, Question 1
A Virginia solar contractor is designing a roof-mounted PV system on a 2018
IRC-compliant dwelling. The array is 12 ft from the ridge and 4 ft from the
eave on a 6:12 pitch roof. To comply with the 2023 NEC rapid shutdown
requirements for module-level shutdown, which of the following is the
MINIMUM required labeling and placement?
A. A single placard at the service disconnect stating 'RAPID
SHUTDOWN' with a diagram of the array.
B. Labels at the service disconnect and at the array boundary indicating
rapid shutdown, with a diagram showing the controlled conductors.
C. Labels only on the inverter and at each module junction box.
D. No labeling is required if the inverter is listed as rapid shutdown
compliant.
Correct Answer: B - Labels at the service disconnect and at the
array boundary indicating rapid shutdown, with a diagram
showing the controlled conductors.
RATIONALE
NEC 690.56(C) requires a placard at the service disconnect and at the
array boundary (or at the point of entry) indicating rapid shutdown,
with a diagram showing the controlled conductors. Option A is
incomplete because it lacks the array boundary label. Option C
misplaces labels. Option D is incorrect because labeling is always
required for rapid shutdown systems.
Question 2
A solar thermal system in Richmond, VA uses flat-plate collectors with a
selective surface ( = 0.95, = 0.10). If the average irradiance is 800 W/m² and
the collector area is 4 m², what is the maximum theoretical stagnation
temperature rise above ambient, assuming no heat loss? (Use = 5.67×10
W/m²K, T_amb = 293 K, and assume the absorber emits as a graybody.)
Page 2
, A. Approximately 120 K
B. Approximately 200 K
C. Approximately 80 K
D. Approximately 150 K
Correct Answer: A - Approximately 120 K
RATIONALE
At stagnation, absorbed solar equals emitted radiation: -G = --(T -
T_amb). Solving: 0.95×800 = 0.10×5.67×10×(T - 293). This yields T
413 K, so T 120 K. Options B, C, and D do not satisfy the energy
balance.
Question 3
A geothermal heat pump system in Virginia is designed with a horizontal
ground loop. The soil has a thermal conductivity of 0.85 Btu/h-ft-°F and the
loop length is 400 ft per ton. If the system requires 3 tons of capacity, what is
the approximate total heat rejection to the ground during peak cooling,
assuming a 20°F temperature difference between loop fluid and undisturbed
soil?
A. 12,000 Btu/h
B. 24,000 Btu/h
C. 36,000 Btu/h
D. 48,000 Btu/h
Correct Answer: D - 48,000 Btu/h
RATIONALE
Heat rejection = capacity + compressor work. For a 3-ton system
(36,000 Btu/h cooling), with typical EER ~14, compressor work
36,000/14 2,571 Btu/h, total 38,571 Btu/h. However, the question
asks for approximate heat rejection to ground, which is often
estimated as 1.25× cooling capacity for water-cooled units, giving
~45,000 Btu/h, closest to 48,000. The other options are too low.
Page 3
, Question 4
A small wind turbine in a coastal Virginia site has a cut-in wind speed of 3
m/s, rated power at 12 m/s, and cut-out at 25 m/s. The turbine's power curve
follows a cubic relationship up to rated power. If the average wind speed is 6
m/s, what is the approximate capacity factor if the turbine is rated at 10 kW
and the air density is 1.225 kg/m³?
A. 15%
B. 25%
C. 35%
D. 45%
Correct Answer: B - 25%
RATIONALE
Using a Rayleigh distribution and integrating the power curve, the
capacity factor for a site with average wind speed 6 m/s and rated
speed 12 m/s is typically around 25-30%. Precise calculation yields
~25%. Options A, C, and D are either too low or high for this wind
regime.
Question 5
A lithium-ion battery storage system is installed in a Virginia home for backup
power. The system must comply with the 2023 NEC for energy storage
systems. Which of the following is required for a 10 kWh system installed in a
garage?
A. A listed fire suppression system.
B. A 3-ft clearance from walls and other equipment.
C. A ventilation system providing 1 cfm/ft² of floor area.
D. A smoke detector interconnected with the home's alarm system.
Correct Answer: B - A 3-ft clearance from walls and other
equipment.
Page 4
A Virginia solar contractor is designing a roof-mounted PV system on a 2018
IRC-compliant dwelling. The array is 12 ft from the ridge and 4 ft from the
eave on a 6:12 pitch roof. To comply with the 2023 NEC rapid shutdown
requirements for module-level shutdown, which of the following is the
MINIMUM required labeling and placement?
A. A single placard at the service disconnect stating 'RAPID
SHUTDOWN' with a diagram of the array.
B. Labels at the service disconnect and at the array boundary indicating
rapid shutdown, with a diagram showing the controlled conductors.
C. Labels only on the inverter and at each module junction box.
D. No labeling is required if the inverter is listed as rapid shutdown
compliant.
Correct Answer: B - Labels at the service disconnect and at the
array boundary indicating rapid shutdown, with a diagram
showing the controlled conductors.
RATIONALE
NEC 690.56(C) requires a placard at the service disconnect and at the
array boundary (or at the point of entry) indicating rapid shutdown,
with a diagram showing the controlled conductors. Option A is
incomplete because it lacks the array boundary label. Option C
misplaces labels. Option D is incorrect because labeling is always
required for rapid shutdown systems.
Question 2
A solar thermal system in Richmond, VA uses flat-plate collectors with a
selective surface ( = 0.95, = 0.10). If the average irradiance is 800 W/m² and
the collector area is 4 m², what is the maximum theoretical stagnation
temperature rise above ambient, assuming no heat loss? (Use = 5.67×10
W/m²K, T_amb = 293 K, and assume the absorber emits as a graybody.)
Page 2
, A. Approximately 120 K
B. Approximately 200 K
C. Approximately 80 K
D. Approximately 150 K
Correct Answer: A - Approximately 120 K
RATIONALE
At stagnation, absorbed solar equals emitted radiation: -G = --(T -
T_amb). Solving: 0.95×800 = 0.10×5.67×10×(T - 293). This yields T
413 K, so T 120 K. Options B, C, and D do not satisfy the energy
balance.
Question 3
A geothermal heat pump system in Virginia is designed with a horizontal
ground loop. The soil has a thermal conductivity of 0.85 Btu/h-ft-°F and the
loop length is 400 ft per ton. If the system requires 3 tons of capacity, what is
the approximate total heat rejection to the ground during peak cooling,
assuming a 20°F temperature difference between loop fluid and undisturbed
soil?
A. 12,000 Btu/h
B. 24,000 Btu/h
C. 36,000 Btu/h
D. 48,000 Btu/h
Correct Answer: D - 48,000 Btu/h
RATIONALE
Heat rejection = capacity + compressor work. For a 3-ton system
(36,000 Btu/h cooling), with typical EER ~14, compressor work
36,000/14 2,571 Btu/h, total 38,571 Btu/h. However, the question
asks for approximate heat rejection to ground, which is often
estimated as 1.25× cooling capacity for water-cooled units, giving
~45,000 Btu/h, closest to 48,000. The other options are too low.
Page 3
, Question 4
A small wind turbine in a coastal Virginia site has a cut-in wind speed of 3
m/s, rated power at 12 m/s, and cut-out at 25 m/s. The turbine's power curve
follows a cubic relationship up to rated power. If the average wind speed is 6
m/s, what is the approximate capacity factor if the turbine is rated at 10 kW
and the air density is 1.225 kg/m³?
A. 15%
B. 25%
C. 35%
D. 45%
Correct Answer: B - 25%
RATIONALE
Using a Rayleigh distribution and integrating the power curve, the
capacity factor for a site with average wind speed 6 m/s and rated
speed 12 m/s is typically around 25-30%. Precise calculation yields
~25%. Options A, C, and D are either too low or high for this wind
regime.
Question 5
A lithium-ion battery storage system is installed in a Virginia home for backup
power. The system must comply with the 2023 NEC for energy storage
systems. Which of the following is required for a 10 kWh system installed in a
garage?
A. A listed fire suppression system.
B. A 3-ft clearance from walls and other equipment.
C. A ventilation system providing 1 cfm/ft² of floor area.
D. A smoke detector interconnected with the home's alarm system.
Correct Answer: B - A 3-ft clearance from walls and other
equipment.
Page 4
