A new paper by Carnegie Mellon University (Pittsburgh), titled, “Accelerating Transmission Capacity Expansion by Using Advanced Conductors in Existing Right-of-Way,” suggests a more viable and less expansive way to address the ever-increasing demand for new transmission.

The reported noted that, “Increasingly, the energy transition discourse is focusing on electricity transmission: the need to build it and the challenges of doing so. The International Energy Agency estimates that the global length of transmission lines must increase from 5.5 million to 15 million km—approximately 2.7 times—to reach net zero emissions by 2050, not including the eventual replacement of aging infrastructure.”

It went on to note that the integration of renewable energy (RE) sources at speed and scale in order to reduce emissions and achieve climate goals will likewise require the increase of transmission capacity at speed and scale.

“Recent rapid declines in the costs of solar, wind, and batteries along with incentives from the Inflation Reduction Act (IRA) have presented an opportunity for a paradigm shift in how transmission is planned and sited,” said the report. Specifically, there is a narrowing gap in cost between RE sited at locations with the highest resource potential and RE sited at locations that are in close proximity to the existing transmission network and load.

This RE capacity could be unlocked through a wide range of technological solutions that can increase the transmission capacity of the existing grid. Some strategies, known under the umbrella term of Grid-Enhancing Technologies (GETs) and including Power Flow Controllers, Flexible AC Transmission Systems devices, Dynamic Line Ratings (DLR), and demand-side measures, can either enhance the physical capability of a transmission asset or the efficiency of power flow throughout the system. However, while these technologies are extremely important to expanding grid capacity, their potential is dependent on real-time operating conditions and thus typically limited and temporary.

The solution, according to the paper, is reconductoring with advanced conductors. “While the build-out of new greenfield lines is often plagued by challenges related to permitting and cost allocation, leveraging existing right-of-way, particularly through reconductoring with advanced conductors, can rapidly expand transmission capacity,” said the paper. Unfortunately, according to the paper, advanced conductors have been traditionally viewed as a niche solution, and their deployment is limited, requiring targeted policy to spur uptake and unlock their potential to contribute to cost-effective decarbonization.

In challenging this belief, the paper suggests that large-scale reconductoring with advanced composite-core conductors can cost-effectively double transmission capacity within existing right-of-way, with limited additional permitting.

“This strategy unlocks a high availability of increasingly economically viable RE resources in close proximity to the existing network,” said the paper. The researchers implemented reconductoring in a model of the U.S. power system, showing that reconductoring can help meet over 80 percent of the new interzonal transmission needed to reach over 90 percent clean electricity by 2035 given restrictions on greenfield transmission build-out.

With $180 billion in system cost savings by 2050, the paper suggests that reconductoring presents a cost-effective and time-efficient, yet underutilized, opportunity to accelerate global transmission expansion.

Other strategies can provide a larger and lasting increase of transmission capacity, such as reconductoring with advanced composite-core conductors, voltage upgrades, and AC-to-DC conversion. Yet whereas voltage upgrades may necessitate widening of the existing ROW and AC-to-DC conversion is generally most suitable for long lines, reconductoring—the replacement of a transmission line’s existing conductors with either larger-diameter conductors or a different type of conductor—is a practice used by utilities to increase ampacity within existing ROW.

“In recent decades, the development of advanced composite-core conductors has opened up new possibilities for rapid transmission capacity expansion through reconductoring,” said the paper. While most of the high voltage grid today is wired with a century-old technology known as Aluminum Conductor Steel Reinforced (ACSR) featuring aluminum strands around a steel core, advanced conductors swap the steel for a stronger yet smaller composite-based core.

This enables higher operating temperatures and more conductive aluminum to fit within an equivalent diameter, allowing advanced conductors to carry approximately twice as much power over ACSR. The composite-based core also reduces line sag, meaning the utilization of advanced conductors in reconductoring projects minimizes the need for and thus the costs of modifying structures to accommodate preexisting clearances, as reconductoring with conventional high-ampacity conductors such as Aluminum Conductor Steel Supported may risk larger sags.

Because reconductoring projects leverage existing transmission towers and ROW, the extensive land acquisition and permitting processes that impede the construction of new lines can be circumvented.