How can a power plant have a capacity factor over 100%?

It can't run harder than it physically can. When the number comes out above 100%, it means the two figures in the calculation are describing slightly different things. Of the 11,454 plants in our data with a capacity factor, 12 report one above 100%.

What capacity factor measures

Capacity factor compares what a plant actually produced over a year with what it would have produced running flat out at its rated size the whole time:

capacity factor = annual net generation (MWh) ÷ (nameplate capacity (MW) × 8,760 hours)

The top of that fraction is measured: meters record what the plant sent to the grid. The bottom is not. It's a rating, a single number on file for the plant. If the rating understates what the plant can really do, or describes the plant at a different moment than the generation does, the ratio can climb past 100%.

The four usual reasons

1. Nameplate is a label, not a ceiling

Nameplate capacity is the manufacturer's design rating for the generator. Many machines can run somewhat above it in good conditions. Gas turbines make more power in cold, dense air; steam and nuclear units run more efficiently with colder cooling water; and hydro generators are often rated conservatively, so a small run-of-river plant in a wet year can run almost continuously at or a little above its rating. Hydro is the most common fuel in the list below.

2. Upgrades the paperwork hasn't caught up with

Plants get uprated over their lives: new turbine parts, rewound generators, replaced hydro runners. If the plant produces more after an upgrade but the rating on file isn't changed, the capacity factor rises above what's physically possible for the listed size.

3. The plant changed during the year

The capacity figure is a snapshot. If units were added, repowered or retired during the year, the generation total and the capacity number can describe two different versions of the plant.

4. Reporting quirks

Generation and capacity are reported to federal agencies on different filings, and small mismatches happen. They show up most at small plants, where a few thousand megawatt-hours is a big share of the total, and at industrial sites like mills, where output from several on-site sources can be reported unevenly.

How to read a number above 100%

A few points over, say 100.5% or 103%, is usually reason 1 or 2: a plant that genuinely ran near flat out all year, measured against a rating that's a little low. A number far over is almost always a data issue. A wind farm at 138% would have needed the wind blowing at full strength every hour of the year, and then some. That doesn't happen, so the figure tells you something is off in the reported generation or capacity, not that the turbines beat physics.

We haven't confirmed which reason applies to each plant below. The figures are shown as reported in EPA eGRID, and we don't edit federal data to make it look tidier.

Every plant in our data over 100%

For comparison

Nuclear plants typically run above 90%, combined-cycle gas in the 50–60% range, and wind and solar between 25–40%. See the plants with the highest capacity factors or how we build these numbers on the methodology page.