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## Solar Thermal System UNIT 3

The section contains MCQs on solar collectors, solar water heater, solar passive space, solar refrigeration, air conditioning systems, solar cookers, solar furnaces and dryer, solar distillation and solar thermo mechanical systems.

• Solar Collectors – 1
• Solar Collectors – 2
• Solar Water Heater
• Solar Passive Space – Heating and Cooling Systems
• Solar Industrial Heating Systems
• Solar Refrigeration and Air-Conditioning Systems – 1
• Solar Refrigeration and Air-Conditioning Systems – 2
• Solar Cookers – 1
• Solar Cookers – 2
• Solar Furnaces
• Solar Dryer
• Solar Distillation or Desalination of Water
• Solar Thermo-Mechanical Systems – 1
• Solar Thermo-Mechanical Systems – 2

### Solar Energy Multiple Choice Questions & Answers (MCQs) focuses on “Solar Collectors – 1”.

1. What is a solar collector?
a) A system to collect heat by absorbing sunlight
b) A system to collect rainwater using sunlight
c) A system to collect electricity by using sunlight
d) A device to reflect sunlight back

Explanation: A solar collector is a system to collect heat by absorbing sunlight and use it for various applications. It is neither a system to collect rainwater nor electricity. However, it could be used to perform such processes.

1. What is aperture area in a solar collector?
a) Area of the system
c) Area occupied by the system after installation
d) Cross-sectional area of the receiver

Explanation: Aperture area of a receiver is that area which receives the solar radiation. It need not be same as the entire size of the receiver. It is not same as the area occupied by the system after installation.

1. Aperture area of a solar collector is roughly equal to _
a) Coolant area
b) Generator area
c) Absorber area
d) System area

Explanation: In a solar collector, the aperture area is approximately equal to absorber area. This enables absorption of (almost) all the sunlight that is incident on the aperture area.

1. What are the components of a flat plate collector?
a) Flat box, a plate with reflective coating and fluid circulation passageways, an opaque cover, a circulating fluid
b) Flat box, a dark coloured plate with fluid circulation passageways, an opaque, a circulating fluid
c) Flat box, a dark coloured plate with fluid circulation passageways, a transparent cover
d) Flat box, a dark coloured plate fluid circulation passageways, a transparent cover, a circulating fluid

Explanation: A flat plate solar collector consists of various components. Firstly, it consists of a flat box or an enclosure to hold the entire setup. A dark coloured plate is fitted with fluid circulation passageways and transparent cover. Finally, a circulating fluid which flows through the entire setup.

1. Why is a transparent cover used in a flat plate collector?
a) To maximize transmission of the incident sunlight into the box
b) To minimize transmission of the incident sunlight into the box
c) To entirely reflect the incident sunlight back
d) To ensure partial transmission of the incident sunlight into the box

Explanation: A transparent cover is used in a flat plate collector. This is because it maximizes the transmission of the incident sunlight into the box thereby collecting maximum sunlight for thermal energy.

1. Which of the following is generally used as circulating fluid in tropical and sub-tropical climates?
a) A mixture of ethylene glycol and water
b) Water
c) A mixture of propylene glycol and water
d) Glycerol

Explanation: Water is used as circulating fluid in tropical and sub-tropical climates. This is because it has good properties as a coolant. A mixture of water with ethylene glycol or glycerol or propylene glycol is not used as coolant in tropical and sub-tropical climates.

1. Which of the following is generally used as circulating fluid in freezing climates?
a) Liquid carbon dioxide
b) Water
c) A mixture of propylene glycol and water
d) Liquid nitrogen

Explanation: In freezing climates, antifreeze solution like a mixture of water with propylene glycol or ethylene glycol or glycerol is used as coolants. Liquid carbon dioxide, water and liquid nitrogen are not used as coolants in freezing climates.

1. Why are antifreeze solutions (antifreeze agents with water) used as coolants in freezing climates?
a) To increase boiling point of water
b) To decrease boiling point of water
c) To increase freezing point of water
d) To decrease freezing point water

Explanation: Antifreeze solution is used as coolants in freezing climates. This is because they decrease the freezing point of water thereby preventing it from solidifying into ice.

1. Adding antifreeze agents to water _
a) increases its durability as coolant
b) decreases its durability as coolant
c) turns water into a coolant
d) prevents water from acting as a coolant

Explanation: Adding antifreeze agents to water increases its durability as coolant. This is because it depresses the freezing point of water and prevents it from becoming ice.

1. Which of the following is a circulating fluid in evacuated flat-plate solar collectors?
a) Water
b) Steam
c) Nitrogen
d) Hydrogen

Explanation: Evacuated flat-plate solar collectors are a more recent technology. It uses steam as its circulating fluid. Nitrogen and hydrogen are not used as circulating fluid. Water is mainly used in flat-plat collectors.

1. Evacuated flat-plate solar collectors are a type of _
a) concentrating collectors
b) photovoltaic technology
c) non-concentrating collectors
d) solar stills

Explanation: Evacuated flat-plate solar collectors are a type of non-concentrating collectors. Solar stills and photovoltaic technology are not solar collectors.

1. Which of the following are used as absorbers in evacuated-tube solar collectors?
a) Carbon tubes
b) Wooden or metallic tubes
c) Plastic or glass tubes
d) Metallic or glass tubes

Explanation: Metallic or glass tubes are used as absorbers in evacuated-tube solar collectors. Wood and plastic are thermal insulators and hence, cannot be used to create passageways for the heat carrying circulating fluid.

1. What is a heat pipe?
a) A heat-transfer device
b) A pipe made of heat
c) A pipe that consists of heat
d) A heat pumping device

Explanation: A heat pipe is a heat-transfer device. It combines the principles of thermal conductivity and phase transition to effectively transfer heat between two solid interfaces.

1. For better efficiency, solar collectors do not coat their transparent cover with an anti-reflective coating.
a) True
b) False

Explanation: For better efficiency, solar collectors coat their transparent cover with an anti-reflective coating. The anti-reflective coating reduces the amount of reflection dramatically. Thus, the amount of sunlight collected is increased.

1. Evacuated tube solar collectors use a glass tube to surround absorber with high vacuum.
a) True
b) False

Explanation: Evacuated tube solar collectors use a glass tube to surround absorber with high vacuum. This is used to effectively resist atmospheric pressure and reduce conductive and convective losses.

## Solar Energy Questions and Answers – Solar Collectors – 2

Solar Energy Multiple Choice Questions & Answers (MCQs) focuses on “Solar Collectors – 2”.

1. Which of the following is used to make a glass-glass evacuated tubes?
a) Borosilicate glass
b) Carbon
c) Wood
d) Plastic coating

Explanation: As the name suggests, glass-glass evacuated tubes is a type of evacuated-tube solar collector. It is made up of two borosilicate glass tubes fused together at one or both ends.

1. Which of the following is a problem with evacuated tubes?
a) Underheating
b) Overheating
c) Poor absorption of sunlight
d) Poor reception of sunlight

Explanation: Overheating is a common problem with evacuated-tube solar collector. This is because of the high temperatures of the circulating fluid caused by collection of large amount of sunlight.

1. Why does flat plate collector perceived to have higher efficiency than evacuated tube solar collector in terms of area?
a) Because flat plate collector has a large installation area
b) Because evacuated tube collector is compact
c) Because of the vacuum gap in evacuated tube collectors
d) Because of the vacuum gap in flat plate collectors

Explanation: In terms of area, flat plate solar collectors are generally perceived to have a higher efficiency than evacuated-tube solar collectors. This is because of the vacuum gap in evacuated tube collectors which increases their net occupied area.

1. _ lose more heat to the environment than evacuated-tube solar collectors.
a) Photovoltaics
b) Solar stills
c) Solar air conditioners
d) Flat-plate collectors

Explanation: Flat-plate collectors lose more heat to the environment than evacuated-tube solar collectors. Photovoltaics, solar stills and solar air conditioners are not solar collectors.

1. Which of the following are combined to form an evacuated flat plate solar collector?
a) Flat plate solar collectors and evacuated-tube solar collectors
b) Flat plate solar collectors and bowl collectors
c) Bowl collectors and evacuated-tube solar collectors
d) Polymer collectors and bowl collectors

Explanation: Evacuated flat plate collectors combine the technologies of both, flat plate solar collectors and evacuated-tube solar collectors. There are not a combination of bowl and polymer type collectors.

1. Which of the following provides highest energy conversion efficiency in non-concentrating solar collectors?
a) Flat plate collectors
b) Evacuated flat plate collectors
c) Evacuated-tube collectors
d) Parabolic collectors

Explanation: Evacuated flat plate collectors provide the highest energy conversion efficiency in non-concentrating solar collectors. Parabolic collector is not a non-concentrating collector.

1. What is the metal sheet absorber surrounded with in an evacuated flat plate collector?
a) Low volume inside flat envelope
b) Low vacuum inside curved envelope
c) High vacuum inside flat envelope
d) Low vacuum inside thick curved envelope

Explanation: In an evacuated flat-plate solar collector, the metal sheet absorber is surrounded with a high vacuum. This is then placed inside a flat envelope made of glass and metal.

1. Which of the following organisations developed first high vacuum insulation?
a) NASA
b) IIT
c) Stanford
d) CERN

Explanation: CERN developed the first collector making use of high vacuum insulation. However, the first company to commercialise the technology was TVP SOLAR SA of Switzerland.

1. Why does an evacuated flat plate collector require a glass-metal seal?
a) To join the glass plate to the rest of metal envelope
b) To join the glass plate to a part of metal envelope
c) To disconnect the glass plate to the rest of plastic envelope
d) To disconnect the glass plate to the rest of metal envelope

Explanation: An evacuated flat plate collector requires a glass-metal seal. This is to join the glass plate to the rest of metal envelope. It also requires an internal structure to support such a plate against atmospheric pressure.

1. Which of the following pumps is used in an evacuated-tube solar collector?
a) Non-evaporable getter
b) Flash getter pump
c) Heat pump
d) Water pump

Explanation: Evacuated flat-plate solar collectors use a barium flash getter pump. This pump is used to keep the internal pressure stable throughout the operation. They do not use non-evaporable getter pumps.

1. Evacuated flat-plate solar collectors use _ pumps.
a) Heat pump
b) Flash getter pump
c) Non-evaporable getter
d) Internal combustion

Explanation: Evacuated flat-plate solar collectors use non-evaporable getter (NEG) pumps to keep the internal pressure stable throughout the operation. This pump enables some regeneration in-situ by exposure to sunlight.

1. What advantage does polymer collector have over metal collector?
a) Better sales as they are produced in Europe
b) Poor sales as they are produced in Europe
c) They cannot be used in cold climate
d) They can be used in cold climate

Explanation: The primary advantage of a polymer collector over a metal collector is that they can be used in cold regions with low temperatures. This is because they are freeze-tolerant. Whether they are manufactured in Europe or not does is neither an advantage nor a disadvantage.

1. Bowl collectors operate similarly to _
a) parabolic dish
b) flat plate collector
c) evacuated-tube collector
d) evacuated flat tube collector

Explanation: Bowl collectors operate similarly to a parabolic dish. However, they have a fixed receiver unlike a parabolic dish. This reduces efficiency but is much cheaper to build and operate.

1. Polymer flat plate collectors can use plain water.
a) True
b) False

Explanation: Polymer flat plate collectors can use plain water. This is because they are freeze-tolerant and do not require antifreeze agents to prevent water from solidifying.

1. Bowl collectors use a fixed curved receiver.
a) True
b) False

Explanation: Bowl collectors use a fixed curved receiver. They have a fixed spherical mirror with a tracking receiver.

## Solar Energy Questions and Answers – Solar Water Heater

Solar Energy Multiple Choice Questions & Answers (MCQs) focuses on “Solar Water Heater”.

1. What is solar water heater?
a) Use solar energy to heat water
b) Use solar energy to generate current which is then used to heat water
c) Use water to generate heat
d) Use solar energy to generate steam

Explanation: Solar water heater is a system that converts sunlight into heat. This heat is then used to heat water. As the water gets heated, steam may be produced but the purpose of solar water is to heat water and not produce steam. It does not generate current.

1. Which of the following determines complexity and size of solar water heating system?
a) Food
b) Changes in ambient temperature
c) Chemicals

Explanation: Changes in ambient temperature during day-night cycle is one of the factors that determines the complexity and size of solar water heating system. Food, chemicals and solar radiation constant does not influence the complexity and size of the system.

1. What is freeze protection in a solar water heating system?
a) Ensures that the system is frozen
b) Prevents the operation of drainback system
c) Prevents damage to system due to freezing of transfer fluid
d) Ensures that the transfer fluid is frozen

Explanation: Freeze protection in a solar water system prevents the system being damaged due to freezing of transfer fluid. It does not prevent the operation of drainback system.

1. What are drainback systems in solar water heating system?
a) The system that reverses the direction of flow of transfer fluid
b) The system that tracks the sun
c) The system that pumps excess transfer fluid
d) The system that drains the transfer fluid

Explanation: Drainback systems are systems that drain the transfer fluid particularly to ensure freeze protection. This prevents the freezing of transfer fluid and any unwanted damage to the system.

1. How does freeze-tolerance work?
a) By expansion of pipes carrying transfer fluid
b) By compression of pipes carrying transfer fluid
c) By increasing the temperature of pipes carrying transfer fluid
d) By increasing the pressure inside pipes carrying transfer fluid

Explanation: Freeze-tolerance works by expansion of pipes carrying the transfer fluid. The low pressure pipes are made of silicone rubber that expands on freezing.

1. Which of the following metals are used to make pipes of low cost solar water heating system?
a) Gold
b) Copper
c) Polymer
d) Silver

Explanation: Copper is used to make pipes of low cost solar water heating systems. Though silver and gold are good thermal conductors they are expensive. Polymer is not a metal.

1. Direct solar water heating systems __
a) offer great overheating protection
b) are called pumped systems
c) offer no overheating protection
d) offer great freeze protection

Explanation: Direct solar water heating systems are also called compact systems. They offer little or no overheating protection unless they have a heat export pump.

1. How is the heat transferred from transfer fluid to potable water in indirect solar water heating systems?
a) By directly exposing the substance to sunlight
b) By using an electrical heater
c) By circulating potable water through the collector
d) By using heat exchanger

Explanation: An indirect solar water heating system uses a heat exchanger to transfer heat from the transfer fluid to the potable water. It does not expose the transfer fluid directly to the sunlight and does not use an electrical heater.

1. How is water heated in a direct solar water heating system?
a) By circulating potable water through the collector
b) By directly exposing water to sunlight
c) By using convection from a different transfer fluid
d) By using heat exchanger
2. Passive systems rely on heat-driven convection.
a) False
b) True

Explanation: Passive systems rely on heat-driven convection. If not, they also use heat pipes to circulate the working fluid through the collector and heat it. Hence, they are cheap and are easily maintained.

1. Which of the following is an example of direct solar water heating system?
a) Pressurised antifreeze system
b) Pumped systems to circulate transfer fluid
c) Convection heat storage system
d) Drainback system

Explanation: Convection heat storage system is similar to an integrated collector storage system. Both these systems are examples of direct solar water heating systems. Renewable Energy Multiple Choice Questions

1. How is the heat transfer fluid (HTF) heated in bubble pump systems?
a) By subjecting the closed HTF circuit to high pressure
b) By subjecting the closed HTF circuit to high pressure and by increasing the volume
c) By subjecting the closed HTF circuit to low pressure and by decreasing the volume
d) By subjecting the closed HTF circuit to low pressure

Explanation: In a bubble pump system, the heat transfer fluid circuit is subjected to a low pressure. This causes the liquid to boil at low temperatures as the sun heats it. The volume is not changed.

1. Batch collectors reduce heat loss by thermally insulating the storage tank.
a) True
b) False

Explanation: Batch collectors reduce heat loss by thermally insulating the storage tank. This is done by covering the tank in a glass-topped box that allows heat from sun to reach the water tank and traps it – greenhouse effect.

1. Overheat protection is done by passing hot water through collector during night.
a) False
b) True

Explanation: Overheat protection is done by passing hot water through collector during night or when there is less sunlight. This is extremely effective in direct or thermal store plumbing and ineffective in evacuated-tube collectors.

## Solar Passive Space – Heating and Cooling Systems

Solar Energy Multiple Choice Questions & Answers (MCQs) focuses on “Solar Passive Space – Heating and Cooling Systems”.

1. What is solar heating and cooling?
a) Use solar energy to regulate the internal temperature of a given space
b) Use solar energy to regulate the temperature of environment
c) Use solar energy to monotonically increase the internal temperature of a given space
d) Use solar energy to monotonically decrease the temperature of a given space

Explanation: Passive solar heating and cooling, also called as passive solar design uses solar energy to regulate the internal temperature of a given space. The space is essentially some kind of closed/isolated area.

1. Which of the following is used to regulate temperature in solar heating and cooling system?
a) Air conditioners
b) Specific building systems
c) Water heaters
d) Room heaters

Explanation: Building systems designed specifically for a solar heating and cooling system is used to regulate the temperature of a given space. It could be done with the help of temperature controlling systems like an air conditioner embedded into the building.

1. Which of the following is not used in a passive solar heating/cooling system?
a) Building walls
b) Building roofs
c) Air conditioners
d) Building floors

Explanation: Air conditioners are not used in a passive solar heating and cooling system. This is simply because the system is passive. Wall, floors and roofs are included in a passive system?

1. What is a passive solar heating and cooling system?
a) Uses building design with mechanical systems to regulate the temperature outside a given space
b) Uses building design with mechanical systems to monotonically increase the temperature inside a given space
c) Uses building design without any solar heating (and cooling) system to regulate the temperature outside a given space
d) Uses building design without any solar heating (and cooling) system to regulate the temperature inside a given space

Explanation: As the name suggests, a passive solar heating and cooling system does not use any kind of active system. Instead, it uses building design without any solar heating (and cooling) system to regulate the temperature inside a given space.

1. Which of the following is extremely important with respect to a passive solar heating and cooling system?
a) Materials used to construct the building
b) Electrical systems used to perform heating/cooling operation
c) Mechanical systems used to perform heating/cooling operation
d) Material used to build heating/cooling systems

Explanation: A passive solar heating and cooling system does not consist of any active element. Hence, materials used to construct the building plays a major role in regulating the amount of heat trapped within the room.

1. Which of the following is an example of passive solar technology?
a) Photovoltaic
b) Solar furnace
c) Active solar water heating systems
d) Solar thermo-mechanical systems

Explanation: Solar furnace is a well known example of passive solar technology. It uses concentrated solar power to generate high temperatures for industrial purposes. Active solar water heating systems and solar thermo-mechanical systems are active systems.

1. What is a sunroom?
a) A room with a sun fitted inside it
b) A room that does not allow sunlight to pass through it
c) A room that transmits a lot of sunlight and has a scenic view
d) A room that does not pass sunlight and has a scenic view

Explanation: A sunroom, also known as a solarium is a room that permits a lot of sunlight through it. It also has a beautiful scenic view for recreational purposes. This is an example of a passive solar technology.

1. Which of the following process is involved in heat transfer through building?
a) Seebeck effect
b) Peltier effect
c) Hall effect
d) Conduction

Explanation: Heat transfer in buildings occurs through conduction, convection and radiation. Seebeck effect and Peltier effect are about an electric potential difference due to thermal gradient and Hall effect are not related to heat transfer.

a) Roof
b) Side walls
c) Floor
d) Doors

Explanation: When compared to side walls, floor and doors, roofs receive majority of solar radiation. The heat from sun flows into the building mainly through radiation and supported by convection and conduction.

1. Which of the following is a site-specific design consideration for a passive solar heating and cooling system?
a) Orientation of the building
b) Latitude
c) Building window size
d) Placement of rooms

Explanation: Site specific design considerations are dependent on the location of the site. Hence, latitude, sun path and insolation are some examples of site-specific design considerations.

1. Which of the following is a design element for residential buildings in temperate and tropical climates?
a) Latitude
b) Diurnal variations in temperature
c) Using thermal mass to store excess solar energy during winter
d) Obstacles

Explanation: Using thermal mass to store excess solar energy during winter is a design element for residential buildings in temperate and tropical climates. Thermal mass is a property of the mass of a building to store heat. Latitude, obstacles and diurnal variations in temperature are site-specific design considerations.

1. A building with excessive glass cover __
a) results in freezing
b) results in a pleasant temperature within the building
c) damages the building material
d) results in overheating

Explanation: A building with excessive glass cover results in overheating. This is basically due to trapping of heat within the building and is explained by greenhouse effect. It will not result in freezing.

1. A solar roof constructed on a building uses water stored __ to temper hot and cold internal temperatures of the building.
a) on building roofs
b) on building walls
c) beneath building floors
d) on an auxiliary building

Explanation: A solar roof constructed on a building uses water stored on building roofs to temper hot and cold internal temperatures of the building. It is also called as roof pond passive solar heating system and is usually deployed in desert environments.

1. A “cool roof” uses reflective surfaces.
a) False
b) True

Explanation: A “cool roof” uses reflective surfaces. This is to ensure that major amount of the incident solar radiation is reflected back and the temperature within the building is maintained. Green roof is another variation that uses vegetation instead of reflective surfaces.

## Solar Energy Questions and Answers – Solar Industrial Heating Systems

Solar Industrial Heating Systems”.

1. Which of the following is/are applications of solar heating systems?
a) Pasteurisation and drying
b) Wetting
c) Rainfall
d) Battery and capacitor technology

Explanation: Pasteurisation and drying are applications of solar heating systems. Battery and capacitor technology are used to store energy from various sources like wind, sun, geothermal, etc. Wetting and raining are not applications of solar heating systems.

1. What is a solar heating system?
a) A system which uses heat to generate sunlight
b) A system which uses sunlight to generate heat
c) A system which uses earth’s heat to generate sunlight
d) A system which uses earth’s heat to generate electricity

Explanation: A solar heating system is a system which uses sunlight to generate heat. This heat can either be directly used or converted to other usable forms of energy like electricity. Geothermal energy is using earth’s heat to generate usable forms of energy.

1. What solar thermal technologies are useful for industrial processes?
a) Photovoltaics and solar air collectors
b) Solar air collectors and geothermal energy
c) Solar air collectors and solar water systems
d) Geothermal and photovoltaics

Explanation: Solar air collectors, solar water systems and solar concentrators are three well known solar thermal technologies used in industrial processes. Geothermal energy and photovoltaics are not solar thermal processes.

1. Which industry primarily uses solar air collectors?
a) Industries manufacturing plastic
b) Industries melting metals
c) Semiconductor industry
d) Food processing industry

Explanation: Food processing industry primarily uses solar air collectors. They replace traditional gas or oil-based drying in the industry. Melting metals requires extremely high temperatures that are not provided by solar air collectors.

1. How does using a solar air collector benefit food processing industry?
a) Reduce gas-or-oil-based drying and/or reduce food spoilage
b) Reduce food spoilage and increase gas-or-oil base drying
c) Increase food spoilage
d) Increase gas-or-oil-based drying and/or increase food spoilage

Explanation: Solar air collectors benefit food processing industry in many ways. They primarily reduce gas-or-oil-based drying and/or reduce food spoilage due to open air drying. Also, they can be built locally and their cost depends on local building materials and labor.

1. Which of the following is a conventional solar water system?
a) Solar air collectors
b) Flat-plate collectors
c) Parabolic dish collectors
d) Linear Fresnel collectors

Explanation: Conventional solar water systems consists of flat-plate collectors (FPC) or evacuated tube collectors (ETC). Solar air collectors are not solar water system.

1. Which application is best suited for a solar water system?
a) Food industry
b) Semiconductor industry
c) Residential applications

Explanation: Solar water systems are best suited for residential applications and if required can be installed on rooftops to meet temperature demands upto 125 degree Celsius. Solar air collectors are mainly used in food industries.

1. Which of the following are types of solar concentrators?
a) Solar air collectors
b) Flat-plate collectors
c) Parabolic flat plate collectors
d) Linear Fresnel collectors

Explanation: Solar concentrators include parabolic dish collectors, linear Fresnel collectors and linear parabolic trough collectors. Solar air collectors are not a type of solar concentrators. There is no such thing as parabolic flat plate collector because the shape can either be parabolic or flat.

1. What is a solar cooling technology?
a) Sun’s thermal energy is transferred to a heat transfer fluid which passes through a heat exchanger
b) Sun’s thermal energy is transferred to a heat transfer solid which passes through a heat exchanger
c) Sun’s nuclear energy is transferred to a heat transfer fluid which passes through a cold exchanger
d) Sun’s thermal energy is transferred to a heat transfer fluid which passes through a cold exchanger

Explanation: A solar cooling technology is a system that transfers sun’s thermal energy to a heat transfer fluid (also called as working fluid). This fluid then passed through a heat exchanger where the heat is moved from one system to another thereby achieving cooling.

1. Which of the following is an example of solar air heating/collection technology?
a) Drying food using hair dryer
b) Drying food under direct sun
c) Heating the food in oven
d) Grilling food in a barbeque

Explanation: Drying food under direct is one of the simplest and naturally occurring techniques of solar air heating. Drying food using hair dryer is not a solar air heating technology as electricity is used to run the hair dryer.

1. Which of the following groups are types of solar drying technology?
a) Indirect, direct and active, photovoltaic
b) Photovoltaic, direct and indirect, active
c) Indirect, direct and active, passive
d) Indirect, passive and active, direct

Explanation: Solar drying technology can broadly be grouped into indirect/ direct and active/passive technologies. Directly drying under the sun is an example of direct drying. Photovoltaic is not a solar drying technology.

1. Active solar drying systems control _ by fans.
a) water flow rate
b) food flow rate
c) electricity
d) air flow rate

Explanation: Active solar drying systems control air flow rate by fans. They can reduce drying time by a third and are compact. However, they require more electricity to operate machines like fans.

1. Solar air collectors transfer sun’s thermal energy to air via __
a) conduction
b) convection
c) Seebeck effect
d) Peltier effect

Explanation: Solar air collectors transfer sun’s thermal energy to air via conduction. Convection is the transfer of heat by movement of fluid between areas of different temperature. For this to happen, some region of air must first have a higher temperature which is achieved by conduction.

1. Solar concentrators are used for temperatures beyond 500 degree Celsius.
a) True
b) False

Explanation: Solar concentrators are used for temperatures beyond 500 degree Celsius. Such industrial applications include generation of electricity or melting metals.

1. Solar heat industrial systems are used for desalination.
a) True
b) False

Explanation: Solar heat industrial systems are used for desalination. They are thermally driven systems with operating temperatures around 110 degree Celsius. Desalination is the process of removing minerals from saline water.

## Solar Energy Questions and Answers – Solar Refrigeration and Air-Conditioning Systems – 1

1. Which of the following are types of photovoltaic refrigeration?
a) Vapour compression refrigeration and thermoelectric refrigeration
b) Vapour compression refrigeration and vapour jet refrigeration
c) Photovoltaics and concentrated solar power systems
d) Rankine cycle and vapour jet refrigeration

Explanation: Vapour compression refrigeration and thermoelectric refrigeration are types of photovoltaic refrigeration. Photovoltaic is used to perform solar refrigeration. Like Rankine Cycle and concentrated power systems, it is not a type of refrigeration.

1. What is a solar powered refrigerator?
a) A refrigerator that is directly sourced by electricity
b) A refrigerator that is sourced by solar energy
c) A refrigerator that is sourced by wind and sun
d) A refrigerator that is sourced by biomass and sun

Explanation: A solar powered refrigerator is a refrigerator that is sourced by solar energy. Photovoltaics or solar thermal energy is used to convert solar energy into a usable form (electricity) for refrigeration.

1. What is refrigeration?
a) A process where is work is done is to add heat from one system to another
b) A process where heat is used by the system to do work
c) A process where work is done to move heat from one system to another
d) A process where work is done to add cold air into the system

Explanation: Refrigeration is a process in which work is done to (re)move heat from one system and add it to another. This results in temperature decrement in the system from which heat was (re)moved.

1. What are the types of popular refrigeration systems?
a) Vapour compression and vapour adsorption
b) Vapour adsorption and vapour absorption
c) Vapour compression and liquid compression
d) Vapour compression and vapour absorption

Explanation: Refrigeration systems are broadly classified into vapour compression (VCR) and vapour absorption systems (VAR). Liquids are not compressed in refrigerating systems.

1. Vapour compression refrigeration systems use __ energy to perform compression.
a) mechanical
b) thermal
c) gravitational
d) nuclear

Explanation: Vapour compression refrigeration systems use mechanical energy. The electrical energy is converted into mechanical energy to perform the process of compression. Renewable Energy Mcq

1. What type of energy does vapour absorption refrigeration system use?
a) mechanical
b) thermal
c) nuclear
d) electrodynamic

Explanation: Vapour absorption refrigeration systems use thermal energy. The electrical energy is converted into thermal energy to perform the process of absorption.

1. Which of the following refrigeration systems are used in air-conditioning systems?
a) Vapour absorption
b) Vapour jet
c) Vapour compression

Explanation: Vapour absorption refrigeration systems are used in air-conditioning systems. It is also used in domestic and commercial refrigerators, large-scaled warehouses for storing food items by freezing.

1. Which of the following best describes the process of vapour compression refrigeration?
a) Warm air → compressor → condenser → expansion valve → evaporator → colder air
b) Evaporator → compressor → condenser → expansion valve → evaporator → colder air
c) Warm air → compressor → expansion valve → evaporator → colder air
d) Warm air → evaporator → compressor → condenser → expansion valve → evaporator → colder air

Explanation: In vapour compression refrigerator, warm air is first evaporated and then passed into a compressor. This compresses the vapour which is then passed through a condenser to obtain a liquid. The liquid is expanded through an expansion valve to form a combination of liquid and vapour which is then passed through an evaporator to obtain cold air.

1. What does a refrigerant do in a vapour compression refrigeration system?
a) Removes heat from one system and empties it into another system
b) Adds heat to the system
c) Absorbs heat continuously
d) Converts thermal energy into electrical energy

Explanation: A refrigerant in a vapour compression refrigeration system removes heat from one system and empties it into another system. It is a circulating liquid that basically performs operation of “refrigeration”.

1. Which of the following is an example of a refrigerant?
a) Platinum
b) CFCs
c) Argon
d) Nitrogen

Explanation: CFCs are common examples of refrigerants. Freons like R-11, R-12, R-21, R-22 and R-502 are also used. Platinum, Argon and Nitrogen are not used as refrigerants.

1. How does a photovoltaic refrigeration system work?
a) By converting sun’s thermal energy into electricity which is used to drive a motor coupled to a compressor
b) By converting sun’s thermal energy into electricity which is used to drive an AC motor coupled to a compressor of a vapour compression system
c) By converting sunlight into DC current to drive a DC motor which is coupled to a compressor of a vapour compression system
d) By converting sunlight into DC current which is used to drive an AC motor coupled to a compressor of a vapour compression system

Explanation: A photovoltaic refrigeration system works by converting sunlight into DC current. This DC current drives a DC motor which is coupled to a compressor of a vapour compression system.

1. It is important to ensure that _ characteristics of motor matches that of PV array.
a) mechanical
b) thermal
c) insulating
d) electrical

Explanation: It is important to ensure that electrical characteristics of motor matches that of PV array. This is to ensure that the power delivered by the PV array sufficient to drive the motor which in turn drives the system.

1. How does the compression process between vapour compression and vapour absorption systems differ?
a) Vapour compression uses mechanical compression while vapour absorption uses thermal compression
b) Vapour compression and vapour absorption use thermal compression
c) Vapour compression and vapour absorption use thermal compression
d) Vapour compression uses electrical compression while vapour absorption uses mechanical compression

Explanation: The compression processes differ in the compression technique and energy conversions. Vapour compression uses mechanical compression while vapour absorption uses thermal compression.

1. Solar thermal energy is used to perform vapour absorption refrigeration.
a) True
b) False

Explanation: Solar thermal energy is used to perform vapour absorption refrigeration. Since vapour absorption refrigeration uses thermal compression, the thermal energy is directly used to extract heat from the working fluid.

1. Freon is a trade for a family of haloalkane refrigerants.
a) True
b) False

Explanation: Freon is a trade for a family of haloalkane refrigerants manufactured by DuPont. Haloalkanes are derivatives of alkanes containing one or more halogens like chlorine, fluorine, etc.

## Solar Energy Questions and Answers – Solar Refrigeration and Air-Conditioning Systems – 2

1. Solar air conditioning system uses _ as its energy source.
a) sun
b) wind
c) electricity
d) motor

Explanation: Solar air conditioning system uses sun as its energy source. It is just like any other air conditioning system except that it uses solar power. A motor is not an energy source. Solar energy is converted to electricity to run the system.

1. Which of the following types of solar energy can be used to source air conditioning systems?
a) Passive solar and wind
b) Passive solar and photovoltaics
c) Vapour compressor and photovoltaics
d) Wind and solar thermal energy

Explanation: Passive solar, solar thermal energy and photovoltaics can be used to source air conditioning systems. Wind and vapour compressor are not types of solar energy.

1. What are the three heat exchangers used in an absorption type refrigeration?
a) Compressor, absorber and generator
c) Absorber, regenerating intermediate heat exchanger and generator

Explanation: The three heat exchangers used in an absorption type refrigeration system are absorber, regenerating intermediate heat exchanger and generator. These heat exchangers replace the compressor in a vapour compression refrigeration system.

1. What is the working fluid in vapour absorption type systems?
a) Platinum
b) CFCs
c) Freons
d) Ammonia

Explanation: Ammonia or lithium bromide is the working fluid in vapour absorption type systems. CFCs and freons are used in vapour compression type systems and are called refrigerants. Platinum is not used as a working fluid.

1. Absorption of ammonia in a liquid solution analogous to _
a) condensation
b) evaporation
c) vapourisation
d) convection

Explanation: Absorption of ammonia in a liquid solution is analogous to condensation process. Evaporation and vapourisation concern with liquids turning into gas. Convection is a process of heat flow. Renewable Energy Mcq

1. Which of the following best describes the process of vapour absorption refrigeration?
a) Absorbing fluid vapour into liquid carrier → producing vapours from solution by heating → thus cooling → pumping into a high pressure cycle
b) Absorbing fluid vapour into liquid carrier → pumping into a high pressure cycle → producing vapours from solution by heating → thus cooling
c) Absorbing fluid vapour into liquid carrier → thus cooling → pumping into a high pressure cycle → producing vapours from solution by heating
d) Absorbing fluid vapour into liquid carrier → producing vapours from solution by heating → thus cooling → pumping into a high pressure cycle

Explanation: The working fluid is absorbed into a liquid carrier which is then pumped into a high pressure cycle. This cycle produces vapours from solution by heating thereby cooling.

1. Which of the following use absorption refrigeration system?
a) Heating systems
b) Solar cooker
c) Waste heat from cogeneration
d) Solar stills

Explanation: Absorption refrigeration systems are used in large commercial and industrial installations. For instance, waste heat from cogeneration or process steam plants.

1. Which of the following is/are considered for calculating the overall efficiency of solar absorption refrigeration system?
a) Coefficient of performance of absorption system
b) Solar collection efficiency
c) Solar insolation
d) Solar collection efficiency and coefficient of performance of absorption system

Explanation: Solar collection efficiency and coefficient of performance of absorption system are considered for calculating the overall efficiency of a solar absorption refrigeration system. One can assume the solar insolation to be fairly constant and hence does not contribute towards efficiency calculation.

1. What is coefficient of performance?
a) Ratio of refrigeration capacity to input solar energy
b) Ratio of input solar energy to refrigeration capacity
c) Product of input solar energy and refrigeration capacity
d) Ratio of refrigeration capacity to input electrical energy

Explanation: Coefficient of performance can be defined as the ratio of refrigeration capacity to input solar energy. It basically describes the efficiency of the refrigerating system as it compares the input to output.

1. In solar vapour compression cycle, efficiency of Rankine cycle increases with _
a) decrease in temperature of heat exchanger
b) increase in temperature of heat exchanger
c) the amount of heat supplied to the evaporator
d) the amount of cold air released from the system

Explanation: In solar vapour compression cycle, efficiency of Rankine Cycle increases with increase in temperature of heat exchanger. It does not depend on the amount of heat supplied to the evaporator and the amount of cold air released.

1. Efficiency of solar collector decreases with __
a) decrease in temperature of heat exchanger
b) increase in temperature of sun
c) increase in temperature
d) the amount of cold air given to the system

Explanation: Efficiency of solar collector decreases with increase in temperature. This is because as the temperature of the working fluid increases, the difference between its maximum heating temperature and the current running temperature decreases. This decreases the ability to hold more heat.

1. Absorption refrigeration uses _ mechanical power input as compared to vapour compression refrigeration.
a) greater
b) the same
c) the same working fluid as
d) negligible

Explanation: Absorption refrigeration uses negligible mechanical power input as compared to vapour compression refrigeration. Ammonia is used as working fluid in absorption refrigeration.

1. How is pressurization achieved in absorber refrigeration?
a) By dissolving refrigerant in absorbent in the absorber section
b) By dissolving refrigerant in absorbent in the evaporation section
c) By evaporating refrigerant from absorbent in the absorber section
d) By evaporating refrigerant in absorbent in the evaporation section

Explanation: In absorber refrigeration, pressurisation is achieved by dissolving refrigerant in absorbent in the absorber section. Evaporator section is used to evaporate the refrigerant.

1. In absorber refrigeration, the solution of working fluid (ammonia) is pumped to a low pressure with a big pump.
a) True
b) False

Explanation: In absorber refrigeration, the solution of working fluid (ammonia) is pumped to a high pressure. This is done with the help of a small/ordinary pump.

1. Vapour compression refrigeration system is less complex than absorber refrigeration system.
a) True
b) False

Explanation: Vapor compression refrigeration system is less complex than absorber refrigeration system. This is because the absorber refrigeration system uses thermal compression and not mechanical compression.

## Solar Energy Questions and Answers – Solar Cookers – 1

1. What is solar cooker?
a) Uses direct sunlight to produce heat and cook food
b) Uses solar energy to evaporate water and collect it within the same closed system
c) Uses solar energy to dry substances
d) Uses concentrated solar power to for industry

Explanation: Solar cookers are devices that use direct sunlight to produce heat and cook food. Solar dryers are devices that use solar energy to dry substances. Devices that use solar energy to evaporate water and collect its condensate within the same closed system are called solar stills.

1. What is pasteurization?
a) Process of treating water by biological techniques
b) Process of treating water by heating it mildly
c) Process of producing water
d) Process of capturing sun’s heat

Explanation: Pasteurization is the process of treating water, packaged and non-packaged food by heating it mildly. This is done to eliminated pathogens and extend shelf life.

1. Which of the following principles is used to concentrate sunlight in solar cookers?
a) Rarefaction
b) Evaporation
c) Specular reflection

Explanation: Specular reflection is used to concentrate sunlight in solar cookers. Evaporation is the process of liquid, particularly water turning into gas. Rarefaction is the reduction in density of air or gas.

1. Which of the following majorly affects the phenomenon of concentrating sunlight?
a) Non-reflecting surface
b) Black surface
c) Type of food
d) Geometry of the reflecting structure

Explanation: Geometry of the reflecting structure majorly affects the phenomenon of concentrating sunlight. The amount of sunlight being concentrated can be controlled by the geometry of the reflecting structure.

1. What is the typical temperature (range) used in domestic cooking? Note that C indicates Celsius.
a) 50 – 70 degree C
b) 1000 degree C
c) 3500 degree C
d) 300 – 500 degree C

Explanation: The typical temperature used in domestic cooking is around 65 degree C. It falls in the range of 50 – 70 degree C. Temperatures beyond 1000 degree C are used for industrial purposes.

1. What is the maximum temperature used in cooking? Note that C indicates Celsius
a) 100 degree C for boiling water and related dishes
b) 400 degree C for grilling and searing
c) 800 degree C for melting metals
d) 30 degree C for melting food items like butter

Explanation: The maximum temperature used in cooking is 400 degree C for grilling and searing purposes. Boiling water and melting food items like butter do not require temperatures beyond 100 degree C. Temperatures beyond 500 degree C are used in industries.

1. The cooking pan used in solar cookers convert _ energy to _ energy.
a) electrical, heat
b) heat, light
c) light, heat
d) electrical, light

Explanation: The cooking pan used in solar cookers convert light energy to heat energy. After reflecting and concentrating the light onto the cooking pan, the pan conducts heat to cook the required food/substance.

1. Which of the following materials are used to make the cooking pan in a solar cooker?
a) Wood
b) Plastic
c) Rubber
d) Iron

Explanation: Iron is a good conductor of heat. It is used to make the cooking pan to heat food in a solar cooker. Wood, plastic and rubber are thermal insulators in Renewable Energy Mcq

1. Which of the following are used to manufacture parabolic dish concentrator?
a) Anodized aluminum
b) Wood
c) Bakelite
d) Iron

Explanation: Parabolic dish (and trough) are made of anodized aluminum (or coated with aluminum) to reflect sunlight and concentrate it onto a receiver. Wood, iron and bakelite are not used as they do not have reflective properties. Moreover, wood and bakelite are thermal insulators.

1. Which of the following pot surfaces are preferred for solar cookers?
a) White coloured
b) Black coloured
c) Red coloured
d) Silver coloured

Explanation: Black coloured pot surfaces are best suited to be used on cooking pans of solar cookers. This is because black absorbs most amount of heat as compared to any other colour. White, aluminum and silver coated surfaces are good reflectors of light and heat.

1. Convection should be reduced by isolating air inside the cooker from air outside the cooker.
a) True
b) False

Explanation: Convection should be reduced by isolating air inside the cooker from air outside the cooker. This is to prevent escape of heat via convection.

1. Covering the pot with a glass lid __ convection.
a) increases
b) does not affect
c) changes the direction of
d) reduces

Explanation: Covering the pot with a glass lid reduces convection. This results in a greenhouse effect thereby trapping heat to cook the food inside the pot.

1. Evacuated tube solar cookers use __ glass tube for the cooking chamber.
a) highly insulated
b) thermal conducting
c) parabolic
d) cone shaped

Explanation: Evacuated tube solar cookers use highly insulated double-wall glass tube for the cooking chamber. They do not require large reflectors to concentrate sunlight.

1. Which of the following best describes the working of a solar cooker?
a) Concentrating sunlight → trapping heat → cooking
b) Concentrating sunlight → converting light to heat energy → trapping heat →cooking
c) Concentrating sunlight → cooking → trapping heat
d) Trapping heat → converting heat to light energy → radiating light → cooking

Explanation: Sunlight is concentrated onto a receiver by reflective surfaces of the structure. This light is converted to heat by the receiver. The heat is then trapped by the pots used for cooking.

1. Solar cookers do have operating costs.
a) True
b) False

Explanation: Solar cookers have negligible or no operating costs. Since the entire system is built to be self-operating, it does not require any external fuel for initiation and operation.

## Solar Energy Questions and Answers – Solar Cookers – 2

1. In terms of cost, solar panel cookers use _ material.
a) low-cost
b) specially designed expensive
c) low-cost inefficient
d) expensive and extremely efficient

Explanation: In terms of cost, solar panel cookers use low-cost material. However, due to their low-cost material they can be easily constructed and are the most commonly used cookers.

1. What type is a solar panel cooker?
a) Absorber type
b) Reflector type
d) Convection type

Explanation: Solar panel cookers are reflector type cookers. They are the most type available due to their ease of construction and low-cost material.

1. How is sunlight concentrated in solar panel cooker?
a) From below the cooker onto the cooking pan
b) Using photovoltaics
c) From above
d) From right side

Explanation: Sunlight is concentrated from above and not from sides in solar panel cookers. This leads to limited cooking power and is not very desirable because of low efficiency. However, the solar panel cookers are some of the cheapest designs in the market.

1. What was CooKit?
a) A solar parabolic cooker
b) A solar box cooker
c) A vapour compressor
d) A solar panel cooker

Explanation: Cookit is a popular solar panel cooker. It was designed by Dr. Roger Bernard and is manufactured by cardboard and foil. Its main advantage was that it was affordable, convenient and effective.

1. Solar panel cookers are not effective under _
a) cloudy conditions
b) sunny conditions
c) dry and sunny conditions
d) desert conditions

Explanation: Solar panel cookers are not effective under cloudy conditions. Like any other technology using solar energy, it requires the sun to be shining brightly without any hinderance. Any hinderance drastically drops its effectiveness.

1. What type of solar cooker is a sun basket?
a) Solar panel cooker
b) Solar parabolic cooker
c) Solar box cooker
d) Vapour absorption compression

Explanation: Sun basket is a solar parabolic cooker. It is neither a solar panel nor a solar box cooker. Vapour absorption compression is a refrigeration technique used in refrigerators and not in solar cookers.

1. Which of the following materials are used to make sun basket?
a) Paper mache, parabolic mirror, gold and bakelite
b) Parabolic mirror, aluminum foil, paper mache and gold
c) Paper mache, aluminum foil, jute fabric and bamboo frame
d) Bamboo frame, parabolic mirror, gold rod for support and rubber for insulation

Explanation: A sun basket is basically a parabolic mirror made from paper mache supported by jute fabric and held in place by a bamboo frame. Aluminum foil is used as the reflecting lining and is glued to the inner side of the basket. Rubber and bakelite are thermal insulators. Gold is an expensive metal and is not used to make solar basket.

1. Solar basket is a/an __
a) active cooker
b) vapour compression technique
c) vapour absorption technique
d) passive cooker

Explanation: Solar basket is a passive cooker. Vapour compression and vapour absorption are compression techniques used in refrigeration. They are not related to solar cookers.

1. What is a solar box type cooker?
a) An insulated box with a transparent glass cover and reflective surface directing sunlight into the box
b) An insulated parabolic mirror which is used to reflect the sunlight onto the conduction pan
c) A thermal conducting box with a transparent glass cover and reflective surface directing sunlight into the box
d) A thermal conducting parabolic mirror which is used to reflect the sunlight onto the insulated pan

Explanation: A solar box type cooker is an insulated box with a transparent glass cover and reflective surface directing sunlight into the box. It is not a parabolic mirror type solar cooker.

1. Which of the following colours can be used to paint the insulated box in a solar box cooker?
a) White
b) Black
c) Silver
d) Pink

Explanation: The insulated box in a solar box cooker is painted black. This is because black maximizes absorption of sunlight. White is one of the best reflectors of sunlight and is not used for absorption.

1. What type of cooking containers are used to cook food on a solar cooker?
a) Gold
b) Wooden
c) Steel
d) Plastic

Explanation: Cooking containers made up of aluminum and/or steel are used to cook food on a solar cooker. Cooking containers made of thermal insulators like wood and plastic are not used. Gold is an expensive metal and is not used for this purpose.

1. To reduce heat loss, where are insulators used in a solar box cooker?
a) On the reflective material
b) On the cooking platform
c) Reflective materials are made of insulators
d) Space between the outer and inner box

Explanation: The space between outer and inner box in a solar box type cooker are thermally insulated to prevent any loss of heat. Cooking platform and reflective material are not made up of thermally insulating material.

1. Solar cooker takes __ to cook as compared to conventional cooking methods.
a) longer
b) less time
d) more electricity

Explanation: Solar cooker takes longer to cook as compared to conventional cooking methods. It need not convert sunlight into electricity. Also, it does not use electricity from the grid.

1. Solar cooking is pollution free.
a) True
b) False