In April 2021, U.S. President Joe Biden set a national goal of creating a completely carbon-free electric power grid by 2035. Reaching that goal, however, will require massive use of renewables — including wind, solar, and hydroelectric power — and getting that clean energy from where it is generated to where it is needed, day or night, anywhere in the U.S.

Delivering that clean energy will also require a significant expansion of the nation's transmission capabilities, perhaps doubling or tripling our current capacity, notes nonprofit Energy Systems Integration Group.

An Interstate "Highway" for Electricity

Enter macrogrid, a concept for a national network of multi-regional, high-capacity, high-voltage direct current (HVDC) transmission lines that would connect the major sub-grids or interconnections that make up the national electric power grid. HVDC transmission lines would connect to existing or updated alternating current (AC) networks that distribute electricity within regions.

Likened by some to a Federal Interstate Highway System for electricity, macrogrid first emerged as a concept circa 2016 in the writings of Dale Osborn, a transmission planning engineer and consulting advisor for regulatory and economic studies for the Midcontinent Independent System Operator.

Fortifying the Grid

"It's important to note that macrogrid is a network, not simply a connection from one point to another," notes Dr. Jim McCalley, an Anson Marston Distinguished Professor of Engineering and the Jack London Chair in Power Systems Engineering at Iowa State University (ISU) — a national authority on the macrogrid. "It would interconnect major load (electricity demand) centers with major sources of renewable energy, including wind, solar, hydroelectric power, even offshore wind."

In addition to helping decarbonize the national grid, McCalley points out, a macrogrid would also add resilience, reliability and multiregional power and capacity-sharing capabilities to the grid.

"With infrastructure, you sometimes have short- or medium-term events you didn't expect, such as the widespread, cold-weather-induced power outages in Texas in Feb 2021," he explains. "Macrogrid facilitates the strength of the grid and its ability to deal with these types of issues in a very positive fashion."

Sharing of power generation capacity between regions, McCalley suggests, would also allow each part of the country to meet its annual peak power demand — the Midwest typically peaks in July or August, for example, while the Pacific Northwest peaks in winter or early summer — without having to invest in additional power generation infrastructure.

Opening up the Seam

According to the U.S. Department of Energy (DoE), the nation's power grid comprises three major sub-grids: the Western Interconnection, the Eastern Interconnection and the Texas interconnection (overseen by the Electric Reliability Council of Texas.) These grids are large — the eastern grid, with a total capacity of 1,460 MW, actually cross the so-called "Seam" between the two regions. The Seam follows a north-south, slightly meandering path from eastern Montana to the western edge of the Texas panhandle.

In 2016, the DoE commissioned a two-year Interconnections Seam Study led by the U.S. National Renewable Energy Laboratory (NREL). The study, which included national lab, university and industry partners, quantified the benefits and costs of several options, including macrogrid, for transmitting power across the U.S. electric grid. A McCalley-led team from Iowa State supported the study by developing computer models for different ways that transmission capacity could evolve.

Delivering Value, Managing Costs

The Seam Study produced two major findings, explains Joshua Novacheck, an NREL electricity system research engineer and the technical lead on the study:

"We concluded that there's a lot of economic value in being able to trade power between the Eastern and Western Interconnections, whether you're using macrogrid or some other transmission expansion approach," he says. "We also found that HVDC transmission across the Seam enables dynamic power trading among regions, which adds important diversity to the power options available to these regions."

To explain interregional power trading, Novacheck suggests that California could share its peak (and less expensive) mid-afternoon solar power with East Coast consumers as they enter their early evening peak demand period. Similarly, less expensive wind energy generated in the Midwest in the mid-evening could be shared with West Coast consumers as they enter their early-evening high-demand period.

"Cross-country power trading would be preferable," Novacheck advises, "to having communities rely on local but very expensive fossil-fuel-powered, greenhouse-gas-emitting power plants to fill gaps in power supplies."

Some of these gaps could also be filled by hydroelectric power, he suggests. While most U.S. sources of such power have already been developed, hydropower remains an important part of the overall macrogrid equation, primarily as a backup to other renewable sources on calm or cloudy days.

Leveraging Mature Technology

According to McCalley, HVDC is the most mature, most desirable transmission technology to use for the macrogrid.

"Today's HVDC lines can carry large amounts of current with little loss," he explains, "which makes them perfect for connecting renewable wind and solar resources — often located in remote parts of the country — to distant load centers."

In addition, according to Rob Gramlich, founder and President of Grid Strategies LLC, the technology used in modern HVDC converter stations — the "on-ramps" and "off-ramps" of macrogrid that convert current back and forth between DC and AC — will help ensure a stable, reliable macrogrid.

"The newest voltage-source converter technology can shift the magnitude and direction of power flowing through converter stations almost instantaneously, which will make it easier to control how much power enters or leaves the macrogrid network at any particular substation," says Gramlich.

Rethinking Energy Policy

Gramlich also notes that the road to the macrogrid is unfortunately anything but clear, even though it provides an opportunity to move large amounts of renewable energy quickly and inexpensively over long distances.

"Our current electricity system and regulatory structure were not set up to handle an opportunity like macrogrid," he explains. "The 330 transmission owners in the country generally operate locally and are regulated locally or at the state level. It's only in recent years that the Federal Energy Regulatory Commission (FERC) has come in to encourage more interregional transmission system planning."

There is also the matter of macrogrid cost and who should pay for it. A network of transmission lines that crosses multiple states makes it difficult to pinpoint exactly who benefits and by how much, Gramlich observes. But just as the Federal Interstate Highway System allows consumers to travel freely as needed from east to west, north to south, etc., a macrogrid would benefit most consumers at one time or another.

"There's a national interest in avoiding long-duration outages because we've seen how society can completely fall apart without electric power," he points out. "A robust macro grid is one of the best things we can do to avoid such outages. That benefit alone provides a good justification for taxpayer funding."

Shifting the Paradigm

A transition to macrogrid or other new types of interstate transmission networks will also require a culture shift of sorts, as Novacheck points out:

"Many communities currently rely on a local nuclear energy or fossil-fuel-burning power plant to fill gaps in their renewable energy supplies on short notice," he says. "If we're suddenly talking about massive exchanges of energy between regions, that paradigm will have to change. It could cause communities to wonder if they can count on their neighbors to deliver the power needed to serve load reliably and cost effectively."

Starting the Investment

President Biden's Infrastructure Investment and Jobs Act (IIJA) provides funding for much-needed transmission infrastructure, including a $2.5 billion revolving fund managed by the DoE to fund eligible projects.

That funding is merely a down payment on what would eventually be needed to fund the macrogrid, notes Gramlich, but "it can help in the near term with specific projects, get them deployed and over the finish line." In the longer term, he believes, the DoE can help states and grid stakeholders plan and elevate everyone's vision toward a larger opportunity such as the macrogrid.

The DoE plans to manage and fund IIJA-motivated transmission upgrade projects through its "Building a Better Grid" initiative launched in Jan. 2022.

Looking to the Present

In addition to IIJA commitments to transmission, McCalley sees other hopeful signs that the nation favors a larger-scale, macrogrid-like transmission network.

"The transmission project for which I have seen the least resistance has been the SOO Green HVDC Link project, which is delivering wind power from Iowa to the Chicago area, all underground," he says. "They are burying their transmission lines along railroad rights of way."

Burying transmission lines is more expensive than constructing overhead lines by a factor of about two, McCalley admits, but it often eliminates consumer resistance as well as the visual, land and environmental impacts of above-ground transmission lines.

He's also excited about Power from the Prairie (PftP), a proposed 600-mile, 4,000 MW HVDC transmission line that would run from southeast Wyoming to northwest Iowa. It would be a critical leg of a two-way renewable energy superhighway connecting Southern California to Chicago and the PJM Interconnection grid that extends to the East Coast.

McCalley believes that PftP could also serve as a demonstration or pathfinder project for how the macrogrid might one day be implemented.

Solving the Puzzle

Novacheck believes that HVDC transmission remains one of the most mature and cost-effective technologies for meeting national decarbonization goals. But for all of the resilience and reliability benefits it offers, it's still only part of a larger puzzle.

"At NREL, we don't see a single solution to achieve a completely decarbonized power grid," he suggests. "A macrogrid alone is not going to do it, storage alone is not going to do it, renewables technology alone is not going to do it. It's really a system of potential solutions. By piecing these solutions together, however, we can help put the nation on the fastest, cheapest path to decarbonization."

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