PV Industry Glossary
- Jeanine
- May 4
- 14 min read
Updated: Jun 30
Definitions of the many abbreviations & acronyms commonly used when talking about PV systems & ESS
I've been in the industry for a long time, and I still come across abbreviations I've never heard before. Acronyms can be especially difficult to find in a Google search (EMS in our industry does not, in fact, refer to Emergency Medical Services).
So I made my own list. Below are commonly-used terms and abbreviations that are specific to the PV and ESS industry.
Jump to:
General Concepts
Abbreviation | What it refers to |
|---|---|
Array | PV Array |
Backfeed | Solar Backfeed or Battery Backfeed |
BESS | Battery Energy Storage System |
DER | Distributed Energy Resources |
DG | Distributed Generation |
ESS | Energy Storage System |
Grid | Utility Grid |
Microgrid | Microgrid |
PV | Photovoltaic |
Definitions
Array
A grouping of PV modules. This term is flexible. Most often, an array refers to modules that are physically grouped together and facing the same direction. Arrays can also be used to designate which inverter a group of modules is assigned to. Sometimes an entire install is referred to as an array.
Backfeed
Typical loads (like lights, or your refrigerator) pull power from the grid (or other main power source). Backfeed refers to power created or stored on-site that flows in the opposite direction, from your PV or battery system to the grid.
Battery Energy Storage System (BESS)
A type of ESS. This is the newest iteration of what has historically been called a battery backup system. A battery is a single electrochemical component which stores energy. In the past, an installer would pair it with the appropriate inverters, transfer switches, etc. A BESS is all-in-one. It refers to all the combined equipment that stores, converts, and electronically manages the battery's energy. All components need to be certified to work together.
Distributed Energy Resources (DER)
'Distributed Energy' refers to any technology (solar, batteries, wind, generators, EV) that generates and/or stores electricity near the location that the energy is used. The opposite of 'Distributed Energy' is 'Centralized Energy' -- traditional power plants which create and store electricity and send it elsewhere. Distributed Energy Resources can either refer to the individual components (PV panels, batteries, controllers), or to entire systems (a combined PV + ESS installation on a residence).
Distributed Generation (DG)
A type of DER, with a focus on technology that generates electricity. PV panels or wind turbines fall under this category, as they produce electricity. Batteries only store existing energy, so would not be considered 'distributed generation'.
Energy Storage System (ESS)
A power system that stores energy. It includes all the combined equipment that stores, converts, and electronically manages the system's energy. All components need to be certified to work together. Many companies use 'ESS' and 'BESS' interchangeably. BESS is a type of ESS. Other ESS systems may use flywheels, fuel cells, or capacitors.
Grid
The physical network of power lines owned by an energy utility.
Microgrid
An electric power system that can operate off-grid, and is also capable of interconnecting to a larger distribution network (either the utility grid, or another primary power source).
Photovoltaic (PV)
'PV' refers to technology that converts sunlight into electricity. This is different from solar thermal technology, which converts sunlight into heat.
Sectors
Abbreviation | What it refers to |
|---|---|
Residential | Residential PV & ESS |
C&I | Commercial and Industrial PV & ESS |
Utility-Scale | Utility-Scale PV & ESS |
O&M | Operations & Maintenance |
Definitions
Residential
The solar sector that installs systems for residential homes. System sizes are usually less than 20kW.
Commercial and Industrial (C&I)
The solar sector that installs on commercial buildings, factories, warehouses, shopping centers, and institutions. This is the intermediate scale of solar installation.
Utility-Scale
The solar sector installing PV power plants that directly backfeed the grid. Typically exceeding 1 MW, these projects are usually ground-mounted. This is the largest scale of solar installation.
Operations & Maintenance (O&M)
Management and service work for already-installed systems. Critical for large-scale projects, it includes monitoring, maintenance, cleaning, and repairs.
Installation & Equipment
Abbreviation | What it refers to |
|---|---|
BOM | Bill of Materials |
BOS | Balance of System |
Bus | Busbar |
Combiner | Combiner Box |
ELP | Essential Loads Panel |
EV | Electric Vehicle |
Footing | Footing |
Inverter | Inverter |
JBox | Junction Box |
MBD | Main Breaker Derate |
MID | Microgrid Interconnect Device |
MLPE | Module-Level Power Electronics |
MPU | Main Panel Upgrade |
MSP | Main Service Panel |
PV Module | Photovoltaic Module |
RS | Rapid Shutdown |
RSD | Rapid Shutdown Disconnect |
SES | Service Entrance Section / Service Entrance Switchboard |
Definitions
Bill Of Materials (BOM)
Sometimes called a 'quantity take-off'. A detailed list of all components needed for installation - from PV modules to nuts and bolts.
Balance of System (BOS)
All parts of PV and ESS systems that aren't the main components (solar modules & battery banks). This includes racking, inverters, wiring, and disconnects.
Busbar (Bus)
A bar of metal inside an electrical panel that acts as a conductor, and is the junction point all the individual circuits connect to (usually via a breaker).
Combiner Box (Combiner)
This is a flexible term. Originally, it exclusively meant a DC combiner box, which contains fuses to combine PV strings. After microinverters hit the market, the term came to be used for AC combiner boxes -- dedicated subpanels containing breakers to combine microinverter branch circuits.
Essential Loads Panel (ELP)
Also called a 'critical loads panel'. A dedicated electrical panel that receives power from the battery or ESS when the utility is unable to supply power.
Electric Vehicle (EV)
A vehicle that uses power stored in battery packs, instead of an internal combustion engine. Newer technologies are allowing homeowners to use their car batteries as more generalized energy storage - to run house loads or backfeed the grid.
Footing
Can refer to two different things: for roof-mounted installations, it is the attachment point between the racking and the roof; for ground-mounted installations, the footing refers to the (usually buried) concrete block or column that provides the structural base for the array.
Inverter
A device that converts DC electricity (from PV modules and batteries) into the AC electricity we use in our homes. Note that it is impossible for PV modules and batteries to naturally produce AC electricity. Anything marketing itself as an 'AC module' or an 'AC battery' has an integrated inverter.
Junction Box (J-Box)
A protective enclosure where conductors are terminated, combined, or spliced.
Main Breaker Derate (MBD)
Swapping out the existing main breaker for a smaller one. A main breaker derate makes it possible to install a larger PV system without incurring the cost of a main panel upgrade (MPU).
Microgrid Interconnect Device (MID)
The piece of equipment that allows a microgrid system to connect to, or disconnect from, a primary power source (like the utility grid). It often is controlled by the Energy Management System (EMS) and acts as a smart, automatic transfer switch.
Module-Level Power Electronics (MLPE)
Devices that control PV modules individually (or sometimes in pairs). DC optimizers, rapid shutdown devices, and microinverters are all considered MLPE.
Main Panel Upgrade (MPU)
Replacing the existing MSP with a newer, usually larger one. A main panel upgrade allows for a larger PV system, or may be needed when the main panel is no longer up-to-code. EV chargers may require an MPU due to increased load demand from the utility.
Main Service Panel (MSP)
An electrical panel that serves as the main distribution point for a residence's electrical system. It receives power from the utility and has breakers to the house loads.
Photovoltaic Module (PV Module)
Solar panels are referred to 'PV modules' in the industry for two reasons: 'PV' indicates that it is photovoltaic, not solar thermal; 'module' is used to differentiate it from other typical electrical panels on-site -- like subpanels and main service panels.
Rapid Shutdown (RS)
In older systems, the DC wires between the PV modules on the roof and the equipment on the ground is energized whenever the sun is shining. Rapid shutdown is a safety feature that ensures the wires between the PV modules and the equipment will have their voltage reduced to safe levels when activated. This is primarily to ensure the safety of firefighters who need to access the roof in an emergency.
Rapid Shutdown Disconnect (RSD)
The dedicated switch that activates rapid shutdown. Some systems have multiple methods that meet rapid shutdown requirements.
Service Entrance Section / Service Entrance Switchboard (SES)
An electrical panel that serves as the main distribution point for a facility's electrical system. It receives power from the utility and contains the utility meter, main disconnect, and load breakers/fuses.
Plans & Permitting
Abbreviation | What it refers to |
|---|---|
AGL | Above Ground Level |
AHJ | Authority Having Jurisdiction |
(E) | Existing |
EE | Electrical Engineer |
HO | Homeowner |
HOA | Homeowners Association |
Load Calcs | Load Calculations |
(N) | New |
PE | Professional Engineer |
SE | Structural Engineer |
SFR | Single Family Residence |
SLD | Single-Line Diagram |
Soils Report | Soils Report |
UNO | Unless Noted Otherwise |
Definitions
Above Ground Level (AGL)
A term used on plans and blueprints when noting the height of an object relative to the ground.
Authority Having Jurisdiction (AHJ)
The government body responsible for enforcing safety standards (electrical codes, fire codes, etc). Often it is the city where the address is located. Counties (or boroughs or parishes) are the AHJ's for addresses outside of city boundaries. The state is often the AHJ for manufactured and mobile homes.
Existing (E)
A designation used on plans and blueprints to differentiate existing equipment from new equipment.
Electrical Engineer (EE)
'Electrical engineer' refers to anyone with an electrical engineering degree. However, when using the term EE in the construction industry, it is often assumed they are also state-certified as a Professional Engineer (PE) with the accreditation to sign and stamp plans.
Homeowner (HO)
The person who owns the property.
Homeowners Association (HOA)
A private organization that governs a community and sets rules for its residents. Some HOA's have aesthetic restrictions on solar module placement. Note that California's Solar Rights Act prohibits any entity from reducing a PV system's efficiency by more than 10%.
Load Calculations
This most often refers to electrical load calculations, which determine the total power demand on a subpanel or main electrical panel.
New (N)
A designation used on plans and blueprints to differentiate existing equipment from new equipment.
Professional Engineer (PE)
An engineer licensed with the state to sign and seal plans and perform or verify calculations. While this term covers all engineering disciplines, it most commonly refers to civil engineers when used in the solar industry.
Structural Engineer (SE)
A Professional Engineer (PE) with an additional, advanced license to analyze the structural integrity of buildings and other infrastructure.
Single Family Residence (SFR)
A term used on plans and blueprints to indicate a single-family home.
Single-Line Diagram (SLD)
A simplified schematic using symbols to represent an electric power system. Multiple conductors that run together (i.e. phase 1, phase 2, and neutral) are depicted as a single line, instead of each conductor being drawn separately.
Soils Report
Also called a 'Soil investigation' or 'Geotechnical report'. A report prepared by a state-licensed geotechnical engineer that assesses ground conditions for construction by taking soil samples at various depths. This information is then used in calculations by civil and/or structural engineers designing foundations and drainage. Most often required for ground-mounted PV arrays.
Unless Noted Otherwise (U.N.O.)
A term used on plans and blueprints to indicate that a note or specification refers to all repeat instances of that object, unless an exception is noted.
PV & Battery Technical Terms
Abbreviation | What it refers to |
|---|---|
AGM | Absorbed Glass Mat |
Azimuth | Azimuth |
BB / BOB | Black-on-Black |
Bifacial | Bifacial Modules |
BIPV | Building-Integrated Photovoltaics |
DOD | Depth Of Discharge |
Island Mode | aka 'Islanding' |
kW | Kilowatt |
kWh | Kilowatt-hour |
Lead-Acid | Lead-Acid Battery |
LFP / LiFePO4 | Lithium Iron Phosphate |
Li-Ion | Lithium Ion Battery |
MW | Megawatt |
NMC | Nickel Manganese Cobalt |
PTC | PVUSA Test Conditions |
SoC | State of Charge |
STC | Standard Test Conditions |
Definitions
Absorbed Glass Mat (AGM)
A type of lead-acid battery. While a traditional 'flooded' lead-acid battery contains free-flowing liquid (electrolyte), AGM batteries use fiberglass to absorb the electrolyte. They tend to have a deeper depth-of-discharge, less off-gassing, and less maintenance than a flooded lead-acid battery.
Azimuth
The direction solar panels are facing. (South: 180°, West: 270°, East: 90°, North: 0°)
Black-on-Black (BB / BOB)
Refers to solar modules that have black monocrystalline cells, a black backsheet, and black frame.
Bifacial Modules
PV modules that have solar cells on both sides - the front and back. They capture the direct sunlight, as well as reflected light. This is most advantagous for ground-mounted installations, or tilt-mounted installations on flat, light-colored roofs.
Building-Integrated Photovoltaics (BIPV)
PV technology which is integrated with building materials. Solar shingles, transparent solar glass, and solar skylights fall under this category.
Depth Of Discharge (DOD)
The percentage of a battery's capacity that is used. Lithium ion batteries can be discharged to ~ 90% (leaving 10% in reserve). However, setting a Li-ion battery's DOD to 50% extends a battery's lifespan by thousands of cycles.
Island Mode (aka 'Islanding')
An operating mode used by PV and/or ESS systems that supplies energy to loads that are disconnected from the utility grid (or other primary power source). A similar term to 'microgrid', islanding refers to the operating mode, and microgrid refers to the ecosystem.
Kilowatt (kW)
1000 Watts (W). A Watt is a unit of power; or the rate at which energy is consumed or produced.
Kilowatt-hour (kWh)
1000 Watt-hours (Wh). A watt-hour is a unit of energy. It is more quantifiable than a kW, as measures how much power is used over time. This is the measure used in your electric bill, and this is how we measure the capacity of battery systems.
Lead-Acid Battery
The original battery type used in home backup systems. Similar to a traditional car battery. Compared to Li-Ion batteries, they are bulkier, require a shallower depth-of discharge setting to maximize their lifespan, and need regular maintenance. However, they are less of a fire hazard than Li-Ion batteries, and are 99% recyclable.
Lithium Iron Phosphate (LFP / LiFePO4)
A type of lithium-ion battery. Commonly used for ESS applications, due to having a lifespan of more cycles.
Lithium Ion (Li-Ion)
A rechargeable battery type that has a deeper depth-of-discharge, smaller profile, and longer lifespan than traditional lead-acid batteries.
Megawatt (MW)
1000 Kilowatts (kW).
Nickel Manganese Cobalt (NMC)
A type of lithium-ion battery. Commonly used for EV applications, as they contain more energy in a smaller footprint.
PVUSA Test Conditions (PTC)
A set of specific lab conditions used to measure the output of PV modules. PTC uses different testing parameters than STC, which better reflect real-world performance. A 400W PV module produces 400W at STC , but may produce only 380W at PTC. The PTC value is what the module is more likely to produce when installed.
State of Charge (SoC)
The remaining level of charge in a battery, in comparison to the maximum charge. Noted as a percentage.
Standard Test Conditions (STC)
A set of specific lab conditions used to measure the output of PV modules and create a base for comparison. It defines sunlight strength, temperature, and air mass. A 400W PV module produces 400W at STC - but it will produce differently if it is installed in Alaska vs. California.
Control & Monitoring
Abbreviation | What it refers to |
|---|---|
BMS | Battery Management System |
CT | Current Transformer |
DAS | Data Acquisition System |
EMS | Energy Management System |
PCS | Power Control System |
PCS | Power Conversion System |
SCADA | Supervisory Control And Data Acquisition |
Definitions
Battery Management System (BMS)
An electronic component that manages the cells in a battery pack with a focus on the battery's performance and safety.
Current Transformer (CT)
A loop or clamp which is placed around current-carrying wires, and can measure the current of specific circuits. Used in PV & ESS systems to monitor how much power is used or produced. While 'current transformer' refers to a specific technology, many manufacturers use other technologies (like Rogowski coils). However, in the field, the term 'CT' often refers to any device that monitors current.
Data Acquisition System (DAS)
Also known as a data aggregator. A system that collects data from multiple different field installed devices, and then accumulates that data in a single location. It has limited ability (or no ability) to control the devices it communicates with. (See also, SCADA).
Energy Management System (EMS)
An electronic system that monitors and controls electrical loads and/or an energy storage system. It can manage energy production, storage, and consumption, and reduce costs by backfeeding the grid at optimal times.
Power Control System (PCS)
A type of energy management system (EMS). Its main purpose is to monitor power sources and maintain a safe current on busbars and conductors to prevent overloading. It is useful for avoiding main panel upgrades, and allows for larger PV and battery systems to be installed.
Power Conversion System (PCS)
A term used more often by engineers working with large-scale systems. A component of an energy storage system that includes an inverter and incorporates bidirectional power control. It can operate on- or off-grid, uses communication protocols, and has an incorporated EMS, BMS, and/or PCS.
Supervisory Control And Data Acquisition (SCADA)
SCADA contains the abilities of a DAS (aggregating data from multiple devices) plus the ability to control devices with a site controller. It can use the collected data to supervise and control systems, rather than just report on them.
The Utility
Abbreviation | What it refers to |
|---|---|
NEM | Net Energy Metering |
PCC | Point of Common Coupling |
PCO | Point of Change of Ownership |
POC | Point of Connection |
POC | Point of Common Coupling |
POI | Point of Interconnection |
PTO | Permission To Operate |
TOU | Time Of Use |
VPP | Virtual Power Plant |
Definitions
Net Energy Metering (NEM)
An agreement from the utility that allows the PV system owner to receive credit when they backfeed (export electricity to) the grid.
Point of Common Coupling (PCC)
The demarcation between an individual electricity system and the utility grid (or other primary power source). It represents the change of ownership of the electrical infrastructure, and is located on the utility side of the meter. Usually a shared point from which multiple users connect to the grid. Also called a PCO.
Point of Change of Ownership (PCO)
See PCC.
Point of Connection (POC)
The point at which the PV system or ESS connects to the electrical system - usually on the client's side of the meter, via a breaker in the main service panel.
Point of Common Coupling (POC)
More often known as the acronym 'PCC'. POC is defined as the 'Point of Common Coupling' by some utilities / regions. It has the same definition as 'PCC' but is different to the 'Point of Connection.'
Point of Interconnection (POI)
This term is defined differently by different regions/ utilities. Some use it interchangeably with PCC (Point of Common Coupling). Some use it interchangeably with POC (Point of Connection). Sometimes it defined slightly differently, as the point at which a facility with PV/ESS connects to the grid on an individual level. This is separate from the PCC, which has multiple users connecting at a single node.
Permission To Operate (PTO)
Authorization from the utility company that a PV or ESS system has passed inspection, and is allowed to be turned on and connect to the grid.
Time Of Use (TOU)
A method used by some energy utilities to bill their clients (or credit them for backfeeding the grid). Instead of setting a standard price per kWh, the price varies depending on the time-of-day the energy is consumed or produced.
Virtual Power Plant (VPP)
A collection of power from distributed energy resources (DER's) to function as a single power plant. In regions where utilities have adopted VPPs, individual PV/ESS system owners can enroll their system to be managed remotely by a utility, or by a third-party VPP like Tesla or Sunrun. Enrolled systems are used to increase grid reliability, and can be called upon to sell energy to the grid when the demand peaks, or there is an emergency.
Codes & Regulations
Abbreviation | What it refers to |
|---|---|
Code Adoption | Code Adoption |
ASCE | American Society of Civil Engineers |
IBC | International Building Code |
ICC | International Code Council |
IFC | International Fire Code |
IPC | International Plumbing Code |
IRC | International Residential Code |
IRC | International Residential Code |
NEC | National Electric Code |
NFPA | National Fire Protection Association |
OSHA | Occupational Safety and Health Administration |
UPC | Uniform Plumbing Code |
Title 24 | Title 24, Part 6 |
Definitions
Code Adoption
'Code Adoption' usually refers to which international/national code version a state is currently enforcing. It can also more broadly refer to the legal process of incorporating new building standards. Different states adopt codes at different times. In 2026, California uses a modified version of the 2023 NEC, while Wisconsin uses a modified version of the 2017 NEC. Individual cities or counties within that state are sometimes permitted to adopt and further modify the state codes.
American Society of Civil Engineers (ASCE)
A not-for-profit engineering society that publishes technical codes. ASCE can also refers to the codes themselves. ASCE-7, 'Minimum Design Loads and Associated Criteria for Buildings and Other Structures' is the national standard for determining structural design loads.
International Building Code (IBC)
A building code that outlines the minimum standards of design, and construction for buildings Published by the ICC (International Code Council).
International Code Council (ICC)
A US-based nonprofit standards organization that publishes standard codes adopted by many states.
International Fire Code (IFC)
A building code that outlines minimum fire prevention and life safety requirements. Published by the ICC (International Code Council).
International Plumbing Code (IPC)
A building code that outlines plumbing installation, sanitation, and inspection standards. Published by the ICC (International Code Council).
International Residential Code (IRC)
A building code that outlines building, plumbing, mechanical, and electrical requirements for one- and two-family dwillings and townhouses. Published by the ICC (International Code Council).
International Residential Code (IRC)
A building code that outlines minimum fire prevention and life safety requirements. Published by the ICC (International Code Council).
National Electric Code (NEC)
A building code that outlines safe electrical design and installation practices. Published by the NFPA (National Fire Protection Agency).
National Fire Protection Association (NFPA)
A US-based nonprofit standards organization that publishes standard codes adopted by many states.
Occupational Safety and Health Administration (OSHA)
A US agency that creates and enforces standards to assure safe working conditions for employees.
Uniform Plumbing Code (UPC)
A building code that outlines plumbing installation, sanitation, and inspection standards. Published by the IAPMO (International Association of Plumbing and Mechanical Officials).
Title 24 (Title 24, Part 6)
Building Energy Efficiency Standards published by the California Energy Commission, with the purpose of reducing wasteful energy consumption. It mandates PV systems for most new developments and also requires ESS on many new commercial buildings. It prescribes calculations to determine the minimum PV system size for new construction.
