A recent study co-authored by Minghao Qiu, an assistant professor at Stony Brook University, finds that the climate benefits of solar power are not uniform across the United States. The research, published in Science Advances, shows that both the location and timing of solar energy deployment significantly influence its effectiveness in reducing greenhouse gas emissions.
The study estimates that a 15 percent increase in U.S. solar power generation could cut annual carbon dioxide emissions by 8.54 million metric tons. However, the reduction varies greatly depending on where new solar capacity is added.
“We wanted to go beyond the national average and understand the finer details of how solar generation affects carbon emissions hour by hour, region by region,” said Qiu, who holds joint appointments at Stony Brook’s School of Marine and Atmospheric Sciences and Program in Public Health. “It’s about producing clean electricity, but also about knowing when and where that electricity replaces the dirtiest generation sources.”
The research team—led by Rutgers University with collaborators from Harvard T.H. Chan School of Public Health—analyzed five years of hourly data from the U.S. Energy Information Administration. They divided the country into 13 regions to model how increased solar output at different times would affect local and neighboring CO₂ emissions.
Results indicate significant regional differences: areas such as California, Florida, the mid-Atlantic, Midwest, Texas, and Southwest saw substantial emission reductions with small increases in solar power. In contrast, similar increases in New England, Tennessee, and central U.S. regions produced smaller impacts.
“If you have limited resources to invest in solar, you want to place those resources where they displace the most fossil-fuel-based electricity,” Qiu said. “That’s where you get the biggest bang for your buck, both for emissions reductions and for public health benefits from improved air quality.”
The interconnected nature of the U.S. power grid means clean energy generated in one area can reduce fossil fuel use elsewhere. For example, a 15 percent boost in California’s solar capacity was linked to daily CO₂ reductions exceeding 900 metric tons in the northwest and nearly 2,000 metric tons in the southwest.
“This interconnectedness means that clean energy investments can have benefits far beyond the state or region where they’re installed,” Qiu explained. “It shows the value of coordinated efforts between regions and across state lines.”
Qiu noted that their statistical model captured both immediate emission reductions when solar replaces fossil fuels and delayed effects occurring hours later due to changes in how power plants operate throughout a day.
“Electricity systems are dynamic,” he said. “When you add solar in the middle of the day, it doesn’t just reduce emissions right away—it can also affect which power plants are running in the evening, which changes the emissions profile later on. Our model was able to capture those subtler downstream effects.”
Reducing fossil fuel combustion has direct health implications because it lowers fine particulate matter linked to asthma and heart disease.
Qiu emphasized practical applications for policymakers as well as private-sector stakeholders: “Utilities, grid operators, and investors all have a stake in making solar deployment as effective as possible,” he said. “This kind of analysis provides a roadmap for where investments will have the highest returns in terms of CO₂ reduction.”
He added that strategic placement is crucial: “We’re going to need a lot more clean energy to meet our climate targets but we also need to be strategic,” he said. “The same amount of solar power can have dramatically different impacts depending on where and when it’s generated.”
Large companies seeking sustainability often invest through power purchase agreements; this data can help them target regions with maximum climate benefit.
Transmission infrastructure also plays a role: some regions may generate more clean electricity than they can use during peak sunlight hours—a problem known as curtailment—because there isn’t enough transmission capacity to export surplus energy elsewhere.
“Strengthening the grid and building more transmission capacity could allow regions to export that clean energy to neighbors increasing total emissions reductions,” Qiu said.
Timing matters too; pairing solar with battery storage could help replace fossil fuel generation during high-demand evening hours when sunlight wanes but demand remains high.
“These findings are directly applicable to decisions being made right now about where to put solar farms how to design energy storage systems and how to coordinate clean energy policies across regions,” Qiu explained noting similar modeling could be applied for wind hydropower or emerging technologies like green hydrogen.
“As the energy transition accelerates we need tools that can help us navigate complexity,” he said. “Our work demonstrates how big data and computational modeling can provide clarity needed to make informed impactful choices.”
“This study is about making sure we get most out of every solar panel we build,” Qiu concluded.“If we can target our investments places where they make biggest difference we can accelerate transition cleaner healthier more sustainable energy future.”
