Grid Glossary

TRENDING TERM

Critical Issue Fast Path (CIFP)

An accelerated stakeholder process used in PJM Interconnection to resolve urgent, contentious, and time-sensitive issues that cannot be resolved through the normal stakeholder process. The process involves several stages of discussion and proposal development, culminating in a submission to the Federal Energy Regulatory Commission (FERC) for approval. The CIFP process has been used in recent years to discuss large load additions (2025) and resource adequacy (2023).

TRENDING TERM

Effective Load Carrying Capability (ELCC)

Measurement used to calculate how much an energy resource–such as a wind farm or solar array–contributes to the overall reliability of the grid. It assesses the resource’s ability to meet electricity demand, particularly during peak usage periods, and is especially useful for variable renewable energy sources whose output depends on factors like weather conditions. 

TRENDING TERM

Disturbance

Refers to any unwanted or unplanned electrical event that interferes with the normal operation of the electrical grid. These can manifest in power outages, surges, and other events, and can originate from various sources within the electrical grid, such as loss of a large generating unit or another grid asset, such as a transmission line or transformer.

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Generation

The process of creating electricity. 

Geothermal energy

Heat derived from the Earth’s interior, which can be harnessed for electricity generation. It’s a renewable resource, as the Earth’s internal heat is continuously replenished.

Grid

The electrical grid is a vast, interconnected network comprising power plants, transmission lines, substations, and distribution lines. Its purpose is to generate, transmit, and deliver electricity from producers to consumers across a wide geographic area. 

Grid enhancing technologies (GETs)

A variety of technologies that improve the capacity, efficiency, and reliability of existing power grids. They are often lower cost and faster to deploy than major grid infrastructure upgrades like building new transmission lines. These technologies optimize the flow of electricity across existing infrastructure.

Grid following inverter

Refers to the ability of an inverter to synchronize with frequency and voltage on the grid. These are more common than grid forming and refer to how this technology takes its cues from the grid, not the other way around.

Grid forming inverter

Refers to the ability of an inverter to actively control frequency and voltage on the grid, helping to ensure grid stability. They can provide ancillary services, such as inertia, voltage regulation, and frequency response, essential for maintaining grid stability.

Grid hardening

Refers to the many solutions that help the grid withstand major events, such as extreme weather, natural disasters, or cyber attacks, without disruption.

Independent Market Monitor (IMM)

An entity that is hired by an Independent System Operator (ISO) or Regional Transmission Organization (RTO) to oversee and assess the operations of the wholesale electricity market. Its primary role is to ensure fair and competitive market practices by monitoring market participant behavior and identifying potential market manipulation or design flaws.

Independent System Operator (ISO)

A non-profit organization that manages the electricity grid and wholesale electricity markets within a specific geographic region. Its primary role is to ensure the reliable and efficient delivery of electricity, balancing supply and demand in real-time and overseeing fair competition among market participants. 

  • List of ISOs and RTOs:
    • CAISO – California ISO
    • NYISO – New York ISO
    • Electric Reliability Council of Texas (ERCOT); also a Regional Reliability Council
    • MISO – Midcontinent Independent System Operator, serves northern Midwest, southeast, and parts of Canada
    • ISO-NE – ISO New England
    • SPP – Southwest Power Pool
    • PJM – Pennsylvania-New Jersey-Maryland Interconnection- services 13 states in Midatlantic and Midwest region
Inertia

In the context of the grid, it refers to the energy stored in the rotating machinery of generators, such as the turbines of a gas plant or hydropower station. 

The turbines rotate at the same rate as the grid–60 cycles per second (hertz) in the United States–and help provide stability for the grid, particularly during spikes in power demand or other disturbances. If the power plant goes offline for any reason, the inertia of the turbines maintains the grid’s frequency for a window of time while another power source is brought online to replace the offline generator. 

Certain types of renewable energy, such as wind and solar photovoltaic, do not use rotational generators, instead using electronic inverters. But these renewable technologies include electronic sensors that can respond to changes in frequency quickly, and can replace the need for rotational inertia.Synthetic inertia – Inertia provided without synchronous generators and refers to the transfer of active power into the grid from a grid-forming inverter. This type of inertia can provide the same, or even better, stabilization services as traditional inertia because it has an instantaneous effect.

Interconnection

The process of connecting new power sources, like renewable energy generators or energy storage systems, to the existing grid infrastructure. It involves integrating these new sources with the grid’s transmission and distribution networks, ensuring a stable and reliable flow of electricity.

Interconnection queue

The line in which power generation and transmission projects must wait after they have requested to connect to the electric grid. These queues are managed by grid operators like ISOs (Independent System Operators) or RTOs (Regional Transmission Organizations). Projects are evaluated for their impact on the grid and the necessary upgrades before they can connect and deliver electricity.

Intermittent power

A power source whose availability and output fluctuate due to natural variations in its energy source. This means the power supply isn’t consistently available, often linked to weather conditions like wind speed, time of day, or season. Renewable energy output can be forecast and stored in battery systems to maintain grid reliability.

Inverter

Technology that provides the interface between the grid and energy sources like solar panels, wind turbines, and energy storage, converting direct current to alternating current (which is how electricity is delivered in the United States). It is used to convert power output from solar cells, batteries, and wind turbines into power that can be injected into the grid.

Inverter-Based Resources (IBR)

A power generation or storage device (such as a battery) that connects to the electrical grid through an inverter, a power electronic device that converts direct current (DC) to alternating current (AC). These resources, including solar photovoltaic (PV) systems, wind turbines, and battery energy storage systems, are increasingly important for grid stability.

ISO-NE

ISO New England

MISO

Midcontinent Independent System Operator, serves northern Midwest, southeast, and parts of Canada

Offshore wind

Wind turbines erected in bodies of water that harness the power of wind, converting it into electricity that is then transmitted to the mainland to power homes and businesses. Offshore wind farms are considered a renewable energy source.

Operational reliability

The real-time balancing of energy supply and demand to maintain frequency and voltage within safe operating limits. It is the shorter-term dimension of reliability and requires regular monitoring and control of the entire grid. It includes the ability to quickly respond to sudden changes, like the loss of a major power plant or transmission line, and to handle normal variations in supply and demand.

Queue

(see: Interconnection Queue)

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