A dam's size is not its output

Capacity is a rating

Every generator carries a nameplate capacity in megawatts (MW). It is the maximum power the unit is rated to produce at one instant. Grand Coulee's operating generators add up to 6,809 MW across 33 count units, as listed in the 2024 EIA-860 inventory. A rating says nothing about how often the units run.

Grand Coulee on the capacity map ↗(opens the atlas in a new tab)

Output is measured over time

Net generation is energy delivered over a period, in megawatt-hours (MWh). In 2024 Grand Coulee reported 15,443,458 MWh. The chart shows the reported annual totals since 2015. Years differ because the plant sits on the Columbia River: seasonal runoff varies with snowpack and precipitation [4], and the federal projects are operated for several purposes at once, including flood risk management and fish passage, not only power [3]. Which of those explains a particular year is not asserted from these two numbers; the atlas shows the reported totals and their sources.

Annual net generation · MWh. Bars below zero are negative net generation; a hollow mark means not reported. Missing years are not filled.

Grand Coulee on the generation map ↗(opens the atlas in a new tab)

The ratio is the capacity factor

Divide the year's energy by what the nameplate could have produced over every hour of the year (8,784 hours in 2024) and you get the capacity factor: 0.258 fraction. For Grand Coulee that is roughly a quarter. A low capacity factor is not a defect. A hydro plant with a large nameplate is valuable precisely because it can produce a lot of power on demand when the water is there, then hold back.

The atlas computes this ratio only when the operating fleet was stable across the year. If a unit started or retired mid-year, the fact reads "not supported" rather than using a denominator that changed.

Who owns and runs it

Explore Bureau of Reclamation ↗

The reported operator is Bureau of Reclamation, a federally owned utility [1]. EIA's ownership schedule lists only jointly or third-party owned units; Grand Coulee's units are absent from it and carry ownership code S, so the pipeline applies EIA's rule that such units are wholly owned by the operator and labels the result as derived. Ownership is not the same as who buys the power: the Bonneville Power Administration markets the output of the federal Columbia River dams [2]; the contracts and quantities behind that are not part of this release.

Every plant Reclamation runs or owns ↗(opens the atlas in a new tab)

Where it reports

Explore Bonneville Power Administration ↗

Grand Coulee reports its operations within the Bonneville Power Administration balancing authority. That is an accounting relationship, not a wire to any customer. The BA's operating nameplate (27,571.3 MW) and reported 2024 generation (95,441,873 MWh) come from summing published plants that report this BA; plants without an EIA-923 row for the year are counted as unknown, not zero.

Hydro plants reporting to BPA ↗(opens the atlas in a new tab)

What this story does not claim

No household is traced to this dam. No monthly curve is invented for annual reporters. Nameplate is never presented as output, and output is never presented as a rating.