BIG STONE
OperatingCoal power plant
- Capacity
- 457 MW
- Primary fuel
- Coal
- County
- Grant County
- Operator
- OTTER TAIL POWER CO
- Status
- Operating
- Commissioned
- 1975
- EIA plant ID
- 6098
- Generators
- 2
- Technology
- Conventional Steam Coal
- Net generation (2024)
- 1,566 GWh
- Capacity factor (2024, EIA nameplate)
- 40%
- Data vintage
- EIA-860 2024 final; EIA-923 2022-2024 final
- Coordinates
- 45.3036, -96.5101
BIG STONE, a 457 MW Coal power plant in Grant County, South Dakota. Operated by OTTER TAIL POWER CO, commissioned 1975.
How BIG STONE compares
With 457 MW of capacity, BIG STONE ranks 3rd among the 28 operating power plants Bywatts maps in South Dakota and is the largest of the 2 operating Coal plants in the state. It accounts for about 77% of South Dakota's operating Coal capacity and 11% of all operating capacity in the state. Nationally it is the 167th-largest of the 324 operating Coal plants in the database. Commissioned in 1975, it is older than 65% of the 26 operating South Dakota plants with a recorded commissioning year. Its operator, OTTER TAIL POWER CO, runs 2 operating plants in South Dakota totaling 481 MW.
EIA-860 lists 2 generators at the site with 451 MW of nameplate capacity, all conventional steam coal technology. Net generation was 1,566 GWh in 2024 (a 40% capacity factor), down 17% from 2022.
Grid neighborhood
The closest transmission line found within 10 miles is a 230 kV line owned by OTTER TAIL POWER CO, under 0.1 miles away.
Computed by Bywatts from HIFLD power plant and transmission line records and EIA-860/923 survey data; distances are straight-line. Sources and methodology
Weather peril exposure
BIG STONE is a 457 MW coal power plant in Grant County, SD, operated by OTTER TAIL POWER CO, commissioned in 1975. Grant County carries moderate modeled catastrophe exposure in the FEMA National Risk Index, scoring 2.5 of 5 at the 38th national percentile. Heat wave is the leading peril, rated Very Low by FEMA at the 87th percentile.
The Bywatts loss layer is calibrated to solar PV hardware, so it is not applied to a coal plant. The ratings below are the FEMA National Risk Index county hazard ratings for this location.
Grant County hazard ratings
| Peril | FEMA rating | National percentile | Peril score | Events per year |
|---|---|---|---|---|
| Heat wave | Very Low | 87th | 4.5 of 5 | 2.7 |
| Ice storm | Relatively Moderate | 79th | 4.2 of 5 | 0.57 |
| Tornado | Relatively Low | 77th | 4.1 of 5 | 0.43 |
| Strong wind | Relatively Low | 72nd | 3.9 of 5 | 2.7 |
| Wildfire | Very Low | 71st | 3.9 of 5 | <0.01 |
| Winter weather | Relatively Low | 70th | 3.8 of 5 | 23.2 |
| Riverine flooding | Very Low | 65th | 3.6 of 5 | 1.0 |
| Hail | Relatively Low | 45th | 2.8 of 5 | 3.9 |
| Lightning | Very Low | 26th | 2.1 of 5 | 33.5 |
| Earthquake | Very Low | 11th | 1.4 of 5 | <0.01 |
Perils not assessed in Grant County
These perils carry no usable National Risk Index figure for this county, so they are excluded from the scoring rather than scored zero. A zero would claim the peril was assessed and found benign.
| Peril | Why it is not scored |
|---|---|
| Hurricane | FEMA rating is "Not Applicable" for this county |
| Coastal flooding | FEMA rating is "Not Applicable" for this county |
Model hail, wind and flood exposure for Grant County in the weather risk calculator
Ratings are the FEMA National Risk Index county hazard ratings; the peril score is a Bywatts transform of the FEMA national percentile. Full data sources and the solar vulnerability methodology are in the weather risk calculator.
Modeled estimate for screening and negotiation. Built from FEMA National Risk Index county hazard data and a solar vulnerability layer documented above. Not a quote, a binder, or actuarial advice, and not a substitute for a carrier's own model. Hazard data: FEMA National Risk Index December 2025, synced 2026-07-24. Resolution is county level, not site level.