Dictionary of Solar Terms

This is our online Dictionary of Solar and Electrical Terms we hope you find this information helpful and if you find a error or  would like to contribute to this document please email us at  info@GlobalSolarSupply.com with your suggestion or correction. 

Absorbed Glass Mat (AGM): A valve-regulated lead-acid battery with the electrolyte suspended in a fiberglass matrix. (See also: Lead-acid battery)  

Alternating Current (AC): An electric current which switches voltage polarity at a given frequency; the US electrical grid supplies AC electricity with a frequency of 60 Hz. 

American National Standards Institute (ANSI): Originally established by multiple engineering societies and several government agencies as the American Engineering Standards Committee, ANSI is responsible for reviewing, approving and maintaining standards for measurements, manufacturing and safety.  

Ampere (A or Amp): The standard unit of electrical current, equal to 1 Coulomb per second.  

Anode: The proper term for the “negative” terminal in a discharging battery, an anode is any material or component that acts as a current input point for an electrochemical reaction. The anode eventually dissolves in such reactions and coats the positively charged cathode material. Recharging a battery effectively reverses the anode and cathode. (See also: Cathode)  

Anodized: Refers to metal components, such as aluminum module frames or rails, that have a thick layer of oxidation to protect them from the environment. Anodized components are typically also sealed and can be dyed as well. 

Arc-Fault Circuit Interrupter (AFCI): A device designed to detect an unintended electrical arc and disconnect the power before the arc starts a fire. 

American Society of Civil Engineers (ASCE): The oldest national engineering society, ASCE publishes a wide variety of engineering standards and recommendations, such as wind-loading guidance and soil mechanics data. 

 Amorphous silicon (a-Si): A non-crystalline form of silicon used in some thin-film transistors and PV cells.  

Authority Having Jurisdiction (AHJ): The state or local agency responsible for permitting and inspection of new construction or electrical installations.  

Azimuth: For PV systems, the azimuth is the angle between a line normal to the face of the PV modules and true North. Ideal azimuth for PV arrays in the Northern hemisphere is typically 180°.  

Back Plate: A specialized wall-mount bracket for mounting inverters or power systems. Back Sheet: The material, usually high-density polyethylene, that protects the rear surface of a PV module.  

Balance of System (BOS): All parts needed to complete the PV system that are not expressly called out. i.e. “modules, inverter and BOS.”  

Ballasted mounting: Typically refers to PV mounting systems on flat roofs that use ballast blocks or stones to reduce the number of roof penetrations.  

Battery: A device that stores electrical energy by converting it to chemical energy. Several chemistries and formfactors are used for batteries. (See also: Lead-acid battery, Lithium-ion battery, Sodium-ion battery, Nickel-iron battery)  

Battery Backup: A battery bank and inverter used to provide power during a grid outage. Battery-based inverter: An inverter that converts DC power from a battery bank into AC power suitable for use by common loads or for export to the grid. Typically, battery-based inverters must be installed with batteries in order to function and may or may not be grid interactive. (See also: Inverter, Grid-interactive)  

Battery Management System (BMS): A computer-controlled-electronics package that ensures a battery bank is properly charged and discharged. Many advanced chemistries, such as lithium-ion, require a BMS for safety and longevity.  

Bonding (electrical): Bonding refers to the practice of electrically connecting all exposed metal components so that they can be reliably connected to ground for safety. Also referred to as equipment grounding.  

British Standard (BS) 6290: A safety standard relating to stationary lead-acid batteries that specifies mechanical, electrical and material requirements.  

Bronze anodized: Typically refers to aluminum rail or other mounting components that are anodized with a dark bronze dye so as to appear black. (See also Anodized)  

Bus/busbar: A conductor used to distribute current between multiple sources and loads, analogous to a manifold.  

Cathode: The proper term for the “positive” terminal of a discharging battery, a cathode is the material and/or point where current leaves an electrochemical reaction.  

Cell: A photovoltaic cell generates a DC voltage (usually ~0.5 V) when exposed to light. Cells are typically assembled into modules prior to use.  

California Energy Commission (CEC): The CEC is California’s primary energy policy and planning agency. It is responsible for energy forecasting, setting energy efficiency standards, supporting, promoting and developing renewable energy technologies and resources, certifying thermal power plants and responding to energy emergencies.  

Canadian Standards Association (CSA): Now CSA Group, CSA is a standards organization similar to Underwriters’ Laboratories (See UL) in the U.S.A. Like UL, CSA also performs certification testing as an NRTL to its own and many other US and Canadian standards.  

Combiner: A bus assembly used to connect module strings in parallel. Usually includes overcurrent protection for each string. May be integrated with inverter or in separate enclosure.  

Composition (Comp) shingle: Also known as asphalt shingles, this thin, flexible roofing material is common on sloped residential roofs and is relatively easy to work with.  

CSA 22: Also known as the Canadian Electrical Code, CSA 22.1 contains prescriptive standards for electrical and related work while CSA 22.2 contains safety and testing standards for related equipment. Analogous to the NEC and associated UL standards used in the U.S.A.  

Class I Division 2 (CI-D2): Usually encountered in oil & gas extraction applications, special equipment certification (typically by Factory Mutual) is required to operate in a Class I environment – where flammable gasses or vapors are likely to be present in sufficient concentrations to ignite. Division refers to whether the flammables are normally present (Division 1) or only in abnormal conditions (Division 2). Certification testing is designed to verify that the product does not present an ignition source, such as a spark or hot surface.  

Cradle to Cradle™ (C2C): A product standard that evaluates products with respect to material health and reutilization, energy and carbon management, water stewardship and social fairness.  

Current transducer (CT): A current sensor that generates a voltage signal proportional to the current passing through a conductor it is placed around. Most revenue-grade metering systems use CTs.  

Demand Charge: Part of a utility rate structure that assesses a fixed charge based on the peak kW demand, usually sustained for 15 minutes or more.  

Derate Factor (Derate): Can apply to any reduction of a device’s safety or output ratings when normal operating conditions (usually temperature) are exceeded. Often also applied to a value used in the PVWatts calculator where it represents losses in the system due to the difference between the PV module’s nameplate DC ratings, and actual expected output in real-world conditions, module mismatch, losses in diodes, connections and wiring, module soiling, array shading, tracking error, system aging, and the inverter efficiency at maximum power. The default 0.82 derate is based on 14% systemic losses and 96% inverter efficiency.  

Direct Current (DC): An electric current with constant voltage; PV modules and batteries supply DC electricity. 

Dual in-line package (DIP) switch: A manual switch packaged in a group on a circuit board; typically used to customize an electrical device, such as a charge controller, by changing settings or logic.  

Delta: A three-phase power configuration where transformers or loads are connected between each of the current carrying lines. (See also: Three-phase power)  

Deutsches Institut für Normung (DIN) rail: A standard rail used to mount circuit breakers or other control equipment in enclosures or racks. Several DIN standards are used globally, but the top hat EN 50022 profile is most common in the U.S.A.  

Disconnect (Disco): A switch that electrically isolates a given component or portion of a system from the load or generator. i.e. Most inverters feature a DC Disco that isolates the PV array from the inverter.  

Dynamic load: A load who’s direction and amplitude changes with time, i.e. a PV module in gusty winds will tend to flex toward and away from the roof.  

Electric Current: The flow of an electric charge, typically carried by electrons through a conductor; analogous to the flow of liquid through a pipe.  

Electrolyte: Any substance that forms an electrically conductive solution with water. While electrolytes such as sulfuric acid are vital to battery chemistry, others, such as salt water or even rain, are the primary cause of corrosion in metal components.  

Energy: The ability of a system to perform work; the standard unit of energy is the Joule, but electrical energy is most often measured in kilowatt-hours.  

Equalization charge (Equalize): A sustained charge cycle intended to “boil” the electrolyte in a flooded battery in order to prevent or correct stratification of varying electrolyte concentration.  

Flash test: A test performed on PV modules to determine their nameplate capacity. The flash test is performed under standard test conditions (1,000 W/m2 of light at 25 °C) typically at the factory or by an NRTL 

Flashing: Thin pieces of material, usually aluminum or steel, used to prevent water intrusion through a roofing system at joints and transitions.  

Federal Communications Commission (FCC) Part 15: Properly known as the Code of Federal Regulations, Title 47, part 15, “FCC Part 15” regulates unlicensed radio emissions, such as those from power electronics like inverters. Any product sold in the U.S.A. that emits radio energy, but doesn’t require a license to operate, must comply with 47 CFR 15.  

Float Charge: A low-current charge applied to a battery bank at roughly the rate of self-discharge. Float charge voltage is regulated to prevent overcharging the battery.  

Flooded battery: Refers to battery types where the electrolyte is in liquid form and can be added to or spilled. Typically applied to traditional lead-acid batteries, but also describes some nickel-iron batteriesl.  

Galvanized: Refers to iron or steel that has been coated with zinc to prevent corrosion. The zinc provides both a protective layer as well as a sacrificial anode to both prevent and mitigate rust formation.  

Galvanic corrosion: Dissimilar metals, such as copper and steel, brought into contact by a conductive electrolyte, such as rain or salt-spray, will react much like a battery and dissolve the anode into the electrolyte. This is why equipment grounding methods must prevent dissimilar metals from coming into contact with one another.  

Grid: The electric grid is an electric distribution system that provides power to connected loads from geographically dispersed generators.  

Grid-interactive: Able to export power to the electrical grid. Usually refers to a battery-based “Hybrid” or “dual function” inverter that can operate with or without a grid connection.  

Grid-Support: Inverters capable of meeting the interconnection standards as laid out in UL 1741 Supplement A  

Grid-tied: Connected to the electrical grid; usually referring to a PV system.  

Hanger bolt: A specialized fastener used for mounting structures that has wood-screw thread on the bottom and machine thread on the top.  

Harmonic: A whole-number multiple of a fundamental frequency. i.e. an inverter outputting 60 Hz may have harmonic outputs at 120 Hz, 180 Hz and so on, so distortions caused by certain types of loads (battery chargers, variable frequency drives, etc.) will also have effects at each of the higher harmonic frequencies.  

Harmonic Distortion: The extent to which certain types of electrical loads can cause increased peak currents, heating and EMF emissions in an inverter or other AC power source.  

Head: The vertical distance, typically expressed in feet, between a water source and where it is being delivered. Also used as a shorthand for pressure, 1 foot of head = .43 psi.  

Hybrid Inverter: A battery inverter that can interconnect with the grid for net metering.  

IEEE 1547: The Standard for Interconnecting Distributed Resources with Electric Power Systems establishes acceptable frequency and voltage windows, and related parameters, that govern how and when a generator or inverter can feed into the electrical grid. Compliance with IEEE 1547 is part of the UL 1741 test standard.  

IEEE 929: IEEE’s Recommended Practice for Utility Interface of Photovoltaic (PV) Systems contains guidance to ensure that grid-tied PV systems are safe and effective.  

IEEE C62.41: IEEE’s Recommended Practice for Surge Voltages in Low-Voltage AC Power Circuits provides guidance for testing whether a given device can withstand surge voltage.  

IEC 60034: IEC’s standard for rotating electrical machines, such as motors and generators.  

IEC 60896: This section of IEC’s battery standard covers stationary lead-acid batteries. Various subsections cover materials and test protocols.  

IEC 61000: Refers to IEC standards starting with 61, which covers most electrical devices.  

IEC 61215: The IEC standard for testing PV modules, analogous to UL 1703.  

IEC 62109: The IEC standard defining minimum requirements for power-conversion equipment in PV systems.  

IEC 62109 is analogous to UL 1741, but includes performance requirements as well as safety standards.  

IEC 62509: The IEC standard that establishes minimum requirements for function and performance of battery charge controllers used with lead-acid batteries in PV systems.  

IEC 62446: IEC’s Grid connected photovoltaic systems – Minimum requirements for system documentation, commissioning tests and inspection defines the minimal tests, inspections and documentation that should be presented to a customer upon completion of a PV installation.  

Institute of Electrical and Electronics Engineers (IEEE): The largest association of electrical engineers, IEEE is very active in the development of codes and standards. While not typically binding as such, IEEE standards are often incorporated into IEC, UL, ANSI and other standards that are referenced by building and electrical codes. 

International Electrotechnical Commission (IEC): The leading global standards developer and publisher. IEC standards are commonly referred to in the European Union and other parts of the world, much like UL standards in the U.S.A. While IEC standards are not binding in the U.S.A., they are often incorporated, in part or in whole, into UL, ANSI and other standards that are referenced by building and electrical codes.  

International Fire Code (IFC): A comprehensive fire safety code, similar  to the NFPA, parts of which are incorporated into the building codes of some jurisdictions in the U.S.A.  

Inspector: A Code inspector is a representative of the AHJ who physically inspects construction or electrical installations to determine whether they are compliant with the standards of the jurisdiction.  

Inverter: A device that converts DC electric power into AC power for use by AC loads and/or for export to the electric grid.  

Ingress Protection (IP ##): The IP rating specifies the level of environmental protection provided by an enclosure. The first number rates protection from particulates (e.g. dust) from zero to six, with zero being unprotected and six being completely protected. The second number rates protection against liquid ingress from zero (no protection) to eight, which denotes fully submersible. IP 67 is typical for module junction boxes.  

Insolation: The amount of solar energy received over a unit of time per a unit of surface area. Often expressed as sun-hours, which is equivalent to kWh/m2 . Most solar resource maps provide sun-hours per day. (See also: Irradiance)  

Irradiance: The amount of electromagnetic or solar power received by a unit surface area. Standard solar irradiance is considered to be 1,000 W/m2 , also referred to as one sun. (See also: insolation)  

Junction Box (J-box): A container for electrical connections that protects them from weather and/or tampering. Many types of electrical j-box are used for PV installation and modules typically feature a sealed j-box on the back which connects the output leads to the positive and negative bus.  

Jurisdiction Having Authority (JHA): See: Authority Having Jurisdiction.  

Kilowatt (kW): A commonly used unit of power equal to 1,000 W. A PV system is typically referred to by the kilowatt rating of either the modules or inverter  

Kilowatt-hour (kWh): A common unit of energy used to express the consumption or production of electrical power over time, especially for billing purposes. A PV system which produces 1 kW consistently for 1 hour will have produced 1 kWh.  

Laminate: A subassembly of a PV module consisting of the cells, busses, encapsulant, glass and back sheet. Lead-acid battery: A rechargeable battery which makes use of the conversion between lead-oxide and lead-sulfate in sulfuric acid to charge and discharge. Common variants include flooded, sealed and valve-regulated.  

Listed: Certified by an NRTL as meeting the requirements of a given standard. PV modules must be listed to UL 1703 and inverters must be listed to UL 1741 per NEC article 690.  

Lithium-ion (Li-ion) battery: A rechargeable battery which relies on the transfer of lithium ions to charge and discharge. Lithium-ion batteries offer higher energy and power density than most other battery chemistries but require sophisticated battery management systems to operate. 

 Lithium-cobalt-oxide (LiCoO2 ): Most notably used by Tesla for both EVs and stationary power, LiCoO2 batteries provide greater energy density than other common lithium chemistries, but are susceptible to thermal runaway when overcharged or over-heated.  

Lithium-iron-phosphate (LiFePO4 ) battery: Common in power tools and most stationary energy storage with lithium-ion batteries, LiFePO4 batteries provide less energy density than their cobalt counterparts, but offer improved safety and cycle life due to greater thermal stability.  

Marked: Products listed by an NRTL are allowed to bare the mark of that laboratory. Inspectors look for these marks whenever a listing is required by the Code.  

Maximum-Power Point (MPP): The corresponding voltage and current that yields maximum power from a PV cell, module, or array in the given conditions. The MPP will vary according to available light and cell temperature.  

Maximum-Power-Point-Tracking (MPPT): A feature of most grid-tie inverters, optimizers and MPPT charge controllers that continually seeks the maximum-power point of the module or array to ensure maximum energy harvest.  

Meter: An electric meter is used to measure the amount of energy produced or consumed. (see also: Meter form, Revenue-grade metering)  

Meter form number: The meter form designation, i.e. Form 2S, Form 16S, etc, describes the number and arrangement of meter terminals as well as the number and internal connection of meter elements. 

 Microinverter: A small inverter used with a single module.  

Mill-finish: Typically refers to stamped or extruded metals that have been formed but not polished, anodized, painted nor otherwise finished. 

Modbus: Originally developed by Modicon (now part of Schneider Electric) and maintained by the non-profit Modbus Organization, Modbus is an open serial-communications protocol commonly used for communication between industrial devices and controllers. Most PV inverters use Modbus to communicate with third-party monitoring or control platforms.  

Module-Level Power Electronics (MLPE): Refers to optimizers or microinverters used with each module. (See also: Microinverters, Optimizers)  

Module: An assembly of PV cells (usually 36, 60 or 72 in series) that outputs a DC voltage when exposed to light. “AC modules” incorporate a microinverter to output AC power. 

 Monocrystalline (mono): Refers to wafers or cells made from a single crystal of silicon, which tend to have higher efficiencies than multi-crystalline cells.  

MulticrystallineCommonly referred to as “poly-crystalline,” this refers to wafers or cells that are made from a silicon casting, which tends to have lower production costs than the monocrystalline process.  

National Electrical Code (NEC): Also known as NFPA 70, the NEC is a standard published by the National Fire Protection Association (NFPA) for the safe installation of electrical wiring and related equipment. It is generally adopted with or without modification by states or city/county AHJs. Article 690 addresses solar PV installation specifically but many other sections, such as article 250, apply as well.  

Nationally Recognized Testing Laboratory (NRTL): Laboratories designated by the federal Occupational Safety & Health Administration (OSHA) to test products for adherence to applicable standards. Solar products sold in the U.S.A. are most often Listed by Underwriters’ Laboratories (UL) or Intertek (ETL).  

Nameplate Capacity: The nominal output or throughput of a device or machine. PV modules typically have a nameplate capacity based on the output of the module at standard test conditions as determined by a “flash test”  

National Electrical Manufacturers Association (NEMA): An association of electrical equipment and medical imaging manufacturers, NEMA provides standards for electrical connectors and Enclosures. (See also: NEMA enclosure types, Ingress protection)  

NEMA enclosure types: Defined in the NEMA ICS 6 Enclosures Standard, common NEMA enclosure types include NEMA 1 – indoor use only, NEMA 3/3R – weather resistant and 4 – watertight. X (as in NEMA 4X) denotes additional corrosion resistance. 

Net Energy Metering (NEM): The prevalent utility billing mechanism for distributed energy systems, such as solar PV, which credits energy exported to the grid at the same (retail) rate as energy consumed from the grid. Such systems are said to be “net metered.”  

Network Equipment Building System (NEBS): Developed by Bell Labs, NEBS provides a standard for communications equipment used in a central office and is now managed by Telcordia. NEBS has three levels that each refer to various parts of the GR-63-CORE and GR-1089-CORE standards. Level 1 concerns just personnel and equipment safety while Levels 2 and 3 expand to cover operability and reliability requirements.  

Non-isolated: Most transformerless inverters are “ungrounded” on the DC side in that there is no “neutral” wire. Rather, both the positive and negative inputs have an absolute voltage and require combiner boxes with overcurrent protection on both legs.  

Normal Operating Cell Temperature (NOCT): The temperature of a particular PV cell when operated at 800 W/m2 of irradiance in average 20 °C ambient air with a 1 m/s average wind velocity across the back of the module. In order to better understand the performance of a PV module through a variety of operating conditions, the NOCT is typically measured by an NRTL for a sample set and reported on the module data sheet.  

Off-grid: Not connected to the electrical grid; usually referring to a standalone PV or wind system on a home or industrial site. See also: Grid  

Ohm (Ω): The standard unit of electrical resistance; a circuit with 1 Ω resistance will induce 1 A of current when 1 V of electric potential is applied.  

Ohm’s Law (V=IR): The mathematical relationship between the current (I), voltage (V) and resistance (R) of an electric circuit.  

Open-circuit voltage (VOC): The absolute difference in electrical potential across a device, such as a battery or PV module, when it is not connected in a circuit. For PV modules, VOC is typically measured and reported at standard test conditions and must be corrected for actual temperature and irradiance.  

Optimizer: module-level power-electronics device that provides MPPT and monitoring for each individual module in the array. 

Panel:  

• Several PV modules mounted together on a single rail set. 

 • An electrical load center or breaker access point.  

• A solar-radiation collector used for a solar hot-water system. 

 • See: Module Parallel: Electrical wiring scheme where the positive leads/terminals from multiple modules, batteries or strings are connected together to increase current. 

Partial State of Charge (PSoC): PSoC refers to the status of batteries that are less than fully charged. Lead-acid batteries can experience irreversible sulfation if in a PSoC condition for more than a week or two. (See also: Sulfation)  

Photovoltaic (PV): Famously characterized by Einstein, the photovoltaic effect is the physical phenomenon at the heart of all technology for generating electricity from light. See also: Cell and Module  

Powder coated: A type of surface coating that is applied as a powder then cured at elevated temperatures. Powder coating can provide thicker layers in a single coat than is achievable from liquid paints and is often used for metal components, such as steel racking or metal enclosures. 

Power: The rate at which work is performed or energy converted from one type to another.  

Power factor: The ratio, from -1 to 1, of real power (ability to do work) going to the load vs. apparent power (V x I) in the circuit. A power factor less than 1 indicates that voltage and current waveforms are out of phase, leading to losses in the power system.  

Polyamide 6,6 (PA66): More commonly known as Nylon 66, PA66 is a common industrial polymer often used in molded parts for its high strength and dimensional stability. The addition of carbon to improve UV resistance typically renders it black.  

Polycrystalline (poly): See Multi-crystalline.  

Polysilicon (poly-Si): Typically refers to the purified silicon feedstock used to produce multicrystalline and monocrystalline silicon wafers, the precursors to PV cells.  

PV-direct (or Array-direct): A type of off-grid system where the load is run directly from a PV module or array rather than from a battery bank. PV System: Usually refers to complete system and includes all components necessary for energy production: modules, inverter, racking, etc. 

 Photovoltaics for Utility Scale Applications (PVU.S.A.): A joint government/industry project in the 1980’s that included a 650 kW PV array in Davis, CA and another in Kerman, CA. The project led to a number  valuable insights and established some of the earliest benchmarks and best practices for utility-scale solar, most notably the PTC module rating.  

PVU.S.A. Test Conditions (PTC): Developed by the PVU.S.A. project to better characterize field performance of PV modules, PTC tests are performed at 1,000 W/m2 with 20 °C ambient temperature and a 1 m/s average wind speed. The California Energy Commission lists PTC values in the equipment listings for the CSI incentive program.  

Quarter points: The ideal mounting points for a beam (or PV module frame) are 25% of the total length from each end. i.e. if a module frame is 1 m long, the quarter points are located 25 cm from each end. This is typically where the mounting holes in the bottom flange of the module are located.  

Racking: Typically refers to the module mounting system, which fixes the PV modules to a roof, carport or other ground-mount structure.  

Rapid Shutdown (RSD): Article 690.12 in both the NEC 2014 and NEC 2017 codes require a means of rapid shutdown, accessible to emergency responders, that can limit the DC voltage in PV system conductors on or in a building. Most module-level power electronics are inherently compliant, but string inverters and other systems typically require a separate device.  

Rate Structure: The calculation method used by the electric utility to determine how a rate payer’s electricity use is billed. Common rate structures include “flat” $/kWh rates, “tiered” rates that increase as more energy is consumed and “time-of-use (TOU)” rates which vary throughout the day. Commercial rate structures often include demand charges based on peak kW use.  

Relay: An electrically-operated switch where a low-voltage/low power control signal is used to switch a much larger load or power source. A wide variety of relay types are used for different applications.  

Remote Temperature Sensor (RTS): Also referred to as a battery temperature sensor (BTS) this is a temperature probe, usually a thermocouple, used to measure the operating temperature of a battery so that the associated charge controller can adjust charging voltage appropriately. A missing or improperly installed RTS is the leading cause of premature battery failure. 

Revenue-Grade Metering (RGM): RGM as a requirement or capability typically refers to an electric meter that meets ANSI C12.20 standards. RGM can be Class .5 (± 0.5%) or Class .2 (± 0.2%). Which class is required depends on whose revenue you’re interested in.  

Recommended Standard (RS)-485: Officially known as TIA-485-A, the RS-485 standard is maintained by the Telecommunications Industry Association (TIA) and defines the electrical characteristics of the signal generator and receiver in a local communications network. Most solar inverter communication gear is compliant to RS-485 regardless of protocol.  

Rectifier: An electrical device that converts AC into DC power.  

Registered Jack (RJ): A standardized telecommunications network interface for voice and data signals. 

RJ-11: This four-pin connector is most commonly used for single-line telephone jacks but is often adapted for use with proprietary Datacom systems, such as connecting temperature sensors to battery-based inverters.  

RJ-45: Also specified by IEEE 802, this eight-pin connector is used world-wide for Ethernet devices and often for many RS485/Modbus devices used in PV installations.  

S-Tile: A type of roof tile, usually terra cotta or ceramic, with an “S” shaped cross-sectional profile. This type of roofing material requires special care and often special attachment hardware to prevent breaking the tiles and/or leaving the under layer exposed.  

SEIA:  The Solar Energy Industries Association (SEIA®) is the driving force behind solar energy and is building a strong solar industry to power America through advocacy and education. As the national trade association of the U.S. solar energy industry, which now employs more than 250,000 Americans, we represent all organizations that promote, manufacture, install and support the development of solar energy. SEIA works with its 1,000  member companies to build jobs and diversity, champion the use of cost-competitive solar in America, remove market barriers and educate the public on the benefits of solar energy. 

Self-Consumption: In solar industry parlance, self-consumption refers to an application were all PV electricity generated on site is consumed rather than exported to the grid – as distinct from net-metered applications. Most self-consumption applications require batteries.  

Self-Discharge: Batteries slowly lose charge over time, even when no loads are applied. The rate of self-discharge increases with temperature and varies according to battery type and chemistry.  

Series: Electrical wiring scheme where the positive lead/terminal from a module or battery is connected to the negative lead lead/terminal of the next one to increase the voltage of the resulting string.  

Shake: Typically refers to a wooden roofing material. Primarily used for aesthetic reasons, shake roofs can become fire hazards and are not recommended for use with PV systems. 

 Short Circuit Current (ISC): In solar PV applications, ISC usually refers to the prospective short-circuit current or available fault current. In this case, it represents the maximum electrical current that a device, such as a battery or PV module, can output. ISC is typically measured and reported at standard test conditions and may need to be adjusted for expected temperature, irradiance, etc. ISC is important to know for sizing current-carrying components such as breakers, wires, charge controllers and inverters.  

Sodium-ion battery: A type of rechargeable battery that uses sodium ions as charge carriers. While comparable to lead-acid batteries in terms of size and weight, sodium-ion batteries have much longer cycle life, can remain at low states of charge for extended periods without damage and can be manufactured without hazardous or toxic materials. Aquion Energy is the first commercial manufacturer of sodium-ion batteries.  

Standard Test Conditions (STC): Typically refers to the conditions, (1,000 W/m2 of light at 25 °C) under which, a PV module’s nameplate capacity is measured. More broadly, the term can refer to any set of conditions deemed standard for rating a particular device.  

Static Load: A load that is steady or fixed for a long period of time, i.e. snow or constant wind on a PV module.  

String: A group of modules or batteries wired in series is a string. 

SulfationThe crystallization of lead sulfate on the plates of lead-acid batteries. Sulfation typically results from leaving the battery at a partial state of charge for an extended period of time.  

Sun-hour: A unit of solar insolation equivalent to 1 kWh/m2. (See also: Insolation)  

SunSpec Alliance: A solar/storage distributed energy trade alliance dedicated to establishing standards, protocols and related documents that improve the interoperability of solar and energy storage equipment.  

Three-phase power (3-P or 3Φ): Commonly used for larger, non-residential loads, a three-phase power system applies an AC current using three separate conductors with the voltage waveform offset by one-third of the period. This arrangement enables much greater power delivery using fewer conductors since each of the conductors can serve as a return path for the others.  

Transformerless (TL): Most inverter manufacturers have transitioned to topologies that use high-speed switching to avoid the need for a transformer. These inverters are typically non-isolated. 

Telcordia Technologies: Formerly known as Bellcore and now a subsidiary of Ericsson, Telcordia provides technology and other standards for the telecommunications industry. 

Telcordia SR4228: Now GR-4228, this standard covers the design, testing, installation and maintenance of VRLA batteries used in telecommunications backup applications.  

Thin-film PV: Refers to a class of photovoltaic cells that are produced by depositing nm or µm-thick layers of PV material on a metal, glass or polymer substrate. Popular thin-film PV chemistries include Amorphous silicon (a-Si), Cadmium telluride (CdTe or Cad-tel), Copper indium gallium selenide (CIGS) and Gallium Arsenide (GaAs).  

Tilt Angle (Array tilt): Typically refers to the angle between a line normal to the face of the PV modules and flat ground. Tilt is an important variable when determining expected kWh production of a PV array.  

Ungrounded System: See Non-isolated.  

Uniform Building Code (UBC): Now the International Building Code, the UBC is published by the International Council of Building Officials and contains construction and materials standards for buildings. 

Underwriter’s Laboratory (UL): Both an NRTL and a creator of safety-related testing standards, UL standards are some of the most referenced in the NEC and related safety codes.  

UL 1004: The NEC-referenced test standard for motors and generators, including wind turbines.  

UL 1703: The NEC-referenced test standard for PV modules includes tests for fire resistance, electrical insulation, etc. The tests are designed to demonstrate safety of the module in operation or failure conditions.  

 UL 1741: The NEC-referenced test standard for inverters and related equipment incorporates IEEE 1547 interconnection requirements as well as additional safety requirements.  

UL 2703: The NEC-referenced test standard for PV module racking and grounding systems.  

UL 1699B: The NEC-referenced standard for Arc-Fault Circuit Interrupt (AFCI) devices.  

UL 1998: A safety standard for software used in programmable embedded microprocessors that is primarily concerned with preventing fires.  

UL 467: The NEC-referenced standard for grounding and bonding equipment.  

UL 508A: The NFPA-referenced standard for industrial control panels. UL 60950: The NEC-referenced standard for IT equipment.  

UL 1564: Standard for Industrial Battery Chargers. UL 1236: Standard for Battery Chargers for Charging Engine-Starter Batteries.  

UL 458: Standard for Power Converters/Inverters and Power Converter/Inverter Systems for Land Vehicles and Marine Crafts. 

Valve-Regulated Lead Acid (VRLA): A type of “sealed” lead-acid battery where the electrolyte is suspended in some form and outgassing is regulated by check valves on the lid; includes Gel and AGM battery types.  

Volt (V): The standard unit of electric potential; One V of potential with an electric current of 1 A will dissipate 1 W of power between the points, across which, it is measured. 

 Watt (W): The standard unit of power; equal to 1 Joule/second.  

Washer, Electrical Equipment Bonding (WEEB): Used to bond solar modules to aluminum solar mounting rails, eliminating the need for a bare copper wire to each module.  

Wye: A three-phase power configuration where three current-carrying lines use a common reference point and/or neutral line. (See also: Three-phase power)