of useful heat removed by flowing fluid in the tubes to the rate of heat transfer to the fluid. 

Mathematically:

Q_u = useful heat removed by flowing fluid in the tubes, and 

T_f = local fluid temperature. 

Q23. Define collector heat removal factor (F_H) for flat plate collector.  

Ans. It is defined as the ratio of actual useful energy gain by fluid to the rate of heat transferred to the fluid, if the fin is at inlet fluid temperature. 

Mathematically: 

where, m = mass flow rate of fluid per unit area of collector, 

C_f = specific heat of fluid,

T_fo = outlet fluid temperature, and 

T_fi = inlet fluid temperature. 

Q24. Discuss collector efficiency (η_c) for flat plate collector. 

Ans. It is defined as the ratio of useful energy absorbed by collector to the incident solar energy over it.  

Q25. Define concentrating collector or focusing collector. 

Ans. Concentrating Collector: It is a device that collects high-intensity solar radiation on an absorbing surface using the energy of a reflector or refractor.  

Q26. Differentiate between concentrating collector and flat plate type collectors. 

Ans. 

Q27. Discuss the various materials used for solar flat plate collector. 

Ans.

• i. Transparent cover is made of glass or radiation transmitting plastic sheet or transparent glass fibre reinforced composite material. 
• ii. Tubes, passages or channels are integral with collector plate are made by brass, copper or aluminium metals. 
• iii. Absorber plate normally metallic is blackened with black paint. 
• iv. Casing or container which encloses all components is made by G.I. sheets.  

Q28. On what factors does at the collector efficiency of a solars flat plate collector depend ? 

Ans. The different factors which affects the performance of flat plate collector: 

• i. Incident solar radiation, 
• ii. Number of cover plate, 
• iii. Spacing between absorber plates and glass cover, 
• iv. Collector tilt, 
• v. Selective surface, 
• vi. Fluid inlet temperature, and 
• vii. Dust on cover plate, etc. 

Unit-III: Geothermal Energy, MHD and Fuel Cells (Short Question)

Q1. Define geothermal energy. 

Ans. Geothermal Energy: Geothermal energy refers to the tremendous amount of energy available inside the ground in the form of heat. Geothermal energy is a type of renewable energy that is not dependent on the sun and has its source of natural heat within the earth. 

Q2. Why is geothermal considered a renewable energy resource ?

Ans. The geothermal resource of the earth is estimated to be more than 2.11% 10²⁵J, which is equivalent to 10⁹ MTOE (million tonnes of oil equivalent). This isa huge amount of energy, enough to supply our energy needs at current rates for 3,50,000 years. Thus, it is considered an inexhaustible and renewable source. 

Q3. Describe various geothermal energy resources. 

Ans. Geothermal resources are of five types: 

• i. Hydrothermal energy resources. 
  • a. Hot water, and
  • b. Wet steam.  
• ii. Vapour dominated resources. 
• iii. Hot dry rock resources. 
• iv. Geo pressured resources. 
• v. Magma resources. 

Q4. Define thermal gradient. 

Ans. Thermal gradient is defined as the ratio of heat flux to thermal conductivity. 

Mathematically:

Q5. Write down the types of geothermal power plants. 

Ans. Electric power from geothermal resources can be developed in the following manner: 

• i. Vapour dominated power plant, and 
• ii. Liquid dominated power plant. 

There are two types of liquid dominated power plants: 

• a. Flashed steam system. 
• b. Binary cycle system. 

Q6. What are the sources of heat for hot springs ?

Ans. Steam, Hot water, Matter Rock. 

Q7. Define MHD (Magneto Hydro Dynamics). 

Ans. Magneto Hydro Dynamics: Magnetohydrodynamics is concerned with the formation of an electrical field when an ionised fluid at high temperature flows through a magnetic field. The technology generates direct current at the expense of heat energy. 

Q8. What are the different types of magneto hydro dynamic system ? 

Ans. MHD systems may be classified as:  

• i. Open cycle systems, and 
• ii. Closed cycle systems.  

Q9. What are the advantages of MHD generator ?  

Ans. Advantages:

• i. Less wear and tear because of no moving parts and needs less maintenance. 
• ii. Instant operation and is suitable as peak load plant. 
• iii. Less operating cost. 
• iv. Less costly than coal fired steam and gas power plant.  

Q10. What are the disadvantages of MHD generator ?  

Ans. Disadvantages: 

• i. High thermal and frictional (12%) losses are involved. 
• ii. The reverse flow of electrons occurs at the end of magnetic field, through the conducting gases. 
• iii. High temperature around 2500 °C is required to ionize the gases. 
• iv. There are problems for manufacturing duct, heat exchanger and reactor to withstand high temperature.  

Q11. Define fuel cell. 

Ans. Fuel cell: A fuel cell is an electrochemical device that converts chemical energy into electricity and heat without combustion, but in the case of a fuel cell, the conversion of chemical energy into electrical energy is an isothermal process. 

Q12. What are the various type of fuel cell ?  

Ans. Based on electrolyte, the fuel cell can be classified as: 

• i. Alkaline fuel cells (AFC). 
• ii. Direct methanol fuel cells (DMFC). 
• iii. Phosphoric acid fuel cells (PAFC). 
• iv. Proton or polymer exchange membrane fuel cells (PEMFC). 
• v. Molten carbonate fuel cells (MCFC). 
• vii. Solid oxide fuel cells (SOFC). 
• vii. Zinc air fuel cells (ZAFC). 
• viii. Regenerative fuel cells (RFC).  

Q13. Describe regenerative fuel cell. 

Ans. Regenerative fuel cell: It works in a closed loop. The hydrogen and oxygen in a fuel cell are used to generate power, heat, and water. The hydrogen would be produced by electrolysis of water, which means that water may be split into hydrogen and oxygen using renewable energy sources such as the sun, wind, and so on. As an oxidant, oxygen can be employed, and the water produced is recirculated for electrolysis. 

Q14. Discuss the advantages and disadvantages of PEMFC.

Ans. Advantages: 

• i. It has high power density. 
• ii. It can be start rapidly. 
• iii. Less expensive. 
• iv. It has fewer problems with corrosion. 

Disadvantages: The main disadvantage of this type of fuel cell is that due to low operating temperature, these are not enough to perform useful cogeneration. 

Q15. What do you mean by efficiency of fuel cell ?  

Ans. The efficiency (η_F) of energy conversion of a fuel cell is defined as the ratio of the useful work to the heat of combustion of the fuel. 

Q16. What are the various types of characteristics of fuel cells ? 

Ans. The various characteristics of fuel cell are: 

• i. Current-voltage characteristics (V-I), and 
• ii. Power-current characteristics (P-I). 

Q17. What is the difference between fuel cell and a battery ? 

Ans. 

Q18. What are the environmental effects of geothermal energy sources ?

Ans. Geothermal energy is not entirely pollution-free. The main negative environmental implications of fluid extraction include air pollution (waste steam is sometimes released directly to the atmosphere), thermal pollution (pumping additional thermal energy into the atmosphere), surface disturbance, and physical effects (land subsidence). 

Q19. How does geothermal heat get up to the earth’s surface ?

Ans. The heat from the earth’s core is constantly emitted. It transfers (conducts) to the mantle, the surrounding layer of rock. Some mantle rock melts and becomes magma when temperatures and pressures are high enough. The magma then rises (convects) because it is lighter (less dense) than the surrounding rock, gently flowing up towards the earth’s crust and bringing heat from below.  

Q20. Write the chemical reaction takes place in alkaline fuel cell. 

Ans. The chemical reaction in the alkaline fuel cell expressed as:

Unit-IV: Thermoelectrical and Thermionic Conversion and Wind Energy (Short Question)

Q1. Define joule effect.

Ans. Joule Effect: In a closed electrical circuit, if the current I flows through a resistance R, the heat generated by the resistance is equal to I²R. It is known as Joule effect. 

Q = I²R

where,

I = Current flow,  

R = Resistance. 

Q2. What is Seebeck thermoelectric effect ?  

Ans. Seebeck Effect: It asserts that an emf is created in a circuit if a closed circuit is formed of two dissimilar metals and the two junctions are kept at different temperatures. The size of the current is determined by the metals as well as the temperature difference between the junctions. 

The emf produced is the function of the difference in temperature between hot and cold junction, and is given by, 

Mathematically:

E = 𝛂_s ∆T 

where,  ∆T = Difference between hot and cold junction, and 

𝛂_s = Seebeck coefficient. 

Q3. What is Peltier effect ?

Ans. Peltier Effect: When an electric current passes through an isothermal junction of two dissimilar materials, heat is either evolved or absorbed at the junction. This is known as the Peltier effect. 

Mathematically: 

Q4. Define Peltier coefficient. 

Ans. Peltier Coefficient: The heat evolved or absorbed at the junction per unit current flow, per unit time is defined as the Peltier coefficient a. 

Mathematically:

Q5. What is Thomson effect ?  

Ans. Thomson Effect: It states that “Any current carrying conductor with a temperature difference between two points will either absorb or emit heat, depending upon the material”. 

Q6. Define Thomson coefficient.  

Ans. Thomson Coefficient: The Thomson coefficient (σ) is defined as the heat absorbed or evolved per unit time per unit electric current and per unit temperature gradient. 

Mathematically:

Q7. Define Seebeck coefficient.

Ans. Seebeck Coefficient: It is defined as the ratio of the resulting voltage and temperature difference.

Q8. What is thermoelectrical conversion ? 

Ans. Thermoelectric Conversion: Heat energy (thermal energy) is turned into electrical energy via semiconductors or conductors in thermoelectrical conversion. The Seebeck effect lies at the heart of this procedure. 

Q9. Define thermionic conversion. 

Ans. Thermionic Conversion: Thermionic conversion converts heat energy directly into electrical energy by utilising the thermionic emission effect. Electrons are emitted from the surface of a heated metal in such a device. The work function, which is expressed in electron volts, is the amount of energy required to extract one electron from a metal.  

Q10. What are the different types of semiconductors used in thermoelectric power generation ? 

Ans. Semiconductors used in thermoelectric power generation are: 

• i. Bismuth telluride (Bi₂Te₃). 
• ii. Lead telluride (PbTe). 
• iii. Germanium telluride (GeTe). 
• iv. Cesium sulphide (CeS). 
• v. Zinc antimonide (ZnSb).  

Q11. Differentiate between thermoelectric and thermionic conversion system. 

Ans. 

Q12. What do you understand by wind energy ?

Ans. Wind is the movement of air caused by the pressure difference between two unevenly heated areas. Wind energy is the energy produced by the wind. It is a clean, environmentally friendly, safe, and sustainable energy source. 

Q13. What is the basic principle of wind energy conversion ?

Ans. Principle: The basic principle of wind energy is to convert wind kinetic energy into more useful forms such as mechanical and electrical power. 

Q14. Give the classification of wind mills. 

Ans.

• i. Based on orientation of the axis of rotor: 
  • a. Horizontal axis, and
  • b. Vertical axis. 
• ii. Based on type of rotor:
  • a. Propeller type (horizontal axis), 
  • b Multiple blade type (horizontal axis), 
  • c. Savonius type (vertical axis), and 
  • d. Darrieus type (vertical axis).

Q15. Define the term solidity. 

Ans. Solidity: It is the ratio of the projected area of the rotor to the swept area of the rotor. 

where, 

N = number of blades, 

b = average breadth of blade, and 

d = diameter of the circle described by a blade. 

Q16. What is the maximum energy conversion efficiency of a wind turbine for a given swept area ?

Ans. 

Q17. What do you understand by “coefficient of performance of a wind mill rotor” ? 

Ans. Coefficient of Performance (Power Coefficient): A wind mill’s coefficient of performance is defined as the ratio of the wind rotor’s power to the entire maximum power available in the wind. 

Mathematically: 

The maximum theoretical power coefficient is 0.593. 

Q18. Discuss pitch angle and pitch control. 

Ans. Pitch Angle: It is the angle between the direction of wind and direction perpendicular to the plane of blades. 

Pitch Control: It is the control of pitch by turning the blades or blade tips. 

Q19. What do you mean by tip speed ratio ?

Ans. Tip speed ratio: The tip speed ratio is the ratio of the speed of the rotor blade tips to the speed of the wind. 

Q20. Define nacelle and yaw control.  

Ans. Nacelle: Assembly consists of wind turbine, gears, bearings, generator etc., mounted in a housing. 

Yaw Control: Control of orienting the axis of wind turbine in the direction of wind. 

Q21. What is wind turbine (wind machine) ? 

Ans. Wind Turbine: A wind turbine is a machine that converts wind power into rotary mechanical power. The rotor of a wind turbine is equipped with aerofoil blades. The wind propels the rotor, generating rotary mechanical energy. 

Q22. Discuss the main criteria’s for site selection for setting up a wind firm. 

Ans. The main criteria’s are: 

• i. The area should be open and away from cities. 
• ii. Minimum wind speed is available throughout the area. 
• iii. Ground surface should be stable and high soil strength. 
• iv. The proposed altitude is to be selected by taking average wind speed data. 
• v. Approach road up to site.  

Q23. How much of our daily CO₂ emissions can wind avoid ?

Ans. According to one estimate, wind energy prevented the emission of 140 million tonnes of CO₂ in 2011. It is expected to save 342 million tonnes in 2020 and 646 million tonnes by 2030. 

Unit-V: Biomass, OTEC and Wave and Tidal Wave Energy (Short Question)

Q1. What do you understand by biomass ?

Ans. Biomass: It is organic stuff derived from plants, animals, and microorganisms that grow on land and in water, as well as its derivatives. Biomass energy is the energy derived from biomass. 

Q2. What are the various processes used for biomass conversion ?  

Ans. The following processes are used for biomass conversion to energy or to biofuels:

• i. Direct combustion, 
• ii. Thermochemical conversion, and 
• iii. Biochemical conversion. 

Q3. What is OTEC? Discuss in brief. 

Ans. It is a method of turning thermal energy from the water into usable energy. OTEC is a technology that turns solar energy into electricity. Based on the second law of thermodynamics, it generates power by utilizing the temperature gradient of the water. 

Q4. What is the efficiency of OTEC?

Ans. The maximum efficiency of a heat engine operating between two temperature limitations cannot be greater than the maximum efficiency of a Carnot cycle operating between the same temperature limits. 

Q5. What are the types of OTEC systems ? 

Ans. There are two basic types of OTEC system: 

• i. Closed cycle system or Anderson cycle system, and
• ii. Open cycle system or Claude cycle system.  

Q6. Give the advantages of OTEC.  

Ans. Advantages: 

• i. It is eco-friendly.  
• ii. The thermal resources of the ocean ensure that the power source is available during day or night. 
• iii. It can provide employment. 
• iv. It eliminates the need for a surface heat exchanger. 

Q7. Explain the disadvantages of OTEC.

Ans. Disadvantages: 

• i. It needs very large vacuum pumps. 
• ii. Due to low pressure, large size of steam turbine is used. 
• iii. Cost of plant is high. 
• iv. Cost of electrical energy from open cycle OTEC is very high. 

Q8. Discuss the resources of biomass.  

Ans. i. Biomass obtained from cultivated fields, crops, forests and algae. 

ii. Biomass derived from waste like municipal waste, animal and human excreta, etc. 

iii. Biomass converted from liquid fuels. 

Q9. Define fermentation in biomass energy.  

Ans. Fermentation is the chemical transformation in organic matter caused by living organisms such as bacteria. All organic matter can undergo two main forms of organic breakdown. Both animal and vegetable can be broken down by these two processes: 

• i. Aerobic, and
• ii. Anaerobic. 

Q10. What is an aerobic digestion ? 

Ans. Aerobic decomposition occurs in the presence of oxygen and produces tiny amounts of carbon dioxide, ammonia, and other gases as well as huge amounts of heat. The end result can be used as fertiliser.  

Q11. Define anaerobic decomposition. 

Ans. Anaerobic decomposition occurs in the presence of oxygen and produces carbon dioxide, ammonia, and other gases in tiny amounts with very little heat. The final product has a higher nitrogen content and is utilised as a fertiliser as a result of the aerobic fermentation process. 

Q12. Define wave energy. 

Ans. Solar energy, such as wind and OTEC, directly causes ocean and sea waves. Wave energy is derived from wind energy, which is derived from solar energy. Wind friction causes waves to form on the surface of the water, resulting in the radial depression of energy from the blowing wind in all directions. 

Q13. What are the advantages of wave energy ? 

Ans. Advantages: 

• i. It is a concentrated form of energy and can naturally accumulate Over time. 
• ii. It is an eco-friendly renewable source of energy. 
• iii. Large concentrated power carried in wave’s motion. 
• iv. No space coverage on land as required by wind and solar device. 

Q14. What are the disadvantages of wave energy ?

Ans. Disadvantages: 

• i. Capital cost of system is high. 
• ii. Problems in maintenance occur. 
• iii. The equipment functions in the ocean and must be constructed, maintained, and reliable. 

Q15. How tides are generated ?  

Ans. Tides are caused by the sun’s and moon’s gravitational forces acting on the ocean, the world spinning on its axis, and the relative positions of the earth, moon, and sun. High tide is the highest level of tidal water, and low tide is the lowest level of tidal water. 

Q16. What is the principle of tidal power plant ?  

Ans. Principle: To use tidal energy, water must be trapped behind a barrier or barrage during high tides and then used to drive turbines when it returns to sea at low tides. The available energy is proportional to the amplitude squared. 

Q17. What do you mean by recycling ?

Ans. Recycling entails a number of procedures, including the collection of recyclable materials, sorting them, and utilising them as raw material after palletizing. It also involves the processing, manufacture, and sale of finished goods. The collected materials are sorted and cleaned before being processed into two products. 

Q18. What are the advantages of recycling of waste ? 

Ans. Advantages:

• i. The amount of waste which goes for disposal reduces. 
• ii. The amount of raw material to produce a new product reduces. 

Q19. What are the disadvantages of recycling of waste?  

Ans. Disadvantages: 

• i. Reprocessing of recovered materials is not always free of contamination. 
• ii. Because recycling paper produces salt in the environment, the consequences of de-inking and re-pulping waste paper are relatively important in measuring environmental effects. 
• iii. Collection, transportation, and reprocessing costs are higher.

Q20. What are the factors affecting the size of biomass plant ?

Ans. To following factors are affecting the size of biomass plant: 

• i. Volume of waste to be digested daily. 
• ii. The type and amount of waste available for digestion consistently. 
• iii. Period of digestion. 
• iv. Method of stirring. 
• v. Climate condition of the region. 
• vi. Efficiency of the collection of the raw waste. 

Q21. Write down the name of popular biogas plant developed in India.  

Ans. Following biogas plant are developed in India: 

• i. Khadi village industries commission (KVIC) model. 
• ii. Janta biogas plant. 
• iii. Deen Bandhu biogas plant. 
• iv. Pragati design biogas plant. 
• v. Ganesh biogas plant. 

Q22. What are the advantages of tidal power ?

Ans. Advantages:

• i. Providing a barrage to protect the shoreline from damage caused by high storm tides. 
• ii. It consistently generates electricity. 
• iii. It is devoid of pollution. 
• iv. The fundamental advantage of tidal power plants is that they are infinite.  

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