21 Solar Resource & System Components Practice Questions & Answers

1. 1. At any instant the sun's position in the sky is fixed by two angles. Which statement describes the altitude angle and the azimuth angle correctly?

   • A.Altitude is the sun's height above the horizon; azimuth is its compass bearing.✓ Answer
   • B.Altitude is the site's elevation above sea level; azimuth is the day's length.
   • C.Altitude is the array's tilt from horizontal; azimuth is the site's latitude.
   • D.Altitude is the sun's compass bearing; azimuth is its height above the horizon.

   Altitude is measured upward from the horizon, from 0° at the horizon to 90° straight overhead, while azimuth is a compass bearing measured from true north, so 180° is true south. The same two angles describe an array's tilt and orientation, which is why a compass reading taken on site must be corrected from magnetic to true north before it is used.

   Source: Standard solar geometry: solar altitude and azimuth angles; NABCEP PV Associate task analysis, solar resource and array orientationReport a problem with this question

2. 2. In the northern hemisphere, how does the sun's daily path in late June differ from its path at the equinox?

   • A.It rises north of east, stays lower at midday and sets south of west.
   • B.It rises south of east, climbs higher at midday and sets south of west.
   • C.It rises exactly due east, stays lower at midday and sets exactly due west.
   • D.It rises north of east, climbs higher at midday and sets north of west.✓ Answer

   Solar declination reaches about +23.45° at the June solstice, so the sunrise and sunset points swing north of due east and due west and the arc across the sky is both longer and higher. At the equinoxes declination is 0° and the sun rises due east and sets due west from any latitude, which is why an equinox day is the reference for east-west shading checks.

   Source: Standard solar geometry: solar declination varies between +23.45° and −23.45°; NABCEP PV Associate task analysis, sun path and site orientationReport a problem with this question

3. 3. A homeowner in the northern United States has two unshaded roof planes of equal area available for a fixed array: one faces true south and one faces true west. Which statement about annual production is correct?

   • A.The south-facing plane produces the same, since both get equal insolation.
   • B.The south-facing plane produces less, since the afternoon sun is stronger.
   • C.The south-facing plane produces more, since it faces the sun's average position.✓ Answer
   • D.The south-facing plane produces more only in winter; in summer west wins.

   North of the tropics the sun stays in the southern half of the sky all year, so a plane facing true south sits closest to perpendicular to the average direction of the sunlight and collects the most annual plane-of-array irradiation. A west-facing plane collects noticeably less energy over a year, although it may still be attractive where late-afternoon energy is worth more.

   Source: NABCEP PV Associate task analysis, array orientation and factors affecting performance; solar geometry for northern-hemisphere sitesReport a problem with this question

4. 4. A fixed array is being planned, and the installer compares a tilt steeper than the site latitude with a lower tilt. What is the seasonal trade-off of the steeper tilt?

   • A.Steeper tilt favors summer yield and gives up some winter yield.
   • B.Steeper tilt favors winter yield and gives up some summer yield.✓ Answer
   • C.Steeper tilt favors nothing seasonally; only soiling and snow change.
   • D.Steeper tilt favors every month, since the array sits nearer the sun.

   The winter sun stays low in the sky, so a steeper plane meets its rays closer to perpendicular and gains winter energy, while the high summer sun strikes that same steep plane at a poorer angle and summer energy falls. A tilt near the site latitude is the usual compromise for maximum annual energy, and steeper tilts also shed snow and shed dust more readily.

   Source: NABCEP PV Associate task analysis, array tilt and seasonal performance; standard fixed-tilt PV design practiceReport a problem with this question

5. 5. A sensor in the plane of the array reads 850 W/m² in mid-morning, and the same plane's total for the day is logged as 5.4 kWh/m². How should these two numbers be described?

   • A.The first is irradiation, an energy total; the second is irradiance, a power density.
   • B.Both are irradiation, differing only in the units the datalogger was set to.
   • C.The first is irradiance, a power density; the second is irradiation, an energy total.✓ Answer
   • D.Both are irradiance: one instantaneous and one averaged over daylight hours.

   Irradiance is the power of sunlight arriving on a unit of area at this instant, expressed in watts per square metre, while irradiation, also called insolation, is that power accumulated over a period and is expressed in watt-hours or kilowatt-hours per square metre. Mixing the two is the classic error behind sizing mistakes, because one is a rate and the other is a quantity of energy.

   Source: Standard solar radiation terminology: irradiance in W/m² versus irradiation or insolation in kWh/m²; NABCEP PV Associate task analysis, solar resourceReport a problem with this question

6. 6. A resource dataset gives 5.5 kWh/m² per day in the plane of a proposed array. How many peak sun hours does that value represent?

   • A.5.5 peak sun hours, since one such hour means 1,000 W/m² for an hour.✓ Answer
   • B.0.55 peak sun hours, since one such hour means 10,000 W/m² for an hour.
   • C.55 peak sun hours, since one such hour means 100 W/m² for an hour.
   • D.5.5 peak sun hours, but only if the sky stays clear for 5.5 hours.

   One peak sun hour is defined as one hour of sunlight at 1,000 W/m², which delivers exactly 1 kWh/m², so a day's irradiation in kWh/m² and that day's peak sun hours are numerically the same number. Peak sun hours are a way of repackaging a whole day of changing irradiance into an equivalent block at the reference level, not a count of cloud-free hours.

   Source: Standard definition of peak sun hours: 1 kWh/m² equals one hour at 1,000 W/m²; NABCEP PV Associate task analysis, solar resourceReport a problem with this question

7. 7. A 6.0 kW dc array is proposed at a site with 5.5 peak sun hours per day in the array plane. Applying an overall system derate of 0.80, what average daily ac energy should be estimated?

   • A.About 4.4 kWh per day.
   • B.About 33 kWh per day.
   • C.About 26 kWh per day.✓ Answer
   • D.About 48 kWh per day.

   Daily energy is estimated as array dc rating multiplied by peak sun hours multiplied by the derate factor: 6.0 kW × 5.5 h × 0.80 = 26.4 kWh. Dropping the derate gives 33 kWh, using total daylight hours instead of peak sun hours inflates the figure badly, and multiplying only the peak sun hours by the derate leaves out the array size altogether.

   Source: Standard PV production estimate: array kW(dc) × peak sun hours × derate factor; NABCEP PV Associate task analysis, estimating system performanceReport a problem with this question

8. 8. A grid-connected array still delivers a fraction of its usual power on a heavily overcast day. What accounts for that output?

   • A.Because the inverter feeds grid power backward to steady the array.
   • B.Because heat radiated down by the cloud deck drives current in the cells.
   • C.Because the modules release energy stored on the previous sunny day.
   • D.Because diffuse light scattered by cloud and sky still reaches the modules.✓ Answer

   The sunlight reaching an array is the sum of a beam component straight from the sun, a diffuse component scattered by the atmosphere and clouds, and a component reflected from the ground. Overcast skies block almost all of the beam component but the diffuse component remains, so the array keeps producing at a reduced level; PV cells respond to light, not to warmth, and modules store no energy.

   Source: Solar radiation components: beam, diffuse and ground-reflected irradiance; NABCEP PV Associate task analysis, factors affecting performanceReport a problem with this question

9. 9. After a snowfall the ground around a ground-mounted array is bright white, and the array briefly exceeds the clear-sky expectation. Which part of the plane-of-array irradiance has increased?

   • A.The extraterrestrial component, measured above the earth's atmosphere.
   • B.The diffuse component, scattered by water vapour high in the atmosphere.
   • C.The reflected component, bounced onto the modules by the bright ground.✓ Answer
   • D.The beam component, arriving in a straight line from the sun's disc.

   Plane-of-array irradiance is the sum of beam, diffuse and ground-reflected light, and the reflected share depends on the albedo of the surrounding surface. Fresh snow and light-coloured roof membranes reflect strongly, so a tilted array picks up extra irradiance, and the cold air that comes with snow raises module voltage at the same time.

   Source: Plane-of-array irradiance components and ground-reflected (albedo) gain; NABCEP PV Associate task analysis, factors affecting performanceReport a problem with this question

10. 10. An array reaches higher instantaneous ac power on a cold, clear March morning than on a hot, hazy August afternoon. What best explains this?

    • A.Cool cells hold a higher operating voltage, and clear air passes more light.✓ Answer
    • B.Cool cells hold a higher operating current, since resistance falls in the cold.
    • C.Warm cells hold a higher operating voltage, but haze reflects heat back down.
    • D.Warm cells hold their rated power exactly, while cool cells run below rating.

    Module voltage carries a negative temperature coefficient, so cool cells operate at a higher voltage and therefore at higher power for the same light, while the small positive coefficient on current nowhere near compensates on a hot day. Clean, dry, cold air also scatters and absorbs less sunlight than a hot hazy sky, so more irradiance actually reaches the array.

    Source: Module temperature coefficients (voltage and power fall as cell temperature rises) and atmospheric attenuation of irradiance; NABCEP PV Associate task analysis, temperature and irradiance effectsReport a problem with this question

11. 11. What physically distinguishes a thin-film module from a crystalline silicon module?

    • A.Its semiconductor is a thin layer deposited on a substrate, not a sawn wafer.✓ Answer
    • B.Its semiconductor is replaced by a heat absorber that makes current from warmth.
    • C.Its semiconductor is the same wafer, mounted behind thinner glass and unframed.
    • D.Its semiconductor is a thicker silicon wafer, cut from a grown crystal.

    Crystalline silicon modules are built from wafers sliced from a grown ingot and soldered into series strings, while thin-film modules are made by depositing a semiconductor layer only micrometres thick onto a glass or flexible substrate and scribing it into cells. That difference in construction is why thin-film modules generally convert a smaller share of the light and need more area per watt, though they often behave better in heat and in weak light.

    Source: Photovoltaic device technologies: wafer-based crystalline silicon versus deposited thin-film semiconductors; NABCEP PV Associate task analysis, PV modulesReport a problem with this question

12. 12. A module's nameplate power is stated at standard test conditions (STC). Why does a working rooftop array seldom reach that number?

    • A.STC assumes the inverter is bypassed, so an ac system never reaches it.
    • B.STC assumes a battery absorbs the output, which grid-tied systems lack.
    • C.STC assumes 1,000 W/m² and a 25 °C cell temperature, rarely met on a sunlit roof.✓ Answer
    • D.STC assumes a brand-new module, so only the first month of service counts.

    Standard test conditions fix 1,000 W/m² of irradiance, a 25 °C cell temperature and a defined reference spectrum so that modules from different makers can be compared on the same footing. A module in full sun runs far hotter than 25 °C, and irradiance, soiling, wiring and inverter losses all move the real output away from the label, so the nameplate is a reference rating rather than a promise of production.

    Source: Standard test conditions for PV module ratings (1,000 W/m², 25 °C cell temperature, AM1.5 reference spectrum); NABCEP PV Associate task analysis, equipment specificationsReport a problem with this question

13. 13. A technician measures the voltage across the leads of one module in full sun with nothing else connected. Which datasheet value should that reading be compared with?

    • A.Isc, the module's current when the leads are shorted together.
    • B.Pmax, the module's power when loaded at its peak power point.
    • C.Voc, the module's voltage when no current is being drawn.✓ Answer
    • D.Vmp, the module's voltage when loaded at its peak power point.

    With nothing connected no current can flow, which is by definition the open-circuit condition, so the meter reads the open-circuit voltage Voc. Vmp and Imp describe the loaded operating point where power peaks, Isc is the current with the output shorted, and Voc itself climbs as cell temperature falls, which is why the coldest sunny conditions set the highest array voltage.

    Source: PV module datasheet parameters at STC: Voc, Isc, Vmp, Imp and Pmax; NABCEP PV Associate task analysis, equipment specificationsReport a problem with this question

14. 14. What is the fundamental job of the inverter in a grid-connected PV system?

    • A.It converts sunlight into dc before the current reaches the modules.
    • B.It converts grid ac into dc so the modules are kept charged overnight.
    • C.It converts array dc into ac matched to the grid's voltage and frequency.✓ Answer
    • D.It converts service ac into a lower ac voltage for the branch circuits.

    Modules generate direct current, but a building's wiring and the utility grid run on alternating current, so the inverter's core task is converting dc into ac and synchronizing that ac to the utility's voltage and frequency. The same unit normally also performs maximum power point tracking and the grid-support and anti-islanding functions required of utility-interactive equipment.

    Source: Function of a utility-interactive PV inverter: dc-to-ac conversion synchronized to grid voltage and frequency; NABCEP PV Associate task analysis, system componentsReport a problem with this question

15. 15. Maximum power point tracking is best described as which of the following?

    • A.A metering function that logs the highest power reached on each day.
    • B.A control function that trims operating voltage to keep the array at peak power.✓ Answer
    • C.A mechanical function that turns the array to follow the sun across the sky.
    • D.A protective function that opens the circuit when array power exceeds rating.

    An array's current-voltage curve has one knee where the product of voltage and current is greatest, and that knee moves continuously as irradiance and cell temperature change. Maximum power point tracking is the control action, performed inside an inverter or an optimizer, that keeps shifting the operating voltage so the array stays at that knee; it is a function, not a separate piece of hardware, and it has nothing to do with mechanical tracking of the sun.

    Source: Maximum power point tracking as an inverter control function on the module or array I-V curve; NABCEP PV Associate task analysis, inverters and power electronicsReport a problem with this question

16. 16. Dc optimizers mounted on individual modules exist mainly to address which problem?

    • A.Battery imbalance, in which cells in the storage bank charge unevenly.
    • B.Module mismatch, in which a weak module limits the whole series string.✓ Answer
    • C.Conductor ampacity, in which string current exceeds the wire's rating.
    • D.Grid instability, in which utility voltage swings during the afternoon.

    Because series-connected modules share one current, a module that is shaded, soiled, damaged or simply weaker holds back every module in the string. A dc-dc optimizer performs maximum power point tracking at the module and adjusts that module's contribution to the string, so the mismatch is contained; the same devices usually add module-level monitoring and can serve as a means of reducing conductor voltage in the array.

    Source: Module-level power electronics: dc-dc optimizers and mitigation of series-string mismatch; NABCEP PV Associate task analysis, power electronicsReport a problem with this question

17. 17. Which statement correctly pairs a mounting approach with what it asks of the supporting structure?

    • A.A ground-mounted array needs no foundation, because the soil carries the weight.
    • B.A ballasted flat-roof array adds dead weight to the roof instead of penetrations.✓ Answer
    • C.A tilted rack on a roof lowers the wind load compared with flush mounting.
    • D.A flush-mounted pitched-roof array transfers its load to the sheathing, not framing.

    A ballasted array is held in place by weight rather than by fasteners, so it avoids roof penetrations but adds dead load that the existing roof structure must be verified to carry. A flush-mounted array on a pitched roof must land its attachments in framing members with each penetration properly flashed, tilted racks catch more wind and raise uplift forces, and ground mounts need engineered footings for uplift and, where it applies, frost depth.

    Source: PV mounting systems: ballasted low-slope, attached pitched-roof and ground-mounted structures and their structural demands; NABCEP PV Associate task analysis, mounting and rackingReport a problem with this question

18. 18. Which pairing of a balance-of-system item with its function is correct?

    • A.PV connector — provides the bonding path between module frames and racking.
    • B.Combiner box — joins several source circuits into one output circuit with fusing.✓ Answer
    • C.Overcurrent device — synchronizes the array output with the utility waveform.
    • D.Dc disconnect — limits the current a faulted circuit can carry to the inverter.

    A combiner box parallels several source circuits into a single output circuit and commonly houses the overcurrent protection for each of them. A disconnecting means exists to open a circuit so equipment can be worked on or isolated, overcurrent devices protect conductors from currents beyond their rating, and connectors are mating terminations for conductors, while equipment bonding is done with listed bonding hardware and an equipment grounding conductor.

    Source: Balance-of-system functions: combiner boxes, disconnecting means, overcurrent protection, conductors and connectors; NABCEP PV Associate task analysis, system componentsReport a problem with this question

19. 19. What does a monitoring system contribute once a PV array is in service?

    • A.It raises production by holding the array at its best operating point.
    • B.It replaces the periodic visual inspection the owner would otherwise need.
    • C.It reports production data so shortfalls can be spotted and investigated.✓ Answer
    • D.It protects the array by opening the circuit when a ground fault occurs.

    Monitoring measures and communicates power and energy, often at string or module level, so actual output can be compared with what the site and weather should be producing and any deviation can be traced to soiling, shading, a fault or an equipment failure. It is an information tool: it does not regulate the array, it does not provide protection, and it does not remove the need for physical inspection.

    Source: Role of PV monitoring and production data in system operations; NABCEP PV Associate task analysis, monitoring and system performanceReport a problem with this question

20. 20. In a PV system with battery storage, what distinguishes dc coupling from ac coupling?

    • A.Dc-coupled batteries charge from array dc through a charge-control stage.✓ Answer
    • B.Dc-coupled batteries charge only from the utility and never from the array.
    • C.Dc-coupled batteries charge from the ac output through a second inverter.
    • D.Dc-coupled batteries charge with no conversion stage at all between them and loads.

    In a dc-coupled system the array's direct current reaches the battery through a charge controller or the dc bus of a hybrid inverter, so the energy is stored without being inverted first. In an ac-coupled system the PV inverter makes ac and a separate battery inverter-charger turns that ac back into dc to charge, which costs an extra conversion but makes it easy to add storage to an existing PV system.

    Source: AC-coupled versus DC-coupled photovoltaic and energy storage architectures; NABCEP PV Associate task analysis, energy storageReport a problem with this question

21. 21. A customer with an ordinary grid-tied PV system and no battery asks why the lights go out during a utility outage, even at noon on a sunny day. What is the correct explanation?

    • A.The inverter must cease output until utility crews reset it at the meter socket.
    • B.The inverter must cease output because the modules stop producing dc in an outage.
    • C.The inverter must cease output because the array's dc voltage collapses at noon.
    • D.The inverter must cease output into a dead line, and it cannot island the house alone.✓ Answer

    Utility-interactive inverters include anti-islanding protection, which shuts the output down when the grid goes away so that no energy is pushed onto lines that crews and the public may treat as de-energized. The array is still making dc, but backing up a home requires storage together with an inverter able to form its own island and a load panel separated from the utility, which a plain grid-tied system does not have.

    Source: Anti-islanding function of utility-interactive inverters and the requirement for storage with an islanding-capable inverter to supply loads during an outage; NABCEP PV Associate task analysis, PV system typesReport a problem with this question

Practice questions based on the published knowledge domains of the NABCEP PV Associate Job Task Analysis and on standard photovoltaic engineering and safety references. NABCEP is not affiliated with this site and does not endorse it. Answers here deliberately avoid code dimensions, manufacturer specifications, incentive rules and prices, all of which change and vary by jurisdiction — always apply the electrical and building codes adopted by the authority having jurisdiction, the equipment manufacturer's instructions, and your employer's safety program. Confirm current exam requirements with NABCEP before testing. About the NABCEP Associate program →