Experts agree that America needs more transmission capacity to carry cheap wind and solar power to where it’s needed. They also agree that it needs to make better use of the transmission grids it already has.
Congestion costs on key U.S. transmission networks rose from $3.8 billion in 2016 to just over $5 billion in 2018, according to research group Grid Strategies, adding to the costs of energy delivered to customers. Lack of capacity on key portions of the country’s grid is also barring new renewable energy projects from being brought online.
Building new transmission to solve the problem is an expensive and time-consuming effort, and even if renewables developers and their offtakers can afford it, projects can be derailed by landowner lawsuits and unfavorable regulatory rulings.
That’s driving a call for federal regulators to align policies that impact how transmission operators and owners invest in their systems with technologies that can help solve the problem.
That’s the goal of the Watt Coalition, which has asked the Federal Energy Regulatory Commission to find a way to implement the 2005 Energy Policy Act’s guidance to “encourage, as appropriate, the deployment of advanced transmission technologies.” FERC has yet to implement that legislative mandate, according to a July filing from the Watt Coalition and the Advanced Energy Economy.
The groups are asking FERC to create a “modest, targeted incentive to support the adoption of advanced transmission technologies.” Right now, transmission owners and investors are largely compensated via rates of return on capital invested, giving them an incentive to over-invest in transmission but little incentive to operate more efficiently.
That might make sense for a massively complex transmission system that “was essentially ‘fixed’ in capacity and configuration,” the groups state. But new technologies can enable more flexible control over those power grids, and computing power can allow grid operators to calculate the value of that flexibility at speeds that make it a practical reality.
The call for incentivizing new technologies was taken up in an August letter from 13 U.S. senators including Bernie Sanders, Dianne Feinstein, Martin Heinrich and Sheldon Whitehouse, arguing that “conventional incentives based on return-on-equity combined with high benefit-cost thresholds are not likely to accomplish the Commission’s statutory obligation to encourage deployment of smart grid technologies.”
The Senators asked FERC to create incentives for “commercial smart grid technologies that can deliver more power over existing lines or reduce transmission congestion," including:
- Power flow control
- Dynamic line ratings
- Storage-as-transmission
- Topology optimization
“There are technologies that can be integrated into the grid fairly inexpensively [and] that can relieve significant amounts of this congestion,” Jon Wellinghoff, FERC chairman from 2009 to 2013, told Greentech Media in a January interview.
So what are these technologies, and how do they help solve the problems the transmission grid is facing? Let’s take a look.
1. Dynamic line rating: A clearer view of transmission line conditions
Overloaded power lines can overheat, sag, melt or fail, something grid operators must avoid at all costs. But the static line ratings used to assess transmission lines’ physical limits don’t account for changing operating conditions like temperature, wind speed, or aging of lines. That leads to both overly conservative schemes to protect them, and uncertainty about whether they’re being taxed beyond their limit.
Dynamic line rating (DLR) technologies actively collect data on transmission lines to let grid operators push them to their actual, rather than assumed, limits. They can also find power lines reaching unplanned limits, to forestall failures that can cause outages or spark wildfires.
DLR is being used by a handful of utilities in the U.S. and Europe, using various technology approaches. Ampacimon, a member of the Watt Coalition, has deployed its line-mounted systems on more than 50 transmission lines with five North American utilities including Arizona Public Service and New York Power Authority.
LineVision is working with four large U.S. utilities including American Electric Power and federal power authority Tennessee Valley Authority. It’s also working with European utilities in Hungary, Greece, Slovenia and Austria as part of a cross-border transmission project dubbed Farcross.
LineVision’s devices are mounted at the base of transmission pylons and capture electrical and physical data about power lines via electromagnetic field and lidar sensors, CEO Hudson Gilmer said. That’s a less expensive and more flexible approach that line-mounted devices that require planned outages or risky "live-line" work to install.
Those sensors measure line sag and sway under different temperature and wind conditions, and capture weathering and aging data that affect their strength. Combined with grid operator systems, “we can unlock anywhere between 15 and 40 percent additional capacity,” depending on current weather conditions, primarily wind speeds that are highly correlated to cooling lines and increasing their capacity.
That link between wind speed and line capacity is particularly important for transmission systems trying to increase the flow of wind power, said Jay Caspary, vice president at Grid Strategies and former director of research and development at Midwestern grid operator Southwest Power Pool. After all, if the wind is blowing hard enough to push wind turbines to their maximum output, it’s also blowing hard enough to cool the transmission lines carrying that power.
LineVision’s sensors can also detect anomalies that might indicate that power lines are in danger of failing, or need to be replaced before their expected end of life. While static ratings may underestimate transmission capacity most of the time, there are rare cases when “you’re actually taking a risk using a static rating because the actual weather conditions are worse than what you assume,” Caspary said.
A 2019 Department of Energy report noted wide industry acceptance that “DLR can provide congestion-management benefits” and increased reliability. But the report also noted that the U.S. has seen less uptake than in Europe since current cost-recovery regulations provide “little incentive to deliver more power over existing lines.”
Gilmer said that LineVision’s early deployments are filling the knowledge gap. “We now have customers coming back to us with more scaled deployments, multiple units covering wider geographic areas, to understand what’s happening on a network level.”
2. Topology optimization: Supercomputing to find system flexibility
Optimizing transmission power flows is a massively data-heavy task, with variables in the trillions and beyond. That’s a major challenge for grid operators trying to calculate the day-, hour- and minute-ahead prices and dispatches that coordinate energy markets, and sets strict limits to how quickly they can reconfigure it to reduce congestion.
Topology optimization uses high-performance computing and mathematical innovations to open these decision-making bottlenecks. In recent years, it’s been moving from virtual testing to real-world use, backed by DOE funds and national laboratory supercomputing capacity.
Pacific Northwest National Laboratory’s High-Performance Power-Grid Optimization project has shown massive parallel computing can speed the day-ahead energy market optimization of Midcontinent Independent System Operator from about two hours to less than 20 minutes.
Similar advances could allow the grid operator to test new market designs much more quickly, and allow market structures that resolve economic signals with changing grid conditions at speeds that weren’t possible before, said Yonghong Chen, MISO’s lead on the project.
Boston-based startup NewGrid has used grants from the U.S. Energy Department’s ARPA-E blue-sky research program to put these concepts to the test with Southwest Power Pool (SPP), mid-Atlantic grid operator PJM and Texas grid operator ERCOT. It has shown that its technology can relieve between 30 percent and 50 percent of congestion on key bottlenecks in transmission networks, first in simulations using historical data and more recently in real-world applications, CEO Pablo Ruiz said.
SPP, for example, found through historical analysis that it could reconfigure its network around a heavily congested area in southeast Oklahoma “by opening one transmission line several substations upstream of the bottleneck,” he said, reducing flows through the congested circuit by more than 25 percent.
SPP then used that reconfiguration on its grid, reducing the price of power at the congested network nodes from about $600 per megawatt-hour to close to the average SPP price of $25 per MWh, as highlighted in a report.
Finding that solution would likely have taken a major engineering study without NewGrid’s technology, which found it within minutes, Erik Desrosiers, founder of Merkaba Group, a consultant to NewGrid, said.
“Historically, the way operators have managed the network is to consider the topology of the network to be fixed, and you optimize around the edges,” he said. “What topology optimization does is to change it from being a constraint to being something more like a variable.”
NewGrid wants to expand from solving reliability problems in a planning context to more active grid operator use, in order “to make it possible to deploy resources in places that are currently constrained or in ways that affect overall performance of the system.”
3. Power flow controls: Routing power on transmission networks
Transmission constraints along heavily loaded circuits set upper limits on systemwide capacity, which can leave other parts of the system underutilized. Devices that can modify the carrying capacity of transmission lines by impeding flows along some lines and increasing them along others could unlock that capacity.
Large-scale transmission system power-flow control devices like series compensation systems, static VAR compensators, synchronous condensers or static synchronous compensators, collectively known as "flexible AC transmission systems," or FACTS for short, are available and in use today. But they’re expensive and purpose-designed to meet specific grid needs.
Modern digital power control technologies can package FACTS capabilities in more modular and flexible formats, expanding the potential scope of their use. Siemens’ new Unified Power Flow Controller devices use a modular multilevel converter architecture, developed for managing high-voltage direct current lines connecting offshore wind farms to far-off power grids, to provide reactive power compensation, voltage control and active power load flow control.
Modular flexibility is also the goal of Smart Wires. The San Francisco-based company won ARPA-E grants to develop modular FACTS devices, starting with its first device, the line-mounted PowerLine Guardian, which showed it could impede voltages to shift flows to alternate paths in deployments with utilities on three continents.
Smart Wires’ latest device, the SmartValve, can both decrease and increase transmission line carrying capacity. The modular static synchronous series compensators inject voltage waveforms of controllable magnitude independent of line current, allowing it to act like a series reactor or series capacitor.
In the U.K., National Grid has a five-year agreement with Smart Wires with a long-range goal of increasing the capacity of its network by 1.5 gigawatts. Irish grid operator EirGrid is exploring SmartValves to reduce congestion and new transmission builds to manage its rising share of wind power. And a pilot project with German transmission system operator Amprion will test their use to increase transmission capacity on a system that’s facing increasing congestion and redispatch costs.
4. Storage-as-transmission: Boosting the capacity on critical circuits
The previous three technologies help grid operators wring more capacity out of their existing networks. But even with them, it’s likely that certain transmission lines will still face congestion and overloading, particularly those connecting remote generation resources where alternative paths to market don’t exist.
Energy storage could serve as an alternative to building new transmission lines to solve these problems, according to Kiran Kumaraswamy, vice president of market applications at Fluence. Over the past few years, the Siemens-AES joint venture has been proposing projects to use batteries to bolster transmission line capacity,
One example is a proposal to add two 250-megawatt batteries to both ends of a transmission line connecting the provinces of Victoria and New South Wales in Australia. Simultaneously charging one battery and discharging the other could create “counterforce” in the opposite direction of the flow of power that might otherwise overload the circuit, freeing up capacity.
Not only is this a cheaper alternative to new transmission, but it can also be completed much more quickly, Kumaraswamy noted. They’re also a far more flexible solution to maintaining grid reliability under what are called “N-minus-1” contingencies, the rare but potentially destabilizing conditions that grids must be designed to manage.
Similar concepts inform Germany’s GridBooster project and Project Ringo in France. Two storage-as-transmission projects are awaiting approval in MISO and PJM, said Jason Burwen, senior policy director for the Energy Storage Association.
