South Mills Solar, LLC
Big Horn County, Montana · EIA plant ID 61290 · Operator: Enerparc Inc.
Nameplate3MWSummer 3 MW
Generators1in service
Net generation5GWh12 mo to Aug 2026
Capacity factor18%solar units, summer MW
Heat rate—thermal plants only
First online2017
The 12-month figures include preliminary EIA-923 months, which EIA revises. Final data runs through Dec 2025.
Monthly net generation
EIA-923, all units at the plant. Net of station use; storage can go negative.
FinalPreliminary
Capacity factor by year
Net MWh ÷ (summer MW × hours), solar units. Each year uses that year's EIA-860 ratings; the hollow dot is the latest 12 months.
Heat rate by year
Electric fuel MMBtu × 1000 ÷ net MWh (Btu/kWh, HHV), fossil units only; CT + CA counted as one combined-cycle block.
Heat rate applies to fuel-burning (thermal) units only.
Annual data table
| Year | Net GWh | Capacity factor | Heat rate (Btu/kWh) |
|---|---|---|---|
| 2017 | 4.2 | 21.4% | — |
| 2018 | 5.8 | 22.1% | — |
| 2019 | 4.3 | 16.5% | — |
| 2020 | 5.6 | 21.1% | — |
| 2021 | 6.4 | 24.3% | — |
| 2022 | 5.9 | 22.3% | — |
| 2023 | 5.9 | 22.5% | — |
| 2024 | 5.7 | 21.6% | — |
| 2025 | 4.9 | 18.7% | — |
Generators
EIA-860 (annual) with EIA-860M updates through Sep 2026. EIA-923 reports generation by plant, prime mover and fuel, not by unit, so unit-level output isn't shown.
| Gen ID | Technology | Prime mover | Nameplate MW | Summer MW | Online | Status | Planned retirement | OEM / model |
|---|---|---|---|---|---|---|---|---|
| SMSMT | Solar Photovoltaic | PV | 3 | 3 | Apr 2017 | Operating | — | coming soon |
Owner / operator
Operator: Enerparc Inc.. Ownership shares by in-service nameplate MW (EIA-860 Schedule 4; units not listed there are wholly owned by the operator).
| Enerparc Inc. | 100.0% | 3 MW |
Nearby plants
Within 80 km.
| Hardin Generator Project | 116 MW | 4 km |
| Yellowtail | 278 MW | 53.4 km |
| Yellowstone Energy LP | 68 MW | 62.3 km |
| Phillips 66 Billings Refinery | 2 MW | 66.8 km |
| Western Sugar Cooperative - Billings | 2 MW | 67.4 km |
| MTSUN | 80 MW | 76.4 km |