NCCER Solar PV flashcards
NCCER Solar PV · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Standard Test Conditions
- Reference conditions of 1000 W/m² irradiance, 25 °C cell temperature, and AM 1.5 spectrum used to rate module nameplate power. Field conditions rarely match, so actual output differs from STC.
- Irradiance vs. Insolation
- Irradiance is instantaneous solar power density in W/m². Insolation is energy over time, expressed as kWh/m²/day, also called peak sun hours. Design energy estimates use insolation.
- Series vs. Parallel Strings
- Series connections add voltages and hold current constant. Parallel connections add currents and hold voltage constant. String design uses both to match the inverter input window.
- PV DC Shock Hazard
- PV source and output circuits are live whenever illuminated. No switch de-energizes them, so conductors must be treated as energized at all times.
- Fall Protection Threshold
- OSHA general industry requires fall protection at 6 ft (1.8 m) or more. Guardrails, personal fall arrest systems, and ladder tie-offs are common controls on roof work.
- Lockout/Tagout on PV
- LOTO isolates AC and utility-side equipment. DC circuits cannot be switched off, so physical covering, connector separation, or night work is used instead.
- Ohm's Law and Power
- V = I × R describes the voltage-current-resistance relationship. Power equals voltage times current, P = V × I, which is used to size conductors and overcurrent devices.
- Maximum Power Point
- The operating voltage and current where a module produces the most power. Inverters and charge controllers use MPPT tracking to stay at this point as conditions change.
- Temperature Coefficient of Voc
- Voc rises as cell temperature falls. Cold-record temperatures produce the highest array voltage, which sets the inverter maximum input voltage limit.
- Bypass Diode Function
- A bypass diode provides an alternate path around a shaded or failed cell group, limiting hot-spot heating and preserving string current. It is built into module junction boxes.
- Blocking Diode Purpose
- A blocking diode prevents reverse current from flowing into a weaker or shaded parallel string. It protects against backfeed and is common in battery-based systems.
- MPPT vs. PWM Controller
- MPPT controllers track the array maximum power point and harvest more energy when array voltage exceeds battery voltage. PWM controllers are simpler and lower cost but less efficient.
- Inverter DC Input Window
- The voltage range an inverter accepts at its DC input. The array's cold-temperature Voc and hot-temperature Vmp must fall within this window for safe operation.
- Continuous Current Factor
- Continuous loads require conductors and overcurrent devices sized at 125% of the continuous current. PV output circuits are treated as continuous.
- Equipment Grounding
- Bonding metal enclosures, racks, and module frames to the grounding system provides a fault-current path. It protects people from shock if insulation fails.
- Solar Window
- The portion of the day when the site has unobstructed sun, typically about 9 a.m. to 3 p.m. year-round. Shading outside this window has less impact on yield.
- Azimuth Angle
- The compass direction a module faces, measured in degrees from true north. In the northern hemisphere, 180° (true south) generally yields the most annual production.
- Optimal Tilt Rule
- A common starting estimate for fixed tilt is latitude minus 15°. Steeper tilt favors winter production; shallower tilt favors summer and reduces row shading.
- Annual Energy Estimate
- Array size in kW times peak sun hours times 365 times a derate factor, typically 0.75 to 0.85. The derate accounts for soiling, wiring, inverter, and temperature losses.
- Row Spacing Design
- Inter-row spacing must prevent winter shadows from reaching the next row. Required spacing increases with array tilt angle and site latitude.
- Fire Setback Requirements
- Codes require clear access pathways and setbacks on roofs to allow firefighter movement. These reduce usable array area and must be planned in layout.
- 120% Busbar Rule
- A backfed breaker plus the main breaker may not exceed 120% of the busbar rating. This limits the size of a PV interconnection on an existing service panel.
- Roof Attachment Flashing
- Penetrations through shingle roofs require listed flashing sealed to shed water. Lag screws must engage structural members such as rafters, not just decking.
- Module Clamp Zones
- Manufacturers mark allowable clamp locations on the module frame. Clamping outside these zones can crack glass or void the warranty and structural rating.
- Rapid Shutdown Requirement
- Module-level or string-level devices reduce conductor voltage to a safe level within a set time after AC disconnect. This protects firefighters and service personnel.
- Connector Matching Rule
- Mating connectors from different manufacturers is not permitted. Mixed connector types can fail, overheat, or lose their listing, causing arcing and reliability problems.
- Conduit Expansion Fittings
- Long exterior conduit runs expand and contract with temperature. Expansion fittings prevent buckling, joint separation, and conductor damage on sun-exposed runs.
- Commissioning Sequence
- Visual inspection, grounding and continuity checks, insulation resistance testing, polarity verification, Voc and Isc measurement, then energization. Each step confirms safety before power is applied.
- String Voc Comparison
- Measured string voltage is compared to a temperature-corrected expected value. A low reading suggests an open connector, missing module, or bypassed section.
- Insulation Resistance Test
- A test applying elevated voltage to isolated conductors to detect insulation degradation. Low readings indicate moisture intrusion, damaged cable, or contaminated junction boxes.
- Thermal Imaging Inspection
- An infrared camera under load reveals hot spots, loose terminations, and failing bypass diodes. Comparing similar modules helps identify anomalies quickly.
- Ground Fault Diagnosis
- An inverter ground-fault indication requires isolation before inspection. Use a clamp meter to locate faulted circuits; never open DC conductors while the fault may be active.