Mossyrock
Lewis County, Washington · EIA plant ID 3918 · Operator: City of Tacoma - (WA)
Nameplate300MWSummer 343 MW
Generators2in service
Net generation1,018GWh12 mo to Aug 2026
Capacity factor34%hydro units, summer MW
Heat rate—thermal plants only
First online1968
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), hydro 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) |
|---|---|---|---|
| 2001 | 485.8 | 17.3% | — |
| 2002 | 1,059.8 | 34.6% | — |
| 2003 | 965.7 | 31.5% | — |
| 2004 | 749.6 | 24.4% | — |
| 2005 | 538.1 | 17.5% | — |
| 2006 | 1,161.8 | 37.9% | — |
| 2007 | 940.5 | 30.2% | — |
| 2008 | 1,003.1 | 32.2% | — |
| 2009 | 995.9 | 29.3% | — |
| 2010 | 1,026.7 | 31.0% | — |
| 2011 | 1,325.5 | 40.0% | — |
| 2012 | 1,416.8 | 42.6% | — |
| 2013 | 1,075.9 | 33.1% | — |
| 2014 | 1,287 | 39.6% | — |
| 2015 | 1,006.6 | 30.9% | — |
| 2016 | 1,202.1 | 36.9% | — |
| 2017 | 1,265.6 | 42.1% | — |
| 2018 | 907.8 | 30.2% | — |
| 2019 | 583.5 | 19.4% | — |
| 2020 | 1,110.3 | 36.9% | — |
| 2021 | 1,048.6 | 34.9% | — |
| 2022 | 1,125.6 | 37.5% | — |
| 2023 | 713.4 | 23.7% | — |
| 2024 | 811.6 | 26.9% | — |
| 2025 | 902.7 | 30.0% | — |
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 |
|---|---|---|---|---|---|---|---|---|
| 51 | Conventional Hydroelectric | HY | 150 | 186 | Nov 1968 | Operating | — | coming soon |
| 52 | Conventional Hydroelectric | HY | 150 | 157 | Oct 1968 | Operating | — | coming soon |
Owner / operator
Operator: City of Tacoma - (WA). Ownership shares by in-service nameplate MW (EIA-860 Schedule 4; units not listed there are wholly owned by the operator).
| City of Tacoma - (WA) | 100.0% | 300 MW |
Nearby plants
Within 80 km.
| Mayfield | 162 MW | 13 km |
| Cowlitz Falls | 70 MW | 25.3 km |
| Alder | 51 MW | 30.9 km |
| LaGrande | 64 MW | 34.1 km |
| Skookumchuck | 1 MW | 35.7 km |
| Chehalis Generating Facility | 593 MW | 38.6 km |