The transmission network—the backbone of the electric grid—represents a major component of the nation’s critical infrastructure. It is operated at very high voltages (typically 69–765 kV), allowing for much more power flow through the wires than would be possible at distribution-class voltages (typically 5–25 kV), as power flow capacity increases with the square of the voltage. Most transmission lines are above ground, running through undeveloped land or along highways. Where possible, they are buried underground, and with the advent of offshore wind generation, undersea.

The approximately 400,000 miles of transmission lines across the United States (depicted in blue in the diagram) connect larger generating units to bulk substations, where the voltage is changed, or “stepped down,” to the lower distribution class voltages through large power transformers.

Three major drivers

Per the Bipartisan Infrastructure Law, $65 billion could flow to projects to help ensure the grid is reliable, resilient and ready for the future. The law renews emphasis on the vast U.S. transmission network, paves the way for significant expansion and modernization over the coming decades and provides opportunities for industries poised to lead these efforts. Naturally, technical, financial, social and political forces are at play, which will evolve over the long timeline. This will require the industry to reassess strategy while navigating the opportunities provided by these large investments. 

There are three major drivers of grid investment: aging grid infrastructure, reliability and resilience improvement, and lower-carbon energy transition.

The transition to lower-carbon energy has implications for the design, buildout and operation of the transmission system. Upgrade and expansion work will 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 and the integration of significant distributed energy resources like wind, solar and battery storage.

Electrification will affect medium-voltage (5–25 kV) distribution grids and low-voltage secondaries, such as pole-top transformers and service wires to homes. Utilities will likely have to add distribution circuits, and potentially upgrade substation transformers, when significant charging infrastructure is needed for bus, truck and ferry fleets.

What about all this load?

Don Kane, senior electrical engineer at Parsons Corp., Centreville, Va., said “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.” 

Kane said EV charging can be encouraged, when possible, to avoid traditional system peak loads and leverage local renewable generation. EV battery storage can support the grid during nontravel times, which has the potential to minimize the load impacts of EV charging and support local renewable generation integration. 

Still, the projected demand increase from EV charging is daunting. A 2018 study by researchers at the University of Texas at Austin provided a rough, state-by-state estimate of the increased energy for vehicle charging. They broke out the approximately 3 trillion annual miles driven and converted it to electric energy based on average EV efficiency. Increased energy usage for each state varied from 10%–50% beyond current use, with the total additional increase at several thousand gigawatt-hours per day. 

How and when that charging occurs plays a critical role in the hourly electric demand increase. The rate of EV adoption in the future is critical, as well as whether it gets ahead of appropriate rate policy. It is extremely likely there will be localized transmission and substation capacity increases needed, especially where current grid congestion issues exist.

The proliferation of large, utility-scale wind and solar generation is causing a big increase 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. 

Latest forecasts from the Energy Information Administration indicate solar and wind capacity will increase from around 250 gigawatts (GW) today to around 550 GW by 2030 and 800 GW by 2050. The Department of Energy’s prediction, in line with aggressive grid decarbonization and electrification goals, is around 1,500 GW by 2035 and 2,500 GW by 2050 (along with a staggering 1,800 GW of energy storage).

Header image: Gordon Feller