Glossary of Terms

A (Ampere Symbol)

A is the SI symbol for the ampere, the SI unit of electric current.

AC (Alternating Current)

Electric current that periodically reverses direction. New Zealand and Australian public electricity supplies operate at a nominal frequency of 50 Hz.

Active Conductor

A conductor maintained at a voltage above earth potential in normal operation. In New Zealand and Australia, “active” is normally used rather than the North American term “hot”.

AEM Electrolyser

An anion-exchange-membrane electrolyser that transports negatively charged hydroxide ions through a polymer membrane. The technology aims to combine responsive operation with less reliance on precious-metal catalysts, but is less commercially mature than established alkaline and PEM electrolysers.

Additionality

A principle used in renewable-energy and hydrogen certification to assess whether energy demand is supported by new or additional renewable generation rather than existing supply.

Ammonia (NH₃)

A compound of nitrogen and hydrogen used widely as an industrial feedstock and fertiliser input. Ammonia may also be used as a hydrogen carrier or fuel, but introduces its own toxicity, handling, emissions and conversion considerations.

Alkaline Electrolyser

An electrolyser that uses an alkaline liquid electrolyte, commonly potassium hydroxide, with electrodes separated by a diaphragm.

Alkaline Fuel Cell (AFC)

A fuel cell using an alkaline electrolyte and hydroxide-ion conduction. It can operate efficiently but normally requires very pure reactant gases because carbon dioxide can degrade electrolyte performance.

Alternating Voltage

A voltage that changes magnitude and periodically reverses polarity.

Ambient Temperature

The temperature of the air or other medium surrounding equipment at the location where it operates.

Ampere (A)

The SI unit of electric current.

Ampere-Hour (Ah)

A unit of electric charge commonly used to describe battery capacity. One ampere-hour is the charge transferred by one ampere flowing for one hour.

Anode

The electrode at which oxidation occurs. In a fuel cell, hydrogen is oxidised at the anode.

Armoured Cable

An electrical cable incorporating a protective metallic armour. Its selection and installation must comply with the applicable AS/NZS wiring requirements.

AS/NZS 3000

The joint Australian/New Zealand Wiring Rules standard for electrical installations. The current applicable edition and amendments should always be confirmed for a project.

Auto-Ignition Temperature

The lowest temperature at which a substance can ignite in air without an external spark or flame, under specified test conditions.

Autotransformer

A transformer in which the primary and secondary windings share a common electrical portion.

Array

An electrically connected group of photovoltaic modules arranged to provide a required DC voltage, current and power output.

Azimuth

The horizontal compass direction faced by a solar array. The azimuth convention should be stated because design tools do not all use the same reference direction.

Balance of Plant (BoP)

The equipment required to support the main process equipment. For a hydrogen system this can include water treatment, cooling, power conversion, controls, compression, ventilation and safety systems.

Battery

One or more electrochemical cells connected to store and supply electrical energy. In common usage, a single packaged cell may also be called a battery.

Battery Capacity

The amount of charge or energy a battery can store or deliver under specified conditions, commonly expressed in ampere-hours (Ah) or kilowatt-hours (kWh).

Battery Management System (BMS)

An electronic system that monitors and manages battery operation, including cell voltage, temperature, current, state of charge and protective limits.

Black Start

The capability of a generating system or microgrid to start and energise a network without an external electricity supply.

Blue Hydrogen

An informal label for hydrogen produced from fossil fuels where a portion of the resulting carbon dioxide is captured and stored. The actual emissions depend on the production pathway, capture rate and upstream emissions.

Branch Circuit

The part of an electrical installation between the final protective device and the connected load or outlets. In New Zealand and Australia, “final subcircuit” is often the preferred term.

Busbar

A conductive bar or assembly used to distribute electrical power to multiple circuits.

Battery Energy Storage System (BESS)

A complete system that stores electrical energy in batteries and includes battery assemblies, management, power conversion, controls, protection and supporting equipment.

Behind-the-Meter

Generation, storage or controllable load installed on the customer side of the electricity meter and primarily used to serve that site.

Bifacial Module

A photovoltaic module designed to generate electricity from light received on both its front and rear surfaces.

Capacity Factor

The actual energy produced by equipment over a period divided by the energy it could have produced if operated continuously at rated output over the same period.

Carbon Dioxide Equivalent (CO₂e)

A measure that expresses the climate effect of different greenhouse gases as an equivalent amount of carbon dioxide.

Carbon Intensity of Hydrogen

The lifecycle greenhouse-gas emissions associated with producing and delivering hydrogen, commonly expressed as kilograms of CO₂e per kilogram of hydrogen.

Cascade Storage

A group of hydrogen storage banks at different pressures used in sequence to transfer gas efficiently during refuelling.

Catalyst

A material that increases the rate of a chemical or electrochemical reaction without being consumed by the overall reaction.

Catalyst Poisoning

Loss of catalyst performance caused by contaminants that block or alter active reaction sites. Fuel cell catalysts can be sensitive to contaminants such as carbon monoxide, sulphur compounds and ammonia.

Cathode

The electrode at which reduction occurs. In a hydrogen fuel cell, oxygen is reduced at the cathode.

Cell

The basic electrochemical unit that converts chemical energy to electrical energy, or electrical energy to chemical energy.

Cell Voltage

The electrical potential difference between the two electrodes of an electrochemical cell.

Circuit

A closed conducting path through which electric current can flow.

Circuit Breaker

A resettable protective switching device designed to interrupt current automatically under specified abnormal conditions such as overload or short circuit.

Combined Heat and Power (CHP)

The useful production of electricity and heat from the same energy-conversion process.

Composite Overwrapped Pressure Vessel (COPV)

A pressure vessel with a structural fibre-composite overwrap around a liner. Type III and Type IV hydrogen cylinders are forms of COPV.

Compressed Gaseous Hydrogen (CGH₂)

Hydrogen stored as a compressed gas in pressure vessels or associated equipment.

Compressor

Equipment that increases the pressure of a gas. Hydrogen compressors must be designed for the intended hydrogen purity, pressure, flow and duty.

Controllable Load

An electrical demand whose timing or power level can be adjusted without compromising its required service, allowing it to use periods of plentiful energy or reduce demand during constrained periods.

Conduit

A metallic or non-metallic tube or system used to route and protect electrical conductors.

Continuous Power

The electrical power equipment can deliver continuously under stated operating and environmental conditions.

Continuous Rated Power

The manufacturer-declared electrical output that equipment can maintain continuously under stated conditions and limitations.

Critical Load

An electrical load that must be maintained, restored quickly or managed in a controlled way because interruption could create safety, operational, financial or community consequences.

Curtailment

A reduction in available electricity generation, often because network capacity, demand or system constraints prevent the energy from being used.

Cycle Life

The number of charge-discharge cycles a battery can complete before reaching a specified end-of-life condition.

Clipping

Loss of potential solar generation when available DC power exceeds the inverter or another component's maximum usable output, causing power to be limited.

Connection Agreement

An agreement setting the technical and commercial conditions for connecting generation, storage or load to an electricity network. Requirements vary by network and project size.

C-Rate

Battery charge or discharge current expressed relative to rated capacity. A 1C rate would theoretically charge or discharge the stated capacity in one hour, subject to operating limits.

DC (Direct Current)

Electric current that flows in one direction. Its magnitude may be steady or may vary with time.

DC Bus

A common direct-current connection that transfers power between equipment such as fuel cells, batteries, converters and inverters.

Deflagration

Combustion in which the flame front travels through the unreacted mixture at less than the local speed of sound.

Delivered Hydrogen Cost

The total cost of hydrogen at the point of use, including production, conditioning, storage, transport and dispensing where applicable.

Demand Response

A deliberate change in electricity use or generation in response to price, network conditions or a request from the electricity system.

Depth of Discharge (DoD)

The proportion of a battery’s usable or rated capacity that has been discharged, usually expressed as a percentage.

Derating

Operating equipment below its nominal rating because of temperature, altitude, ventilation, fuel quality, ageing or another stated condition.

Detonation

Combustion accompanied by a shock wave travelling at or above the local speed of sound in the unreacted mixture.

Diode

A two-terminal electronic component with strongly asymmetric current-voltage behaviour, commonly used to conduct current primarily in one direction.

Direct Methanol Fuel Cell (DMFC)

A fuel cell that converts methanol directly into electricity without first reforming it into a separate hydrogen stream. It is commonly considered for smaller portable and low-power applications.

Dispenser

The assembly used to transfer hydrogen to a vehicle or receiving system, normally incorporating metering, controls, hose, nozzle and safety functions.

Distributed Energy Resource (DER)

A smaller-scale energy resource connected within a distribution network or customer installation, such as solar generation, batteries, fuel cells or controllable loads.

Dry-Year Risk

The risk of reduced hydroelectric generation during periods of low inflows. It is particularly relevant to electricity resilience planning in New Zealand.

Dual-Fuel Hydrogen–Diesel System

An engine system that uses hydrogen alongside diesel, with diesel normally retained for ignition and as a fallback fuel. The substitution rate and emissions benefit vary with engine load, controls, operating pattern and hydrogen supply.

DC-Coupled System

A solar and battery arrangement in which the PV array and battery connect on a common DC side before conversion to AC.

DC-to-AC Ratio

The rated DC power of a photovoltaic array divided by the rated AC output power of its inverter. A ratio above one can improve inverter utilisation, with some possible clipping.

Distribution Network

The lower-voltage electricity network that distributes power to customers and may also receive electricity exported by distributed generation.

Earth

The conductive mass of the ground whose electrical potential is conventionally taken as zero. In NZ/Australian electrical terminology, “earth” is generally preferred to “ground”.

Electric Charge

A physical property of matter measured in coulombs (C). In circuit calculations, charge is the time integral of electric current.

Electrical Efficiency

Useful electrical energy output divided by the energy input over the same boundary and period. For hydrogen systems the heating-value basis, system boundary and whether output is gross or net should be stated.

Electrolyser

Equipment that uses electricity to produce hydrogen through electrolysis. A complete system includes the electrolyser stack and supporting balance-of-plant equipment.

Electrolyser Stack

An assembly of electrolysis cells electrically and mechanically connected to produce hydrogen.

Electrolysis

The use of electrical energy to drive a non-spontaneous chemical reaction. Water electrolysis separates water into hydrogen and oxygen.

Electrolyte

A material containing mobile ions that conducts ionic charge within an electrochemical cell.

Electromagnetic Compatibility (EMC)

The ability of equipment to operate satisfactorily in its electromagnetic environment without introducing unacceptable electromagnetic disturbance to other equipment.

Emergency Shutdown (ESD)

A safety function that places equipment or a process into a defined safe condition when specified hazardous or abnormal conditions are detected.

Energy

The capacity to do work, measured in joules (J). Electrical energy is commonly billed or specified in watt-hours or kilowatt-hours.

Energy Carrier

A substance or system that stores and transports energy for later use. Hydrogen is an energy carrier, not a primary source of energy.

Energy Density

The amount of energy stored per unit mass or volume. The measurement basis and whether LHV or HHV is used should be stated for hydrogen.

Energy-Management System

A control system that monitors and coordinates generation, storage, loads and reserve levels according to operating, resilience and cost objectives.

Energy Resilience

The ability of an energy system to anticipate, withstand, adapt to and recover from disruption while maintaining or restoring priority services.

Energy Security

The reliable availability of energy in the required forms and quantities at an acceptable cost, including the ability to manage supply, infrastructure and price disruptions.

Energy Sovereignty

The degree of practical control a country, region or community has over its essential energy sources, infrastructure and choices. It does not necessarily mean complete self-sufficiency or an end to energy trade.

Energy for Industry

Energy used for industrial processes, facilities and equipment, including electricity, process heat, fuels and feedstocks.

Explosive Atmosphere

A mixture with air, under atmospheric conditions, of flammable substances in the form of gas, vapour, dust, fibres or flyings in which combustion spreads after ignition.

Electricity Distribution Business (EDB)

A New Zealand business that owns or operates a local electricity distribution network. Its connection requirements apply to solar, batteries and other distributed energy resources connected to that network.

Export Limit

The maximum power a site is permitted or configured to export to an electricity network. An inverter or site controller may dynamically limit output to remain within this value.

Farad (F)

The SI unit of capacitance.

Fault

An abnormal condition in an electrical or process system that may require protective action.

Fill Protocol

A defined method for controlling hydrogen transfer during refuelling, including pressure, temperature, flow and communications where required.

Final Subcircuit

The part of an electrical installation from the final overcurrent protective device to the connected outlets or equipment.

Flammability Limits

The concentration range of a gas or vapour in air within which flame propagation is possible under specified conditions. The lower and upper limits are commonly abbreviated LFL and UFL.

Fuel Cell

An electrochemical device that converts the chemical energy of a continuously supplied fuel and oxidant directly into electricity, heat and reaction products.

Fuel Cell Degradation

A reduction in fuel cell performance or capacity over time due to operating conditions, ageing, contamination, material changes or cycling.

Fuel Cell Efficiency

Useful energy output divided by fuel energy input. The result must state whether it is electrical or total efficiency, the system boundary, and whether hydrogen LHV or HHV is used.

Fuel Cell Electric Vehicle (FCEV)

An electric vehicle in which a fuel cell system supplies electricity to the propulsion system, normally alongside a traction battery.

Fuel Cell Stack

An assembly of individual fuel cells connected to provide the required voltage and power.

Fundamental Frequency

The lowest-frequency sinusoidal component of a periodic waveform. New Zealand and Australian public electricity systems have a nominal fundamental frequency of 50 Hz.

Feed-in Tariff (FiT)

A payment rate or credit for electricity exported from a customer's generation system to the network. In New Zealand this is commonly described as a solar buy-back rate and is offered under retailer-specific terms.

Gaseous Hydrogen (GH₂)

Hydrogen in the gas phase. It may be supplied at low pressure or compressed for storage and transport.

Green Hydrogen

An informal label generally used for hydrogen produced by electrolysis using renewable electricity. The production boundary, electricity source and lifecycle emissions should also be stated.

GHS 7

New Zealand’s implementation of the seventh revised edition of the Globally Harmonized System of Classification and Labelling of Chemicals. It is used to classify and communicate hazardous-substance hazards.

Grey Hydrogen

An informal label generally used for hydrogen produced from fossil fuels without carbon capture and storage.

Grid-Connected

Connected to a public or private electricity network and able to exchange electricity subject to the connection arrangement.

Gross Electrical Output

The total electrical output produced before deducting the electricity consumed by supporting equipment.

Guarantee of Origin

A certificate or tracking instrument that records specified attributes of an energy product, such as production pathway, source and emissions information.

Global Horizontal Irradiance (GHI)

The total solar power received per unit area on a horizontal surface, including direct and diffuse sunlight, normally expressed in watts per square metre.

Grid-Following Inverter

An inverter that synchronises its output to an existing AC voltage and frequency reference. Most conventional grid-connected solar inverters operate this way.

Grid-Forming Inverter

An inverter capable of establishing or supporting an AC voltage and frequency reference, allowing suitable systems to energise or stabilise an islanded network or microgrid.

Harmonics

Sinusoidal components of a periodic waveform at integer multiples of its fundamental frequency.

Hazardous Area

An area in which an explosive gas atmosphere is present, or may be expected to be present, in quantities requiring special precautions for equipment selection, installation and use.

Higher Heating Value (HHV)

The heat released by complete combustion when the water formed is returned to a specified reference state as liquid. HHV includes the recoverable heat of water condensation.

HSWA

New Zealand’s Health and Safety at Work Act 2015, which establishes duties for managing work health and safety risks.

Hybrid Energy System

A coordinated system that combines complementary energy sources, storage, controllable loads or backup supply so each component performs the tasks best suited to it.

Hybrid Fuel Cell and Battery System

A power system in which a fuel cell and battery share electrical demand. Controls allocate power, manage battery state of charge and keep each component within its operating limits.

Hydrogen (H₂)

The lightest chemical element. Molecular hydrogen is a colourless, odourless gas at normal ambient conditions and can be used as an energy carrier, industrial feedstock or reducing agent.

Hydrogen Blending

The controlled addition of hydrogen to another gas, commonly natural gas, for transport or use through shared infrastructure. A blend percentage must state whether it is measured by volume, mass or energy because these values differ substantially.

Hydrogen Combustion

Burning hydrogen in an engine, burner or turbine to produce heat or mechanical power. It produces no carbon dioxide from the hydrogen itself, but can form nitrogen oxides and its lifecycle emissions depend on the hydrogen supply pathway.

Hydrogen Derivative

A substance made using hydrogen and used to carry energy or as a feedstock, such as ammonia, methanol or a synthetic hydrocarbon.

Hydrogen Embrittlement

A reduction in the ductility, toughness or load-bearing capability of susceptible materials caused by the presence and interaction of hydrogen.

Hydrogen Leak Detection

Detection of hydrogen releases using suitable sensors, monitoring arrangements and alarm or shutdown functions.

Hydrogen Refuelling Station (HRS)

A facility that receives or produces hydrogen, conditions and stores it, and dispenses it to vehicles or other receiving systems.

Hydrogen-Ready

Describes a site, design or item of equipment prepared for a possible future hydrogen function. The exact preparation and any limits must be stated; the term does not by itself confirm immediate compatibility or approval for hydrogen use.

Hydrogen Supply Chain

The connected activities and infrastructure used to produce, condition, store, transport, distribute and deliver hydrogen.

Hard-to-Abate

Describes activities for which greenhouse-gas emissions are technically difficult or costly to eliminate because of process requirements, high-temperature heat, feedstock use, long asset lives or limited alternatives.

Hard-to-Electrify

Describes an application where direct use of electricity is technically impractical or commercially difficult because of factors such as energy density, range, duty cycle, location, charging time or network constraints.

Health and Safety at Work (Hazardous Substances) Regulations 2017

New Zealand regulations governing work involving hazardous substances, including requirements relating to information, training, emergency management, storage, location compliance and certified handlers or locations where applicable.

Hydrogen Storage — 350 bar

Compressed-hydrogen storage with a nominal working pressure of 35 MPa (350 bar). It is used in a range of transport, mobile and stationary applications; the complete storage and refuelling system must be designed for the applicable standard and service.

Hydrogen Storage — 700 bar

Compressed-hydrogen storage with a nominal working pressure of 70 MPa (700 bar), commonly associated with light-duty fuel cell vehicles. Refuelling requires compatible equipment, temperature management and an applicable fill protocol.

Hybrid Inverter

A power converter designed to coordinate multiple energy sources or storage devices, commonly a solar PV array, battery and grid connection, within one control system.

Inerting

Replacing or diluting an atmosphere with a non-reactive gas to reduce oxygen or fuel concentration and prevent ignition or reaction.

Inverter

Power-electronic equipment that converts direct current to alternating current.

Inverter Capacity

The maximum electrical power or current an inverter can process under stated operating conditions.

Islanding

Operation of part of an electricity system while electrically separated from the wider network. Intentional islanding requires appropriate protection, control and approval.

Isolation

Separation of an energy source or hazardous medium so that work or operation can proceed under defined safe conditions.

Installation Control Point (ICP)

The New Zealand identifier and point used for the connection between a customer's installation and an electricity network. Metering, import and export arrangements are associated with the ICP.

IP Rating (Ingress Protection Rating)

An IP Code defined by IEC 60529 classifies the protection provided by an electrical enclosure against access to hazardous parts, solid foreign objects and water. The letters IP are normally followed by two digits.

First digit — access and solid objects: 0, no specified protection; 1, objects 50 mm or larger and access with the back of a hand; 2, 12.5 mm or larger and access with a finger; 3, 2.5 mm or larger and access with a tool; 4, 1 mm or larger and access with a wire; 5, dust-protected; and 6, dust-tight.

Second digit — water: 0, no specified protection; 1, vertically falling drops; 2, drops when the enclosure is tilted up to 15 degrees; 3, spraying water; 4, splashing water; 5, water jets; 6, powerful water jets; 7, temporary immersion; 8, continuous immersion under conditions agreed by the manufacturer and user; and 9, high-pressure, high-temperature water jets.

Common examples: IP20 provides finger protection but no water rating; IP43 resists objects 1 mm or larger and spraying water; IP54 is dust-protected and splash-resistant; IP65 is dust-tight and resists water jets; IP66 adds protection against powerful jets; IP67 adds temporary-immersion protection; and IP68 covers continuous immersion under the manufacturer's stated conditions.

An X in either position means that protection level has not been specified; it does not mean zero protection. An IP rating applies to the tested enclosure in its specified, correctly installed condition. It does not by itself confirm corrosion resistance, outdoor service life, chemical compatibility or suitability for a hazardous or explosive atmosphere. Immersion ratings IPX7 and IPX8 also should not be assumed to include water-jet protection unless the equipment carries the relevant additional rating.

Irradiance

Solar power incident on a surface at a particular time, expressed in watts per square metre (W/m²).

Irradiation

Solar energy received per unit area over a period, commonly expressed in kilowatt-hours per square metre (kWh/m²).

Isc (Short-Circuit Current)

The current produced by a photovoltaic device when its output terminals are short-circuited under specified test conditions. Isc is used when sizing conductors and protective equipment.

Joule (J)

The SI unit of energy. One joule equals one watt-second.

Kilogram of Hydrogen (kg H₂)

A mass measure used for hydrogen production, storage, delivery and consumption. The energy associated with one kilogram depends on whether LHV or HHV is used.

Kilovolt-Ampere (kVA)

A unit of apparent electrical power equal to 1,000 volt-amperes.

Kilowatt (kW)

A unit of power equal to 1,000 watts.

Kilowatt-Hour (kWh)

A unit of energy equal to one kilowatt supplied for one hour, or 3.6 megajoules.

Kilowatt-Peak (kWp)

A commonly used expression for the rated peak DC power of a photovoltaic array under standard test conditions. The formal SI unit remains the kilowatt.

Levelised Cost of Hydrogen (LCOH)

The discounted lifetime cost of producing hydrogen divided by the discounted quantity of hydrogen produced, using a clearly stated boundary and assumptions.

Liquid Hydrogen (LH₂)

Hydrogen cooled below its boiling point so that it is stored and transported as a cryogenic liquid.

Liquid Organic Hydrogen Carrier (LOHC)

An organic liquid that can absorb hydrogen through a chemical reaction and release it later. LOHC systems require hydrogenation and dehydrogenation equipment and associated energy inputs.

Load

Equipment or a process that consumes electrical power, or the amount of power being consumed.

Load Profile

A record or model of electrical demand over time.

Low-Emissions Hydrogen

Hydrogen whose lifecycle greenhouse-gas emissions are below a stated threshold or meet a specified certification scheme. The threshold and assessment method must be identified.

Lower Heating Value (LHV)

The heat released by complete combustion when the water formed remains as vapour. LHV excludes the heat that could be recovered by condensing that water.

Methanol

A liquid alcohol used as an industrial feedstock, fuel and potential hydrogen derivative. Renewable methanol can be produced using low-emissions hydrogen and a suitable carbon source.

Molten Carbonate Fuel Cell (MCFC)

A high-temperature fuel cell using a molten carbonate electrolyte. It can use hydrogen-rich gases and provide useful heat, but has demanding materials, start-up and durability requirements.

Manifold

A pipe or valve assembly that connects multiple gas sources, vessels or outlets into a controlled common flow path.

Maximum Allowable Working Pressure (MAWP)

The maximum pressure permitted for equipment at a specified temperature and condition, as determined by its design code and certification.

Membrane Electrode Assembly (MEA)

The core electrochemical assembly in a PEM fuel cell or electrolyser, normally comprising the membrane, catalyst layers and gas-diffusion layers.

MEN System

The Multiple Earthed Neutral system used for low-voltage electrical supply and installations in New Zealand and Australia.

Microgrid

A group of connected loads and distributed energy resources that can be controlled as a single system and may operate grid-connected or islanded.

Minimum Continuous Power

The lowest electrical output at which equipment is intended to operate continuously while meeting its specified performance and operating limits.

Minimum Ignition Energy

The lowest spark energy capable of igniting a specified flammable mixture under defined test conditions.

Maximum Power Point (MPP)

The operating voltage and current at which a photovoltaic module or array produces its greatest power under the prevailing irradiance and temperature.

Maximum Power Point Tracking (MPPT)

An electronic control method used by an inverter or DC converter to operate a photovoltaic array near its maximum power point as conditions change.

Module-Level Power Electronics (MLPE)

Power-electronic equipment installed at individual photovoltaic modules, such as microinverters or DC power optimisers, to provide conversion, optimisation, monitoring or shutdown functions.

N+1 Redundancy

A design arrangement with one more unit or capacity element than is required for normal operation, allowing service to continue following one defined failure or outage.

Natural Hydrogen

Molecular hydrogen generated by natural geological processes below ground. It is also called geological hydrogen and sometimes white or gold hydrogen; a surface occurrence does not by itself establish a commercially recoverable resource or prove that it is renewable.

Net Electrical Output

Gross electrical output minus the electricity consumed by supporting equipment within the stated system boundary.

Nitrogen Oxides (NOx)

A group of nitrogen-and-oxygen gases that can form during high-temperature combustion, including hydrogen combustion. Burner or engine design and emissions controls influence the amount produced.

Nominal Working Pressure (NWP)

The reference pressure assigned to a compressed-gas storage system for normal service under specified conditions.

National Metering Identifier (NMI)

The unique identifier used for an electricity connection point in Australia's National Electricity Market. It is the Australian counterpart to, but not the same as, New Zealand's ICP identifier.

Off-Grid System

An energy system that operates without a normal connection to the public electricity network.

Offtake Agreement

A contract under which a customer agrees to purchase a defined quantity of future production under stated terms. Long-term hydrogen offtake can support project financing by making demand and revenue more predictable.

Ohm (Ω)

The SI unit of electrical resistance.

Orange Hydrogen

An informal label for hydrogen generated by deliberately stimulating water–rock reactions below ground, potentially using injected water or carbon dioxide. The technology, resource response and lifecycle emissions must be assessed for each project.

Over-Discharge

Discharging a cell or battery below its specified minimum voltage or state-of-charge limit.

Overcharge

Continued charging of a cell or battery beyond its specified full-charge condition or operating limit.

Overvoltage

A voltage greater than the applicable nominal or declared upper limit. Its classification depends on magnitude, duration and the relevant standard.

PCBU

A person conducting a business or undertaking under New Zealand health and safety law. A PCBU has duties to eliminate or minimise work health and safety risks so far as is reasonably practicable.

Peak Power

The highest power required or delivered during a stated interval and under stated conditions.

PEM Electrolyser

A proton-exchange-membrane electrolyser that uses a solid polymer electrolyte and produces hydrogen at the cathode.

PEM Fuel Cell (PEMFC)

A proton-exchange-membrane fuel cell operating with a solid polymer electrolyte, commonly at relatively low temperature.

Phosphoric Acid Fuel Cell (PAFC)

A medium-temperature fuel cell using phosphoric acid as its electrolyte. It is principally used for stationary power and combined heat and power.

Permeation

The passage of gas through a material at the molecular level. Hydrogen permeation must be considered in material selection, sealing and ventilation.

Power

The rate at which energy is transferred or converted, measured in watts (W).

Power Factor

Real power divided by apparent power for an AC system. It is a dimensionless value between zero and one when expressed as a magnitude.

Power Quality

Characteristics of voltage, current and frequency that affect the operation of electrical equipment and networks.

Power-to-X (PtX)

Conversion of electrical energy into another energy carrier, fuel, material or product, such as hydrogen, ammonia, methanol or heat.

Pre-Cooling

Cooling hydrogen before or during fast refuelling to manage gas and vessel temperatures.

Pressure Rating

The pressure limit assigned to equipment under stated design, temperature and service conditions.

Pressure Regulator

A device that reduces and controls gas pressure from a higher-pressure source to a required downstream pressure.

Pressure Relief Device (PRD)

A device designed to relieve pressure automatically to protect equipment from exceeding a specified pressure.

Prime Rated Power (PRP)

For a generating set, the maximum power available during a variable-load sequence for an unlimited number of operating hours per year under stated reference conditions, subject to the manufacturer’s permissible average power and maintenance requirements. Fuel cell products should use their manufacturer-declared continuous rating unless PRP is explicitly specified.

Pulse-Width Modulation (PWM)

A control technique that varies pulse duration or duty cycle to regulate average output or synthesise a required waveform.

Purging

Removing an unwanted gas or contaminant from equipment or pipework by displacement or dilution with a suitable purge gas.

Peak Sun Hours

Daily solar irradiation expressed as the equivalent number of hours at an irradiance of 1,000 W/m². It is an energy-equivalent measure, not the number of daylight hours.

Performance Ratio

The actual AC energy produced by a photovoltaic system divided by the energy it would produce from measured in-plane irradiation at its rated DC capacity, using a defined calculation method.

Photovoltaic Effect

The physical process by which light absorbed in a semiconductor produces an electrical voltage and current.

Photovoltaic Module

An environmentally protected assembly of interconnected photovoltaic cells that converts sunlight into DC electricity. It is commonly called a solar panel.

PV Array

One or more electrically connected photovoltaic modules forming the DC generating part of a solar power system.

Rated Capacity

The capacity assigned to equipment by its manufacturer for specified operating and test conditions.

Rectifier

Power-electronic equipment that converts alternating current to direct current.

Renewable Hydrogen

Hydrogen produced using renewable energy through a defined and verifiable production pathway.

Renewable-Energy Firming

The use of storage, flexible generation, demand management or network support to reduce variability and improve the dependable supply of renewable electricity.

Residual Current Circuit Breaker with Overcurrent Protection (RCBO)

A protective device combining residual-current protection with overload and short-circuit protection.

Residual Current Device (RCD)

A protective device that disconnects a circuit when it detects a residual current above its operating threshold. Selection and installation must follow applicable AS/NZS requirements.

Round-Trip Efficiency

Energy recovered from a storage system divided by the energy supplied to it over a complete charge-storage-discharge cycle, using a stated system boundary.

Safety Data Sheet (SDS)

A document providing prescribed information about a hazardous substance, including hazards, safe handling, storage, emergency measures and disposal.

Scope 1 Emissions

Direct greenhouse-gas emissions from sources owned or controlled by the reporting organisation.

Scope 2 Emissions

Indirect greenhouse-gas emissions associated with purchased electricity, steam, heating or cooling consumed by the reporting organisation.

Scope 3 Emissions

Other indirect greenhouse-gas emissions occurring in the reporting organisation’s value chain, both upstream and downstream.

Separation Distance

A distance maintained between equipment, hazards, people, buildings or boundaries to reduce the consequences or likelihood of an incident. Required distances depend on inventory, pressure, equipment, barriers, land use and applicable standards or approvals.

Serpentinisation

A group of water–rock reactions that alter iron- and magnesium-rich ultramafic rocks and can generate molecular hydrogen. Suitable source rock alone does not prove that hydrogen has accumulated in an economic reservoir.

Short Circuit

An unintended conductive path with very low impedance that can produce excessive current.

Sine Wave

A periodic waveform described by a sine function. An ideal AC voltage supply is commonly represented as a sine wave.

Solid Oxide Electrolyser Cell (SOEC)

A high-temperature electrolyser using a solid oxide electrolyte, normally supplied with steam rather than liquid water.

Solid Oxide Fuel Cell (SOFC)

A high-temperature fuel cell using a solid oxide electrolyte.

Specific Energy Consumption

Energy input per unit of product. For electrolysis it is commonly expressed as kilowatt-hours of electricity per kilogram of hydrogen produced, with the system boundary stated.

Stack

A connected assembly of electrochemical cells used to achieve a required voltage, current, production rate or power.

State of Charge (SoC)

The available charge in a battery expressed as a percentage of a stated full-charge capacity.

Steam Methane Reforming (SMR)

A process that reacts methane with steam to produce a hydrogen-rich synthesis gas, followed by further processing and purification.

Surge

A transient increase in voltage, current or energy. The exact meaning and test method depend on the applicable electrical standard.

Self-Consumption

The portion of electricity generated on site that is used by the site rather than exported to the network. Batteries and load scheduling can increase solar self-consumption.

Shading

Reduction of sunlight reaching part or all of a photovoltaic array because of buildings, vegetation, terrain, dirt or other obstructions. Partial shading can disproportionately reduce string output.

Smart Meter

An electronic electricity meter capable of recording consumption and, where configured, exported generation in time intervals and communicating readings remotely.

Solar Inverter

An inverter that converts DC electricity from a photovoltaic array into AC electricity suitable for local loads, storage interfaces or an approved grid connection.

Solar Irradiance

The instantaneous solar power received per unit area of a surface, normally expressed in watts per square metre.

Solar Irradiation

The solar energy received per unit area over a specified period, commonly expressed in kilowatt-hours per square metre.

Solar-Plus-Storage

A coordinated system combining solar photovoltaic generation with energy storage, normally batteries, so energy can be shifted in time or retained for backup and other services.

Solar Tracker

A mounting system that changes the orientation of photovoltaic modules during the day or year to increase solar exposure.

Specific Yield

The electrical energy generated by a photovoltaic system over a period divided by its rated DC capacity, commonly expressed as kilowatt-hours per kilowatt-peak (kWh/kWp).

String

A group of photovoltaic modules connected in series so their voltages add while the same current flows through each module.

String Inverter

A solar inverter that receives DC power from one or more series-connected strings of photovoltaic modules and converts it to AC power.

Temporal Correlation

A requirement or measure describing how closely the timing of renewable-electricity generation corresponds with electricity used to produce hydrogen.

Thermal Storage

Storage of useful heating or cooling for later use, for example in hot water, ice, chilled water or another heat-storage medium.

Thermally Activated Pressure Relief Device (TPRD)

A pressure relief device intended to open when exposed to a specified temperature, allowing gas to discharge in a controlled manner.

Three-Phase Power

An AC system using three sinusoidal voltages of the same frequency displaced by approximately 120 electrical degrees.

Total Cost of Ownership (TCO)

The total lifecycle cost of owning and operating an asset, including acquisition, financing, energy or fuel, maintenance, downtime, replacement and disposal, within a stated boundary.

Transformer

Equipment that transfers AC electrical energy between circuits by electromagnetic induction, commonly to change voltage or provide isolation.

Tube Bundle

An assembly of pressure tubes or cylinders connected to a common manifold for storing or transporting compressed gas.

Tube Trailer

A road trailer carrying interconnected high-pressure tubes or cylinders for transporting compressed gas, including hydrogen, between a production or filling site and a user or refuelling location.

Type I Hydrogen Cylinder

A seamless all-metal pressure vessel.

Type II Hydrogen Cylinder

A metal pressure vessel with a fibre-composite hoop wrap over part of its cylindrical section.

Type III Hydrogen Cylinder

A pressure vessel with a load-sharing metal liner fully wrapped in fibre composite.

Type IV Hydrogen Cylinder

A pressure vessel with a non-metallic liner fully wrapped in fibre composite.

Tilt Angle

The angle between the plane of a photovoltaic module or array and the horizontal. Tilt affects solar exposure, drainage, soiling and wind loading.

Uninterruptible Power Supply (UPS)

Equipment that provides conditioned or backup electrical power to a load for a defined duration when the normal supply is interrupted or outside specified limits.

Usable Hydrogen Capacity

The mass of stored hydrogen that can be delivered between specified maximum and minimum operating conditions, which may be less than the total contained mass.

Ventilation

The intentional movement or replacement of air to prevent accumulation of hydrogen or other hazardous substances and maintain acceptable environmental conditions.

Volt (V)

The SI unit of electric potential difference and electromotive force.

Voltage

Electric potential difference between two points, measured in volts.

Voltage Dip

A temporary reduction in RMS supply voltage below a specified threshold. The threshold and duration should be stated by reference to the applicable standard.

Voc (Open-Circuit Voltage)

The voltage across a photovoltaic device when no current is flowing under specified conditions. Array design must account for the increase in Voc at low temperatures.

Watt (W)

The SI unit of power. One watt equals one joule per second.

Watt-Hour (Wh)

A unit of energy equal to one watt supplied for one hour, or 3,600 joules.

Waveform

The shape of a voltage, current or other signal as it varies with time.

Wobbe Index

A measure used to compare the heat input of fuel gases through the same burner orifice at the same supply conditions. It is calculated from heating value and relative density and is relevant when assessing gas interchangeability and hydrogen blends.

Well-to-Gate Emissions

Lifecycle emissions from resource extraction through production up to the point the product leaves the production facility, using a stated boundary.

Well-to-Wheel Emissions

Lifecycle emissions from energy-resource extraction and fuel production through distribution and final use in a vehicle.

Working Pressure

The pressure at which equipment is intended to operate in normal service under stated conditions.