3.11.2021 Update: After the initial posting of this blog, further research indicates that the Darien Solar Energy Center would have a *capacity factor likely closer to 0.24, not .30. Using this updated capacity factor of .24 for the Darien Solar Energy Center, emissions would decrease by 423,000 tons of carbon dioxide (CO2), 602,000 pounds of nitrogen oxides (NOx), 745,000 pounds of sulfur dioxide (SO2), and 76,000 pounds of particulate matter (PM10) annually for the lifetime of the project. These emissions reductions would lead to decreased mortality of about one life per year, annual health savings between $15 to $34 million, and yearly climate savings of over $17 million

Capacity factor expresses in percentage form the expected production of a power plant relative to its maximum possible output. This ratio takes into account variables such as maintenance-related downtime and the availability of the energy source fueling the plant. All power plants have a capacity factor of less than one. 

Consider a solar farm sized to produce a theoretical maximum of 10,000 megawatt-hours/year. If the plant is estimated to have a capacity factor of 0.30, it can be expected to produce 3,000 megawatt-hours a year. A solar farm could not have a 1.0 capacity factor because the sun doesn’t shine all day. In fact, with nighttime constituting half of the hours in a year, a solar farm could not have a capacity factor greater than 0.50.

The Darien Solar Energy Center is a proposed 250-MW solar PV facility in Walworth county, Wisconsin currently under review at the Wisconsin Public Service Commission. If approved, developers hope to have the project constructed and energized by 2023, offering significant health, environmental, and economic benefits to local Wisconsin communities.

Using the EPA’s Avoided Emission and Generation tool, RENEW Wisconsin estimates that the Darien Solar Energy Center could reduce emissions by 538 thousand tons of carbon dioxide (CO2), 700 thousand pounds of nitrogen oxides (NOx), 1 million pounds of sulfur dioxide (SO2), and 98 thousand pounds of particulate matter (PM10) annually for the lifetime of the project. Carbon dioxide is a greenhouse gas that contributes to climate change, and sulfur dioxide, nitrogen oxides, and particulate matter contribute to health problems including asthma, cardiopulmonary disease, and premature mortality. Fossil fuel power plants are the primary emission sources of these pollutants. Transitioning to the clean energy produced by the Darien solar project, Wisconsin would reduce its fossil fuel generation, providing significant human health and environmental benefits to its residents.

RENEW Wisconsin completed in-house research on the health benefits of the Darien project. Using the EPA’s Co-Benefit Risk Assessment model, the Darien Solar Energy Center is estimated to reduce mortality by up to one life per year for 30 years in Wisconsin. The health impacts are substantial for Wisconsin, a state highly dependent on coal-fired electricity generation. Energizing the Darien Solar Energy Center could directly save Wisconsin lives.

In addition to the health benefits of clean energy, there are also significant economic benefits this solar project could deliver. Using the EPA’s health benefit factors for Wisconsin, the annual savings ranged from $18 to $42 million depending on population, pollution burden, and other differentiating factors. Moreover, Darien could produce up to $22 million in annual savings resulting from avoided climate impacts. Climate impacts are estimated from the EPA’s social cost of carbon values. These monetized health impacts are significant and illustrate the benefits that the Darien Solar Energy Center could bring to the Wisconsin economy.

Overall, these findings detail the benefits that the Darien Solar Energy Center offers Wisconsin by reducing pollution, decreasing human mortality, helping to mitigate climate damages, and providing millions of dollars in economic benefits to the state. Other significant benefits related to Wisconsin GDP, employment, and environmental and water impacts were not discussed in this article. To learn more about the Darien Solar Energy Center and its additional benefits, please visit the Town of Darien website.