NYISO selects modeling technique for power resource capacity accreditation

As the New York Independent System Operator advances its approach to valuing the capacity of various power generation resources, the grid operator has proposed using the Marginal Reliability Improvement technique with a 100 MW size for the representative unit.

NYISO had been working to implement, by the third quarter, power capacity accreditation factors that will be determined annually and reflect the marginal reliability contribution of each resource class as more renewables enter the system.

However, project completion has been delayed and the grid operator now expects to complete it in the fourth quarter, according to a presentation given during an Oct. 27 Installed Capacity Working Group and Market Issues Working Group meeting that was held in person and remotely.

Specifically, NYISO has been working on implementation details and technical specifications for establishing Capacity Accreditation Factors, or CAFs, and Capacity Accreditation Resource Classes, or CARCs.

Working with GE Energy Consulting, the grid operator has evaluated a variety of representative unit modeling characteristics and modeling techniques for calculating CAFs, with NYISO and GE testing these techniques under current and future system conditions, according to the presentation.

Based on the testing, NYISO is proposing unit modeling for calculating CAFs using the Marginal Reliability Improvement, or MRI technique, which has "consistently produced similar CAFs" to the effective load carrying capability, or ELCC, technique and "requires a fraction of the computational time," the grid operator said.

Faster approach

On average, the MRI approach can produce a CAF within 3.4% of the CAF results produced from the ELCC technique and an MRI run requires two and a half to three hours compared to an ELCC run which can require 15 to 30 hours, according to the presentation.

NYISO is also proposing the use of a 100 MW "step size" for the calculations, which it said is "sufficiently large to produce stable CAFs and sufficiently small to reflect a marginal reliability contribution."

"We think these techniques are the right answer and the 100 MW step size gives us the least amount of variance and gives us the most appropriate way to model that," Zach Smith, capacity market design manager at NYISO said during the meeting.

Once NYISO decided to use a marginal instead of an average modeling approach, which the Federal Energy Regulatory Commission approved, the grid operator worked to determine the best methodology for doing that calculation. ELCC takes a very long time and was not producing enough of a spread in results to spend a lot of resources on for that small amount of difference, another NYISO staff member said.

NYISO has been updating its internal capacity market rules and tariff to reflect the updated capacity accreditation methodology and will return to the working group with additional revisions in November, according to the presentation.

More broadly, the capacity accreditation project is expected to involve continuous model improvement and implementation for the next five years, NYISO said. In 2023, the grid operator plans to focus on implementing the capacity accreditation process and software, as well as conducting research on natural gas constraints, start-up time, and additional modeling.