The Federal Energy Regulatory Commission on Thursday largely approved plans by the California and New York grid operators, plus four utilities, to use ambient-adjusted ratings, called AARs, to measure how much electricity their transmission lines can carry.
Plans submitted by Arizona Public Service, Black Hills Power, Louisville Gas and Electric and Tampa Electric take effect in mid-2025.
FERC in December 2021 ordered all transmission owners to consider ambient conditions when determining how much power can flow through their power lines.
Generally, transmission owners use conservative assumptions about the worst-case, long-term air temperature and other weather conditions when setting line ratings. Those line ratings, called seasonal or static ratings, are typically updated only when equipment is changed or weather assumptions are revised.
AARs, which are already used by some utilities, take into account near-term changes in temperature and solar heating values to measure capacity on transmission lines. They can increase the effective capacity on transmission lines, making them more efficient and in some cases reducing renewable energy curtailment.
They will allow utilities to squeeze more capacity out of the existing system at minimal cost, according to FERC Commissioner Allison Clements.
FERC has dockets open, including an inquiry about dynamic line ratings, in its interconnection and transmission planning proposed rulemakings, she said Thursday during the agency’s monthly meeting.
“I’m looking forward to moving forward with opportunities to promote various kinds of grid-enhancing technologies, which are really no-brainers when it comes to the commission's responsibility to ensure fair rates,” Clements said.
FERC approved compliance plans by the California Independent System Operator and the New York ISO, subject to additional compliance filings they must make to the agency. NYISO, for example, expects transmission owners in its footprint will calculate AARs on a rolling 48-hour basis with submissions by transmission owners to NYISO at least every hour, according to FERC’s decision.
The grid operator and transmission owners are still developing the procedures for AAR submissions. FERC gave NYISO until Nov. 12, 2024, to file those procedures with the agency.
