Transmission and Renewables Would Reduce Carbon Emissions, Generation Costs in Western United States

RICHLAND, Wash.—If all the high-voltage transmission currently under construction and in advanced stages of permitting is built by 2030 in the Western United States—enabling the construction of new renewable energy projects—carbon dioxide emissions in the Western United States would drop by 73 percent compared to 2005.

Energy generation costs would also decrease 32 percent by 2030, compared to a reference case where most of these projects are not built.

These are the results of a new report by the Department of Energy’s Pacific Northwest National Laboratory that looks at how new transmission and renewable energy projects in the Western United States could bring economic benefits and reduce carbon dioxide emissions. The report, called the Western Interconnection Baseline Study, published September 13, 2024. The report is part of the National Transmission Planning Study, funded by DOE’s Grid Deployment Office.

“The Western Interconnection Baseline Study uses the grid industry’s most reliable data to look at how future transmission and renewable energy projects would lower carbon emissions and save money, all while keeping the western grid stable and reliable,” said Konstantinos Oikonomou, a staff power systems research engineer at PNNL and lead author of the study. 

Across the United States, more than 700,000 miles of transmission lines transport energy from generators like fossil fuel power plants, nuclear power plants, wind and solar farms, energy storage systems and hydropower plants. This backbone of the electricity grid allows energy to then be distributed to cities, neighborhoods and eventually to individual consumers.

Recently, DOE has been studying how expanding transmission could help integrate more renewable energy, lower the cost of energy generation and decrease carbon emissions from grid operations. In support of this effort, a PNNL team did a baseline analysis considering only the impact of major new transmission projects that are in the pipeline for the Western Interconnection, the electrical grid that powers 16 western states and 2 Canadian provinces.

Modeling more transmission, renewables

To investigate the impacts of new transmission and renewables, the research team built a model of the Western Interconnection that incorporated 12 transmission projects currently in advanced stages of development or permitting. These 12 projects would add more than 3,000 miles of new transmission, connecting places like Wyoming to southern California, Nevada and western Arizona.

The researchers then added the likely wind and solar power projects and energy storage systems that would be built taking advantage of this new transmission capacity. As of July 2024, the Western Interconnection hosts 30 gigawatts of wind power, 38 GW of solar power and 14 GW of energy storage. The report’s scenario would add an additional 35 GW of wind, 31 GW of solar and 12 GW of energy storage by 2030.

With their new model of a Western Interconnection that has more transmission and 68 more GW of renewable energy, the researchers simulated a typical year of energy demand and generation. The simulation included realistic conditions with electricity demand and generation dipping and rising due to time of day, temperature and weather conditions. The researchers also looked at how cost of energy generation and transportation fluctuated over the year.

The model showed that more, cheaper renewables integrated in the grid by the year 2030 would displace 15 percent of the generation output of existing fossil power plants and reduce carbon dioxide emissions by 73 percent (compared to 2005 levels). The cost of generation would also drop by 32 percent.

What’s more, the new transmission lines unlock new energy import opportunities for states like California, which currently imports some energy from the Pacific Northwest’s hydropower generators. New transmission lines in the Southwest would allow California to import wind energy from windy areas in New Mexico and Wyoming, the report notes. 

“Because we have developed power flow cases that show how electricity actually moves through the grid for different operating hours under different generation mixes, grid planners in the Western Interconnection can use these study cases in future planning,” said Nader Samaan, a chief power systems research engineer at PNNL and co-author on the study.

Renewable energy for a stable grid

Researchers also wanted to find out whether this hypothetical future Western Interconnection could withstand a significant failure. They considered two scenarios: a loss of power generation and a loss of power transmission.

Both failures were simulated to occur on July 29, 2030, at 4 p.m. The researchers chose this date because previous analysis suggests that electricity demand tends to peak mid-summer as people turn on their air conditioners. They chose 4 p.m. because solar power starts to dip in the late afternoon as the sun begins its evening descent. 

In the first emergency scenario, an Arizona nuclear plant loses two generating units—the equivalent of “two to three large thermal power plants,” Samaan said. That loss would be a huge hit on the grid, potentially leading to outages for thousands of customers.

The researchers found that on a grid with a high proportion of renewables, energy storage systems would kick in, providing stability needed to brace the grid against a large generation loss.

“Before the generator goes down, the energy storage systems are charging. But once the system loses that generation, the energy storage devices have enough reserved energy to cease charging and ramp up their generation to stabilize the grid,” Samaan said.

In the second emergency scenario, a transmission line delivering 3,100 MW from southern Oregon to northern California fails. In this case as well, the grid remains stable with the new transmission lines supporting the existing network, which would reroute power through alternative paths.

National Transmission Planning Study

The new report “shows that with careful planning by utilities, developers and reliability working groups, new transmission lines and renewables are able to keep the grid stable even with large demand growth,” said Paul Wetherbee, a grid advisor at PNNL. 

It also supports DOE’s National Transmission Planning Study, which investigates different transmission expansion scenarios and offers recommendations to policymakers. The Western Interconnection Baseline Study acts as a “base case” for the models used in the NTP study, slated to publish later this year.

Led by DOE’s Grid Deployment Office and in partnership with PNNL and the National Renewable Energy Laboratory, the NTP study aims to identify transmission options that will provide broad-scale benefits to electric customers, inform regional and interregional transmission planning processes and identify interregional and national strategies to accelerate decarbonization while maintaining system reliability.

The NTP study is complemented by several companion reports, including this latest report on the economic benefits new transmission and renewable energy projects would bring to the Western United States, and two previous reports on market and operating practices and interregional renewable energy zones.