Glossary Category 3: Transmission & Interconnection
Covering the critical infrastructure terms and processes needed to connect renewable projects to the grid.
Interconnection
Definition: The physical and regulatory process of connecting a power generation facility (like solar, wind, or battery) to the electric grid.
Example: A 100 MW solar project submits an interconnection request to ERCOT to connect to a nearby 138 kV transmission line.
Note: Each ISO/RTO or utility has its own rules, timelines, and cost structure for interconnection (e.g., PJM, MISO, CAISO, SPP, ERCOT).
Point of Interconnection (POI)
Definition: The exact location where a renewable energy facility connects to the grid, typically at a substation or on a transmission line.
Example: A wind project taps into a 230 kV transmission line located half a mile from its collector substation.
Importance: POI selection affects project cost, feasibility, and transmission studies.
Collector Substation
Definition: The facility that aggregates energy from all the turbines, solar inverters, or batteries onsite before stepping up voltage to connect to the grid.
Example: A 300 MW solar farm uses a 34.5 kV collector system that feeds into a 345 kV collector substation for interconnection.
Note: Usually located on-site and may be owned by the developer or transferred to the utility.
Switchyard
Definition: A fenced area where high-voltage power is routed, switched, or redirected between a generator and the grid; often adjacent to substations.
Example: A battery storage facility installs a switchyard next to a utility substation to control delivery into the transmission network.
Use: Important for control, reliability, and redundancy.
Gen-Tie Line (Generation Tie Line)
Definition: A private high-voltage transmission line that connects a generation facility (or battery) to the grid at the POI.
Example: A solar developer builds a 2-mile 230 kV gen-tie to interconnect with the utility’s substation down the road.
Note: Developer is typically responsible for design, permitting, land rights, and construction of the gen-tie.
Interconnection Request (IR)
Definition: A formal application submitted to a utility or grid operator requesting to connect a new generation resource to the grid.
Example: A 50 MW solar + storage project submits an IR to CAISO including proposed location, capacity, and POI.
Triggers: Starts the study process and requires proof of site control and technical data.
Interconnection Studies
Definition: A series of technical reviews performed by the grid operator to assess the impact of the proposed project on the grid. These include feasibility, system impact, and facilities studies.
Example: ERCOT performs a system impact study to determine whether the solar project will overload nearby substations.
Result: Identifies what upgrades are needed and assigns costs.
Network Upgrades
Definition: Grid infrastructure improvements (such as new transmission lines or substation enhancements) required to accommodate a new project.
Example: A wind project triggers a $15 million upgrade to increase capacity on a 138 kV line shared by multiple generators.
Who pays: Often the developer, although some markets offer cost-sharing or reimbursement mechanisms.
Queue Position
Definition: The project's place in the interconnection request queue, which determines when its study begins and what other projects may impact or be impacted by it.
Example: A solar project in MISO enters the queue in April 2023 and must wait behind 200 other projects in the same zone before studies can begin.
Note: Queue position can affect timelines by months or years.
Congestion
Definition: A condition where transmission lines are at or near full capacity, limiting the ability to deliver additional power without upgrades.
Example: A Texas wind project faces curtailment due to congestion on a 345 kV line during high wind periods.
Effect: Congestion can reduce project revenue and interconnection approval.
Curtailment
Definition: A reduction in power output required by the grid operator when generation exceeds demand or transmission capacity.
Example: A solar farm is curtailed during sunny afternoons when local transmission lines are overloaded.
Key Concern: Storage can help reduce curtailment risk by shifting output to off-peak times.
FERC Order 841
Definition: A federal regulation requiring RTOs and ISOs to allow battery storage to participate in wholesale markets and interconnect on equal footing with traditional generation.
Example: A 100 MW battery storage project in PJM benefits from Order 841, allowing it to earn revenue from frequency regulation and energy arbitrage.
Applies To: All FERC-jurisdictional markets (e.g., MISO, SPP, PJM, CAISO, NYISO).
Transmission Right-of-Way (ROW)
Definition: The legal and physical corridor needed to install, maintain, and operate transmission lines.
Example: A developer acquires a 150-foot-wide ROW across three parcels to construct a 230 kV gen-tie line to the POI.
Agency Note: May involve state utility commissions, local governments, or federal agencies if crossing public land.
Reactive Power / Voltage Support
Definition: The ability of a generator or battery to help maintain voltage stability on the grid. Most interconnection requirements now mandate a minimum level of reactive power performance.
Example: A solar facility must include inverters capable of supplying reactive power to maintain voltage at the substation.
Required By: Interconnection agreements, especially in CAISO, ERCOT, and PJM.
Grid Operator (ISO/RTO)
Definition: An Independent System Operator (ISO) or Regional Transmission Organization (RTO) manages electric grid reliability and energy markets in a given region.
Example: CAISO manages the grid in most of California; ERCOT covers most of Texas.
Role: Reviews interconnection requests, dispatches power, and runs wholesale markets.
Balancing Authority
Definition: The entity responsible for maintaining the balance between electric supply and demand in real time within a specific area.
Example: ERCOT serves as both the ISO and balancing authority for most of Texas.
Why It Matters: Projects must coordinate with the local balancing authority for grid injections and compliance.