The researchers evaluated two policy approaches to expanding the U.S. electricity grid: One would concentrate on regions with more renewable energy sources, and the other would create more interconnections across the country. For instance, some of the best untapped wind-power resources in the U.S. lie in the center of the country, so one type of grid expansion would situate relatively more grid infrastructure in those regions. Alternatively, the other scenario involves building more infrastructure everywhere in roughly equal measure, which the researchers call the "prescriptive" approach. How does each pencil out?
After extensive modeling, the researchers found that a grid expansion could make improvements on all fronts, with each approach offering different advantages. A more geographically unbalanced grid buildout would be 1.13 percent less expensive, and would reduce carbon emissions by 3.65 percent compared to the prescriptive approach. And yet, the prescriptive approach, with more national interconnection, would significantly reduce power outages due to extreme weather, among other things.
"There's a tradeoff between the two things that are most on policymakers' minds: cost and reliability," says Christopher Knittel, an economist at the MIT Sloan School of Management, who helped direct the research. "This study makes it more clear that the more prescriptive approach ends up being better in the face of extreme weather and outages."
The paper, "Implications of Policy-Driven Transmission Expansion on Costs, Emissions and Reliability in the United States," will be published in Nature Energy.
The authors are Juan Ramon L. Senga, a postdoc in the MIT Center for Energy and Environmental Policy Research; Audun Botterud, a principal research scientist in the MIT Laboratory for Information and Decision Systems; John E. Parson, the deputy director for research at MIT's Center for Energy and Environmental Policy Research; Drew Story, the managing director at MIT's Policy Lab; and Knittel, who is the George P. Schultz Professor at MIT Sloan, and associate dean for climate and sustainability at MIT.
The new study is a product of the MIT Climate Policy Center, housed within MIT Sloan and committed to bipartisan research on energy issues. The center is also part of the Climate Project at MIT, founded in 2024 as a high-level Institute effort to develop practical climate solutions.
In this case, the project was developed from work the researchers did with federal lawmakers who have introduced legislation aimed at bolstering and expanding the U.S. electric grid. One of these bills, the BIG WIRES Act, co-sponsored by Sen. John Hickenlooper of Colorado and Rep. Scott Peters of California, would require each transmission region in the U.S. to be able to send at least 30 percent of its peak load to other regions by 2035.
That would represent a substantial change for a national transmission scenario where grids have largely been developed regionally, without an enormous amount of national oversight.
"The U.S. grid is aging and it needs an upgrade," Senga says. "Implementing these kinds of policies is an important step for us to get to that future where we improve the grid, lower costs, lower emissions, and improve reliability. Some progress is better than none, and in this case, it would be important."
To conduct the study, the researchers looked at how policies like the BIG WIRES Act would affect energy distribution. The scholars used a model of energy generation developed at the MIT Energy Initiative - the model is called "Gen X" - and looked at the changes the proposed legislation would bring about.
With a 30 percent level of interregional connectivity, the study estimates, the number of outages due to extreme cold would drop by 39 percent, for instance, a substantial increase in reliability. That would help avoid scenarios such as the one Texas experienced in 2021, when winter storms damaged distribution capacity.
"Reliability is what we find to be most salient to policymakers," Senga says.
On the other hand, as the paper details, a future grid that is "optimized" with more transmission capacity near geographic spots of new energy generation would be less expensive.
"On the cost side, this kind of optimized system looks better," Senga says. Although, he adds, "It is not that much cheaper. It's single percentage points."
A more geographically imbalanced grid would also have a greater impact on reducing emissions. Globally, the levelized cost of wind and solar dropped by 89 percent and 69 percent, respectively, from 2010 to 2022, meaning that incorporating less-expensive renewables into the grid would help with both cost and emissions.
"On the emissions side, a priori it's not clear the optimized system would do better, but it does," Knittel says. "That's probably tied to cost, in the sense that it's building more transmission links to where the good, cheap renewable resources are, because they're cheap. Emissions fall when you let the optimizing action take place."
To be sure, these two differing approaches to grid expansion are not the only paths forward. The study also examines a hybrid approach, which involves both national interconnectivity requirements and local buildouts based around new power sources on top of that. Still, the model does show that there may be some tradeoffs lawmakers will want to consider when developing and considering future grid legislation.
"You can find a balance between these factors, where you're still going to still have an increase in relaiability while also getting the cost and emission reductions," Senga observes.
For his part, Knittel emphasizes that working with legislation as the basis for academic studies, while not generally common, can be productive for everyone involved. Scholars get to apply their research tools and models to real-world scenarios, and policymakers get a sophisticated evaluation of how their proposals would work.
"Compared to the typical academic path to publication, this is different, but at the Climate Policy Center, we're already doing this kind of research," Knittel says.
Research Report:Implications of policy-driven transmission expansion for costs, emissions and reliability in the USA
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