What is available transfer capacity (ATC)?
Available transfer capacity (ATC) refers to the remaining power transfer capability within a transmission network. It represents the maximum amount of power that can be transmitted over a transmission line without compromising grid reliability and stability.
Why is ATC important for power project developers?
With the increasing demand for electric power and the integration of renewable energy into the U.S. power market, the process of adding new power to the grid and navigating interconnection has become more complex. Historically, fossil fuel plants have been built in centralized locations, simplifying interconnection to the grid. However, an influx of renewables in the U.S. power market is resulting in a decentralized grid, creating a more complex interconnection process.
How does ATC impact injection studies during the interconnection process?
In Texas, the rapid growth of renewable development has created a competitive landscape for developers seeking ideal project sites and interconnection points. The Electric Reliability Council of Texas (ERCOT) manages the electric power delivery to more than 26 million customers. For renewable developers connecting to the ERCOT grid, injection studies are essential to ensure that their projects support grid reliability and stability. These studies analyze the potential impact of proposed projects on the chosen point of interconnection and the surrounding area. Consequently, developers may incur significant costs to complete these studies successfully. To mitigate study costs, developers now seek ways to assess their projects’ impact on the grid early in the site selection process. Understanding the available capacity of substations within the grid is crucial for this purpose.
How can Enverus Power & Renewables ATC solutions help you with your injection study?
Enverus Power & Renewables offers ATC solutions to help developers screen for substations with available capacity early in the project siting process. Using the Enverus PRISM® application, developers can track historical ATC values at the busbar level to identify substations with promising injection capabilities for their future power plants.
When screening all of Texas for less congested areas where interconnection seems feasible, developers need to quickly find counties where historically there has been available capacity to interconnect. Figure 1 outlines counties with the highest available capacity in Texas.
Since ATC values can fluctuate overtime with seasonality and changes to the grid, developers not only need to find areas with higher ATC values, but also areas where available capacity does not significantly fluctuate. This ensures that if they were to interconnect their power plant to a substation within these areas, it is more likely to have constantly high ATC values to support their project’s capacity and not need to be concerned with curtailing any power. Sutton, Kimble and Grimes counties stand out in Figure 2 as regions where both the Average ATC (MW) is consistently high as well as the Minimum Daily ATC, meaning there is likely minimal volatility in ATC values.
There are 14 substations in Sutton, Kimble and Grimes counties with these ATC values in Enverus PRISM. To further assess interconnection feasibility, a developer must also understand the futuristic condition of the given substations that may impact their interconnection. The planned capacity at these substations can help a developer get a full view of how the existing available capacity may decrease based on the up and coming power plants at that point of interconnection. In Kimble County, there are no planned projects that may be interconnecting to the two substations within that area. The two substations in Sutton County have a combined mean ATC that is much higher than the planned capacity at those points of interconnection (Figure 3). Meanwhile, the 10 substations in Grimes County, have a combined mean ATC that is lower than the planned capacity at those points of interconnection (Figure 3). Grimes County thus has more planned capacity than the historical available capacity, meaning interconnection in this region would likely be challenging. This type of assessment allows developers to quickly find regions where the delta between the available capacity and the planned capacity supports the connection of their new power plant in the area.
At this point, a developer can begin to assess at a substation level, where they can potentially interconnect given the grid’s availability for new capacity. Figure 4 outlines, by substation, in Kimble and Sutton Counties, the Average Available ATC in MW over an 11-month period. Segovia and Cauthorn substations, located in Kimble and Sutton Counties respectively, have historically had low ATC values. Meanwhile, Edison and Orsted substations, located in Kimble and Sutton Counties, respectively, consistently have much higher ATC values.
With this knowledge of available capacity at a substation level, the developer can start to consider other project site attributes such as land suitability to continue in their project siting process. The available capacity gives them the confidence to find sites around the Orsted and Edison POIs. When assessing suitability for solar projects, developers can consider metrics such as Average Global Horizontal Irradiance (GHI) to interpret how a solar plant may perform. Between the Orsted and Edison substations, which have comparable available capacity, Orsted sits more optimally amongst parcels with higher GHI values, making it likely more suitable for solar (Figure 5).
As a developer continues in their project siting process, they can also consider land buildability. With Customizable Buildable Acreage in PRISM, they can run a custom buildable analysis of the parcels around the Orsted substation to find potentially suitable sites for their project. Figure 6 outlines the parcels above 100 acres around the Orsted substation, which has the available capacity to support new projects. The green represents areas where a project could likely be built based on the customized buildability model.
Ultimately, developers need to understand the available capacity to interconnect to the grid prior to other steps in their project siting process to ensure successful interconnection and reduce injection study costs further down the line. Enverus PRISM assists developers in quickly finding substations with available capacity, and subsequently the land to support projects around those sites. To further analyze the point of interconnection (POI), available transfer capacity can be viewed in Enverus Panorama.
