To compare different ways of making electricity, you need to know both how much electricity a power plant can make at its peak, known as its “capacity,” and the percentage of the year the plant runs at that rate, called its “capacity factor.”

Today, nuclear reactors range in capacity from about 300 megawatts—for small reactors that are still being experimented with—to about 1600 megawatts (1). The average nuclear reactor has about 900 megawatts of capacity (2). (Larger nuclear plants use multiple reactors to achieve much higher capacities.) By comparison, the average capacity of a land-based wind turbine installed in 2022 was about 3 megawatts (offshore wind turbines are larger) (3).

So even if both types of plants ran at their top performance day in and day out, hundreds of wind turbines would be needed to produce the same amount of electricity as the average nuclear project, says John Parsons, the deputy director of the MIT Center for Energy and Environmental Policy Research.

But nuclear plants also have the highest capacity factor of any energy technology. Once a nuclear plant is powered on, it runs at its top performance the majority of the time: 93% of the time in the U.S., according to the U.S. Energy Information Administration (4). That’s significantly higher than the capacity factor of even coal or natural gas, generally considered reliable “baseload” sources we can count on whenever we need them. Wind, on the other hand, has a capacity factor of around 36 percent, because turbines are limited by the amount of wind blowing past them, as well as their turbine size (4).

Multiply these energy sources’ maximum capacities by their capacity factors, and you’ll find that it would take almost 800 average-sized wind turbines to match the output from a 900-megawatt nuclear reactor.

These types of calculations are important because we’ll need much more clean energy than we have now to avoid the worst impacts of climate change. Understanding how much we’ll have to build, and how much land and other resources they’ll take up, can help us decide which types of power to add where.

When it comes to land use, nuclear plants take up as little as 10 hectares per terawatt-hour of electricity produced per year, while wind uses about 100 hectares, measuring just the area taken up by turbines (5). (This rises to an astounding 10,000 hectares if you include all the land covered by a wind farm, but most of this space is open land and can be used for ranching or farming.)

Different power plants also emit different amounts of climate-warming carbon dioxide (CO2). For technologies like wind and nuclear, CO2 emissions are “dramatically less than the smokestack emissions from fossil fuel fired systems,” says Parsons, but there is still some climate pollution from manufacturing the power plant equipment. Producing a median kilowatt-hour of either wind or nuclear power emits 11 or 12 grams of CO2—compared to over 800 grams for coal (6).

How about other clean technologies? The process to manufacture solar panels and build large solar plants emits a median 48 grams of CO2 per kilowatt-hour produced (6). In terms of land, a solar plant can use more than 1,000 hectares per terawatt hour of electricity produced per year—roughly 10 times as much as wind energy (5). And only solar energy has a lower capacity factor than wind: about 24% (4). Producing the same amount of electricity as the average nuclear reactor using solar panels would require around 8.5 million of them.

Hydropower can also give us clean electricity, but, says Parsons, it is difficult to compare to other resources. That’s because there are different types of hydro installations, which are highly dependent on the bodies of water they’re built on. Many of the world’s largest power plants are hydroelectric, but there are also “micro” hydroelectric systems that power only a single home. Capacity factors vary a lot, because water flow can change depending on the project’s structure and environmental conditions, and hydro operators sometimes move water around to store power as well as produce it. For land use, hydropower projects can use as little as 100 hectares or up to thousands of hectares per terawatt hour of electricity produced per year, because dams and reservoirs can vary significantly in size. And in terms of CO2 emissions, hydropower plants can be among the cleanest in the world. But in some hydro projects, new reservoirs can also release climate-warming emissions as plants in the flooded area decay, which can make them a much dirtier energy source (7).

So there are many factors communities will juggle as they decide which clean energy technologies to embrace—including also the way a plant looks to its neighbors, or the waste that it produces. “Those are all considerations that different communities will assess differently,” says Parsons.

Published January 4, 2024

FOOTNOTES

1 World Nuclear Association: Small Nuclear Power Reactors. Updated October 2023.

2 International Atomic Energy Agency: Nuclear Power Capacity Trend. Updated January 2, 2024.

3 U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy: Wind Turbines: The Bigger, the Better. August 24, 2023.

4 U.S. Energy Information Administration: Electric Power Monthly. Capacity Factors for Utility Scale Generators Primarily Using Non-Fossil Fuels. Figures are for 2022.

5 Lovering, Jessica, Marian Swain, Linus Blomqvist, and Rebecca Hernandez, "Land-use intensity of electricity production and tomorrow’s energy landscape." PLoS ONE, Volume 17, Issue 7, 2022, doi:10.1371/journal.pone.0270155.

6 Intergovernmental Panel on Climate Change: "Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change." Annex III: Technology-Specific Cost and Performance Parameters. 2014.

7Ocko, Ilissa, and Steven Hamburg, "Climate Impacts of Hydropower: Enormous Differences among Facilities and over Time." Environmental Science & Technology, Volume 53, Issue 23, 2019, doi:10.1021/acs.est.9b05083.