What is a good capacity factor for solar?
For US utility-scale solar photovoltaic plants, a good capacity factor is one at or above the national average, which has sat in a fairly narrow band of roughly 23 to 25 percent in recent years, according to the US Energy Information Administration's Electric Power Monthly. In 2025 the average was 24.4 percent, and in 2024 it was 23.2 percent. A plant well below that band for its year deserves a closer look; a plant near or above it is performing in line with its technology.
Capacity factor is a percentage that compares what a generator actually produced over a period with the maximum it could have produced in that same period. The US Energy Information Administration defines it as a measure of how often a generator operates, expressed as the ratio of actual output to maximum possible output. A plant running flat out around the clock would approach 100 percent, while one that rarely runs sits far lower.
[3]The definition matters because capacity factor is easily misread. Generation capacity is the maximum output a generator can produce under specific conditions, while electricity generation is the amount actually produced over time. The EIA illustrates the gap with a simple case: a generator with 1 megawatt of capacity running at full output for one hour produces 1 megawatthour, but running at half capacity for the same hour produces only 0.5 megawatthours. Many generators do not operate at full capacity all the time, and output varies with plant conditions, fuel costs, or instructions from a grid operator.
[3]What the official solar numbers show
The EIA publishes average monthly and annual capacity factors by generator type in Tables 6.07.A and 6.07.B of the Electric Power Monthly, and Table 6.07.B covers utility-scale generators primarily using non-fossil fuels, including solar photovoltaic and solar thermal. The annual capacity factor for utility-scale solar photovoltaic plants has been remarkably stable: 25.0 percent in 2016, 24.4 percent in 2022, 23.2 percent in 2024, and 24.4 percent in 2025. Across the decade of published data it has stayed between roughly 23 and 26 percent. That stability is what makes the national average a sensible yardstick: a 'good' figure for a given plant in a given year is one close to or above that year's published average.
[1][3]The EIA notes that values for 2025 and 2026 are preliminary and subject to revision, while values for 2024 and earlier years are final, so a comparison should always use the same release year.
[1]A worked example of the comparison process
Suppose, hypothetically, you are looking at a 100 megawatt solar plant that reported an annual capacity factor of 25 percent. Using the EIA's definition, that means over the year it produced one quarter of the electricity it could have produced running at maximum output continuously. Before calling that good or poor, you would check the published annual solar photovoltaic average in Table 6.07.B for the same year. If the national average is similar, the plant is performing in line with its technology; if it is well below, that signals a question worth investigating, such as outages, curtailment instructions from the grid operator, or local weather. Note also that the EIA's figures use time-adjusted capacity: monthly figures reflect only generators in operation for the entire month, excluding units that began operation or retired during the month, and annual figures are a time-weighted average of the monthly rows. A fair comparison should use the same basis.
[1][3]Comparing solar with other technologies carefully
- Monthly solar figures swing widely: in 2024, utility-scale solar photovoltaic capacity factors ranged from 13.4 percent in January to 32.3 percent in June. Annual figures are therefore the fairer basis for a good-or-not judgement.
- Solar is a different category of generator: nearly all US solar electricity comes from photovoltaic systems, which convert sunlight directly to electricity, and the EIA reports solar provided about 7 percent of total US utility-scale electricity in 2025.
- The EIA separates utility-scale plants, which have at least 1 megawatt of capacity, from small-scale systems under 1 megawatt. A rooftop array should not be judged against the utility-scale averages in Table 6.07.B without noting the difference.
- Peaking plants and some storage facilities are idle by design, so a low capacity factor is not automatically bad; the EIA notes some generators run only in short bursts and may even consume more power than they produce in a given month while standing ready.
A practical next step: open the EIA's Electric Power Monthly, find Table 6.07.B in the most recent release, and read the annual solar photovoltaic capacity factor alongside the technical note explaining how capacity factors are calculated. That single comparison tells you whether the solar figure you are evaluating is above, at, or below the official national average for its year.
[1][3]Sources and dates
- https://www.eia.gov/electricity/monthly/epm_table_grapher.php?t=epmt_6_07_b · accessed 2026-10-18
- https://www.eia.gov/electricity/Annual/table.php?t=epa_08_04.html · accessed 2026-10-18
- https://www.eia.gov/tools/faqs/faq.php?id=101&t=3 · accessed 2026-10-18
- https://www.eia.gov/energyexplained/electricity/electricity-in-the-us.php · accessed 2026-10-18