Electric transmission lines — capable of carrying large amounts of energy over long distances — may not be the most exciting thing going on in the energy space today. Utility Dive's Propelling the Transition series is highlighting a number of other developments helping to fundamentally change the power sector.

But experts say improvements to the existing transmission system are crucial to broader decarbonization of the United States' grid, and that several developing technologies can make lines more efficient and affordable.

The topic, however, tends to get short shrift, say some developers of new technologies.

"Most people don't care about transmission," said Trey Ward III, CEO of Direct Connect Development Co.

"There are barriers to the adoption of new [transmission] technologies," said Chris Kimmett, director of power grids at Reactive Technologies. "It's all about getting up on the education curve."

The problem is particularly exacerbated in the United States, experts told Utility Dive, where utility incentives are based around large capital investments. That leads to a preference for building new lines rather than improving and optimizing the existing system.

There are thousands of megawatts of renewable energy stuck in interconnection queues, said Ward, as the most robust U.S. wind and solar resources are often located far from demand centers and require new transmission to reach customers.

"Renewables are more subject to congestion and curtailment than other resources," said Rob Gramlich, executive director of the Working for Advanced Transmission Technologies (WATT) Coalition. "There are a lot of renewable projects stuck in interconnection queues. A lot of renewable projects are getting curtailed by grid operators, or just face low energy prices because of congestion."

According to the WATT Coalition, a half dozen grid operators have reported that congestion costs increased by 9% from 2016 to 2017, and by 22% from 2017 to 2018. Those costs result from higher-priced generators serving load when there is insufficient transmission capacity to move less-expensive power.

Transmission improvements can take several forms, said Gramlich. There are different "buckets" of workarounds, improvements and expansions for the grid, including new cable designs, transmission incentives and siting reform.

"I see three big areas of opportunity for transmission," said Rocky Mountain Institute Principal Mark Dyson. Those include two significant new technologies and institutional reform, including centralized planning and changes to how transmission is built across seams.

New siting approaches could spur development 

One new approach is building underground high voltage direct current transmission lines that would "help to alleviate some siting concerns that are hard to address otherwise," Dyson said.

Ward's company is implementing an example of this technology. Direct Connect Development is developing the SOO Green HVDC Link by utilizing a new approach to transmission siting — a key difficulty in the development of new projects. The lines can stretch hundreds of miles, require lengthy and expensive approval processes, and often are forced to use eminent domain to be built. 

SOO Green would follow the SOO Line Railroad — the primary U.S. railroad subsidiary of Canadian Pacific Railway — 350 miles from Iowa to Illinois, linking the Midcontinent ISO with PJM Interconnection's electricity markets.

"Rail corridors provide unique opportunities," Ward said. Siting transmission lines alongside them, he said, avoids eminent domain issues, minimizes environmental impacts and eliminates visual impacts from overhead
transmission facilities.

More on SOO Green below, but first a look at another batch of new technologies increasing the capacity of existing transmission.

Moving more power across existing lines  

"The AC power system in this country is not very easily controllable," said Dyson. Systems to increase transfer capacity can help it operate more efficiently, while also "enabling more control over where energy goes, and, more precisely, doesn't go."

Three primary technologies to develop more flexible transmission systems include: Power Flow Controls, Dynamic Line Ratings and Topolgy Optimization.

"If you think about how transmission lines work in the United States, you realize our overall utilization is extremely low. Typically 50% of the lines, after contingency, are using less than 25% of their capacity," said Gregg Rotenberg, CEO of Smart Wires, a firm which develops power flow control technologies.

Transmission lines must have sufficient spare capacity to account for contingencies — meaning they remain stable even if a worst-possible event occurs, like the loss of a large generator. "We run our electric grid in a conservative way," said Rotenberg, "so the loss of any one asset doesn't affect the grid."

Why don't we use much of the existing transmission line capacity? "The problem is that power flows where it flows. It seeks the path of least resistance," said Rotenberg. And that is often not where lines have the most available capacity.

Smart Wires' technology pushes and pulls power over transmission lines with spare capacity, rather than allowing power to flow as it naturally would across lines with the least resistance.

The technology is called Modular Power Flow Control (MPFC), which the company deploys under the name "SmartValve." Rotenberg said systems cost about 10% to 20% of "legacy solutions" like reconductoring power lines, which in turn runs about 10% of the cost of building new lines.

MPFC works by "harvesting" power from the transmission line itself, said Rotenberg, and injecting voltage. The voltage serves as "a signal to the line that effectively changes the resistance of that line ... You're tricking the electrons into taking a different path," said Rotenberg.

Smart Wires has received funding from the U.S. Department of Energy's Advanced Research Projects Agency, which the company says led to the first deployment of MPFC technology on Tennessee Valley Authority's 161 kV system.

Using MPFC technology, power can now be pushed off an overloaded line and onto an underutilized line. While the systems are more common in Europe, and are growing in use in South America, Rotenberg said in the United States their utilization is somewhat rare.

"The United States is quite late to the party," Rotenberg said. "The problem is all tied to incentives."

Most utilities are compensated based on the amount of capital they've invested, and the cost to install MPFC technology is low compared with other solutions, including raising and reconductoring lines and building new transmission.

The Federal Energy Regulatory Commission in March launched a notice of proposed rulemaking to change electric transmission incentive policy and stimulate infrastructure development. The commission is considering an approach that would shift from a "risks and challenges" framework to a model that grants transmission incentives based on benefits to customers.

According to Kimmett, the problem extends beyond the United States. "We find that, globally, transmission operators are definitely incentivized to invest in capital equipment ahead of software," he said.

Software based solutions 

Dynamic Line Ratings (DLR) and Topology Optimization are examples of software-based solutions. 

DLR systems adjust a transmission line’s operating limits based on thermal conditions, such as temperature and wind, rather than on a set of fixed, pre-set limits. Topology solutions reconfigure the grid, removing and adding lines back into service, to allow power to flow around overloaded portions of the system.

"You literally rate the line at a higher level," said Rotenberg. "You say more megawatts are allowed to be delivered at certain times, based on heat and humidity and other ambient conditions."

This technology is important for clean energy, "particularly for wind," said Rotenberg. "When the wind is blowing and cranking out electricity from turbines at that same time and place, that wind is cooling down transmission lines and enabling more power flow. But the problem is, utilities generally don't adjust line ratings accordingly."

As for topology, Rotenberg explained that transmission lines come out of service for maintenance and other reasons, "but [grid operators] don't generally take economics into account," instead leaving lines in place as long as they are functioning properly — even if that is not the most efficient way to move power.

Other monitoring technology allows transmission organizations to operate the grid more efficiently, as more renewables come online. Reactive Technologies' grid technology is focused on inertia measurement.

The rotating generators of gas and coal plants provide inertia, which helps to stabilize the grid. But as more energy is generated by wind and solar, which do not generate inertia, the grid can become less stable and susceptible to rapid changes in demand.

"Without an accurate view of inertia, system operators may be forced to cap renewables integration or even curtail their output in lieu of fossil fuels," Kimmett said. The company uses a new type of inertia modeling that injects a small amount of power onto the grid and measures the frequency changes to get more accurate measurements.

"If you are modeling inertia and you know the model isn't that accurate, you will be conservative. If you know exactly where the cliff's edge is, you will drive closer. It's all about making better decisions in real time. It's all about preventing artificial curtailment to renewables."

All of these technologies are in various stages of deployment in the United States. Transmission experts say colocation is one of the largest opportunities for development of high voltage transmission systems, and the SOO Green project recently got a boost from federal regulators.

SOO Green case study

The SOO Green line is a discrete project, but project officials say it is a replicable model that can be used to build High Voltage Direct Current (HVDC) transmission that can assist renewable energy buyers in gaining access to low-cost, large-scale wind and solar generation.

It is a first-of-its-kind, rail co-located, interregional transmission project that will use state-of-the-art HVDC technology to integrate large volumes of renewable energy, Ward said.

"We're creating a new industry with this project," Ward said. "SOO Green’s underground HVDC rail co-location model can be replicated to unlock America’s clean energy potential and build a national clean energy grid ... that would constitute the largest infrastructure buildout of our generation.”

SOO Green's plan to connect the MISO and PJM markets through the use of a new generation of high voltage underground cables represents an innovative partnership with the Canadian Pacific Railway subsidiary line.

"Transmission development is real estate development," Ward said. By working closely with the railway and staying within its right of way, developers expect to avoid routing and siting controversy in the process of installing a pair of 525 kV HVDC lines. Operations are planned to start in late 2024, and the project recently got good news from federal regulators.

The Federal Energy Regulatory Commission on July 23 authorized SOO Green to charge negotiated rates for transmission rights on the project, subject to its submission of a compliance filing after an open solicitation. The line would be built with SOO Green as the merchant developer. Users of the system would pay for it, avoiding the complications of an inter-RTO cost allocation process, said Ward.

Ward said the company is planning an imminent solicitation to match buyers and sellers of renewable energy on the line, and the first phase will allow for anchor shippers to obtain capacity early in the process with first-mover advantages. A second solicitation phase will match shippers with upstream generation and downstream offtake, while the third phase will use an auction process to allocate the remaining capacity.

The project, said Ward, represents the potential for "unlocking new sources of renewable energy and creating the first link in an ultra-resilient national transmission superhighway."