Hemmingway BESS
Owyhee County, Idaho · EIA plant ID 66325 · Operator: Idaho Power Co
Nameplate166MWSummer 166 MW
Generators3in service
Net generation-5GWh12 mo to Aug 2026
Capacity factor—not meaningful for storage
Heat rate—thermal plants only
First online2025
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), primary-fuel units. Each year uses that year's EIA-860 ratings; the hollow dot is the latest 12 months.
No capacity factor available.
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) |
|---|---|---|---|
| 2025 | -6.5 | — | — |
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 |
|---|---|---|---|---|---|---|---|---|
| 1 | Batteries | BA | 80 | 80 | Mar 2025 | Operating | — | coming soon |
| 3 | Batteries | BA | 50 | 50 | Jun 2026 | Operating | — | coming soon |
| HGWP2 | Batteries | BA | 36 | 36 | Mar 2025 | Operating | — | coming soon |
Owner / operator
Operator: Idaho Power Co. Ownership shares by in-service nameplate MW (EIA-860 Schedule 4; units not listed there are wholly owned by the operator).
| Idaho Power Co | 100.0% | 166 MW |
Nearby plants
Within 80 km.
| Melba BESS | 2 MW | 8.5 km |
| Mora Drop Hydroelectric Project | 2 MW | 19.5 km |
| Murphy Flat Solar | 20 MW | 23.7 km |
| Kuna BESS | 150 MW | 24.9 km |
| Happy Valley Battery Storage | 82 MW | 25.3 km |
| Swan Falls | 27 MW | 25.9 km |