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NABCEP SW Associate practice questions

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Question 1Photovoltaic systems fundamentals and applications

A PV module's nameplate lists an open-circuit voltage (Voc) of 45.0 V and a temperature coefficient of Voc of −0.30 %/°C. Using the nameplate Voc at 25 °C, what is the approximate Voc at a cell temperature of −10 °C?

  1. 45.3 V
  2. 49.7 V Correct answer.
  3. 47.4 V
  4. 40.3 V

Explanation

The voltage rises as temperature falls, so the change is −0.30 %/°C × (−35 °C) = +10.5 %, giving 45.0 V × 1.105 ≈ 49.7 V. Cold-temperature Voc governs maximum string voltage for conductor and inverter sizing.

Question 2Photovoltaic systems fundamentals and applications

Which condition produces the highest current through a PV cell?

  1. Low irradiance and low cell temperature
  2. Low irradiance and high cell temperature
  3. High irradiance and low cell temperature Correct answer.
  4. High irradiance and high cell temperature

Explanation

Photocurrent scales with irradiance, so high irradiance gives the most current. Current rises slightly as temperature increases, but irradiance dominates, and the standard rating point pairs high irradiance with low temperature.

Question 3Photovoltaic systems fundamentals and applications

A module has a temperature coefficient of power of −0.35 %/°C. Its rated power is 400 W at 25 °C. What is the estimated power at a cell temperature of 65 °C?

  1. 391 W
  2. 456 W
  3. 344 W Correct answer.
  4. 400 W

Explanation

The 40 °C rise above 25 °C times −0.35 %/°C equals a 14 % loss. Applying 400 W × 0.86 gives about 344 W, illustrating why hot rooftop arrays underperform their nameplate.

Question 4Photovoltaic systems fundamentals and applications

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

  1. The operating point where the product of current and voltage is greatest Correct answer.
  2. The point where module current equals short-circuit current
  3. The point where module voltage equals open-circuit voltage
  4. The point where the module's series resistance is zero

Explanation

On the I-V curve, power is the product of current and voltage at each point, and the MPP is where that product peaks. MPPT charge controllers and inverters continuously track this point to maximize harvest.

Question 5Photovoltaic systems fundamentals and applications

A PV array is described as having a fill factor of 0.78. What does this value indicate?

  1. The ratio of maximum power to the product of Voc and Isc Correct answer.
  2. The percentage of modules that pass factory testing
  3. The ratio of cell area to module area
  4. The fraction of sunlight converted to heat

Explanation

Fill factor equals Pmp divided by (Voc × Isc) and reflects how square the I-V curve is. Higher fill factor means less resistive loss and a better-quality cell for the same Voc and Isc.

Question 6Photovoltaic systems fundamentals and applications

Two identical 12 V nominal modules are wired in series. What happens to the array voltage and current compared with a single module?

  1. Voltage stays the same and current stays the same
  2. Voltage doubles and current stays the same Correct answer.
  3. Voltage doubles and current doubles
  4. Voltage stays the same and current doubles

Explanation

Series wiring adds voltages while current is limited by the same series path. So two identical modules in series produce twice the voltage at the single-module current, which suits higher-voltage charge controllers and inverters.

Question 7Photovoltaic systems fundamentals and applications

Four identical modules, each rated 200 W at 30 V and 6.7 A, are wired two in series per string and two strings in parallel. What is the approximate array rating?

  1. 800 W at 60 V Correct answer.
  2. 1600 W at 60 V
  3. 400 W at 30 V
  4. 800 W at 30 V

Explanation

Two in series double voltage to 60 V at 6.7 A per string. Two such strings in parallel double current to about 13.4 A, giving 60 V × 13.4 A ≈ 800 W, matching four 200 W modules.

Question 8Photovoltaic systems fundamentals and applications

Why is partial shading of a single module in a series string disproportionately harmful?

  1. Shading increases irradiance on nearby modules
  2. The shaded module's voltage rises and damages the inverter
  3. The shaded module's reduced current limits the whole series string Correct answer.
  4. Shading only affects the module's frame, not its cells

Explanation

Series-connected cells must carry the same current, so a shaded cell with reduced photocurrent restricts the entire string. Bypass diodes limit the damage but still leave a significant production loss.

Question 9Photovoltaic systems fundamentals and applications

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

  1. To convert DC power to AC power
  2. To boost the module's open-circuit voltage
  3. To provide an alternate current path around shaded or failed cells Correct answer.
  4. To prevent reverse current from the battery at night

Explanation

Bypass diodes let current route around a substring that is shaded or damaged, reducing power loss and preventing hot spots. They are wired in parallel with groups of cells inside the module.

Question 10Photovoltaic systems fundamentals and applications

A grid-tied inverter is rated at 96 % CEC efficiency. An array produces 8,000 kWh of DC energy over a year. Ignoring other losses, how much AC energy is delivered?

  1. 8,320 kWh
  2. 7,680 kWh Correct answer.
  3. 8,000 kWh
  4. 7,200 kWh

Explanation

AC output equals DC energy times efficiency, so 8,000 kWh × 0.96 = 7,680 kWh. The remaining 4 % is lost as heat in the conversion process.

Question 11Photovoltaic systems fundamentals and applications

Which inverter feature allows a grid-tied system to shut down automatically when the utility grid is de-energized?

  1. Ground-fault detection
  2. Maximum power point tracking
  3. Anti-islanding protection Correct answer.
  4. Arc-fault interruption

Explanation

Anti-islanding protection senses loss of grid voltage or frequency and stops the inverter from energizing a de-energized line. This protects utility workers from backfeed during outages.

Question 12Photovoltaic systems fundamentals and applications

What is the purpose of a blocking diode in a battery-based PV system?

  1. To increase the array's short-circuit current
  2. To step up the array voltage to a higher level
  3. To bypass shaded cells within a module
  4. To prevent current from flowing back from the battery into the array at night Correct answer.

Explanation

At night, when module voltage falls below battery voltage, a blocking diode stops reverse current that would otherwise drain the battery. Many modern charge controllers provide this function electronically.

Question 13Photovoltaic systems fundamentals and applications

A PWM charge controller is used with a 12 V battery bank and a PV array with a Vmp of 18 V. What is a key characteristic of this setup?

  1. The controller tracks the array's maximum power point
  2. The array is operated at the battery voltage, wasting the difference Correct answer.
  3. The array voltage is boosted to match a higher battery voltage
  4. The controller converts the excess voltage into additional current

Explanation

A PWM controller simply connects the array to the battery, so the array operates near battery voltage and the extra voltage headroom is lost. MPPT controllers instead convert that headroom into more charging current.

Question 14Photovoltaic systems fundamentals and applications

Which statement correctly describes the difference between a solar cell and a solar module?

  1. A cell contains bypass diodes, and a module does not
  2. A cell is the smallest PV device, and a module is a packaged assembly of interconnected cells Correct answer.
  3. A module is a single semiconductor wafer, and a cell is an assembly of modules
  4. A module produces DC, and a cell produces AC

Explanation

The solar cell is the basic semiconductor device that generates current from light. Cells are wired together, laminated, and framed into a module, which is the practical building block for arrays.

Question 15Photovoltaic systems fundamentals and applications

A PV array's STC rating is based on which set of conditions?

  1. 800 W/m² irradiance, 20 °C cell temperature, AM 1.0 spectrum
  2. 1000 W/m² irradiance, 25 °C cell temperature, AM 1.5 spectrum Correct answer.
  3. 1200 W/m² irradiance, 25 °C cell temperature, AM 2.0 spectrum
  4. 1000 W/m² irradiance, 45 °C cell temperature, AM 1.5 spectrum

Explanation

Standard Test Conditions specify 1000 W/m² irradiance, a 25 °C cell temperature, and the AM 1.5 reference spectrum. Nameplate ratings use these conditions so modules can be compared consistently.

Question 16Photovoltaic systems fundamentals and applications

A PV module's short-circuit current (Isc) is 10.5 A and its Vmp is 34 V. When sizing a series string for a charge controller with a maximum input voltage of 150 V, what is the maximum number of modules that can be placed in series, ignoring temperature corrections?

  1. 3
  2. 4 Correct answer.
  3. 6
  4. 5

Explanation

Using the open-circuit voltage is required for string voltage checks, but with only Vmp given a conservative approach uses it for comparison. Four modules at 34 V give 136 V, while five would exceed 150 V, so four is the maximum here, and real designs must also account for cold-temperature Voc.

Question 17Photovoltaic systems fundamentals and applications

A rooftop array faces due south in the northern hemisphere. Which change would most reduce annual energy production?

  1. Orienting the array due east instead of due south Correct answer.
  2. Increasing the array tilt to match latitude
  3. Cleaning the modules regularly
  4. Tilting the array to a shallower angle than latitude

Explanation

South orientation maximizes annual insolation in the northern hemisphere, so rotating to due east shifts production to mornings and reduces the annual total. Tilt adjustments and cleaning generally improve or modestly affect output.

Question 18Photovoltaic systems fundamentals and applications

What is the main reason PV modules are wired in series strings rather than all in parallel?

  1. To increase the array's short-circuit current
  2. To eliminate the need for a charge controller
  3. To keep the array current low while raising voltage for efficient transmission and inverter compatibility Correct answer.
  4. To allow each module to operate at a different current

Explanation

Series strings raise voltage so current stays low, which reduces resistive losses in conductors and matches inverter input windows. It also means all modules in a string must share the same current.

Question 19Photovoltaic systems fundamentals and applications

A PV cell's I-V curve shifts when irradiance drops from 1000 W/m² to 500 W/m². Which parameter changes most significantly?

  1. Open-circuit voltage
  2. Cell temperature
  3. Short-circuit current Correct answer.
  4. Fill factor only

Explanation

Short-circuit current is nearly proportional to irradiance, so halving irradiance roughly halves Isc. Open-circuit voltage falls only slightly because it depends logarithmically on current.

Question 20Photovoltaic systems fundamentals and applications

What is the primary purpose of a maximum power point tracking (MPPT) charge controller?

  1. To prevent current from flowing backward at night
  2. To convert DC power to AC power for the grid
  3. To continuously adjust the operating point of the array to extract maximum power Correct answer.
  4. To limit battery voltage to a safe level only

Explanation

An MPPT controller varies the effective load on the array to keep it at its maximum power point, which can increase harvest when array Vmp differs from battery voltage. It then converts that power to the appropriate battery charging voltage.

Question 21Photovoltaic systems fundamentals and applications

A module has a Voc of 40 V and an Isc of 9 A. Its maximum power is 280 W. What is its fill factor?

  1. 0.78 Correct answer.
  2. 0.68
  3. 0.58
  4. 0.88

Explanation

Fill factor equals Pmp divided by (Voc × Isc), so 280 W ÷ (40 V × 9 A) = 280 ÷ 360 ≈ 0.78. This is a normal value for a crystalline silicon module.

Question 22Photovoltaic systems fundamentals and applications

Which factor most directly determines the open-circuit voltage of a silicon PV module?

  1. The wire gauge used in the array
  2. The irradiance level alone
  3. The module's surface area
  4. The number of cells wired in series Correct answer.

Explanation

Each silicon cell contributes roughly 0.6 to 0.7 V at open circuit, so module voltage is essentially the sum of series-connected cell voltages. Area and wire gauge affect current and losses, not the voltage count.

Question 23Photovoltaic systems fundamentals and applications

What is the effect of increased cell temperature on a crystalline silicon module's open-circuit voltage?

  1. Voc decreases as temperature rises Correct answer.
  2. Voc is unaffected by temperature
  3. Voc increases as temperature rises
  4. Voc first increases then becomes zero

Explanation

Higher temperature increases intrinsic carrier concentration and reduces the junction's built-in potential, so Voc falls. This is why voltage temperature coefficients are negative and why cold-weather voltage must be checked.

Question 24Photovoltaic systems fundamentals and applications

A designer is comparing a string of modules with a Vmp of 300 V to a battery bank of 48 V through a charge controller. Which controller type is appropriate?

  1. A bypass diode, because it regulates charging
  2. An MPPT controller, because it can convert the high array voltage to the lower battery voltage Correct answer.
  3. A PWM controller, because it converts excess voltage to current
  4. A blocking diode, because it steps down voltage

Explanation

An MPPT controller can operate the array near its high Vmp and convert that power down to the battery voltage. A PWM controller would force the array to battery voltage and waste the large voltage difference.

Question 25Photovoltaic systems fundamentals and applications

Which statement best explains why PV modules are rated in watts under STC rather than under typical operating conditions?

  1. STC ratings account for all system losses
  2. STC ratings guarantee real-world output year-round
  3. STC conditions occur most days in most climates
  4. STC provides a consistent reference that allows fair comparison between modules Correct answer.

Explanation

STC is a standardized laboratory reference, so modules from different manufacturers can be compared on equal terms. Actual field output differs because irradiance, temperature, and soiling vary.

Question 26Photovoltaic systems fundamentals and applications

A PV module has a temperature coefficient of power of -0.40 %/°C. If the cell temperature rises from 25 °C to 45 °C, what is the approximate percentage change in maximum power?

  1. -0.8 %
  2. -20 %
  3. -8.0 % Correct answer.
  4. +0.8 %

Explanation

The power change is the coefficient multiplied by the temperature difference: -0.40 %/°C × 20 °C = -8.0 %. A negative coefficient means power decreases as temperature rises above 25 °C. This linear approximation is standard for crystalline silicon modules over modest temperature ranges.

Question 27Photovoltaic systems fundamentals and applications

Which condition defines Standard Test Conditions (STC) for rating a PV module?

  1. 500 W/m² irradiance, 25 °C cell temperature, AM 1.5 spectrum
  2. 1000 W/m² irradiance, 20 °C ambient temperature, AM 1.5 spectrum
  3. 1000 W/m² irradiance, 25 °C cell temperature, AM 1.5 spectrum Correct answer.
  4. 800 W/m² irradiance, 20 °C ambient temperature, AM 1.0 spectrum

Explanation

STC is defined as 1000 W/m² irradiance, 25 °C cell temperature, and an air mass 1.5 reference spectrum. These conditions allow consistent comparison of module ratings. Note that cell temperature, not ambient temperature, is specified.

Question 28Photovoltaic systems fundamentals and applications

A PV system uses a central inverter with a rated AC output of 10 kW. If the inverter's peak efficiency is 97 % and the array produces 9.5 kW DC at a given moment, what is the approximate AC output?

  1. 9.79 kW
  2. 9.22 kW Correct answer.
  3. 10.00 kW
  4. 9.50 kW

Explanation

AC output equals DC input multiplied by efficiency: 9.5 kW × 0.97 = 9.215 kW, approximately 9.22 kW. Efficiency losses in the inverter reduce the delivered AC power. The inverter cannot output more than its DC input under these conditions.

Question 29Photovoltaic systems fundamentals and applications

Which type of PV system is designed to operate without any connection to the utility grid and typically includes battery storage?

  1. Hybrid system
  2. Stand-alone system Correct answer.
  3. Grid-tied system
  4. Grid-interactive system

Explanation

A stand-alone PV system operates independently of the utility grid and usually incorporates batteries to supply power during periods without sunlight. Grid-tied and grid-interactive systems are connected to the utility. A hybrid system may include multiple energy sources but is not defined by grid independence alone.

Question 30Photovoltaic systems fundamentals and applications

What is the primary safety hazard associated with the DC side of a PV array during daylight hours?

  1. The array current is limited to safe levels by the modules
  2. The array produces dangerous AC voltage
  3. The array voltage drops to zero when the inverter is off
  4. The array remains energized whenever exposed to light Correct answer.

Explanation

PV modules generate voltage whenever illuminated, so the DC conductors remain energized even if the inverter is shut down or the AC disconnect is open. This is a key difference from typical AC circuits. Proper lockout/tagout and covering modules may be required for safe work.

Question 31Photovoltaic systems fundamentals and applications

Which of the following is a common application of PV systems in remote locations?

  1. Building-integrated photovoltaics
  2. Utility-scale generation
  3. Water pumping Correct answer.
  4. Rooftop grid-tied systems

Explanation

PV-powered water pumping is a classic remote application where grid power is unavailable. It uses a PV array to drive a pump motor directly or through a controller. The other options are typically associated with grid-connected or urban installations.

Question 32Photovoltaic systems fundamentals and applications

A PV module has a Vmp of 36 V and an Imp of 8 A. What is its maximum power output under STC?

  1. 288 W Correct answer.
  2. 4.5 W
  3. 36 W
  4. 44 W

Explanation

Maximum power is the product of voltage at maximum power and current at maximum power: 36 V × 8 A = 288 W. This is the module's rated power at STC. The other values result from incorrect arithmetic or using only one parameter.

Question 33Photovoltaic systems fundamentals and applications

Which PV system component converts DC power from the array into AC power for use by household loads?

  1. Bypass diode
  2. Charge controller
  3. Inverter Correct answer.
  4. Combiner box

Explanation

The inverter performs the DC-to-AC conversion. Charge controllers regulate battery charging, bypass diodes protect against shading effects, and combiner boxes merge multiple strings. Only the inverter provides AC output.

Question 34Photovoltaic systems fundamentals and applications

A module has a Voc of 44 V and a Vmp of 36 V. What is the approximate ratio Vmp/Voc, and what does it indicate?

  1. 1.22, the module's voltage gain
  2. 0.50, the module's derating factor
  3. 0.82, a typical fill-factor-related voltage ratio Correct answer.
  4. 0.82, the module's efficiency

Explanation

The ratio Vmp/Voc is about 36/44 = 0.82. This ratio is related to the shape of the I-V curve and is typically between 0.75 and 0.85 for crystalline silicon modules. It is not an efficiency or a derating factor.

Question 35Photovoltaic systems fundamentals and applications

A PV array is rated 5 kW STC and receives an average daily irradiance of 4.5 kWh/m²/day. Assuming a derating factor of 0.8, what is the estimated average daily energy production?

  1. 4 kWh
  2. 22.5 kWh
  3. 5.6 kWh
  4. 18 kWh Correct answer.

Explanation

Daily energy ≈ array rating × peak sun hours × derating factor = 5 kW × 4.5 h × 0.8 = 18 kWh. Peak sun hours are numerically equal to daily irradiance in kWh/m². The derating factor accounts for losses.

Question 36Photovoltaic systems fundamentals and applications

Which statement accurately describes the relationship between cell temperature and module efficiency for crystalline silicon?

  1. Efficiency is independent of cell temperature
  2. Efficiency decreases only when irradiance is below 500 W/m²
  3. Efficiency decreases as cell temperature increases Correct answer.
  4. Efficiency increases as cell temperature increases

Explanation

For crystalline silicon, higher cell temperatures reduce voltage and therefore power and efficiency. This is quantified by a negative temperature coefficient of power, typically around -0.4 %/°C. Irradiance level affects current but not the direction of the temperature effect.

Question 37Photovoltaic systems fundamentals and applications

A grid-tied PV system without battery storage uses a string inverter. What is the primary function of the inverter's anti-islanding feature?

  1. To disconnect from the grid when utility voltage is lost Correct answer.
  2. To protect the array from reverse current at night
  3. To convert DC to AC at the highest possible efficiency
  4. To maximize power output from the array

Explanation

Anti-islanding detects loss of utility voltage and disconnects the inverter to prevent backfeeding an islanded grid, protecting utility workers. Maximum power point tracking maximizes output, and blocking diodes prevent reverse current. Efficiency is a performance characteristic, not the purpose of anti-islanding.

Question 38Photovoltaic systems fundamentals and applications

A PV module has an Isc of 9 A and a Voc of 40 V. Under a certain irradiance, its maximum power point is 250 W. What is the module's fill factor?

  1. 0.90
  2. 0.75
  3. 0.69 Correct answer.
  4. 0.80

Explanation

Fill factor = Pmax / (Voc × Isc) = 250 / (40 × 9) = 250 / 360 ≈ 0.694. Fill factor indicates the squareness of the I-V curve. Values around 0.7 are typical for crystalline silicon modules.

Question 39Photovoltaic systems fundamentals and applications

Why are PV modules typically wired in series strings for grid-tied systems?

  1. To raise the voltage to a level suitable for the inverter Correct answer.
  2. To allow the use of thinner wires for the same power
  3. To reduce the effect of shading on the array
  4. To increase the current output of the array

Explanation

Series wiring adds voltages, allowing the array to reach the high DC input voltage required by many grid-tied inverters. Parallel wiring would increase current instead. Higher voltage reduces current for the same power, which can reduce wire size, but that is a secondary benefit, not the primary reason.

Question 40Photovoltaic systems fundamentals and applications

A PV array is installed at a location with an average daily irradiance of 5.0 kWh/m²/day. If the array is rated 4 kW STC and the system derating factor is 0.75, what is the estimated annual energy production?

  1. 7,300 kWh
  2. 1,500 kWh
  3. 5,475 kWh Correct answer.
  4. 20,000 kWh

Explanation

Daily energy = 4 kW × 5.0 h × 0.75 = 15 kWh. Annual energy = 15 kWh/day × 365 days = 5,475 kWh. This method uses peak sun hours and a derating factor.

Question 41Photovoltaic systems fundamentals and applications

Which of the following best describes the function of a charge controller in a battery-based PV system?

  1. It tracks the maximum power point of the array
  2. It regulates voltage and current to prevent battery overcharge and overdischarge Correct answer.
  3. It provides overcurrent protection for the array
  4. It converts DC to AC for AC loads

Explanation

A charge controller manages the charging and discharging of batteries to protect them from damage. It may also include maximum power point tracking, but that is not its primary function. Inverters convert DC to AC, and overcurrent devices provide protection.

Question 42Photovoltaic systems fundamentals and applications

A string of 10 modules has a Voc of 40 V each at STC. At the coldest expected temperature, the module Voc increases by 10 %. What is the string Voc at that temperature?

  1. 360 V
  2. 400 V
  3. 440 V Correct answer.
  4. 480 V

Explanation

At STC, string Voc = 10 × 40 V = 400 V. A 10 % increase gives 400 V × 1.10 = 440 V. This calculation is important for verifying inverter maximum input voltage.

Question 43Photovoltaic systems fundamentals and applications

A PV module has a temperature coefficient of Voc of -0.30 %/°C. If the cell temperature rises from 25 °C to 65 °C, what is the approximate percentage change in Voc?

  1. -30 %
  2. -0.12 %
  3. +12 %
  4. -12 % Correct answer.

Explanation

The change is -0.30 %/°C × (65 - 25) °C = -12 %. Voc decreases as temperature rises, which is why string voltage is highest on cold days. The calculation uses the temperature difference, not the absolute temperature.

Question 44Photovoltaic systems fundamentals and applications

Which of the following is a key advantage of a microinverter system compared with a string inverter system?

  1. Lower initial cost per watt
  2. Simpler wiring with fewer components on the roof
  3. Module-level maximum power point tracking reduces the impact of shading Correct answer.
  4. Higher individual inverter efficiency

Explanation

Microinverters are installed per module, so each module can operate at its own maximum power point, which mitigates shading and mismatch losses. They typically cost more and involve more rooftop components. String inverters often have similar or higher peak efficiency.

Question 45Photovoltaic systems fundamentals and applications

A PV array is to be installed on a roof with a pitch of 30 degrees facing south in the northern hemisphere. Which tilt angle would typically maximize annual energy production at a latitude of 40 degrees?

  1. 40 degrees Correct answer.
  2. 0 degrees
  3. 60 degrees
  4. 10 degrees

Explanation

For fixed-tilt systems in the northern hemisphere, annual energy is often maximized when the tilt is close to the site latitude. At 40 degrees latitude, a tilt near 40 degrees is a good starting point, though optimization may vary with local climate. Steeper or flatter tilts favor winter or summer respectively.

Question 46Photovoltaic systems fundamentals and applications

A PV module has a bypass diode. Under normal operation, what is the state of the bypass diode?

  1. Short-circuited
  2. Open-circuited
  3. Reverse-biased and not conducting Correct answer.
  4. Forward-biased and conducting

Explanation

In normal operation, the bypass diode is reverse-biased by the module voltage and does not conduct. It becomes forward-biased only when a portion of the module is shaded and the voltage across it reverses. This prevents hot spots and power loss.

Question 47Photovoltaic systems fundamentals and applications

A PV array has a Vmp of 350 V and an Imp of 10 A. The inverter has a maximum DC input current of 12 A and a maximum DC voltage of 500 V. What is the array's maximum power, and is it within the inverter's limits?

  1. 4,200 W; yes, both are within limits
  2. 3,500 W; no, the current exceeds the limit
  3. 3,500 W; yes, both voltage and current are within limits Correct answer.
  4. 3,500 W; no, the voltage exceeds the limit

Explanation

Array maximum power = 350 V × 10 A = 3,500 W. The Vmp of 350 V is below the 500 V maximum, and the Imp of 10 A is below the 12 A maximum. Therefore the array is within the inverter's DC input limits.

Question 48Photovoltaic systems fundamentals and applications

A PV module has an I-V curve with a fill factor of 0.78. If the module's Isc is 8.5 A and its Voc is 42 V, what is its approximate maximum power?

  1. 278 W Correct answer.
  2. 215 W
  3. 357 W
  4. 300 W

Explanation

Pmax = FF × Voc × Isc = 0.78 × 42 × 8.5 = 0.78 × 357 = 278.46 W, approximately 278 W. This calculation uses the definition of fill factor.

Question 49Photovoltaic systems fundamentals and applications

A PV array is composed of two strings in parallel, each with 12 modules in series. Each module has a Vmp of 30 V and an Imp of 5 A. What are the array's Vmp and Imp?

  1. 360 V and 10 A Correct answer.
  2. 720 V and 10 A
  3. 360 V and 5 A
  4. 30 V and 10 A

Explanation

Series modules add voltage: 12 × 30 V = 360 V. Parallel strings add current: 2 × 5 A = 10 A. The array voltage is the string voltage, and the array current is the sum of string currents.

Question 50Photovoltaic systems fundamentals and applications

A grid-tied PV system uses a string inverter with a rated AC output of 5 kW. The array is rated 6 kW STC. The inverter's CEC efficiency is 96 %. At an array DC input of 5.5 kW, what is the approximate AC output, and is it within the inverter's rating?

  1. 5.50 kW; yes, within the 5 kW rating
  2. 5.28 kW; yes, within the 5 kW rating Correct answer.
  3. 5.28 kW; no, exceeds the 5 kW rating
  4. 5.72 kW; yes, within the 5 kW rating

Explanation

AC output = 5.5 kW × 0.96 = 5.28 kW. This exceeds the inverter's rated AC output of 5 kW, so the inverter would limit output to 5 kW. The calculated value is not within the rating.