The low‑cost way to move more clean power—ambient‑adjusted transmission line ratings—won’t arrive on schedule in much of the country. FERC Order No. 881 required transmission providers to calculate and use hourly, weather‑based ratings for near‑term service by July 2025, with transparency and seams provisions baked into the tariff. That timeline is slipping across multiple regions as operators cite software and integration hurdles. (ISO New England)
Two concrete moves set the tone. ISO New England won a 17‑month deferral on May 30, 2025, pushing its effective date to December 15, 2026 to finish the “LEP” software and train market participants. CAISO secured an extension on April 30, 2025, moving its tariff effective date to December 17, 2026 and allowing its transmission owners until October 15, 2027 to complete their upgrades. MISO went further: on June 6, 2025 FERC granted an extension no later than December 31, 2028, with annual progress reports. (ISO New England)
The pattern is broader than a few filings. A January 31, 2025 Reuters survey found all six major RTOs outside Texas expected to miss the July 2025 deadline, citing vendor scarcity and integration complexity. The story also captured what’s at stake: ratings that reflect weather can unlock material capacity—often portrayed as “up to 40%” under favorable conditions—without building new lines. (Reuters)
Why this matters for utility‑scale solar and storage: Order 881’s hourly ambient‑adjusted ratings (AARs) and future dynamic line ratings (DLR) are the fastest, cheapest tools to ease congestion, cut curtailment, and clear room for new interconnections while long‑lead transmission is planned under Order 1920. FERC itself is exploring a DLR framework in a separate proceeding to deepen those gains. Independent studies for DOE and national labs show grid‑enhancing technologies can be cost‑beneficial in avoiding renewable curtailment and deferring expensive upgrades. (Federal Energy Regulatory Commission)
The costs of delay are tangible. In concurring with MISO’s extension, a FERC commissioner flagged the market monitor’s estimate that 2023–2024 customers paid about $500 million extra due to the lack of temperature‑adjusted and emergency ratings—money that could have been saved by implementing 881 on time. (Federal Energy Regulatory Commission)
Bottom line: Order 881 is curtailment relief on a spreadsheet. Until AARs are live, expect higher congestion, tighter interconnection headroom, and more pressure on batteries to paper over midday‑to‑evening constraints. Developers should price in regional slippage, track each ISO’s milestone calendar, and press for interim steps (pilot DLR, advanced conductors, topology control) that deliver near‑term capacity while software catches up. (The Department of Energy’s Energy.gov)
Sources
- ISO‑NE — FERC Order No. 881: Managing Transmission Line Ratings (participant readiness; links to filings). (ISO New England)
- FERC — Notational Order Accepting Deferral of Effective Dates, May 30, 2025 (ISO‑NE to Dec. 15, 2026). (ISO New England)
- FERC — Order Accepting Motion for Extension of Time, Apr. 30, 2025 (CAISO to Dec. 17, 2026; PTOs to Oct. 15, 2027). (California Independent System Operator)
- FERC — Commissioner Rosner concurrence on MISO extension, Jun. 6, 2025 (extension no later than Dec. 31, 2028; IMM: $500M customer impact). (Federal Energy Regulatory Commission)
- FERC — Order No. 881 page (AAR requirements). (Federal Energy Regulatory Commission)
- Reuters — “Power‑boosting project for U.S. grid to miss July deadline,” Jan. 31, 2025. (Reuters)
- FERC — DLR ANOPR Fact Sheet, Jun. 27, 2024. (Federal Energy Regulatory Commission)
- DOE / National Labs — GETs case study and guide on curtailment and cost benefits. (The Department of Energy’s Energy.gov)
