NCCER Solar PV cheat sheet

Standard Test Conditions (STC) are 1000 W/m² irradiance, 25 °C cell temperature, and AM 1.5 spectrum; nameplate ratings use STC.

Irradiance is instantaneous power density (W/m²); insolation is energy accumulated over time, commonly expressed in kWh/m²/day (peak sun hours).

Series strings add voltage while current stays constant; parallel connections add current while voltage stays constant.

Per OSHA, 50 V is the threshold for shock hazard; PV source and output circuits are energized whenever illuminated and cannot be de-energized by a switch.

Arc flash and shock risk persist on the DC side; treat all conductors as live, use insulated tools, and wear arc-rated PPE per the site risk assessment.

Fall protection is required at 6 ft (1.8 m) or more in general industry; guardrails, personal fall arrest, and ladder tie-off are typical controls.

Lockout/tagout applies to AC and utility-side equipment; DC conductors require physical covering, disconnection at connectors, or working at night.

A ground-fault on a PV array may not clear because the source is current-limited; use a clamp meter to locate faulted circuits before touching conductors.

Ladder safety rule: 4-to-1 slope for extension ladders, 3 ft (0.9 m) extension above the landing, and maintain three points of contact.

Power = Voltage × Current (P = V × I); for DC circuits, P(W) = V(V) × I(A).

A module's maximum power point is where the product of voltage and current is greatest; MPPT electronics track this point as irradiance and temperature change.

Open-circuit voltage (Voc) rises as cell temperature falls; use the temperature coefficient of Voc to calculate cold-temperature maximum voltage.

A bypass diode limits hot-spot heating by allowing current to bypass a shaded cell group; a blocking diode prevents reverse current in parallel strings.

An inverter's DC input window must contain the array's expected voltage range from record-low temperature to record-high temperature.

A charge controller regulates battery charging; PWM is simple and lower cost, MPPT harvests more energy when array voltage exceeds battery voltage.

Battery capacity is rated in amp-hours at a specified C-rate; usable energy depends on depth of discharge and round-trip efficiency.

Conductor ampacity must be derated for ambient temperature and conduit fill; continuous currents are multiplied by 1.25 for overcurrent sizing.

Grounding has two roles: equipment grounding bonds metal parts for fault clearing, and system grounding references one conductor to earth.

Solar window: a site needs unobstructed sun roughly 9 a.m. to 3 p.m. year-round; use a solar pathfinder or shading tool to quantify losses.

Azimuth is measured in degrees from true north; in the northern hemisphere, true south is 180° and is the usual optimal orientation.

Tilt angle affects yield; a common rule is latitude minus 15° for year-round production, with steeper tilt favoring winter and shallower favoring summer.

Roof plane dimensions, rafter spacing, and structural capacity must be verified before layout; leave required fire setbacks and access pathways.

Annual energy estimate: array kW × peak sun hours × 365 × system derate factor (typically 0.75–0.85).

Row spacing between arrays must prevent winter shadowing; spacing grows with tilt angle and latitude.

Shading on one module affects the whole series string; string layout and module-level electronics are chosen to limit mismatch losses.

Interconnection limits depend on busbar rating and main breaker size; the 120% rule caps backfed breaker size relative to busbar and main.

Roof attachments must penetrate into structural members or be sealed with listed flashing; lag screws into rafters are typical for composition shingle roofs.

Standing seam metal roofs use non-penetrating clamps; corrugated metal and tile roofs require specific mounting hardware and sealing methods.

Ground mounts use driven or concrete piers; the rack must resist design wind and snow loads per local code and engineering.

Module clamps attach at the zones marked by the manufacturer; clamping outside those zones voids the warranty and can crack frames or glass.

Torque fasteners to manufacturer specifications; loose connections cause arcing and are a common source of field failures.

Conduit expansion fittings are required on long exterior runs; use sunlight-resistant, wet-location-rated conduit and fittings outdoors.

Rapid shutdown requires module-level or string-level devices that reduce conductors to a safe voltage within a specified time after AC disconnect.

Keep module connectors of the same type and manufacturer mated together; mixing connector brands creates a reliability and code risk.

Conductor bending radius, support spacing, and expansion must follow code; PV source circuits in conduit need wet-location-rated insulation.

Commissioning sequence: visual inspection, continuity and grounding checks, insulation resistance test, polarity verification, Voc and Isc measurement, then energization.

Compare measured string Voc to expected temperature-corrected values; a low reading points to a missing module, open connector, or bypassed section.

Isc measured with a clamp meter under known irradiance can reveal a weak string; normalize readings to STC for comparison.

Insulation resistance testing is done with the array isolated; a low reading indicates moisture intrusion or damaged insulation.

Thermal imaging under load reveals hot spots, loose terminations, and failing bypass diodes; compare similar modules for baseline.

Common underperformance causes: soiling, shading, mismatch, inverter clipping, and derated conductors; check production against expected kWh.

Inverter fault codes and event logs are the first diagnostic step; a ground-fault indication requires isolation before inspection.

Preventive maintenance includes cleaning, torque checks, connector inspection, vegetation control, and verifying monitoring data trends.

A sudden drop to zero output on one string often indicates a blown fuse, tripped rapid-shutdown device, or open connector.