Capacity in interconnection queues as of the end of 2021. *Hybrid storage capacity is estimated in some cases using storage: generator ratios from projects that provide separate capacity data. Storage capacity in hybrids was not estimated for years prior to 2020.
Electric transmission system operators (ISOs, RTOs, or utilities) require projects seeking to connect to the grid to undergo a series of impact studies before they can be built. This process establishes what new transmission equipment or upgrades may be needed before a project can connect to the system and assigns the costs of that equipment. The lists of projects in this process are known as “interconnection queues”. The amount of new electric capacity in these queues is growing dramatically, with over 1,400 gigawatts (GW) of total generation and storage capacity now seeking connection to the grid (over 90% of which is for zero-carbon resources like solar, wind, and battery storage). However, most projects that apply for interconnection are ultimately withdrawn, and those that are built are taking longer on average to complete the required studies and become operational. Data from these queues nonetheless provide a general indicator for mid-term trends in developer interest.
This annually updated briefing and data file compiles and analyzes interconnection queue data from all seven ISOs/RTOs in concert with 35 non-ISO utilities, representing over 85% of the total U.S. electricity load. We include all "active" projects in these generation interconnection queues through the end of 2021, as well as data on "operational" and "withdrawn" projects where those data are available.
Key findings from this year’s briefing include:
- The total capacity active in the queues is growing year-over-year, with over 1,000 GW of generation and an estimated 427 GW of storage capacity as of the end of 2021.
- In total, over 930 GW of zero-carbon generating capacity is currently seeking transmission access. Solar (676 GW) accounts for the largest share of generation capacity in the queues. Substantial wind (247 GW) capacity is also seeking interconnection, 31% of which is for offshore projects (77 GW).
- Solar and battery storage are – by far – the fastest growing resources in the queues. Combined, they account for nearly 85% of new capacity entering the queues in 2021.
- Proposed fossil fuel generation is on the decline, with 75 GW of natural gas and less than 1 GW of coal currently proposed.
- Hybrids now comprise a large – and increasing – share of proposed projects, particularly in CAISO and the non-ISO West. 286 GW of solar hybrids (primarily solar+battery) and 19 GW of wind hybrids are currently active in the queues. Nearly half of the battery storage capacity in the queues is paired with some form of generation (mostly solar).
- However, much of this proposed capacity will not ultimately be built. Among a subset of queues for which data are available, only 23% of the projects seeking connection from 2000 to 2016 have subsequently been built. Completion percentages appear to be declining, and are even lower for wind and solar than other resources.
- Interconnection wait times are also on the rise: amongst the regions with available data, the typical duration from connection request to commercial operation increased from ~2.1 years for projects built in 2000-2010 to ~3.7 years for those built in 2011-2021.
For further details on these and other findings, please refer to the short PowerPoint-style briefing, which can be downloaded here. The briefing is also accompanied by an interactive data visualization here.
