A Faster, Cheaper Way to Double Power Line Capacity

As grid operators across the United States plan new transmission lines to keep up with surging investment in renewable energy, electric vehicles and heat pumps, many are neglecting an easier solution: stringing a new set of wires on their existing lines. In fact, such ‘reconductoring’ could provide the bulk of the extra transmission capacity the United States will need through 2035, according to grid modeling research published this week in the Proceedings of the National Academy of Sciences (PNAS).

“If we go all-in on reconductoring now it can meet a very significant portion of our transmission needs,” says lead author Emilia Chojkiewicz, an energy and resources doctoral student at the University of California, Berkeley.

Grid operators are in a race to revamp their grids as climate change drives extreme weather that’s straining their systems. Some grid operators are mapping out dozens of new lines, and state and federal regulators are trying to shorten line construction times from an average of 10 years to as little as 5. But Chojkiewicz says it’s not enough: “Even if we start planning today, that’s still looking at the early 2030s, and I don’t know if we have that kind of time.”

That time pressure is what prompted the PNAS study. Most of the more than 800,000 circuit-kilometers of transmission in the United States over 100 kilovolts use aluminum wires wrapped around a steel core. Chojkiewicz and her colleagues at Berkeley’s Energy and Resources Group and Goldman School of Public Policy studied the use of advanced conductors that wrap more aluminum around a smaller, stronger composite core. These Aluminum Conductor Composite Cores (ACCCs), made by CTC Global, are more conductive and can operate at higher temperatures, resulting in roughly a doubling of capacity for an equivalent diameter wire.

Advanced Conductors: Cost vs. Benefit

Over 145,000 km of ACCC wires are operating worldwide, with some of the fastest deployment occurring in India. However, many U.S. utilities and transmission planners view it as an expensive technology, reserved for niche applications. Chojkiewicz says the Berkeley team spoke with U.S. operators who said they were unaware of ACCC. She calls this “upsetting” given the crucial role grid expansion must play in electrifying industries, buildings and vehicles.

What U.S. operators are missing, according to the PNAS report, is the net savings that advanced conductors offer. The wires themselves can cost two to four times more than steel-core wires. But a reconductoring project adds capacity at less than half the cost of new lines by eliminating the land acquisition and permitting costs. And the job can usually be completed in a year or two, rather than the decade typically required to build a new transmission path in the United States.

More strength and extra aluminum means composite-core conductors [right] can carry twice as much power as conventional steel-core wires [left].University of California, Berkeley/PNAS

The Berkeley team fed those facts and key growth drivers such as the Inflation Reduction Act’s incentives to an open-source grid model. The model then simultaneously optimized when to reconductor with ACCC, and when to build new transmission and add new generation. Chojkiewicz says her team used conservative cost estimates for reconductoring, such as assuming that every project would require a brand-new substation and still, reconductoring beat out new lines in all scenarios.

In a scenario where the model was allowed to crank out new lines, it tapped reconductoring for 66 percent of the transmission capacity added by 2035. When researchers limited new construction to the current pace in the United States, the model chose reconductoring for nearly four-fifths of added capacity. In both of those scenarios the grid delivered at least 90 percent low-carbon energy by 2035 and saved consumers up to $85 billion, largely by expanding access to areas with cheaper wind and solar energy.

Reconductoring Models Influence Regulation

In April, Berkeley and Gridlab, a Berkeley-based consultancy serving advocacy groups, released a less technical version of the researchers’ findings as a white paper. The idea was to inform rules on transmission planning that were being finalized at the Federal Energy Regulatory Commission (FERC) as well as pending legislation in California and several other states.

FERC’s Order 1920, finalized in May, mandates that transmission operators consider reconductoring as an element in long-term regional planning, and excludes reconductoring projects from federal environmental impact reviews. And bills sent to California’s governor earlier this month would streamline state approvals for reconductoring in that state.

But the white paper also generated a few misconceptions and misleading headlines, suggesting that reconductoring is “stupidly easy” or that it leaves all other transmission-boosting technologies in the dust.

That’s not the case. As the peer-reviewed report notes, taking out lines that are heavily loaded is tough because the grid is hard-pressed to operate without them. Workarounds exist: Where multiple circuits share the same right-of-way, utilities can replace one circuit at a time during a low-demand season, especially when maintenance is already scheduled (see photo above). That’s how Belgian utility Elia is replacing all of its big trunk lines with ACCC.

The authors of the PNAS paper cite a more daring approach employed in Texas over a decade ago: swapping out wires for a single-circuit while it remained energized. In that case, lines in southeastern Texas had maxed out, leading to rolling blackouts during a severe ice storm in February 2011. To boost capacity quickly, the operator transferred the live wires to temporary poles as it installed the ACCC wires.

Advanced Conductors vs. Other Grid-Enhancing Technologies

The Berkeley team’s report provides no insight into how reconductoring measures up against alternative strategies to send more power through existing rights-of-way. Other such grid-enhancing technologies (GETs) include boosting line voltage, adding converters so that a line can carry high voltage direct current (HVDC), or installing sensors to indicate when favorable winds and temperatures mitigate the risk that extra power will send overheated lines sagging into the trees below.

When reconductoring is an option [right], transmission expansion between 2022 and 2035 will be greater than it would with new line construction [left], according to the model in Berkeley’s study.University of California, Berkeley/PNAS

Chojkiewicz says her team’s modeling neglected those alternatives because their goal was simply to lay out the “nationwide potential,” of reconductoring. In reality, she says, all strategies available to boost transmission capacity will be needed to get past dependence on fossil energy—a view that’s affirmed by a roadmap for advanced transmission technology released this month by MIT’s Center for Energy and Environmental Policy Research.

Many strategies can compliment reconductoring. Chojkiewicz points to using sensors to temporarily boost power throughout—a GET known as dynamic line rating (DLR)—which is even faster to deploy than reconductoring. “We should definitely be doing DLR today on all of the congested lines in the United States,” says Chojkiewicz.

What’s needed now, says Chojkiewicz, is for utilities and transmission planners to explicitly study how these technologies can add value to their systems. The FERC rule is a start, she says, but she’d like to see regulators take “more forceful” steps that “compel” their use. She also sees a role for standards bodies such as the IEEE, which could consider a national conductor efficiency standard akin to the energy conservation standards for distribution transformers.

Ultimately, it’s up to the utilities to take risks on technologies that they have not used before. “We’re passing the baton to them,” she says.

This article appears in the December 2024 print issue as “A Faster, Cheaper Way to Double Grid Capacity.”