The transmission network is the backbone of the electric grid. It represents a major and highly visible component of critical infrastructure. It is operated at very high voltages—typically 69–765 kilovolts (kV)—allowing for much more significant power flow through the wires than possible at distribution-class voltages (typically 5–25 kV), as power flow capacity increases with the square of the voltage. 

Most transmission lines are located aboveground, but, where possible, they are buried underground or undersea.

There are approximately 400,000 miles of transmission lines across the United States. These lines connect the nation’s larger generating units to bulk substations, where the voltage is changed, or “stepped down,” to lower distribution-class voltages through large power transformers. 

The Bipartisan Infrastructure Law allotted $65 billion for projects to make the grid more reliable, resilient and future-ready. The law placed a renewed emphasis on the nation’s vast transmission network. It will pave the way for significant expansion and modernization over the coming decades and provide massive opportunities for industries poised to lead and support these efforts. Naturally, many technical, financial, social and political forces are at play in this coming grid evolution. Since the timeline is long, these forces will also be evolving, requiring continual reassessment of strategy while navigating the investment opportunities. 

In general, there are three major drivers of future grid investment: aging infrastructure, reliability and resilience improvement and lower-carbon energy transmission.

The transition to lower-carbon energy has major implications for the transmission system’s design, buildout and operation. Upgrade and expansion work prompted by this driver will also likely provide benefits related to aging infrastructure replacement and grid reliability and resilience. The transition to lower-carbon energy has two related components, happening simultaneously: electrification of additional loads such as transportation and home heating, and the integration of significant distributed energy resources such as wind, solar and battery storage.

Electric vehicle charging

Electrification will affect the medium-voltage (5–25 kV) distribution grid and low-voltage secondaries (pole-top transformers and the service wires to homes). Utilities will likely have to add additional distribution circuits and potentially upgrade substation transformers, especially when significant charging infrastructure is needed for fleets of electric vehicles. 

“Ultimately, enough additional load will impact the transmission grid, especially in those locations already experiencing congestion during times of peak load. To minimize the inevitable impact on the T&D system, it will be extremely important early in the electrification transition to establish intelligent regulation and rate policy for proper guardrails and incentives,” said Don Kane, senior electrical engineer at Parsons Corp., Chantilly, Va., at the time of interview. “For example, EV charging can be encouraged to, as much as possible, avoid the times of traditional system peak loads and be incentivized to leverage local renewable generation when available. Vehicle battery storage will also be able to support the grid during nontravel times using emerging vehicle-to-grid technologies.”

Still, the projected demand increase from EV charging is daunting. A 2018 study by researchers at the University of Texas at Austin estimated the increased energy for EV charging. For each state, estimated use ranged from 10% to more than 50% beyond current demand, with a total increase of several thousand gigawatt-hours per day. Actual hourly demand will depend on how and when charging occurs, the rate of EV adoption in the near future and whether it gets ahead of rate policies. Localized transmission and substation capacity increases will almost certainly be needed.

On the DER integration front, the proliferation of large, utility-scale wind and solar generation is already causing a big rise in transmission project work. This trend is set to keep accelerating over the coming decades as renewable generation and energy storage continue to get cheaper and supply a larger chunk of the overall generation mix. Forecasts from the U.S. Energy Information Administration indicate solar and wind capacity will increase from around 250 gigawatts (GW) today to 550 GW by 2030 and 800 GW by 2050. The Department of Energy offers a more robust forecast in line with aggressive grid decarbonization and electrification goals of around 1,500 GW by 2035 and 2,500 GW by 2050 (along with a staggering 1,800 GW of energy storage). 

“Of course, there are numerous technical and political forces at play in these forecasts,” Kane said, “but even in a conservative outlook, it is very obvious that grid planners will be faced with the challenges of integrating a huge amount of intermittent renewable generation over the coming years.” 

Header image: Getty Images / Dmitry Kovalchuk