AZ L-93 Solar Thermal Contractor
Exam Questions And Correct Answers
(Verified Answers) Plus Rationale2026
Q&A| Instant Download Pdf
1. Which type of solar collector is most commonly used for residential hot
water systems?
A. Flat-plate collector
B. Evacuated tube collector
C. Parabolic trough collector
D. Linear Fresnel collector
Rationale: Evacuated tube collectors are highly efficient for residential
water heating, especially in colder climates, because their vacuum
insulation reduces heat loss.
2. What is the primary purpose of a solar thermal storage tank?
A. To circulate water
B. To store thermal energy for later use
C. To collect solar radiation
D. To generate electricity
Rationale: Storage tanks hold heated water or heat transfer fluid,
allowing energy to be available when solar input is insufficient.
3. Which heat transfer fluid is commonly used in closed-loop solar
thermal systems?
A. Water only
B. Air
C. Propylene glycol-water mixture
D. Oil
Rationale: Glycol mixtures prevent freezing in colder climates and
provide safe heat transfer in closed-loop systems.
4. The efficiency of a solar collector decreases primarily due to:
A. Increased sunlight
, B. Heat loss to the environment
C. Proper insulation
D. Correct tilt angle
Rationale: Heat loss through conduction, convection, and radiation
reduces collector efficiency.
5. What is the recommended tilt angle for a fixed solar collector in
Phoenix, AZ?
A. 15°
B. 30°
C. 33°
D. 45°
Rationale: For optimum year-round performance, the tilt angle is
roughly equal to the latitude of the location; Phoenix is at ~33°
latitude.
6. What is the main function of a differential controller in a solar water
heating system?
A. To pump water constantly
B. To measure solar irradiance
C. To turn the circulation pump on or off based on temperature
difference
D. To prevent freezing
Rationale: Differential controllers compare tank and collector
temperatures and operate the pump only when the collector is hotter
than the tank.
7. Which is a common cause of air binding in solar thermal systems?
A. Too much heat
B. Entrapped air in the piping
C. Low glycol concentration
D. Oversized storage tank
Rationale: Air trapped in piping prevents proper fluid circulation,
reducing system efficiency.
8. How often should a closed-loop glycol-based solar system be inspected
for fluid degradation?
A. Every month
B. Every 3 months
C. Every 3–5 years
D. Every 10 years
, Rationale: Glycol degrades over time; manufacturers recommend
testing and replacement every 3–5 years depending on system
conditions.
9. What is the primary reason for using insulation on solar piping?
A. Prevent freezing only
B. Improve aesthetics
C. Reduce heat loss
D. Protect against UV rays only
Rationale: Insulation minimizes thermal energy loss as the heated fluid
travels from collector to storage tank.
10. What type of solar collector is best suited for commercial process
heat applications?
A. Flat-plate collector
B. Parabolic trough collector
C. Unglazed collector
D. Thermosiphon collector
Rationale: Parabolic trough collectors concentrate sunlight to achieve
high temperatures suitable for industrial processes.
11. What is thermosiphon circulation?
A. Pump-driven circulation
B. Natural circulation due to density differences
C. Forced convection with fans
D. Pressure-driven reverse flow
Rationale: Thermosiphon systems rely on natural convection; hot water
rises, and cold water sinks, circulating fluid without a pump.
12. Which type of solar water heater is least likely to freeze?
A. Direct thermosiphon
B. Open-loop flat-plate
C. Closed-loop glycol system
D. Unglazed pool heater
Rationale: Closed-loop systems use antifreeze solutions, protecting
against freezing in cold climates.
13. What is the primary disadvantage of a flat-plate collector
compared to evacuated tube collectors?
A. High cost
B. Complex design
C. Lower efficiency in cold or cloudy conditions
Exam Questions And Correct Answers
(Verified Answers) Plus Rationale2026
Q&A| Instant Download Pdf
1. Which type of solar collector is most commonly used for residential hot
water systems?
A. Flat-plate collector
B. Evacuated tube collector
C. Parabolic trough collector
D. Linear Fresnel collector
Rationale: Evacuated tube collectors are highly efficient for residential
water heating, especially in colder climates, because their vacuum
insulation reduces heat loss.
2. What is the primary purpose of a solar thermal storage tank?
A. To circulate water
B. To store thermal energy for later use
C. To collect solar radiation
D. To generate electricity
Rationale: Storage tanks hold heated water or heat transfer fluid,
allowing energy to be available when solar input is insufficient.
3. Which heat transfer fluid is commonly used in closed-loop solar
thermal systems?
A. Water only
B. Air
C. Propylene glycol-water mixture
D. Oil
Rationale: Glycol mixtures prevent freezing in colder climates and
provide safe heat transfer in closed-loop systems.
4. The efficiency of a solar collector decreases primarily due to:
A. Increased sunlight
, B. Heat loss to the environment
C. Proper insulation
D. Correct tilt angle
Rationale: Heat loss through conduction, convection, and radiation
reduces collector efficiency.
5. What is the recommended tilt angle for a fixed solar collector in
Phoenix, AZ?
A. 15°
B. 30°
C. 33°
D. 45°
Rationale: For optimum year-round performance, the tilt angle is
roughly equal to the latitude of the location; Phoenix is at ~33°
latitude.
6. What is the main function of a differential controller in a solar water
heating system?
A. To pump water constantly
B. To measure solar irradiance
C. To turn the circulation pump on or off based on temperature
difference
D. To prevent freezing
Rationale: Differential controllers compare tank and collector
temperatures and operate the pump only when the collector is hotter
than the tank.
7. Which is a common cause of air binding in solar thermal systems?
A. Too much heat
B. Entrapped air in the piping
C. Low glycol concentration
D. Oversized storage tank
Rationale: Air trapped in piping prevents proper fluid circulation,
reducing system efficiency.
8. How often should a closed-loop glycol-based solar system be inspected
for fluid degradation?
A. Every month
B. Every 3 months
C. Every 3–5 years
D. Every 10 years
, Rationale: Glycol degrades over time; manufacturers recommend
testing and replacement every 3–5 years depending on system
conditions.
9. What is the primary reason for using insulation on solar piping?
A. Prevent freezing only
B. Improve aesthetics
C. Reduce heat loss
D. Protect against UV rays only
Rationale: Insulation minimizes thermal energy loss as the heated fluid
travels from collector to storage tank.
10. What type of solar collector is best suited for commercial process
heat applications?
A. Flat-plate collector
B. Parabolic trough collector
C. Unglazed collector
D. Thermosiphon collector
Rationale: Parabolic trough collectors concentrate sunlight to achieve
high temperatures suitable for industrial processes.
11. What is thermosiphon circulation?
A. Pump-driven circulation
B. Natural circulation due to density differences
C. Forced convection with fans
D. Pressure-driven reverse flow
Rationale: Thermosiphon systems rely on natural convection; hot water
rises, and cold water sinks, circulating fluid without a pump.
12. Which type of solar water heater is least likely to freeze?
A. Direct thermosiphon
B. Open-loop flat-plate
C. Closed-loop glycol system
D. Unglazed pool heater
Rationale: Closed-loop systems use antifreeze solutions, protecting
against freezing in cold climates.
13. What is the primary disadvantage of a flat-plate collector
compared to evacuated tube collectors?
A. High cost
B. Complex design
C. Lower efficiency in cold or cloudy conditions
