MIT Study Explores the Best Ways to Expand the US Electricity Grid While Balancing Cost, Reliability, and Emissions

The United States is heading toward a future where electricity demand will grow rapidly, driven by electric vehicles, data centers, clean energy goals, and population growth. Meeting that demand will almost certainly require a major expansion of the national electricity grid. But how that expansion should happen is far from settled. A new study by researchers at the Massachusetts Institute of Technology (MIT) takes a close look at this question and lays out the tradeoffs policymakers face when deciding how to modernize the grid.

The study focuses on two competing policy approaches currently under discussion in Congress and evaluates how each option performs in terms of cost, carbon emissions, and grid reliability. Rather than offering a single “perfect” solution, the research highlights where each strategy excels and where compromises are unavoidable.

Why the US Electricity Grid Needs Expansion

The U.S. electricity grid was largely designed decades ago, long before renewable energy, climate targets, and extreme weather became defining factors. Much of the system is regionally focused, with limited ability to move large amounts of power between different parts of the country. As renewable energy grows and weather events become more intense, this structure is showing its limits.

The MIT researchers argue that upgrading and expanding transmission infrastructure is essential to keeping electricity affordable, cutting emissions, and preventing widespread outages. The real question is how to do it most effectively.

Two Grid Expansion Strategies Under the Microscope

The researchers analyzed two main approaches to expanding transmission capacity.

1. Regionally Optimized Grid Expansion

The first approach focuses on building transmission lines near areas with the strongest renewable energy resources. In the U.S., this often means investing heavily in the central regions of the country, where wind power potential is especially high. Solar-rich areas also receive targeted infrastructure investments.

This strategy is designed to optimize the grid based on cost and energy availability, allowing large amounts of low-cost renewable electricity to flow from where it is produced to where it is needed.

2. Prescriptive Nationwide Interconnection

The second approach is more uniform and policy-driven. Instead of concentrating infrastructure in specific regions, it requires every transmission region to be strongly connected to others, regardless of local resource advantages. This model is often described as prescriptive, because it sets clear national requirements rather than letting market forces determine where lines are built.

This approach closely aligns with proposed federal legislation aimed at improving nationwide grid connectivity.

What the Study Found About Costs and Emissions

After running extensive simulations, the MIT team found that both approaches improve the grid, but with noticeable differences.

The regionally optimized approach turned out to be 1.13% less expensive overall compared to the prescriptive model. While that may sound modest, even small percentage differences matter when dealing with a national system worth trillions of dollars.

This optimized approach also delivered stronger emissions reductions, cutting carbon emissions by 3.65% more than the prescriptive option. The main reason is simple: it builds more transmission where cheap, clean renewable energy is available, allowing fossil fuel generation to be displaced more efficiently.

Globally, the cost of renewables has fallen dramatically. Between 2010 and 2022, the levelized cost of wind power dropped by 89%, and solar fell by 69%. By tapping into these low-cost resources through targeted transmission expansion, the optimized system naturally achieves lower emissions.

Reliability and Extreme Weather Make the Tradeoff Clear

While the optimized system wins on cost and emissions, the prescriptive approach shines when it comes to reliability.

According to the study, a grid built with strong nationwide interconnections could reduce power outages caused by extreme cold by 39%. This is a major finding, especially in light of recent disasters such as the 2021 Texas winter storm, where limited interregional connections made it difficult to import power during emergencies.

A nationally interconnected grid allows electricity to flow more freely across regions, helping areas under stress draw power from places not affected by the same weather event. This makes the system far more resilient to heat waves, cold snaps, and other climate-driven disruptions.

For policymakers, this creates a clear tradeoff: the system that is cheapest and cleanest is not necessarily the one that performs best during extreme conditions.

The Role of the BIG WIRES Act

A key motivation for the study was proposed legislation known as the BIG WIRES Act. This bill, introduced by lawmakers in both the Senate and House, would require each U.S. transmission region to be able to send at least 30% of its peak electricity load to other regions by 2035.

Such a requirement would represent a major shift away from the current regionally fragmented grid. The MIT researchers used this 30% threshold as a benchmark in their modeling to understand how policy-driven transmission mandates might reshape the system.

Their findings suggest that while the BIG WIRES-style approach may not minimize costs or emissions as effectively as an optimized buildout, it dramatically improves grid reliability, which is often the top concern for lawmakers.

How the Researchers Did the Analysis

To evaluate these scenarios, the researchers used GenX, an advanced energy system model developed at the MIT Energy Initiative. The model simulates electricity generation, transmission, and investment decisions under different policy constraints.

By applying GenX to proposed legislation and future demand scenarios, the team could estimate impacts on system costs, outage frequency, transmission buildout, and emissions levels. This allowed them to compare policy-driven and market-optimized approaches on equal footing.

Hybrid Approaches Could Offer the Best Balance

The study also explored hybrid solutions that combine elements of both strategies. These approaches impose national interconnection requirements while still allowing additional transmission to be built near major renewable energy hubs.

According to the researchers, hybrid models can deliver significant reliability gains without sacrificing most of the cost and emissions benefits of optimized systems. While not perfect, they may offer a practical middle ground for future legislation.

Why This Research Matters Beyond the US

Although the study focuses on the United States, its conclusions are relevant globally. Many countries face similar challenges as they transition to cleaner energy systems: how to move electricity efficiently, how to protect against extreme weather, and how to balance affordability with climate goals.

The research also highlights the value of direct collaboration between academics and policymakers. By grounding their work in real legislative proposals, the MIT team provided insights that lawmakers can directly use when shaping energy policy.

Looking Ahead

The study makes one thing clear: there is no single “best” way to expand the electricity grid. Every option involves tradeoffs. Optimized systems are cheaper and cleaner, while prescriptive systems offer stronger protection against outages. Future grid policy will likely need to blend both ideas to meet the demands of a changing climate and economy.

As electricity becomes the backbone of transportation, heating, and industry, decisions made today about transmission expansion will shape the U.S. energy system for decades to come.

Research paper:
https://www.nature.com/articles/s41560-025-01921-7