ISO-NE has outlined the transmission and economic models it plans to use to evaluate proposals submitted for the longer-term transmission planning (LTTP) process.

The RTO is developing the first request for proposals (RFP) for the LTTP process, which is intended to address transmission needs identified in long-term planning studies. FERC approved the new process in July. (See FERC Approves New Pathway for New England Transmission Projects.)

At the direction of the New England States Committee on Electricity (NESCOE), the first LTTP solicitation focuses on increasing the transfer capability at two interfaces in Maine and facilitating the interconnection of at least 1,200 MW of onshore wind in the state. (See ISO-NE to Work on State-backed RFP for Northern Maine Transmission.)

To help qualified transmission project sponsors (QTPS) develop their proposals, ISO-NE will publish transmission and economic models, said Dan Schwarting, manager of transmission planning at ISO-NE. The models will use the same basic structure as those used by ISO-NE to evaluate projects but will use generic information for generator performance to protect confidentiality.

The economic models outlined at the Planning Advisory Committee (PAC) meeting Jan. 23 will include a capacity expansion model and a production cost model. The capacity expansion model will determine “the amounts and types of generation needed to adequately serve load over multiple years, given emissions constraints and load growth,” Schwarting said. The production cost model will calculate hourly data on generation dispatch, power flow and production cost.

ISO-NE plans to use its version of the models to calculate benefit-to-cost ratios (BCRs) for proposals. These financial benefit calculations will account for production cost and congestion savings, avoided capital costs, avoided transmission investment, reductions of line losses and reductions of unserved energy.

For a project to be selected in the LTTP, the BCR calculation must show that its benefits outweigh its costs. If multiple projects pass this threshold, ISO-NE is not required to select the proposal with the highest BCR and also will consider factors including project scope, permitting challenges and “constructability,” Schwarting said.

If no projects pass the threshold, FERC has approved a “supplemental process” in which one or more states could opt to cover the costs that exceed the threshold.

In February, ISO-NE plans to provide additional modeling details to the PAC, including an outline of its modeling of “representative onshore wind projects in northern Maine,” and the composite load model the RTO will use for stability simulations.

Schwarting said ISO-NE plans to release a draft RFP to NESCOE and the QTPS to solicit feedback prior to publishing the official RFP in March. He said this limited review process would “strike a balance between feedback and timeliness in issuing the RFP.”

Several people asked ISO-NE to expand the opportunity to provide feedback to all stakeholders. Sheila Keane, director of analysis at NESCOE, also expressed an interest in expanding the draft RFP review process.

“As we think about this being the first time through for everyone … it seems like adding in some transparency on the draft RFP might add some value to the process without adding too much time,” Keane said.

After issuing the RFP, ISO-NE plans to give transmission developers six months to submit proposals, followed by a yearlong period for ISO-NE to evaluate and select a proposal. Under this timeline, ISO-NE would likely select a solution by September 2026.

“If it is possible to accelerate this timeline we certainly will,” Schwarting said.

2024 Economic Study

Also at the PAC meeting, ISO-NE presented the final policy scenario results of its 2024 Economic Study, which is intended to evaluate “economic and environmental impacts of New England regional policies, federal policies and various resource technologies on satisfying future resource needs in the region.”

The preliminary results of the policy scenario, presented in November, found the need to add 58 GW of capacity from a range of zero carbon resources including renewables, energy storage and small modular reactors (SMRs).

The study found that carbon constraints will drive capacity expansion from 2033 to 2039, after which both carbon constraints and load growth will drive resource additions.

Overall, the final results indicate New England will need to add a cumulative capacity of 77,176 MW by 2050. Compared to the preliminary results, the increased need for new capacity reflects a reduced SMR buildout, which increases the amount of capacity required from other resources.

As the region decarbonizes, SMRs could help fill an essential firm power role and limit the need to overbuild intermittent renewables. ISO-NE has deemed hydrogen generation, carbon capture and storage, and geothermal generation — other potential low-carbon dispatchable resources — to be infeasible solutions for the region due to geological constraints.

The model found that, in 2050, “without additional revenue incentives, SMRs only operate at a 21% capacity factor, but they successfully provide emission free dispatchable generation in the winter to reduce overall system emissions,” said Elinor Ross of ISO-NE.

The results also indicate that the cost of additional carbon reductions will increase exponentially as the power system nears full decarbonization in the leadup to 2050.

“Hours of high solar and wind generation are easy to decarbonize at a low cost,” said Ross. “The remaining hours left to be decarbonized require energy storage and SMRs, which are more expensive than wind and solar.”

Sensitivity analyses also highlighted the significant cost benefits of land-based wind, which was “consistently the most cost effective resource in a levelized cost analysis,” Ross said.

Reducing the limitations on onshore wind decreased the overall build costs in the model. In the most extreme sensitivity considered by ISO-NE — which allowed the model to build unlimited land-based wind — the model added more than 44 GW of onshore wind, cutting the overall build costs nearly in half relative to the reference case.

ISO-NE is taking feedback on the policy scenario results and requests for additional sensitivity scenarios through the end of February.