How it works
A developer applies to the transmission or distribution operator for a connection of a given size at a chosen point. The operator studies how the plant would affect the network. The studies identify the connection assets the plant needs, such as a substation and a line to the grid, and any wider network upgrades. The developer posts deposits or security, then signs an agreement that sets the capacity, the date and the technical requirements.
Who pays for upgrades varies. In some systems the developer pays the full cost of the upgrades it triggers. In others the cost is shared across network users. Queues have long been first come, first served, and many filled with speculative projects that later dropped out. Reforms now group applications into cluster studies, ask for proof of land and finance, and remove projects that miss milestones. A connection may be firm, or non-firm and curtailed at times of congestion.
Why it matters
For a developer, the connection often decides whether a site is viable at all. Upgrade costs can wipe out a project's margin, and queue delays push back revenue by years. An existing connection is valuable, which is why storage is often added behind one. For a buyer signing a PPA with a project not yet built, the connection's status is a main source of delay. A signed interconnection agreement marks a more mature project.
A worked example
A 200 MW wind project receives a study result requiring $40 million of network upgrades. At a 35% capacity factor, it generates 200 × 0.35 × 8,760 = 613,200 MWh a year. Over 20 years, that is 12,264,000 MWh. Spread evenly, the upgrade adds $40,000,000 ÷ 12,264,000 = $3.26/MWh before financing costs. If the project's expected margin was $5/MWh, the upgrade takes about two-thirds of it.
Illustrative figures.
Across markets
In the US, regional operators run large queues under FERC rules that moved to cluster studies in 2023, and developers often pay for the upgrades they trigger. In Europe, national operators handle connections, and several countries have reformed queues to favour projects that are ready to build. In India, the central transmission utility grants inter-state connectivity under CERC's General Network Access regulations, and state utilities handle intra-state connections.