It's Time for a Macro-Grid Overlay in the U.S.

The U.S. power system is separated into three major components—the Western Interconnection, the Eastern Interconnection, and the Electric Reliability Council of Texas. The three operate almost independently of each other; very little electricity is transferred between the three regions. However, many experts think that’s a flaw. They believe a more-integrated power system would drive economic growth, and increase the efficient development and utilization of the nation’s energy resources, including wind, solar, and natural gas.

The National Renewable Energy Laboratory (NREL) partnered with the Pacific Northwest National Laboratory, Iowa State University, Southwest Power Pool, Midcontinent Independent System Operator (MISO), Western Area Power Administration, and others, on an “Interconnections Seam Study.” The study was designed to identify cost-effective options for upgrading the U.S. electric grid to create a more-integrated power system. On July 26, NREL presented preliminary results of the study at the TransGrid-X 2030 Symposium in Ames, Iowa.

Old Idea, New Insight

Aaron Bloom, group manager of the Grid Systems Analysis Group in NREL’s Strategic Energy Analysis Center, gave a presentation during the event highlighting some of the findings from the study. He pointed out that groups have been studying interconnection possibilities for many years.

Back in the 1920s, the Chicago Daily Tribune proposed a continental-scale power system to link together hydro resources and coal generation. Other studies were conducted by the Bureau of Reclamation (1952), the Bonneville Power Administration (1979), the Western Area Power Administration (1994), and the Department of Energy (2002). All of the studies found value in a continental transmission system. But one of the things that’s different today is that technology has advanced significantly.

“We have pretty much unimaginable computational capabilities today,” said Bloom. “What those computational capabilities allow us to do is roll back our assumptions [and] do the most-detailed mathematics that we could possibly do on these questions. That gives us more confidence in our answers and deeper insights into the regional impacts.”

Furthermore, the technology being deployed on the grid has evolved. New wind and solar generators can not only provide energy to the power system, but they can also contribute essential reliability services to the grid as well. There have been advances in high-voltage direct-current (HVDC) technology, and ultra-high-voltage alternating-current (AC) technology is also offering a lot of opportunities.

Grid Interconnections

The present U.S. transmission system includes seven back-to-back (B2B) HVDC interconnection ties located along a meandering north-south line east of the Rocky Mountains. Combined, the ties can transmit about 1,300 MW between the Eastern and Western Interconnections. Most of the ties were built in the 1970s and 1980s, which means they are nearing the end of their expected lifespans. As such, a significant opportunity exists to improve upon the interconnection scheme.

Bloom posed several questions that the researchers sought to answer. They were:

    ■ What could be done with aging assets?
    ■ Is there any potential value in making them bigger?
    ■ How much bigger?
    ■ What if an HVDC network was built instead?
    ■ Could the rest of the network handle bigger connections?

Of course, building out such a network comes with plenty of challenges. Among them are siting; understanding the value and communicating that value to others in a way that they can use; working with neighbors, and figuring out where strengths and weaknesses can be complemented through the network; and cost—who pays.

Other countries have embarked down similar paths. In China, continental-scale power systems are already being constructed. Europe, too, is undergoing a transmission renaissance, with interconnections being established among many different countries and regions. Bloom asked, “With some of the very best wind, solar, [and] hydro resources in the world, and some of the largest energy demand in the world per capita, what [is the U.S.] doing to get into this new future of power systems?”

Benefits Exceed Costs

The seams study modeled four transmission designs. Design 1, which is essentially the base-case scenario, doesn’t include any new power lines crossing the seam. Nonetheless, it’s not a “business-as-usual” case; it does include large-scale buildouts of AC transmission, and co-optimization of generation and transmission. Design 2A includes the base-case upgrades, but it also increases the size of existing B2B ties, while keeping locations and footprints the same. Design 2B expands the existing B2B ties, and also “leapfrogs” the edges of the system by adding three parallel, long-distance HVDC lines constructed between strong points in the Eastern and Western Interconnections. Finally, Design 3 is a “macro-grid overlay.” It increases north-south and east-west transfer capabilities to take advantage of the diurnal, seasonal, and resource patterns that exist in the U.S.

During the ELECTRIC POWER Conference and Exhibition in March, John Bear, CEO of MISO, gave a presentation and answered questions, which I was fortunate enough to moderate. I asked Bear if he ever expected all U.S. ISOs to merge into something like a national grid. His answer was illuminating.

“I think it would be really efficient, but I think the problem is you’ve got very different structures and cultures under each of the regions in the U.S., and it’s hard to push those folks all together,” Bear said. “We do things sort of the MISO way. PJM does things their way. New England does things their way. And everybody likes their way. So, I think it’s going to be a little bit difficult to get that all pushed in.”

Nonetheless, where there’s a will, there’s a way. The seams study found that increasing the transfer capability between the interconnections provides substantial value. It increases efficiency, and it utilizes wind and solar resources to their maximum benefit.

“We’ve been imagining cleaner, bigger, modern grids for about 40 years,” said Bloom. “Now is the time to make it happen.” ■

Aaron Larson is POWER’s executive editor.

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