Reference
Interconnection Glossary
Plain-language definitions of 32 PJM interconnection terms — from ERIS and NRIS to queue attrition, restudy, and Facilities Studies.
- A
- Affected System
- A neighboring transmission system — outside PJM or in a different control area within PJM — that may be electrically impacted by a new generation project's interconnection. If an Affected System is identified during studies, that system's operator must be notified and may require separate mitigation or coordination.
- B
- BES
- Bulk Electric System. The high-voltage transmission infrastructure — generally 100 kV and above — regulated by NERC reliability standards and overseen by FERC. Most large generation projects interconnect to the BES.
- C
- Capacity Recognition
- The ability of a generation project to participate in PJM's RPM capacity market and receive capacity payments for committing to be available during peak demand periods. Only projects with Network Resource Interconnection Service (NRIS) are eligible for full capacity recognition. Projects with ERIS service are excluded from capacity market participation, which affects their revenue profile and bankability significantly.
- CEII
- Critical Energy Infrastructure Information. A designation by FERC for sensitive grid data — such as detailed substation configurations and transmission ratings — that requires a formal clearance request before access. Some PJM Queue Scope features and full study report details are CEII-restricted.
- Cluster Study
- An interconnection study process in which multiple projects that applied during the same enrollment window are studied together as a group, with shared cost allocation for any network upgrades they collectively require. PJM adopted cluster studies under FERC Order 2023 to replace its legacy serial first-come-first-served study process.
- COD
- Commercial Operation Date. The date on which a generation project begins selling power commercially after completing all testing and receiving applicable regulatory approvals. COD is a key milestone in generator interconnection agreements and is often used to filter or prioritize projects in queue analysis.
- D
- DISIS
- Daisy Chain Interconnection System Study. A PJM study process — now largely replaced by cluster studies under FERC Order 2023 — in which projects were studied in series, with each project's results depending on those of earlier queue entrants. The serial nature contributed to long timelines and high restudy rates.
- E
- ERIS
- Energy Resource Interconnection Service. An interconnection service type in PJM that allows a generator to inject energy into the grid whenever transmission capacity is available, but does not guarantee firm network deliverability during peak conditions. ERIS projects are not eligible for full capacity market recognition and typically have lower interconnection upgrade costs than NRIS.
- F
- Facilities Study
- The third and final formal study in PJM's interconnection process, issued before the Generator Interconnection Agreement is executed. It specifies the exact transmission upgrades required to connect a project, itemized cost estimates with both Transmission Owner-Build and Developer-Build options, a milestone schedule, and any dependencies on other queued projects. PJM posts Facilities Study reports publicly per project.
- Feasibility Study
- The first formal study in PJM's three-phase interconnection study process. It provides a high-level screening of whether a proposed project can physically interconnect at its requested Point of Interconnection and gives a rough order-of-magnitude estimate of required network upgrades. The Feasibility Study does not commit PJM or the Transmission Owner to any specific cost.
- FERC
- Federal Energy Regulatory Commission. The U.S. federal agency that regulates wholesale electricity markets, interstate transmission, and natural gas pipelines. FERC has authority over interconnection processes at ISOs and RTOs, and its orders — including Order 2023 — set mandatory reforms that PJM and other grid operators must implement.
- G
- GIA
- Generator Interconnection Agreement. The binding contract between a generation project developer, PJM, and the applicable Transmission Owner that governs the technical and financial terms of connecting the project to the grid. Signing a GIA typically follows completion of all three study phases and precedes construction of interconnection facilities.
- H
- Headroom
- The remaining capacity available at a Point of Interconnection for new generation to connect without causing thermal, voltage, or stability violations on the existing transmission system. Headroom is a function of existing load, existing generation, and the physical limits of the equipment at and near the substation.
- Hosting Capacity
- The maximum amount of new generation that can interconnect at a given location without triggering reliability violations on the existing grid. ISOs publish hosting capacity maps as a starting screening tool. These maps reflect current grid state and do not account for how the queue — and grid conditions — will evolve by the time a new project would actually energize.
- I
- IISA
- Interim Interconnection Service Agreement. A temporary agreement that allows a generation project to begin limited operation and inject power into the grid before all required network upgrades are complete. An IISA specifies a reduced output cap and the conditions that must be met before the project can ramp to its full MFO. Not all projects are eligible; PJM evaluates whether partial operation can be accommodated safely given the current state of the grid.
- ISO
- Independent System Operator. A nonprofit, FERC-regulated entity that operates a regional transmission grid and manages a wholesale electricity market on a non-discriminatory basis. PJM, MISO, NYISO, ISO-NE, CAISO, and SPP are the major U.S. ISOs and RTOs. The terms ISO and RTO are often used interchangeably in practice.
- L
- LGIA
- Large Generator Interconnection Agreement. The full GIA used for generators above 20 MW. It is a standardized FERC pro forma contract, though individual ISOs may include approved deviations. Projects below 20 MW use a Small Generator Interconnection Agreement (SGIA) and follow a simplified study process.
- M
- MFO
- Maximum Facility Output. The maximum AC output, in megawatts, that PJM has studied and will permit a generation project to inject into the grid at its Point of Interconnection. The MFO is established through the interconnection study process and is documented in the Facilities Study Report and the Generator Interconnection Agreement. Any generation above the MFO must be curtailed at the inverter or by SCADA setpoint. MFO is always expressed in AC MW and should not be confused with DC nameplate capacity, which is typically 10 to 20 percent higher for solar projects.
- N
- Network Upgrade
- A transmission system improvement — such as adding a new line, replacing a transformer, or upgrading a substation — required to reliably accommodate a new generation project's interconnection. Network upgrade costs are typically allocated to the developer who triggers them, though credits may be available if later queue entrants benefit from the same upgrade.
- NRIS
- Network Resource Interconnection Service. An interconnection service type in PJM that grants a generator full network deliverability — the ability to deliver power reliably across the grid under peak conditions. NRIS is required for a project to be recognized as a capacity resource in PJM's RPM capacity market and typically requires higher network upgrade costs than ERIS.
- P
- PJM
- Pennsylvania–New Jersey–Maryland Interconnection. The largest regional transmission organization in the U.S. by peak load, serving 13 states and the District of Columbia. PJM operates the high-voltage transmission grid, manages the wholesale energy and capacity markets, and administers the interconnection queue for generator projects seeking to connect to the grid.
- POI
- Point of Interconnection. The specific physical location — usually a transmission substation bus — where a generation project connects to the grid. POI selection is one of the most consequential early decisions a developer makes: it determines which queued projects compete for headroom, what network upgrades are likely, and which Transmission Owner the developer will work with throughout the study process.
- Q
- Queue
- The ordered list of interconnection requests at an ISO or RTO. Projects enter the queue by submitting an application and deposit, then move through a series of engineering studies — Feasibility, System Impact, and Facilities — before receiving an interconnection agreement. The queue is publicly listed, but historical build rates suggest roughly 80% of projects ultimately withdraw before completing interconnection.
- Queue Age
- The length of time a project has been active in the interconnection queue, measured from its application date. Queue age is a meaningful signal of project seriousness: projects that have remained in the queue through multiple study phases and years without withdrawing are statistically more likely to ultimately interconnect than newer entrants.
- Queue Attrition
- The high withdrawal rate of projects that enter interconnection queues but never complete interconnection. Berkeley Lab research shows that roughly 80% of projects entering U.S. queues between 2000 and 2018 eventually withdrew. Because the queue is publicly visible but withdrawal rates are high, raw queue MW significantly overstates the capacity actually competing for headroom at any given substation.
- R
- Restudy
- A repeat of one or more interconnection study phases triggered when upstream projects withdraw from the queue. Because network upgrade costs are allocated based on which projects are ahead of you, a withdrawal can change which upgrades you are responsible for — sometimes significantly lowering costs, but occasionally raising them. Restudy delays are a major source of interconnection timeline uncertainty.
- RTO
- Regional Transmission Organization. A FERC-jurisdictional entity that operates the bulk power transmission system across a multi-state region and administers competitive wholesale electricity markets. The distinction between RTO and ISO is largely historical; PJM is technically an RTO. Both types must provide open, non-discriminatory access to their transmission systems.
- S
- SIS
- System Impact Study. The second formal study phase in PJM's interconnection process, following the Feasibility Study. The SIS performs a more detailed power-flow and stability analysis to identify which network upgrades are needed to reliably accommodate the project, and provides a more refined cost estimate. SIS results are a key input to the subsequent Facilities Study.
- Surplus Interconnection Service
- A PJM mechanism that allows a new project to use interconnection capacity that has already been studied and contracted for at a substation but is not fully utilized by the existing customer. Surplus interconnection can significantly reduce study time and network upgrade costs, but availability is limited and subject to the consent of the existing interconnection customer.
- T
- TO
- Transmission Owner. The utility or transmission company that owns and maintains the physical transmission infrastructure at and near a project's Point of Interconnection. In PJM, TOs include utilities such as APS, ComEd, PECO, PPL, and Dominion. The TO designs, builds, and owns the network upgrades required for interconnection, and the developer reimburses the TO for those costs.
- W
- Withdrawal
- The voluntary exit of a project from the interconnection queue before receiving an interconnection agreement. Common reasons include network upgrade costs exceeding project economics, loss of site control or offtake agreements, financing falling through, and permitting delays. Withdrawals trigger restudies for remaining projects and are the primary driver of queue attrition.
- WMPA
- Wholesale Market Participation Agreement. The agreement a generator must execute with PJM to participate in PJM's wholesale energy, capacity, and ancillary services markets. The WMPA establishes the operational obligations, settlement procedures, and compliance requirements for market participation once a project has completed interconnection.
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