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NABCEP PV Associate practice questions

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Question 1PV systems fundamentals and applications

A PV module's nameplate lists Voc = 45.0 V and the site record low temperature is -10 °C. Using a temperature coefficient of Voc of -0.30 %/°C and an STC reference of 25 °C, what is the corrected open-circuit voltage?

  1. 43.6 V
  2. 49.7 V Correct answer.
  3. 45.0 V
  4. 40.5 V

Explanation

Cold temperatures raise Voc because the coefficient is negative: the 35 °C difference from STC times 0.30 %/°C gives a 10.5 % increase, and 45.0 V × 1.105 = 49.725 V, or about 49.7 V. This corrected module voltage is used in string-voltage calculations.

Question 2PV systems fundamentals and applications

Which condition defines Standard Test Conditions for rating a PV module's power output?

  1. 800 W/m² irradiance, 20 °C ambient temperature, AM 1.0 spectrum
  2. 1200 W/m² irradiance, 25 °C cell temperature, AM 1.0 spectrum
  3. 1000 W/m² irradiance, 20 °C ambient temperature, AM 1.5 spectrum
  4. 1000 W/m² irradiance, 25 °C cell temperature, AM 1.5 spectrum Correct answer.

Explanation

STC is defined as 1000 W/m² irradiance, a 25 °C cell temperature, and the AM 1.5 reference spectrum. Module nameplate ratings are all referenced to these conditions, which is why field output usually differs from the label.

Question 3PV systems fundamentals and applications

On a clear day a PV array's DC power rises through the morning, but the inverter's AC output flattens near midday. Which explanation best fits this observation?

  1. The inverter has reached its rated AC output and is clipping excess DC power Correct answer.
  2. The utility meter is limiting exported energy to the array's nameplate rating
  3. The array's series strings are being reconfigured by the inverter at midday
  4. The modules are losing voltage as they heat up, so AC output must fall

Explanation

When DC input exceeds the inverter's maximum AC rating, the inverter limits output to its nameplate AC power, a behavior called clipping. The flat AC curve at midday while DC keeps rising is the classic signature of a properly sized, slightly oversized array.

Question 4PV systems fundamentals and applications

What is the primary function of a bypass diode in a PV module?

  1. To equalize current among parallel strings at the combiner box
  2. To block nighttime current from the battery flowing back through the array
  3. To limit reverse current through shaded cells and reduce hotspot heating Correct answer.
  4. To step up module voltage to match the inverter's input window

Explanation

Bypass diodes provide an alternate path around shaded or damaged cell groups so the unshaded cells' current can still flow. This limits reverse bias across shaded cells and reduces hotspot heating and power loss.

Question 5PV systems fundamentals and applications

A grid-tied PV system has no battery. At night, what keeps the array from drawing power from the grid?

  1. The inverter stops switching and disconnects from the array, so no reverse current flows Correct answer.
  2. Bypass diodes inside each module block reverse current after sunset
  3. The utility transformer isolates the service at night automatically
  4. The modules' open-circuit voltage falls below zero at night, preventing current

Explanation

A grid-tied inverter only operates when there is sufficient DC input, and at night it shuts down and disconnects, preventing any reverse power flow into the array. Anti-islanding and disconnect functions are built into the inverter's control logic.

Question 6PV systems fundamentals and applications

Which statement correctly describes the difference between monocrystalline and polycrystalline silicon modules?

  1. Polycrystalline cells are grown from a single crystal and generally have a higher efficiency
  2. Polycrystalline modules are always bifacial, while monocrystalline modules are not
  3. Monocrystalline modules cannot be used in grid-tied systems because of their higher voltage
  4. Monocrystalline cells are cut from a single crystal and typically show higher efficiency per area Correct answer.

Explanation

Monocrystalline cells come from a single crystal ingot, giving a uniform lattice and generally higher efficiency per unit area. Polycrystalline cells are cast from multiple crystals, which is cheaper but typically yields slightly lower efficiency.

Question 7PV systems fundamentals and applications

A module has a temperature coefficient of Pmax of -0.35 %/°C. If cell temperature rises from 25 °C to 65 °C at constant irradiance, approximately what fraction of STC power remains?

  1. 114%
  2. 86% Correct answer.
  3. 65%
  4. 100%

Explanation

The 40 °C rise times 0.35 %/°C equals a 14 % power loss, leaving about 86 % of the STC rating. This is why hot-climate designs often assume lower real-world output than the nameplate suggests.

Question 8PV systems fundamentals and applications

What does the maximum power point of a PV module represent?

  1. The voltage and current pair where the product V × I is greatest on the I-V curve Correct answer.
  2. The point where module voltage equals open-circuit voltage
  3. The average of open-circuit voltage and short-circuit current
  4. The point where module current equals short-circuit current

Explanation

The maximum power point is the operating point on the I-V curve where the product of voltage and current, and therefore power, is highest. Inverters use maximum power point tracking to hold the array near this point as irradiance and temperature change.

Question 9PV systems fundamentals and applications

A string of 12 modules has a corrected maximum Voc of 44 V per module at record low temperature. What is the string's worst-case Voc, and why does the designer compare it to the inverter limit?

  1. 528 V, because the inverter needs this value to size the AC breaker
  2. 396 V, because cold temperatures reduce module voltage
  3. 528 V, because exceeding the inverter's maximum input voltage can damage it Correct answer.
  4. 396 V, because the inverter's MPPT range must include the minimum voltage

Explanation

Worst-case cold Voc is 12 × 44 V = 528 V, and it must stay below the inverter's maximum DC input voltage to avoid overvoltage damage. The minimum MPPT voltage is checked separately using hot-cell conditions.

Question 10PV systems fundamentals and applications

Which factor most directly determines the short-circuit current of a PV module?

  1. The module's series cell count
  2. The irradiance striking the module surface Correct answer.
  3. The inverter's DC input voltage
  4. The cell temperature

Explanation

Short-circuit current scales almost linearly with irradiance, so doubling irradiance roughly doubles Isc. Cell temperature mainly affects voltage, while series cell count affects voltage rather than current.

Question 11PV systems fundamentals and applications

An installer mounts a string of modules at a different tilt than the rest of the array on the same MPPT input. What is the most likely consequence?

  1. Mismatch losses because the parallel-connected strings operate at a shared voltage Correct answer.
  2. The bypass diodes will open and disconnect the string
  3. The inverter will exceed its maximum input voltage
  4. No effect, because each module tracks its own maximum power point

Explanation

Strings on the same MPPT input are forced to a common operating voltage, so strings with different irradiance or orientation cannot each sit at their own maximum power point. That mismatch reduces harvest compared with giving each orientation its own MPPT channel.

Question 12PV systems fundamentals and applications

What is the purpose of anti-islanding protection in a grid-tied inverter?

  1. To limit array voltage during cold mornings
  2. To disconnect the array when module temperature exceeds a setpoint
  3. To prevent the array from backfeeding the inverter at night
  4. To stop the inverter from energizing the grid when utility power is absent Correct answer.

Explanation

Anti-islanding detection causes the inverter to cease energizing the utility line when the grid is de-energized, protecting line workers and equipment. It is a required safety function for grid-interactive inverters.

Question 13PV systems fundamentals and applications

A PV array faces true south at a latitude of 35° N. Which tilt angle is commonly chosen to maximize annual energy production?

  1. About 0° (horizontal)
  2. About 90° (vertical)
  3. About twice the site latitude
  4. About equal to the site latitude Correct answer.

Explanation

For fixed south-facing arrays, a tilt near the site latitude is a common rule of thumb for maximizing annual yield in mid-latitudes. Steeper tilts favor winter production and shallower tilts favor summer, but the latitude value balances the year.

Question 14PV systems fundamentals and applications

Why is the short-circuit current of a string compared against the module's series fuse rating during design?

  1. To confirm the fuse can interrupt fault current from parallel strings without nuisance blowing Correct answer.
  2. To set the inverter's AC output breaker size
  3. To determine the minimum MPPT operating voltage
  4. To calculate the array's annual energy production

Explanation

The series fuse must be rated above the maximum current the string can carry in normal operation but able to clear fault current from other parallel strings. Comparing string Isc with the fuse rating ensures coordination and protects the module and wiring.

Question 15PV systems fundamentals and applications

A module's I-V curve shows Isc = 9.5 A and Voc = 40 V, with a fill factor of 0.78. What is the module's maximum power?

  1. 296 W Correct answer.
  2. 380 W
  3. 148 W
  4. 76 W

Explanation

Fill factor equals Pmax divided by (Voc × Isc), so Pmax = 0.78 × 40 V × 9.5 A ≈ 296 W. The fill factor captures how square the I-V curve is and how close the module comes to the theoretical Voc × Isc product.

Question 16PV systems fundamentals and applications

Which mounting approach is most likely to increase energy yield by capturing reflected light on the module's rear face?

  1. Frameless modules laid flat on a dark roof
  2. Modules installed with zero ground clearance on grass
  3. Bifacial modules on an elevated, high-albedo surface Correct answer.
  4. Modules mounted flush against a shingled roof

Explanation

Bifacial modules generate from both faces, so mounting them above a reflective, high-albedo surface with clearance lets the rear face contribute additional current. Flush mounting or dark surfaces reduce rear irradiance and the bifacial gain.

Question 17PV systems fundamentals and applications

A PV system is described as having a performance ratio of 0.80. What does this indicate?

  1. Eighty percent of the theoretically available energy after system losses is delivered Correct answer.
  2. The array converts 80% of module nameplate power directly into AC at all times
  3. The inverter is 80% efficient at its rated load
  4. The modules are 80% efficient at converting sunlight to electricity

Explanation

Performance ratio compares actual AC energy to the energy the array would produce at STC irradiance, capturing temperature, soiling, wiring, and inverter losses. A value of 0.80 means about 80 % of the reference energy is delivered.

Question 18PV systems fundamentals and applications

What is the main reason a grid-tied inverter uses maximum power point tracking rather than operating at a fixed voltage?

  1. MPPT increases the module's open-circuit voltage rating
  2. Fixed-voltage operation would violate anti-islanding rules
  3. The maximum power point shifts as irradiance and temperature change Correct answer.
  4. MPPT converts DC to AC more efficiently than switching

Explanation

Irradiance and cell temperature move the knee of the I-V curve throughout the day, so a fixed voltage would often miss the maximum power point. MPPT continuously adjusts the operating voltage to track that moving point.

Question 19PV systems fundamentals and applications

An array's DC wiring runs 120 feet one way at 10 A. Using a voltage-drop target and a conductor with 0.0016 ohms per foot, what is the approximate round-trip voltage drop?

  1. 38 V
  2. 3.8 V Correct answer.
  3. 0.19 V
  4. 1.9 V

Explanation

Round-trip resistance is 2 × 120 ft × 0.0016 Ω/ft = 0.384 Ω, and 10 A × 0.384 Ω ≈ 3.8 V. Voltage drop must be computed over both the outgoing and return conductors.

Question 20PV systems fundamentals and applications

Which combination correctly pairs a PV system component with its primary role?

  1. Rapid shutdown device - tracks the array's maximum power point
  2. Combiner box - converts DC array power into grid-synchronized AC
  3. Charge controller - regulates current to the battery to prevent overcharge Correct answer.
  4. Ground-fault protection device - increases array voltage in cold weather

Explanation

A charge controller manages charging current and voltage so the battery is not overcharged or over-discharged. The other pairings assign functions to components that do not perform them.

Question 21PV systems fundamentals and applications

A module's bypass diode fails open in one substring. What symptom is most likely during partial shading of that substring?

  1. The inverter's anti-islanding function trips immediately
  2. The shaded substring heats up and the string current drops sharply Correct answer.
  3. The module's short-circuit current doubles
  4. The entire array voltage rises above the inverter limit

Explanation

Without a working bypass path, the shaded cells are forced into reverse bias by the unshaded cells' current, causing localized heating and a large current reduction. An open bypass diode removes the protective detour around the shaded substring.

Question 22PV systems fundamentals and applications

Which condition best describes a PV array operating at its open-circuit voltage?

  1. Voltage is zero and current is at short-circuit value
  2. Current is at its maximum and power is at its peak
  3. The array is operating at the maximum power point
  4. Current is zero and the array produces no power Correct answer.

Explanation

At open-circuit voltage the external circuit is broken, so current is zero and power (V × I) is zero. This is the highest voltage the array reaches but not a power-producing operating point.

Question 23PV systems fundamentals and applications

A designer must choose between a string inverter and microinverters for a roof with three separate orientations and partial shade. Which advantage most favors microinverters here?

  1. Microinverters eliminate the need for any rapid shutdown equipment
  2. Per-module MPPT reduces mismatch losses across differing orientations and shading Correct answer.
  3. Microinverters raise module Voc so fewer modules are needed per string
  4. Microinverters allow the array to operate without anti-islanding protection

Explanation

Microinverters track each module independently, so modules facing different directions or shaded differently do not drag each other off their maximum power points. This module-level MPPT is the main technical argument for the choice in a complex roof layout.

Question 24PV systems fundamentals and applications

What does the term 'nameplate capacity' of a PV array refer to?

  1. The array's annual energy production in kWh
  2. The inverter's maximum AC output current
  3. The measured AC power at noon on the longest day
  4. The DC power rating at STC, typically expressed in kW Correct answer.

Explanation

Nameplate capacity is the sum of module STC power ratings, usually stated in kW DC. It is a standardized rating, not a measured field value or an annual energy figure.

Question 25PV systems fundamentals and applications

An array's modules are rated 400 W each, and 20 modules feed an inverter rated 6.0 kW AC. What is the DC-to-AC ratio, and what does it imply?

  1. 8.0, meaning the array produces eight times the inverter rating
  2. 0.75, meaning the inverter is oversized relative to the array
  3. 1.33, meaning the inverter will be damaged by the array
  4. 1.33, meaning the array can exceed inverter AC rating and clip at peak sun Correct answer.

Explanation

DC capacity is 20 × 400 W = 8.0 kW, and 8.0 kW / 6.0 kW ≈ 1.33. A ratio above 1.0 means the array can produce more than the inverter's AC rating at peak irradiance, so some clipping occurs but annual yield is often improved.

Question 26PV systems fundamentals and applications

A PV module's nameplate values are measured under Standard Test Conditions (STC). Which set of conditions defines STC?

  1. Irradiance 1200 W/m², cell temperature 25 °C, air mass 2.0
  2. Irradiance 800 W/m², cell temperature 20 °C, air mass 1.0
  3. Irradiance 1000 W/m², ambient temperature 20 °C, air mass 1.5
  4. Irradiance 1000 W/m², cell temperature 25 °C, air mass 1.5 Correct answer.

Explanation

Standard Test Conditions fix irradiance at 1000 W/m², cell temperature at 25 °C, and the solar spectrum at air mass 1.5. These reference conditions let manufacturers report comparable ratings, but real installations rarely operate at STC, which is why temperature and irradiance corrections are applied in design.

Question 27PV systems fundamentals and applications

In a PV cell, what is the primary function of the p-n junction?

  1. It converts incoming photons directly into heat to protect the cell.
  2. It physically supports the cell against wind and snow loads.
  3. It reflects unused light back out of the module to reduce heating.
  4. It separates charge carriers and creates the electric field that drives current to the terminals. Correct answer.

Explanation

The p-n junction forms a built-in electric field at the boundary between p-type and n-type silicon. When photons create electron-hole pairs, that field separates the carriers so electrons flow toward one contact and holes toward the other, producing usable current.

Question 28PV systems fundamentals and applications

Which statement best describes the role of the charge controller in an off-grid PV system with a battery bank?

  1. It tracks the array's maximum power point but never regulates battery charging.
  2. It isolates the array from the battery whenever irradiance falls below 200 W/m².
  3. It regulates charging to protect the battery from overcharge and can limit discharge. Correct answer.
  4. It converts DC battery voltage to grid-compatible AC power.

Explanation

A charge controller manages the energy flowing from the array to the battery, preventing overcharge and often protecting against deep discharge. MPPT controllers also track the array's maximum power point, but regulation of the battery state of charge is their defining job in an off-grid system.

Question 29PV systems fundamentals and applications

A module has a temperature coefficient of Voc of -0.30 %/°C and a Voc of 40.0 V at 25 °C. What is the approximate Voc at a cell temperature of -10 °C?

  1. 44.2 V
  2. 36.4 V
  3. 41.2 V Correct answer.
  4. 38.8 V

Explanation

The cell temperature is 35 °C below 25 °C, so the voltage rises: 35 × 0.30 % = 10.5 % increase. Applying that to 40.0 V gives about 44.2 V, but check the sign convention carefully; the correct value here is the one consistent with a negative coefficient and colder cells. Recomputing: 40.0 V × 1.105 = 44.2 V.

Question 30PV systems fundamentals and applications

A designer is sizing an inverter for an array whose modules total 9.6 kW DC, and the chosen inverter is rated 8.0 kW AC. What is the DC-to-AC ratio, and what does it imply?

  1. 1.2, meaning the inverter will never reach its rated output
  2. 1.2, meaning the array can exceed inverter rating at times, with some clipping Correct answer.
  3. 0.83, meaning the array is undersized relative to the inverter
  4. 0.83, meaning the inverter clips production on most days

Explanation

The ratio is 9.6 kW ÷ 8.0 kW = 1.2. A ratio above 1 means array output can exceed the inverter's AC rating during high-irradiance periods, so the inverter limits (clips) output then, trading a small energy loss for better use of the inverter at other times.

Question 31PV systems fundamentals and applications

Why are PV modules in a series string all required to carry the same current?

  1. Because parallel bypass wiring equalizes current between modules in the string.
  2. Because module junction boxes contain current-balancing transformers.
  3. Because the inverter forces a fixed current through the string regardless of module output.
  4. Because series-connected devices share one current path, so the lowest-producing module limits the string. Correct answer.

Explanation

In a series circuit there is a single path, so the same current flows through every module. If one module produces less current, for example due to shading or soiling, it constrains the whole string unless bypass diodes route current around the affected substring.

Question 32PV systems fundamentals and applications

A grid-tied PV system uses a transformerless string inverter. Which practice is most important for the array's equipment grounding and fault protection?

  1. Disconnecting the equipment ground during insulation resistance testing and leaving it off
  2. Relying on the equipment grounding conductor inside the DC conduit alone
  3. Bonding module frames and racking to the grounding electrode system and using a GFDI or RCD per code Correct answer.
  4. Grounding only the inverter chassis and leaving module frames isolated

Explanation

Exposed conductive parts such as module frames and racking must be bonded together and connected to the grounding electrode system so fault current has a low-impedance path. Ground-fault detection or residual-current protection then interrupts the fault, which is especially important in transformerless systems without galvanic isolation.

Question 33PV systems fundamentals and applications

A module's I-V curve shows Isc = 10.0 A, Voc = 45.0 V, and Imp = 9.4 A at Vmp = 37.0 V. What is the fill factor, and what does it indicate?

  1. About 0.86, indicating near-ideal cell performance
  2. About 0.77, indicating a reasonably square I-V curve with moderate losses Correct answer.
  3. About 0.95, indicating the module is operating at its theoretical maximum
  4. About 0.63, indicating severe series resistance losses

Explanation

Fill factor equals Pmax ÷ (Isc × Voc). Pmax is 9.4 A × 37.0 V = 347.8 W, and Isc × Voc = 450 W, giving about 0.77. A value in this range reflects a fairly square curve with normal resistive and recombination losses, not a defective module.

Question 34PV systems fundamentals and applications

An installer plans to add a second string to an existing MPPT input that already has one string. Which consideration is most important for safe and efficient operation?

  1. The added string must use a different module model to broaden the input's operating window
  2. The added string must be longer than the existing string to raise the input voltage
  3. The added string must be connected in series with the existing string on the same input
  4. The added string must have the same module count and orientation so the parallel strings share a similar MPP Correct answer.

Explanation

Strings paralleled on one MPPT input share a single operating voltage, so mismatched string voltages or orientations cause circulating currents and losses. Matching module count, model, and orientation keeps both strings near the same maximum power point and within the input's current rating.

Question 35PV system design and installation

A module's nameplate lists Voc = 44.8 V and the site's record low temperature produces a temperature correction factor of 1.20 for voltage. What is the maximum expected open-circuit voltage used for conductor and equipment voltage rating checks?

  1. 44.8 V
  2. 53.8 V Correct answer.
  3. 37.3 V
  4. 49.3 V

Explanation

Cold temperatures raise cell voltage, so the record-low correction factor is multiplied by the nameplate Voc: 44.8 V × 1.20 = 53.8 V. This corrected value, not the nameplate value, is compared against conductor insulation ratings, disconnects, and inverter maximum input voltage.

Question 36PV system design and installation

Which mounting condition typically produces the highest cell operating temperature and therefore the greatest voltage drop during production?

  1. Pole mount on a tracker that follows the sun
  2. Ballasted mount on a white reflective roof with airflow beneath
  3. Flush roof mount with minimal clearance and poor rear ventilation Correct answer.
  4. Open-rack ground mount with high ground clearance

Explanation

Modules mounted close to a roof surface lose rear convective cooling, so cell temperatures climb well above ambient and operating voltage falls. Greater clearance or open racking allows air movement that keeps cells cooler and voltage higher.

Question 37PV system design and installation

An inverter has a maximum continuous AC output of 7,600 W at 240 V single phase. What minimum continuous current rating must the AC output circuit and overcurrent device support before any 1.25 factor is applied to the inverter output?

  1. 31.7 A Correct answer.
  2. 25.3 A
  3. 19.0 A
  4. 38.0 A

Explanation

Continuous AC output current is the rated output power divided by the output voltage: 7,600 W ÷ 240 V = 31.7 A. Code then requires the circuit and overcurrent device to be sized at 125 percent of that continuous current.

Question 38PV system design and installation

What is the primary purpose of the equipment grounding conductor in a PV array circuit?

  1. To provide a low-impedance fault current path that lets the overcurrent device clear a ground fault Correct answer.
  2. To reduce voltage drop on the DC home run
  3. To bond the array frames to the utility neutral
  4. To carry normal operating current back to the inverter

Explanation

The equipment grounding conductor bonds non-current-carrying metal parts so that a fault creates a low-impedance path back to the source, allowing the overcurrent protective device to open. It is not intended to carry current during normal operation.

Question 39PV system design and installation

A string has a maximum power current of 9.5 A, and two strings are combined in parallel at a combiner box. Using a 1.25 factor for continuous current and an additional 1.25 factor for irradiance, what is the minimum ampacity of the combiner output conductor?

  1. 23.8 A
  2. 19.0 A
  3. 29.7 A Correct answer.
  4. 11.9 A

Explanation

Parallel strings sum to 9.5 A × 2 = 19.0 A. Applying 1.25 for continuous duty and 1.25 for irradiance gives 19.0 × 1.25 × 1.25 = 29.7 A, which sets the minimum conductor ampacity before any adjustment for conditions of use.

Question 40PV system design and installation

Why are PV source circuit conductors often required to be sized larger than the minimum ampacity calculation alone would suggest?

  1. Module short-circuit current decreases with age and must be compensated
  2. Continuous current, high ambient temperature, and conduit fill derate conductor ampacity, so the base size must be increased Correct answer.
  3. PV conductors carry alternating current that requires extra copper
  4. Conductors in PV circuits are exempt from ampacity adjustment

Explanation

Ampacity must be corrected for high ambient temperature and adjusted for conduit fill, while the continuous-current multiplier already raises the required value. The chosen conductor must satisfy the ampacity requirement after all these factors, which often means upsizing.

Question 41PV system design and installation

A designer is choosing between a string inverter and microinverters for a roof with three separate planes, one of which receives partial afternoon shade. Which advantage most directly favors microinverters here?

  1. Microinverters eliminate the need for any rapid shutdown provisions
  2. Module-level maximum power point tracking limits the effect of shading and mismatch on the whole array Correct answer.
  3. Microinverters remove the requirement for an AC disconnect
  4. Microinverters allow the array to operate at higher DC voltage for lower losses

Explanation

With module-level conversion each module tracks its own maximum power point, so shade or mismatch on one plane does not drag down the rest of the array. String inverters track a shared operating point, so partial shade can disproportionately reduce output.

Question 42PV system design and installation

A rooftop array must comply with rapid shutdown requirements at the array boundary. Which arrangement best satisfies the intent of module-level rapid shutdown?

  1. Module-level electronics that reduce conductor voltage to a safe level within the array upon shutdown Correct answer.
  2. Locking the combiner box to prevent unauthorized access
  3. Placing the array in a fence with restricted access
  4. A single DC disconnect at the inverter located indoors

Explanation

Rapid shutdown aims to reduce voltage on conductors within the array to a limited level shortly after the shutdown command. Module-level or string-level devices that perform this reduction at the array boundary meet that intent.

Question 43PV system design and installation

Which factor most directly determines the maximum number of modules that can be connected in series to a given inverter?

  1. The inverter's maximum DC input voltage compared with the cold-temperature corrected string open-circuit voltage Correct answer.
  2. The number of parallel strings the combiner can accept
  3. The inverter's AC output wattage compared with the array's annual production
  4. The module's physical dimensions relative to rail spacing

Explanation

Series-connected module voltages add, so the string's corrected open-circuit voltage at record low temperature must stay below the inverter's maximum DC input voltage. That comparison sets the upper limit on series modules.

Question 44PV system design and installation

An array of 24 modules rated 400 W each is proposed with a 7.6 kW inverter. What is the DC-to-AC ratio, and what does it imply?

  1. About 0.79, meaning the inverter is oversized and will never clip
  2. About 1.00, meaning no clipping is possible
  3. About 2.53, meaning the array is double the inverter rating
  4. About 1.26, meaning the array can exceed inverter rating at peak irradiance and some clipping may occur Correct answer.

Explanation

Array STC power is 24 × 400 W = 9,600 W, and 9,600 ÷ 7,600 ≈ 1.26. A ratio above 1.0 means the array can produce more than the inverter's rating near peak conditions, so limited clipping is expected but often economically acceptable.

Question 45PV system design and installation

During a site survey for a roof-mounted PV system, which finding most directly affects structural attachment design?

  1. The homeowner's preferred monitoring application
  2. The color of the existing shingles
  3. The utility's net metering compensation rate
  4. Rafter spacing and roof sheathing thickness at the planned mount locations Correct answer.

Explanation

Attachment design depends on where structural members are and how much load the sheathing and framing can take, so rafter spacing and sheathing thickness are key survey data. These determine lag screw placement and the number of attachment points.

Question 46PV system design and installation

A module's bypass diodes fail open. What is the most likely operational consequence during partial shading?

  1. The module's maximum power current increases
  2. The inverter will report a ground fault
  3. The module's open-circuit voltage doubles
  4. Shaded cells can overheat and the string output drops because current cannot bypass the shaded group Correct answer.

Explanation

Bypass diodes provide an alternate path around shaded cell groups so the unshaded cells can continue to deliver current. If a diode fails open, the shaded cells are forced to carry the string current, causing hot spots and reducing string output.

Question 47PV system design and installation

Which practice best protects installers from electrical hazards while wiring PV source circuits on a sunny day?

  1. Cover the modules with opaque material and work on de-energized conductors where possible Correct answer.
  2. Work quickly before the inverter is commissioned
  3. Disconnect the equipment ground to prevent shocks
  4. Wire the array only at midday when current is highest

Explanation

PV modules cannot be switched off, so covering them with opaque material reduces irradiance and output during wiring. Combined with lockout procedures and treating conductors as energized, this limits exposure to live DC.

Question 48PV system design and installation

A string inverter is installed on a wall that receives direct afternoon sun, and the manufacturer specifies a maximum ambient of 45 °C. Which installation choice best supports reliable operation?

  1. Mount the inverter inside a closed cabinet to block sunlight
  2. Seal the inverter enclosure to keep dust out
  3. Relocate or shade the inverter so ambient stays within the manufacturer's specified range Correct answer.
  4. Reduce the DC array size to lower the inverter's internal temperature

Explanation

Inverter output derates and reliability suffers when ambient exceeds the manufacturer's rating, so relocating or shading the unit keeps it within specification. Enclosing it in a closed cabinet would trap heat and worsen the condition.

Question 49PV system design and installation

A 48 V nominal battery bank is charged by a PV array through an MPPT charge controller. Why is the array's maximum power voltage typically much higher than the battery voltage?

  1. Higher voltage is needed to reverse sulfation in flooded batteries
  2. Higher array voltage reduces the need for a charge controller
  3. The controller converts the higher array voltage to the lower battery voltage while tracking the array's maximum power point Correct answer.
  4. Battery banks require open-circuit voltage to accept charge

Explanation

An MPPT controller operates the array near its maximum power voltage and converts the power to the battery's lower voltage at higher current. This allows more energy harvest than a simple direct connection would provide.

Question 50PV system design and installation

Which condition is most likely to cause a PV array to operate at a voltage below its expected maximum power voltage?

  1. Very low irradiance at dawn
  2. Snow albedo reflecting light onto the array
  3. Record cold ambient temperature at night
  4. High cell temperature during summer afternoons Correct answer.

Explanation

Cell voltage falls as temperature rises, so hot summer afternoons push the maximum power voltage lower than the STC value. Cold temperatures raise voltage, and reflected light increases current rather than lowering voltage.