Public Data Sources for Power Capacity: EIA, FERC, OASIS, Queues and Hosting Maps

The question a landowner or developer wants answered is simple: how much contract demand can this site get, and when? No public source answers it. Available capacity at a substation depends on the utility’s internal studies, other customers’ commitments and planned upgrades, and utilities treat much of that as confidential. What public data can do is tell you which utility serves the land, what transmission and generation are nearby, how crowded the region’s queue is, and how fast the planning authority expects load to grow. That is enough to rank sites and to ask the utility sharper questions.

The sources fall into layers, from bulk generation down to the distribution feeder. Mapping layers such as transmission lines and substation points are covered in our guide to GIS data sources; this guide focuses on the datasets that speak to capacity.

Form EIA-860 is a mandatory annual census of every existing and planned U.S. generating facility with at least 1 MW of nameplate capacity, including plans for new plants over a ten-year horizon.¹ EIA publishes the detailed data as Excel files containing nearly everything on the form except tested heat rates and construction costs of new units.⁹ For site work, the useful fields are plant location, nameplate capacity, the transmission or distribution owner, and planned retirement dates. A retiring plant can mean a strong interconnection point with headroom; see our guide to surplus interconnection and retired plant sites.

The annual files drop retired units in later years, so use the monthly EIA-860M for retirements; it has a tab listing utility-scale generators retired since 2002.⁹¹⁰ EIA also cautions that planned addition dates often change and that the 860M is not a forecast.¹⁰

Form EIA-861 covers utilities rather than plants. Its service territory file lists the counties in each state where a utility has distribution equipment, and its sales file reports revenue, megawatt-hours and customer counts by state, sector and balancing authority.² That makes it the quickest way to identify which utilities may serve a county, though county-level territory is coarse and boundaries inside a county need the utility’s own map; see utility service territory. As of October 2026, EIA had posted early-release 2025 data in August with final files scheduled for October.² EIA has used the same sales data to show commercial electricity sales soaring in Virginia because of data centers.¹¹

FERC Form 1 is the annual financial and operating report of major investor-owned electric utilities. It is now filed in XBRL, and FERC also offers older database files for report years 1994 through 2020.¹² Most of it is accounting, but a few schedules matter for siting: Transmission Line Statistics, Transmission Lines Added During the Year, and Substations, which in recent filings appear on pages 422–427.¹³ The substation schedule gives an inventory of the filer’s substations. It does not show loading or committed capacity, and cooperative and municipal utilities generally do not file it.

FERC Form 715 is more technical and more useful. Utilities operating integrated transmission facilities at 100 kV or above must file it, and Part 2 contains solved power flow base cases in standard formats (PSS/E, GE PSLF or PowerWorld), with forward-looking cases such as one-, two-, five- and ten-year summer and winter peaks.³ Utilities in a regional planning process can have the regional organization file the cases.³ FERC treats Parts 2 through 6 as Critical Energy Infrastructure Information (CEII), so you have to request access.³ FERC charges no fee for CEII requests and says they usually carry less burden and a better chance of success than FOIA requests.⁵

Every transmission provider under FERC open access rules posts information on an Open Access Same-Time Information System (OASIS), so that all users see it at the same time; postings include notice of curtailments and the reason a transaction could not be completed.¹⁴ OASIS also carries available transfer capability (ATC) on transmission paths, along with the provider’s tariff, business practices and study reports.

For a data center, OASIS is indirect evidence. ATC measures how much additional power can be moved across a path for transmission service, not how much load a specific substation can serve. But frequent curtailments or near-zero ATC on paths into a load pocket suggest congestion that a large new load will make worse. Many providers also post system impact and facilities studies on OASIS, which can reveal upgrade costs and timelines on nearby requests. Our guide to transmission upgrades and cost allocation explains how those costs get assigned.

ISO and RTO generator interconnection queues are public, and Berkeley Lab compiles them nationally. Its 2026 edition counted roughly 2,061 GW of capacity actively seeking interconnection at the end of 2025; more than 750 GW withdrew during the year and about 600 GW of new requests arrived.⁶ Only about 13% of the capacity that requested interconnection from 2000 to 2020 reached commercial operation.⁶ The prior edition found that the median time from request to operation had more than doubled, to over four years for projects built in 2018–2024.¹⁵

For a load project, queue data helps two ways. Generation projects queued near a site suggest where transmission is being studied and upgraded, and a large planned plant close by can be a useful partner. Heavy queues also mean slow studies. See power timelines and interconnection queues.

Load forecasts are the other public signal. PJM’s 2026 long-term forecast projected a summer peak of about 222,000 MW in 2036, growing about 3.6% a year over ten years, while lowering near-term peaks through 2032 partly through improved vetting of data center and large-load adjustments.⁷ The vetting matters: Maryland’s Office of People’s Counsel calculated that utilities’ requested large-load adjustments for 2028 rose from about 19 GW in the 2025 forecast to 32 GW in the 2026 requests.¹⁶ Forecast filings and stakeholder letters often name the zones where large loads cluster, which tells you where your request will compete.

Hosting capacity maps estimate how much generation or load a distribution feeder can take without upgrades. The Department of Energy’s atlas, updated in July 2025 with data as of May 2024, listed 58 utilities and state agencies publishing maps in 26 states, Washington, D.C., and Puerto Rico, and noted that some utilities publish load-related maps.⁴ Most maps were built for rooftop and community solar, and coverage within a state can be partial.⁴

Accuracy is a known issue. Pacific Gas and Electric’s first map showed little or no room for new solar on 80% of its feeders, results the utility later conceded were erroneous.⁸ Even accurate maps describe distribution feeders, which are far smaller than a campus load. A 100 MW campus will connect at transmission voltage through a dedicated substation, so a feeder map is useful mainly for small edge sites, construction power or an early phase.

1. 01Use EIA-861 and the utility’s territory map to confirm who serves the parcel.
2. 02Pull EIA-860 plants and FERC Form 1 substations within a reasonable radius, and flag planned retirements.
3. 03Check the regional queue and OASIS postings for nearby generation and transmission studies.
4. 04Read the latest load forecast for the zone, including large-load adjustments.
5. 05If the site still looks promising, request Form 715 cases or hire an engineer who has them.
6. 06Then ask the utility directly, through a capacity inquiry or a formal load study.

Public data is a filter, not an answer. Its limits are lag (annual data can be a year or more old), aggregation (county territories, system-wide forecasts) and access (the most useful models are restricted). A utility will-serve letter or study result outranks any public dataset. BlackForge uses these sources in its methodology to screen sites before the utility conversation; you can get a site reviewed or explore our tools.