# Solar Energy Questions and Answers – Solar Thermo-Mechanical Systems -1

This set of Solar Energy Multiple Choice Questions & Answers (MCQs) focuses on “Solar Thermo-Mechanical Systems -1”.

1. Which of the following best describes the flow of energy in a solar thermo-mechanical system?
a) Solar → thermal → mechanical → electricity
b) Electricity → thermal → mechanical → solar
c) Mechanical → solar → electricity → thermal
d) Solar → electricity → thermal → mechanical

Explanation: In a solar thermo-mechanical system, the solar energy is first converted to thermal energy. Then this energy is used to drive mechanical systems thereby being converted to mechanical energy. This mechanical energy is further converted to usable forms like electricity.

2. What is a heat engine?
a) System that converts thermal energy to mechanical energy
b) System that converts thermal and chemical energy to mechanical energy
c) System that converts mechanical energy to thermal energy
d) System that converts mechanical energy to thermal and chemical energy

Explanation: A heat engine is an energy converting system. It converts in the heat or thermal energy and chemical energy to mechanical. This mechanical energy can be used to do mechanical work.

3. How does heat engine convert thermal and chemical energy to mechanical energy?
a) With the help of steam
b) By converting the input energy into electrical energy which is then used to drive mechanical systems
c) By bringing a working substance from a higher state temperature to a lower state temperature
d) By converting the input electrical energy to mechanical energy

Explanation: The heat engine convert thermal and chemical energy to mechanical energy. It does this by bringing a working substance from a higher state temperature to a lower state temperature. During this conversion, any form of energy being used is not converted to electrical energy.

4. Which of the following is/are examples of heat engines?
a) Fuel cell vehicles
b) Fuel cell energy power plants
c) Photovoltaics and concentrating mirrors
d) Rankine cycle and Brayton cycle

Explanation: Rankine cycle and Brayton cycle are examples of heat engines. Photovoltaics and concentrating mirrors are not heat engines. Fuel cells are another type of source that convert chemical energy to electrical energy.

5. Which of the following is a popular solar thermal power system?
a) Central receiver thermal electric power system
b) Photovoltaics
c) Concentrating mirrors
d) Solar reflectors

Explanation: Central receiver thermal electric power system is a popular solar thermal power system. Photovoltaics are not solar thermal power systems. They directly convert solar energy to electrical energy. Concentrating mirrors and solar reflectors are components of various solar thermal power systems.
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6. Which of the following best describes the working of central receiver thermal power system?
a) Sunlight → heliostats absorb solar flux → central receiver → turbine system → electricity
b) Sunlight → heliostats reflect solar flux → central receiver → turbine system → electricity
c) Heliostats reflect solar flux → sunlight → turbine system → central receiver → electricity
d) Heliostats reflect solar flux → sunlight → central receiver → turbine system → electricity

Explanation: In a s central receiver thermal power system, the solar radiation from the incident sunlight is reflected by heliostats onto central receiver. The receiver consists of a boiler to boil the working fluid which is in turn used to drive the turbines to generate electricity.

7. What is the operating temperature of turbines in a central receiver thermal power system? Note that “C” stands for Celsius.
a) 10 – 100 degree C
b) 5000 degree C
c) 500 – 800 degree C
d) 200 – 500 degree C

Explanation: The typical operating temperature of the turbines in a central receiver thermal power system is between 500 – 800 degree C. The temperatures are so high because large concentrations of solar flux are reflected onto the central receiver by several arrays of heliostats (hundreds and sometimes even thousands).

8. Which of the following is a line focus collector used in a distributed power system?
a) Parabolic mirrors
b) Convex mirrors
c) Concave lenses
d) Linear fresnel reflector

Explanation: Linear fresnel reflector is a line focus collector. Parabolic mirrors and convex mirrors may reflect sunlight but they may not be line focused collector. Lenses are not used to collect sunlight in a distributed power system.

9. How is energy collected in a distributed power system?
a) Sunlight → line focused collectors → interconnecting pipes → heat engines → turbines → electricity
b) Line focused collectors → sunlight → interconnecting pipes → heat engines → turbines → electricity
c) Sunlight → line focused collectors → turbines → interconnecting pipes → heat engines → electricity
d) Interconnecting pipes → sunlight → line focused collectors → heat engines → turbines → electricity

Explanation: The solar radiation from the incident sunlight is collected by various line focused collectors. This energy is collected through pipes interconnecting the dispersed collector units and then supplied to the heat engines which in turn use the working substance to drive turbines and generate electricity.

10. The type of heat engine depends on _______
a) material of interconnecting pipes
b) type of collector
c) sunlight
d) photovoltaics

Explanation: The type of heat engine depends on the type collector, temperature of operation, cycle efficiency, working fluid, conversion efficiency, transport fluid, etc. Photovoltaics are not used in solar thermo-mechanical systems.

11. What is Carnot efficiency?
a) Rate of the temperature difference divided by rate of initial temperature change
b) Ratio of relative temperature between source and sink and the relative source temperature
c) Ratio of absolute temperature between source and sink and the absolute source temperature
d) Ratio of rate of the temperature difference and the absolute source temperature

Explanation: Carnot efficiency is ratio of absolute temperature between source and sink and the absolute source temperature. It can also be defined in terms of heat added to the source at some temperature and heat rejected by the fluid at some temperature.

12. Heat engine efficiency increases as the source temperature _______
a) decreases
b) remains the same
c) decrement rate increases
d) increases

Explanation: Heat engine efficiency increases as the source temperature increases. Also, the rate of increase of the source temperature should be greater at lower temperatures than at higher temperatures.

13. Distributed power system is a type of solar thermo-mechanical system.
a) True
b) False

Explanation: Distributed power system is a type of solar thermo-mechanical system. It works on the principle of collecting the incident solar radiation using multiple arrays of line focused reflectors distributed across a large area. These collectors are interconnected by pipes which transfer the energy to the mechanical system.

14. Heat engine efficiency increases with ________ sink temperature.
a) no change in
b) decrease in
c) increment in rate of increasing
d) increase in

Explanation: Heat engine efficiency increases with decrease in sink temperature. It should also be noted that the rate of decrement of sink temperature should be faster than the rate which the source temperature is increased.

15. Isothermal process is a process conducted at constant temperature.
a) True
b) False

Explanation: Isothermal process is a process conducted at constant temperature. Isobaric process is a process conducted at constant pressure.

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