Grid Enhancing Technologies in Generator Interconnection
Grid Enhancing Technologies (GETs) solve problems across the electricity sector. In transmission operations, they reduce transmission congestion and give operators visibility and flexibility to respond to outages and extreme weather. In planning, they can decrease the need for new infrastructure and improve the value of new lines.
For generator interconnection, GETs can reduce upgrade costs and shorten study and construction timelines. Long upgrades or high costs can kill a project, and by improving the viability of projects GETs can reduce withdrawals from the queue.
The examples below illustrate how GETs could the economics of new renewable energy projects. Because policy doesn’t require transmission owners to implement GETs where they are cost-effective, the developers were forced to accept higher upgrade costs, find alternative options, or cancel the projects.
To learn more about Dynamic Line Ratings (DLR) and Advanced Power Flow Control (APFC) technologies, see our explainer here.
APFC can be deployed in place of a phase shifter for the purpose of rerouting power to lines with available capacity, or as an alternative to series compensation. DLR can be deployed to address small line overloads, especially when the overloads occur in high-wind scenarios. Both technologies can address constraints while larger upgrades are under construction, serving as a bridge solution.
System operators and transmission owners should take steps to integrate GETs in interconnection processes. The examples below illustrate that GETs adoption remains slow in the United States, but with these changes they could become common interconnection tools:
- System operators and utilities should consider GETs as a valid mitigation alternative in interconnection studies.
- They should develop procedures to include GETs and document those in business practice manuals.
- There should be detailed reporting on the evaluation of GETs in interconnection studies (including the basis for rejection.)
- System operators and utilities should work with GETs vendors to develop the models to be used in interconnection studies.
- System operators and utilities should update their software to include the GETs models.
Cheaper Advanced Power Flow Control Could Replace Phase Shifters
For a proposed wind generation facility in the eastern interconnection, a phase shifter was identified as a required upgrade in the interconnection studies. The developer proposed an APFC device as a significantly lower-cost alternative that achieved the required power flow control.
After several weeks of discussion with Independent System Operator (ISO) and transmission owner (TO) on details of the APFC technology and models, the TO decided that that the technology was not mature enough and could not be deployed, despite dozens of well-documented deployments around the world.
In the end, the developer paid for the traditional solution, which was more expensive and took longer to get in service.
Dynamic Line Ratings Could Avoid 100 Miles of Line Rebuild
An interconnection study identified line overloads that would cause potential curtailment for a wind facility proposed in the eastern interconnection. The upgrade required rebuilding more than 100 miles of 115kV lines so that the generation facility wouldn’t be curtailed in windy hours during the summer. However, the interconnection study assumed wind at 2 meters per second to calculate the line ratings, while dynamic line ratings could likely increase the line capacity by up to 30% in the conditions that triggered the overload in the study.
However, the TO would not consider installing DLR on its system, and the generator had to either accept high curtailment or pay for a costly upgrade.
Dynamic Line Ratings Could Avoid a $50 Million Line Rebuild
The interconnection study for a wind project in the eastern interconnection showed a line overload of 3%. The transmission owner quoted a $50 million line rebuild to address the overload.
The overload would only occur in a worst case loading scenario occurs during windy hours in the summer and winter, when DLR would have the highest impact on line capacity. Yet again, the TO based its line rating on 2 meter per second wind despite the scenario assumptions of higher wind.
The TO refused to implement dynamic line ratings.
A 1% Line Overload Could Cost $400 Million
A constraint between Regional Transmission Organization (RTO) seams triggered a $400 million upgrade in one interconnection study. The projected overload was only 1%, and only in high-wind scenarios. The upgrade cost made the project inviable, but DLR would likely have resolved the overload at much lower cost. The TO refused to consider it.
GETs Can Provide Interim Solution During Construction
A wind project in the eastern interconnection was likely to see curtailment due to a 5% line overload. However, upgrades to flow gate would resolve that constraint, and they were scheduled to be done in 2026 and 2027. APFC could be dispatched to resolve the constraint in the meantime. As of early 2023, the solution was being considered by the RTO and TO.