NABCEP PV Associate key terms

The process by which a semiconductor material converts absorbed light energy directly into direct-current electricity, producing a voltage difference across the cell's internal junction when photons free electrons.

The smallest electricity-producing unit in a module, typically a thin wafer of silicon with a built-in electric field that separates light-generated charge carriers and delivers current to external terminals.

A factory-assembled, weather-sealed package of interconnected PV cells laminated behind glass, providing a rated voltage and current and the physical unit mounted on a system.

The complete assembly of one or more PV modules together with their support structure and wiring, treated as a single generating unit in code and design calculations.

The instantaneous power density of sunlight falling on a surface, measured in watts per square meter; standard test conditions use 1000 W/m² as the reference value.

The cumulative solar energy received per unit area over a period such as a day, expressed in kilowatt-hours per square meter; it drives energy-yield estimates rather than instantaneous power.

The laboratory reference set of 1000 W/m² irradiance, 25 °C cell temperature, and a defined air-mass spectrum, used to rate module power and compare products on a common basis.

The percentage change in module maximum power for each degree Celsius the cell temperature departs from 25 °C; it is negative, so hot modules produce less than their rated output.

The maximum voltage a module or string develops with no load connected, used for code voltage-limit and equipment-rating checks because it rises as cell temperature falls.

The current that flows when module output terminals are connected through a near-zero resistance; it sets the basis for conductor ampacity and overcurrent device sizing.

The operating point on a module's current-voltage curve where the product of current and voltage is greatest; inverters continuously track this point to maximize harvest.

An inverter or charge-controller function that continuously adjusts its operating voltage to keep the array at its maximum power point as irradiance and temperature change.

The ratio of a module's maximum power to the product of its open-circuit voltage and short-circuit current, indicating how square and efficient its current-voltage curve is.

A series connection of PV modules whose voltages add while the same current flows through each, forming the basic building block of most array wiring.

A central inverter that receives direct current from one or more series strings and converts it to grid-compatible alternating current, typically mounted near the array or service equipment.

A small inverter mounted at or near a single module that converts that module's direct current to alternating current locally, enabling per-module tracking and simplifying array expansion.

A code-required function that reduces conductor voltage at the array to a safe level within a specified time after activation, protecting firefighters and service personnel.

The highest voltage a module or system is rated to withstand, marked on the label; string design must keep cold-temperature open-circuit voltage below this value and code limits.

The maximum current a conductor can carry continuously under stated conditions without exceeding its temperature rating, adjusted for ambient temperature and conduit fill.

A fuse or circuit breaker that interrupts current above its rating to protect conductors and equipment from overheating or fault damage; PV source circuits often require such devices.

A system that detects current leaking from energized conductors to ground and interrupts the circuit, required for many PV installations to reduce shock and fire hazards.

The conductor that bonds non-current-carrying metal parts of modules, racking, and enclosures together and to the grounding electrode system, providing a low-impedance fault path.

The permanent joining of metal parts to form an electrically conductive path that ensures electrical continuity and safe fault-current flow between equipment and the grounding system.

A switch or device that isolates a circuit or equipment from its source of energy so work can proceed safely; PV systems need clearly labeled disconnects for array, inverter, and utility sides.

The reduction in voltage along conductors caused by resistance and current flow; excessive drop wastes energy and can cause equipment misoperation, so designers keep it within a target percentage.

Selecting wire gauge so that ampacity, after correction factors, meets or exceeds the required continuous current while keeping voltage drop and termination temperature limits acceptable.

The physical and contractual connection of a PV system to the utility grid or to a building's electrical distribution, governed by utility rules and code requirements for protection and metering.

An inverter designed to synchronize with and export power to the utility grid, including anti-islanding protection that stops output when the grid is absent.

A protective function that detects loss of utility voltage or abnormal grid conditions and disconnects the inverter, preventing the PV system from energizing an isolated grid section.

A billing arrangement that credits a customer for exported PV electricity, typically by allowing the meter to run backward or by offsetting consumption across a billing period.

The ratio of a system's actual energy production over a period to the energy it would have produced running at rated power continuously, reflecting weather, soiling, and availability.

The ratio of a system's actual energy yield to the theoretical yield from measured irradiance, capturing losses such as temperature, soiling, wiring, and inverter inefficiency.

Accumulation of dust, pollen, bird droppings, or other deposits on module glass that blocks light and reduces output; heavy soiling can also create hot spots.

A localized overheated area on a cell caused by shading, soiling, or damage that forces the cell to dissipate power, potentially degrading the module or posing a fire risk.

A diode wired across a group of cells inside a module that provides an alternate current path when those cells are shaded or faulty, limiting hot-spot heating and power loss.

Blocking of sunlight on modules by trees, buildings, or adjacent rows; partial shading disproportionately reduces string output and must be analyzed during site assessment and layout.

An OSHA-required procedure for de-energizing equipment, applying a personal lock and tag, and verifying absence of voltage before service work begins.

Employer-provided gear such as gloves, eye protection, hard hats, and arc-rated clothing that shields workers from electrical, fall, and physical hazards on the job site.

Systems such as guardrails, personal fall arrest harnesses, and anchor points required by OSHA when workers are exposed to falls from roofs or elevated structures.

OSHA-based practices for selecting, setting, and climbing ladders, including the four-to-one angle rule, three-point contact, and securing the ladder before roof access.