Sensors found up to 63% more line capacity at peak; one line could use less than half its gain

August 2025 — A year after installing 50 sensors on its transmission lines, Minnesota co-op Great River Energy reported up to 63% more capacity at peak demand, the largest dynamic line rating deployment in the U.S., it says. Here's what happened, what it cost, and what went wrong.

Cost and outcome (as of Sept. 9, 2025)

Outcome: up to 63% more transmission capacity during peak demand in the first year. (Great River Energy)
Projected savings: $3.175 million in avoided congestion costs over five years, a forecast. (Great River Energy; T&D World)
Realized on the pilot line: 31 MVA of a 69 MVA conductor gain; other equipment capped flow. (T&D World)
Cost: not disclosed.

What they did

Great River Energy partnered with Heimdall Power to install 50 "Neurons" on 10 transmission lines spanning 175 miles. The sphere-shaped sensors collect real-time data on the line and its surroundings and can be installed by autonomous drones or line technicians on energized lines. (Great River Energy)

Dynamic line rating sets a line's limit from current weather rather than conservative seasonal assumptions, letting the co-op set "safe, new operational limits" and potentially delay or avoid some new lines. (Great River Energy)

"This technology will help us unlock grid congestion and achieve additional transmission capacity from our existing infrastructure, which our members have already invested in," said Priti Patel, vice president and chief transmission officer. (Great River Energy)

What the year showed

Ambient-adjusted ratings, which use air temperature alone, suggested an 8.8% capacity cut in winter 2024. Sensors measuring the cooling effect of wind showed a 22.5% average increase instead, Craig and Cleaver wrote. (T&D World)

Across summer 2024 the pilot line averaged nearly 50% more capacity. Between 4 p.m. and 10 p.m. on hot evenings, when demand peaks, DLR found 63% more conductor capacity than seasonal ratings. (T&D World)

"One year later we've gained real, operational value — not just theoretical gains," said Michael Craig, Great River Energy's manager of energy and distribution management systems. (Great River Energy)

Why it took so long

Dynamic line rating has circulated in utility circles since the early 1990s, but U.S. adoption has been slowed by regulatory friction, limited incentives and internal inertia, Craig and Cleaver wrote. They added that industry headlines touting "40% average capacity gains" oversimplify the technology, and that most utilities want "proven, peer-validated success" before moving. (T&D World)

Great River Energy says knowing real-time capacity also helps it integrate more resources, including renewable energy, into the existing grid. (Great River Energy) Over the summer, DLR showed more than double the capacity of ambient-adjusted ratings on several spans. (T&D World)

The cap

In summer 2024 the pilot line's conductor showed 48.92% more capacity than its static rating: from 142 MVA to a potential 211 MVA, a 69 MVA gain. But connected utility equipment capped flow at 173 MVA, so the realized gain was 31 MVA. (T&D World) Our math: 31 ÷ 69 ≈ 45% of the potential gain was usable.

That 31 MVA feeds into the forecast $3.175 million in avoided congestion charges, for Great River Energy alone, over the five-year scope of the deployment, the authors wrote. (T&D World)

What went wrong

The bottleneck moved. On the pilot line, other equipment limited flow to 173 MVA, so less than half the conductor gain was usable. (T&D World)
Sometimes lower. About 2% to 3% of the time, DLR showed slightly lower ratings than the seasonal baseline, typically in low wind or higher-than-expected heat. (T&D World)
A projection. The $3.175 million is forecast over five years, not money saved. (Great River Energy; T&D World)
What we don't know yet: what the deployment cost, and how much of the savings forecast materializes.

Our follow-up question for Great River Energy

What did the deployment cost, and how will the co-op report realized congestion savings against the $3.175 million forecast?

Sources

Great River Energy, “Great River Energy and Heimdall share dynamic line rating project results,” Aug. 13, 2025. greatriverenergy.com
Michael Craig and Tom Cleaver, “One Year Later: Inside America's Largest Dynamic Line Rating Deployment with Great River Energy,” T&D World, Sept. 9, 2025. tdworld.com

Disclosure: [not in copy] Editor placeholder