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| Fig. 1: Capacity of Electricity Generation Projects in Grid Interconnect Queue By Year. (Images Source: D. Duncan, after W. Gorman et al. [1]) |
Grid interconnection is the process of adding new electricity generation or storage capacity to the existing electric grid. Electric transmission system operators typically require projects seeking to connect to the grid to undergo reliability studies to ensure that the grid can safely accommodate the new capacity. In the meantime, each project must wait in an interconnection queue - a waitlist for projects awaiting permission to connect to the grid. This process has become the focus of renewed attention in recent years, as the number and capacity of projects waiting for interconnection studies has increased significantly. [1]
As of the end of 2023, the capacity of proposed projects seeking interconnection was approximately 2,600 GW. Of that, approximately 1,570 GW was related to electricity generation projects and another 1,030 GW was related to storage projects. [1]
The capacity and number of proposed projects has expanded significantly over the past two decades (Fig.1). The total capacity of projects in the queue increased by more than a factor of five from just 462 GW in 2010. Over the same time period, projects have also spent significantly more time waiting in the interconnection queue. For projects that successfully make it through the queue, the time spent waiting in the queue has increased significantly - from an average of two years in 2008 and three years in 2015 to over five years in 2023.
We can use the data on projects in the interconnection queue to estimate the theoretical annual energy that could be generated by projects currently waiting in the queue. Currently, solar (1,086 GW) and wind (366 GW) comprise the vast majority (93%) of energy generation projects (excluding storage) in the grid interconnection queue. [1] Most of the remaining generation projects are made up of a wide array of project types, including gas, nuclear, hydropower, geothermal, and coal facilities. Because the remaining projects span a wide range of technologies, each with a small overall share, we shall focus on wind and solar energy.
We can estimate the amount of energy generated through each technology in an average year with the average capacity factor numbers (0.27 for solar, 0.28 for wind) provided by FERC. [2] We obtain
| (0.27 × 1.086 × 1012 Watts + 0.28 × 0.366 × 1012 Watts) | |
| × 3600 sec h-1 × 24 h d-1 × 365 d y-1 | |
| = | 1.248 × 1019 Joules per year |
or 12.48 exajoules per year. This is comparable to total U.S. electricity consumption in a given year (14.4 exajoules per year in 2024). [3]
The backlog of energy generation capacity in interconnection queues represents a substantial amount of potential electricity generation. However, the majority of proposed projects in the queue are not realized. Projects that do reach commercial operation spend a median of five years in the interconnection process, and historical data from 2000-2018 shows that around 14% of proposed capacity is actually built. [1]
The queue also reflects underlying physical constraints in energy transmission. A large proportion of the queued capacity is proposed in regions with significant solar or wind resources; often, transmission capacity is limited in these areas. [1] Interconnection studies frequently find the need for extensive grid upgrades and assign the cost of those upgrades to the proposed project; economists identify this as a major source of projects dropping out of the queue, which in turn requires re- studies for other remaining projects in the queue. [4]
These patterns have led system operators to propose reforms such as cluster studies, project-readiness requirements, and centralized transmission planning to speed up the interconnection process and convert a higher rate of proposals into commercially-operational projects. [5]
There is a significant amount of energy generation and storage capacity currently in the grid interconnection queue, awaiting studies to determine if they can safely connect to the grid. In principle, the proposed generation capacity in this queue of solar and wind alone is close to the entire electricity consumption of the United States.
However, long interconnection timelines and low project completion rates indicate that the limiting factor is not a shortage of potential energy generation and storage projects but the capacity of the transmission system to accommodate the requests through the interconnection process. Although individual utilities and FERC have taken steps to reform the grid interconnection queue process to make it more efficient, it remains to be seen if this will increase the number of commercial projects that make it to fruition.
© David Duncan. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] W. Gorman et al., "Grid Connection Barriers to Renewable Energy Deployment in the United States," Joule 9, 101791 (2025).
[2] "2023 Common Metrics," U.S. Federal Energy Regulatory Commission, January 2024.
[3] "2025 Energy Statistics Pocketbook," United Nations, Department of Economic and Social Affairs, 2025.
[4] S. Johnston, Y. Liu and C. Yang, "An Empirical Analysis of the Interconnection Queue," National Bureau of Economic Research, December 2023.
[5] L. Armstrong et al., "Can Federal Grid Reforms Solve the Interconnection Problem?" Science 385, 6704 (2024).