Balancing areas and the plants in them
A balancing authority is the organization that keeps electricity supply and demand matched, second by second, inside its area. Nearly every plant in the 2025 EIA-860 data names one, and 65 different balancing authorities appear. They range from PJM Interconnection, with 226.9 GW at 2,049 plants, to small utility areas with a handful of sites. The five largest hold 59% of US capacity.
Balancing areas matter because they decide which plants run together. A plant in the ERCOT area serves the Texas grid; a plant just across a state line in the Southwest Power Pool serves a different market, even if the two are a few miles apart.
The 40 largest areas
| Area | Plants | Capacity | States | Largest fuel |
|---|---|---|---|---|
| PJM Interconnection | 2,049 | 226.9 GW | 15 | Natural gas |
| MISO (Midcontinent) | 2,383 | 212.6 GW | 15 | Natural gas |
| ERCOT (Texas) | 935 | 173.6 GW | 2 | Natural gas |
| Southwest Power Pool | 713 | 103.2 GW | 14 | Natural gas |
| California ISO | 1,637 | 94.4 GW | 3 | Natural gas |
| Southern Company | 335 | 70.6 GW | 5 | Natural gas |
| New York ISO | 1,093 | 45.6 GW | 2 | Natural gas |
| Tennessee Valley Authority | 152 | 44.0 GW | 6 | Natural gas |
| Florida Power & Light | 153 | 42.0 GW | 1 | Natural gas |
| ISO New England | 1,475 | 38.2 GW | 7 | Natural gas |
| Duke Energy Carolinas | 441 | 31.0 GW | 2 | Natural gas |
| Bonneville Power Administration | 129 | 30.5 GW | 5 | Hydroelectric |
| PacifiCorp East | 172 | 18.7 GW | 5 | Coal |
| Salt River Project | 44 | 18.4 GW | 1 | Natural gas |
| Duke Energy Progress East | 462 | 17.7 GW | 2 | Natural gas |
| Duke Energy Florida | 74 | 16.5 GW | 1 | Natural gas |
| Public Service Company of Colorado | 192 | 16.4 GW | 1 | Natural gas |
| Nevada Power | 106 | 15.7 GW | 2 | Natural gas |
| WAPA Rocky Mountain | 166 | 11.3 GW | 7 | Coal |
| LA Department of Water and Power | 95 | 10.2 GW | 3 | Natural gas |
| Arizona Public Service | 68 | 9,867 MW | 2 | Natural gas |
| Tampa Electric | 45 | 8,684 MW | 1 | Natural gas |
| Dominion Energy South Carolina | 61 | 8,135 MW | 2 | Natural gas |
| PNM (New Mexico) | 102 | 7,538 MW | 1 | Wind |
| WAPA Desert Southwest | 24 | 7,136 MW | 3 | Hydroelectric |
| Associated Electric Cooperative | 34 | 6,706 MW | 4 | Natural gas |
| Santee Cooper | 28 | 5,978 MW | 1 | Coal |
| Balancing Authority of Northern California | 84 | 5,719 MW | 1 | Natural gas |
| Idaho Power | 134 | 4,872 MW | 2 | Hydroelectric |
| Tucson Electric Power | 48 | 4,499 MW | 2 | Coal |
| NorthWestern Energy | 52 | 4,265 MW | 2 | Coal |
| Portland General Electric | 102 | 4,224 MW | 2 | Natural gas |
| Puget Sound Energy | 34 | 3,339 MW | 2 | Natural gas |
| El Paso Electric | 27 | 2,856 MW | 2 | Natural gas |
| PacifiCorp West | 117 | 2,741 MW | 3 | Hydroelectric |
| Southwestern Power Administration | 29 | 2,601 MW | 3 | Hydroelectric |
| Imperial Irrigation District | 58 | 2,324 MW | 1 | Geothermal |
| Avista | 30 | 2,309 MW | 3 | Hydroelectric |
| WAPA Upper Great Plains West | 22 | 1,128 MW | 3 | Hydroelectric |
| Hawaiian Electric | 23 | 894 MW | 1 | Solar |
Markets and single utilities
The largest areas are organized wholesale markets run by independent operators: PJM in the Mid-Atlantic and Ohio Valley, MISO in the Midwest and South, ERCOT in Texas, the Southwest Power Pool on the plains, and the California, New York and New England ISOs. MISO has more plants than PJM (2,383 against 2,049) but less capacity: its average plant has 89.2 MW, against 111 MW in PJM. ERCOT is almost entirely Texan: 99.2% of its capacity is in Texas.
Across the Southeast and the West, most areas are run by a single utility or federal power agency, for example Southern Company, Duke Energy, the Tennessee Valley Authority, Bonneville Power Administration and the regional offices of the Western Area Power Administration.
Plants without a balancing area
Of the 14,286 plants, 200 have no balancing authority on their record. Most are in Alaska (145) and Hawaii (53), whose island and isolated grids are not part of the mainland interconnections, and the rest are small sites whose record leaves the field blank. Their plant pages and the finder still list them; they simply have no area page.
How to use the area pages
Each area page shows the fuel mix of the plants inside it, the 25 largest plants, the states it spans and its biggest operators, plus a chart of capacity by the decade it came online. Plant pages name their balancing area under “Grid and site” and rank the plant within it. Area boundaries do not follow state lines, so for the same comparison by state use the state pages.
Very different mixes
Because balancing areas are drawn around utilities and markets, their fuel mixes differ more than state averages suggest. Wind, solar and batteries together make up 94% of capacity in the Hawaiian Electric area, the highest share among the 40 areas listed above, and 4.2% in the Tennessee Valley Authority area, the lowest. Nuclear weighs most in the Duke Energy Carolinas area, at 24% of capacity.
Where new capacity connected since 2020
The table ranks areas by the nameplate capacity of units that came online from 2020 to 2025 and still operate. The last column sets that against the area’s total, showing how much of each fleet came online in 2020 or later.
| Area | Added 2020–2025 | Share of area capacity |
|---|---|---|
| ERCOT (Texas) | 60.2 GW | 35% |
| MISO (Midcontinent) | 39.5 GW | 19% |
| California ISO | 30.4 GW | 32% |
| PJM Interconnection | 27.8 GW | 12% |
| Southwest Power Pool | 17.8 GW | 17% |
| Florida Power & Light | 10.3 GW | 25% |
| Southern Company | 7,915 MW | 11% |
| PacifiCorp East | 5,022 MW | 27% |
The other 25 balancing authorities each have fewer than 20 plants in the data, 158 plants in all. Plant pages still rank their plants within the area; the areas simply do not get an area page of their own here.
The largest plant in each big area
In the five largest areas, the biggest plants are these: in the PJM Interconnection area it is John E Amos (2,933 MW); in the MISO (Midcontinent) area it is Gibson (3,340 MW); in the ERCOT (Texas) area it is W A Parish (4,008 MW); in the Southwest Power Pool area it is Jeffrey Energy Center (2,160 MW); in the California ISO area it is Diablo Canyon (2,323 MW). Each area page lists its 25 largest plants with their main fuel and the year their first working unit came online.
Federal power agencies
Several balancing authorities are federal: the Tennessee Valley Authority, Bonneville Power Administration, the Southwestern Power Administration and regional offices of the Western Area Power Administration. Together the six federal areas listed above hold 96.7 GW of capacity at their plants, 7.0% of the US total, and hydropower is the largest fuel in four of them, as the table above shows.
Source: U.S. Energy Information Administration, Form EIA-860 (Annual Electric Generator Report), 2025 final data (Sep 2026). Downloaded 2026-10-28. Figures are computed by GridPlants from the plant, generator and ownership files; see how to read the data.