NABCEP PVCMS key terms

The ratio of a plant's actual energy output to the output it would produce at its measured irradiance and module temperature, isolating losses from weather variation and inverter behavior.

Actual energy generated over a period divided by the energy the plant would have generated running at nameplate rating continuously for that same period.

A sweep of current versus voltage across a string or module, used to compare measured shape and key points against expected values for fault diagnosis.

The voltage measured across a module or string with no current flowing; rises as cell temperature falls, so cold-weather design must account for the highest expected value.

The current that flows when module or string terminals are connected through a near-zero-resistance ammeter; scales with irradiance and is used to size conductors and overcurrent devices.

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

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

The inverter control function that continuously adjusts operating voltage to keep each input channel at its maximum power point as irradiance and temperature change.

The range of DC input voltage over which an inverter can operate and track maximum power; strings must stay inside it across expected temperature extremes.

Selecting the number of modules per string so that cold-weather open-circuit voltage stays below the inverter limit and hot-weather MPP voltage stays within the tracking window.

The rate, usually expressed per degree Celsius, at which open-circuit voltage falls as cell temperature rises; used to predict cold-morning maximum voltage and hot-afternoon minimum voltage.

A calibrated pyranometer or reference cell mounted in the array plane that measures incoming solar power, providing the reference needed to normalize performance and detect underperformance.

A structured measurement of plant output and weather conditions over a defined interval, compared against a model or contract guarantee to verify the system meets expectations.

A controlled test, often with a battery or inverter at defined setpoints, that confirms the plant or storage system can deliver its rated power for a specified duration.

The DC power a module or system is rated to produce under standard test conditions; a reference value, not a prediction of real-world output.

The reference conditions of 1000 W/m² irradiance, 25 °C cell temperature, and a specified air mass spectrum used to rate modules and compare equipment.

The structured process of inspecting, testing, and documenting a completed plant before handover to confirm it is safe, complete, and performing as designed.

A tracked list of incomplete or defective items found during inspection that must be corrected and verified before the system is accepted by the owner.

The final drawing set and equipment records updated to reflect what was actually installed, forming the baseline for future maintenance and troubleshooting.

A schematic showing the electrical path from array through combiners, disconnects, inverter, and point of interconnection, with ratings and device labels.

An enclosure where multiple source-circuit strings are paralleled onto a feeder, typically containing fuses or breakers, and often monitoring per-string current.

Per-string current and voltage measurement, usually at the combiner, used to detect underperforming strings, blown fuses, or disconnected connectors.

Circuitry that detects unintended current from array conductors to ground and, depending on design, interrupts the fault or alarms to protect people and equipment.

Monitoring that recognizes the electrical signature of a series or parallel arc in DC wiring and triggers an alarm or shutdown to reduce fire risk.

A required function that reduces voltage in array conductors to a safe level, usually at module or string level, for firefighter safety within a defined time.

A measurement of resistance from current-carrying conductors to ground using an applied test voltage, revealing moisture, damaged cable, or degraded connectors before energization.

Verification that positive and negative conductors are correctly identified and landed at each string, combiner, and disconnect before the system is energized.

Infrared camera inspection that reveals hot spots in modules, cells, connections, and terminations, often used during commissioning and periodic maintenance surveys.

A localized area of elevated cell temperature caused by mismatch, shading, soiling, or a failing cell or solder joint, which can degrade output and damage the module.

A diode inside a module that provides an alternate current path around shaded or faulty cell groups, limiting hot spots and power loss.

A diode placed in series with a string or source to prevent reverse current from flowing back into it from other parallel sources or a battery.

Loss of module performance caused by high voltage stress between cells and frame, often worsened by heat and humidity; detected as voltage or power loss in affected strings.

The reduction in output caused by dust, pollen, bird droppings, or snow on module surfaces; tracked through performance monitoring and addressed by a cleaning schedule.

Scheduled inspection, cleaning, torque checks, and testing performed on a defined interval to prevent failures and preserve plant output and safety.

Repair work triggered by a fault, alarm, or inspection finding, restoring failed equipment to service and often documented with root-cause notes.

A controlled record authorizing and tracking a maintenance task, including scope, safety steps, parts, personnel, and completion sign-off.

A safety procedure that isolates energy sources, applies locks and tags, and verifies de-energization before work begins on electrical equipment.

Supervisory control and data acquisition: the monitoring and control layer that collects inverter, meter, and sensor data and issues alarms to operators.

The share of time a plant or unit is capable of producing power, excluding forced and planned outages, expressed as a percentage over a reporting period.