Solar PV: NABCEP Exam solved MCQs with theory explained - II

Under standard irradiance of 1000 w/m², ten PV modules rated 340 w each produce 3400 w; efficiency matters only when calculating from area under STC.

Determine a suitable PV module combination to keep inverter input within 250–600 V, using two strings of ten 400 W modules to achieve 8000 W.

Calculate the dc voltage drop by doubling the resistance per thousand feet (1.93 Ω) for the return path, then multiply by current; 200 ft at 10 A yields 7.72 V.

Calculate the minimum number of series pv modules by adjusting vmp for 55°C; with vmp about 34 v, eight modules meet the 250 v inverter minimum.

Bypass diodes in PV systems route current around shaded cell groups, limiting shading effects and preserving power when some cells underperform.

Analyze the PV module I-V curve under 1000 w/m2 to identify the maximum power point region and select point B as the MPPT condition.

Explain how albedo, the reflected irradiance, adds to direct and diffuse sunlight on a pv module. Show that increased irradiance raises current while voltage stays nearly constant.

Temperature governs the modified maximum system voltage by altering the PV module's open-circuit voltage through temperature coefficients; a decrease in temperature raises voltage, while an increase lowers it.

Explore why microinverters are the best solution for multiple PV module orientations in a string, delivering per-module MPPT and isolating each panel to minimize shading effects.

Size a net metered PV system by considering energy usage, budget, and available space, and optimize inverter capacity to maximize grid energy revenue.

Determine mppt voltage for four parallel PV strings of ten modules each using Vmp 41V; parallel wiring keeps the inverter input at the single-string voltage, not the total.

Explain how a charge controller uses bulk, absorption, and float stages to charge a 12-volt lead-acid battery, with absorption around 14 V and float around 13 to 13.8 V.

Wash solar panels in Middle East PV systems to remove sand and maintain efficiency; recognize that shading analysis occurs in the design phase, and relocating panels seasonally is unnecessary.

Explain that a supply-side connected PV system is limited by the size of the service entrance conductors, per Article 705, not by the PV cables or inverter output alone.

Learn how cable length and width influence resistance and voltage drop. The lecture explains that long and thin cables have more resistance and higher voltage drop, while short and wide cables have less.

Compute the maximum system size for a 25 m² roof with a 19% efficient PV module under standard irradiance, yielding about 4.75 kW.

Calculate the minimum number of PV modules in series to meet a 275 V inverter low voltage at 70 °C using 41 V modules and a -0.35%/°C Vmp coefficient.

Discover how solar PV inverters detect only dc leakage current from the arrays as the ground fault, while ac earth leakage remains separate and may trigger internal fault protection.

Compute PV module voltage by dividing total volts by total cells to get per-cell voltage. A 42 V module with 72 cells yields 21 V for 36 cells.

Calculate the number of 12-volt, 100-ampere batteries needed to run a 2400-watt load for one hour. Use 200 A and connect two batteries in parallel.

Determine how many 12-volt 100-ampere batteries are needed to run a 40-amp load for three hours through a 120-volt inverter, which results in twelve batteries in parallel.

Determine how long a 250 watt load on 120 volt AC takes to consume 12 kilowatt-hours, showing that 12 kWh equals 48 hours, or about two days.

Apply standard test conditions with a 25°C cell temperature and 1000 w/m^2 irradiance, and derive the nominal module rating as vmp times imp from the datasheet.

Clarify air mass 1.5 under standard test conditions, including 25°C, 1000 W/m^2, and the air mass 1.5 spectrum; air mass 1.5 is defined by air density, not solar distance.

Calculate the power produced by an array of ten solar modules (1.2 m^2 each, 19% efficiency) under 1000 W/m^2, yielding about 2.28 kW.

Apply NEC guidelines to a 20 A interactive inverter output; 25 A is not a standard breaker, so select 30 A.

Reveal that a charge controller's specifications hinge on the maximum voltage within its voltage range, while irradiance limits and minimum current are not specified.

Micro-inverters are connected at the output of each PV module, enabling orientation flexibility and module-level shutdowns when a module fails, with each unit producing 120 or 220 AC.

Explain standard test conditions and their impact on pv module output, comparing stc's 1000 w/m2 and 25°c cell temperature to act and ptc real-world scenarios.

Determine inter-row spacing for PV modules using solar elevation angle and solar azimuth angle, with module dimensions and worst-case shading on December 21st guiding the calculations.

Explore how a current-carrying conductor creates a magnetic field and define inductance as the ratio of voltage to the rate of change of current.

On a hot summer day, PV cell temperature lowers module voltage, risking inverter input falling below 220 V; the likely fault is too few modules meeting the 220–450 V range.

Learn how current through the human body ranges from slight to painful shocks, with 10 million pairs causing pain, and higher levels risking irregular heartbeat and death.

Determine the optimum tilt for an off-grid PV system in the northern hemisphere during summer: tilt equals latitude minus 15 degrees. For on-grid or net-metered systems, tilt equals the latitude.

Compute the maximum number of PV modules in series for a residential system by adjusting open-circuit voltage for temperature using a 25°C reference and temperature coefficient, staying below 600 V.

Use a clamp meter to measure the PV output current safely without disconnecting wiring; clamp meters provide focused current measurement versus general digital meters.

Learn how to calculate energy units (kWh) for home loads by converting watts to kilowatts and multiplying by hours, with sample calculations totaling 11.01 kWh.

The worst design is multiple orientations within a PV source circuit; keep all modules in a string facing the same direction to maximize current with an mppt controller for strings.

Master safety-focused troubleshooting for a solar pv system showing inverter ground fault, and apply lockout tagout before rooftop inspection.

Calculate the maximum PV modules in series by VOC rise at -20°C with a -0.32%/°C correction from 42 V, within a 500 V inverter limit; ten modules fit.

In parallel, PV modules keep the same voltage while the total current increases, as module currents add.

An off-grid PV system often shuts down in winter because low ambient temperature increases module voltage in series, potentially exceeding the inverter rating; too many modules is the probable cause.

OSHA, not the employer or the employee, sets the safety requirements for employees; guidelines come from an independent organization, making OSHA the correct choice for electrical safety standards.

In the northern hemisphere, the longest shadow on PV modules occurs on December 21st, during the winter solstice, when the sun is most tilted.

This lecture explains how solar irradiance changes affect a PV module's current, voltage, and power, showing that voltage remains nearly constant above 200 w/m square and is least affected.

UL 1703 defines the fire safety and fire performance characterization of flat PV modules, aligning rooftop PV systems with IBC class A, B, or C fire ratings.

Learn how magnetic declination affects compass readings, with eastern or positive declination toward the east and western or negative toward the west. Western US typically shows eastern or positive declination.

Nec requirements for pv modules require equipment to be listed or field labeled, approved by the authority having jurisdiction, with no certifications or proof needed; life exceeds 20–25 years.

Learn to survey a prospective PV site using essential tools—measuring tape, compass, and PPE—to assess location, obstructions, sun path, mounting, and how the system interfaces with electrical systems.

Understand why equinox occurs when the sun is directly overhead at the equator on March 21st, and that equinoxes occur twice a year on March 21st and September 21st.

the lecture uses i-v curves to show irradiance increases current and voltage, while higher cell temperature lowers voltage, concluding that high temperature is not a reason for rising voltages.

Replace the stand-alone PV system's inverter with a multi-modal inverter and batteries to meet load requirements, as simply increasing battery size or PV capacity will not suffice.

Identify the critical design month for a standalone PV system, the month with maximum load and minimum irradiance, to ensure sufficient power and avoid oversizing.

Determine the tilt angle for the PV module at 23 degree latitude for best summer performance; the module should be installed horizontally facing the sun.

Use an irradiance meter, multimeter, and thermography meter to troubleshoot a solar PV system, calculate expected power, and compare it with inverter readings while assessing module, temperature, and cable losses.

When replacing a faulty inverter, verify the new inverter's input voltage range covers the PV array voltage across temperature variations and matches the installed system’s current and power.

Troubleshoot a PV system that intermittently shuts down due to earth fault indicated by the inverter; inspect DC cable insulation and grounding paths to locate faulty insulation touching earth.

Analyze how module mismatch reduces pv system power output and compare inverter types—string, central, microinverter, and multi-modal. Highlight that microinverters provide module-level maximum power point tracking and isolation from shading.

Learn how a circuit breaker at a standalone inverter output trips when current exceeds the breaker's rated current, with context on voltage ratings and reset functionality.

In an interactive system, the PV system disconnect is located between the inverter and the grid or load, per NEC; note variations for standalone and AC coupled configurations.

Identify the most difficult pv system to size—standalone or off-grid with batteries—while comparing interactive, on-grid with batteries, and multi-modal configurations in sizing calculations.

Explain self-regulating stand-alone PV systems without charge controllers, including matching array voltage to the battery bank and NEC 690.72's 3% per hour charge limit.

Determine the inverter's maximum output for a 7.5 kW PV system by multiplying 20 V by 24 A, showing a 5,280 W limit due to clipping under STC.

explains the maximum system voltage ratings for residential, commercial, and ground-level PV installations, highlighting that most modules today are 1500 volts and labeled accordingly.

Select a standalone PV system with high surge overcurrent and buck boost protection for a grid-free remote agriculture pump, using an inverter designed for pumping applications.