RICHLAND, Wash.—Across the United States, millions of people rely on electricity delivered by thousands of miles of transmission lines. 

As the nation continues to electrify all aspects of society—vehicles, buildings, appliances—utilities need strategies to provide the necessary power at a reasonable cost to consumers. And with extreme events like heat waves, cold snaps and drought becoming more frequent, the grid must remain reliable when power is needed the most.

Doubling or even tripling the number of transmission lines would both support the growing demand for energy and maintain the grid’s reliability during extreme events, according to a new report from the Department of Energy’s Grid Deployment Office. DOE teamed up with the agency's Pacific Northwest National Laboratory and National Renewable Energy Laboratory to study transmission expansion.

The report, called the National Transmission Planning Study, emphasizes the benefits of interregional transmission. Currently, transmission planning is done at a local or regional level, with utilities generally planning only within the region they serve. Expanding more transmission across regions—say, between the Midwest and the Great Plains—could lead to billions of dollars in savings, they report. By 2050, the researchers calculate that transmission expansion would lead to $270–$490 billion in cost savings. For every one dollar spent on new transmission, the researchers found, $1.60–$1.80 would be saved in system costs.

More transmission lines would allow the connection of more solar power, wind power and energy storage to the electric grid. In turn, carbon emissions would drop. The report estimates that by 2050, carbon dioxide emissions would drop by 10 billion to 11 billion metric tons.

“In this new report, we show that with careful planning and coordination across regions, expanded transmission can lower costs and carbon dioxide emissions while maintaining reliability,” said Nader Samaan, chief systems engineer at PNNL and a contributor to the report. 

Modeling power flow across the nation

To explore how expanded transmission would save money and retain reliability while lowering carbon emissions, the team simulated the nation’s power grid using models at a sub-regional level. The team started with a model developed by NREL that represents the evolution of the power grid through 2035. 

NREL and PNNL researchers then developed a high-resolution model that incorporated data from some 130,000 individual electricity substations across the country. Substations are vital for bringing electricity to customers. They convert high-voltage electricity flowing from transmission lines to low-voltage electricity that flows into neighborhood powerlines. 

Incorporating substations into a model of the power grid allowed researchers to simulate precise power generation and demand fluctuations throughout a typical year. They applied the new model to different scenarios of transmission buildout to see how power generation costs would shift. 

The researchers also subjected part of the simulated grid to extreme weather events, such as droughts and heat waves, to understand the impact of transmission expansion. During a heat wave, people use more air conditioning to stay cool and safe, which puts more demand on the grid. Drought can exacerbate these events by decreasing the amount of hydropower.

The researchers found that interregional transmission can support the grid during such extremes. For instance, transmission that brings wind power from New Mexico, Colorado and Wyoming can support both California and the Pacific Northwest when a heatwave coincides with drought. Interregional transmission can also support potential generation gaps in the early morning before solar power kicks in and overnight energy storage has run out. 

“Even if one part of the grid is disrupted by an extreme event, other, far-away generators will still be producing energy. What this report shows is that interregional transmission can help energy flow where it’s needed most,” Samaan said.

Future transmission planning

Ultimately, the study provides several tools for grid operators who are planning for a future of higher energy demand and more extreme weather, said Paul Wetherbee, a grid advisor at PNNL. Grid operators can use the models developed for the study to coordinate between regions during their own transmission planning.

Still, more work will be needed to fully understand the challenges of expanding transmission, especially between regions. The report notes that future work could focus on better understanding how transmission affects grid reliability, how to best coordinate transmission planning between regions and what technologies would enable the most cost-effective buildouts. 

Read more about the National Transmission Planning Study from DOE.