NABCEP PV key terms

The compass direction a PV array or roof plane faces, expressed in degrees clockwise from true north; 180 degrees means due south. It strongly affects annual energy production.

The angle between a PV array's surface and horizontal ground, usually chosen to balance summer and winter production and to help rain or snow shed.

A site evaluation that identifies objects blocking sunlight and estimates when and how much they shade the array, often using a solar pathfinder or modeling software.

The instantaneous power of sunlight striking a surface per unit area, measured in watts per square meter. It changes with time of day, season, clouds, and orientation.

The equivalent number of hours per day when sunlight averages 1,000 watts per square meter. It converts daily solar energy into a convenient number for sizing calculations.

Laboratory conditions of 1,000 watts per square meter irradiance, 25 degrees Celsius cell temperature, and a specified air mass, used to rate PV modules.

The DC power a PV module is rated to produce under Standard Test Conditions, printed on its label. Real-world output usually differs because operating conditions vary.

The percentage change in a module's maximum power for each degree Celsius its cell temperature differs from 25 degrees. It is usually a negative value.

The maximum voltage a PV module or string produces when no current flows. It rises in cold weather, so it sets the highest voltage the system must withstand.

The current that flows when a module's output terminals are directly connected together. It is used for conductor and overcurrent device sizing.

A graph of current versus voltage for a PV device, showing how output changes across its operating range. Maximum power occurs at the knee of the curve.

An inverter or charge controller function that continuously adjusts operating voltage to draw the most power available from a PV array as conditions change.

A group of PV modules connected in series so their voltages add and the same current flows through each module. String length must match inverter voltage limits.

Choosing how many modules to connect in series so string voltage stays within the inverter's allowed window at record cold and hot cell temperatures.

The ratio of a PV array's DC nameplate power to the inverter's AC output rating. A higher ratio can increase energy harvest but causes more clipping.

A device that converts direct current from PV modules into alternating current suitable for loads or the utility grid, and typically controls array operation.

A diode inside a PV module that provides an alternate path for current when cells are shaded or damaged, limiting hot spots and power loss.

The structural mounting system that supports PV modules and transfers wind, snow, and seismic loads to the roof or ground while setting tilt and orientation.

A weatherproofing detail installed around roof penetrations and mounting hardware to direct water away and prevent leaks into the building.

The percentage of a conduit's cross-sectional area occupied by conductors. Limits prevent overheating and make wire pulling practical.

The systematic verification after installation that a PV system is safe, complete, and operating as designed, including inspections, tests, and documentation before handover.

A test that applies high DC voltage between conductors and ground to check for damaged insulation, moisture, or leakage paths before energizing a system.

A field test that sweeps a string's current and voltage to produce a curve, allowing comparison with expected performance and identification of faults.

The ratio of a PV system's actual energy output to its theoretical output based on measured irradiance, expressing losses from temperature, soiling, wiring, and availability.

Accumulation of dust, pollen, bird droppings, or snow on PV modules that reduces the sunlight reaching cells and lowers energy production until cleaned.

A localized overheated area on a PV module caused by a shaded, cracked, or failing cell, which can damage the module and sometimes pose a fire risk.

A safety procedure that isolates energy sources, applies locks and tags, and verifies zero energy before work begins, preventing accidental energization or release of stored energy.

A dangerous release of energy caused by an electrical arc between conductors, producing intense heat, light, and pressure that can injure workers and damage equipment.

Clothing and equipment such as gloves, arc-rated clothing, eye protection, and fall protection worn to reduce injury from electrical, thermal, and physical hazards.

Systems and practices such as harnesses, anchor points, and guardrails that prevent or arrest falls when working on roofs or elevated structures.

A pre-work review of a job site that identifies electrical, fall, weather, traffic, and other hazards and defines controls before installation or service begins.

A code-required system that reduces voltage at PV modules or conductors near the array to a safe level for firefighters within a specified time after activation.

A protective device that detects characteristic electrical signatures of dangerous DC arc faults in PV circuits and interrupts the circuit to reduce fire risk.

A device that detects current leaking from PV circuits to ground and opens the circuit, protecting people and equipment from fault conditions.

A conductor that connects non-current-carrying metal parts of equipment to the grounding system so fault current has a low-impedance path back to the source.

Electrically connecting metal parts so they remain at the same potential, preventing dangerous voltage differences and providing a path for fault current.

A switch or device that opens all ungrounded conductors of a circuit so equipment can be safely serviced or isolated from all sources of power.

A contract between a PV system owner and the utility that defines technical requirements, metering, and operating terms for connecting the system to the grid.

A billing arrangement that credits a customer for excess PV electricity exported to the grid, often at the retail rate, offsetting energy imported at other times.

A written description of the work a contractor will perform, including equipment, quantities, exclusions, schedule, and responsibilities, used to set customer expectations.