MISO said its set of 20-year transmission planning futures must be further fine-tuned after the Trump administration’s repeal of tax credits for renewable generation.  

The grid operator said introducing the constraints of the One Big Beautiful Bill Act into its capacity expansion modeling returned a build rate that cannot be achieved.  

MISO announced it would take a few months to rework the capacity assumptions in its four 20-year transmission planning futures after passage of the sweeping law in July. (See MISO Revising Transmission Futures After Repeal of Tax Credits.)  

But Director of Economic and Policy Planning Christina Drake said MISO’s modeling using the confines of the law is building too much capacity too fast before the full phaseout of renewable tax credits. Drake said models included an infeasible amount of generation in the first five years.  

MISO’s modeling contemplates a 20-year expansion period and builds according to economic conditions and incentives. 

“We need to have a reasonable band for what can be built in the near term,” Drake told stakeholders at an Aug. 29 workshop to discuss the futures.  

MISO now is looking for “practical limitations to near-term build-out,” Drake said. She said MISO is assessing its queue delays and sluggish supply chains alongside the rollback of incentives for renewable energy to figure out what developers realistically can build. Drake said MISO’s historical build rate with recent supply crunches factored in results of only 9 GW built per year.  

MISO plans to hold more workshops Sept. 24, Oct. 29, Nov. 18 and Dec. 17. MISO added the last two dates after it realized it would need to modify its capacity expansion estimates.  

Drake said MISO did a “hard pivot” in its futures after the passage of the bill.  

The four futures will be used when MISO resumes its long-range transmission planning in 2026.