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arxiv: 2509.24959 · v2 · submitted 2025-09-29 · 📡 eess.SY · cs.SY

Coordinated vs. Sequential Transmission Planning

Maya Domeshek , Christoph Graf , Bur\c{c}in \"Unel This is my paper

Pith reviewed 2026-05-18 12:33 UTC · model grok-4.3

classification 📡 eess.SY cs.SY
keywords transmission planningco-optimizationsequential planningPJMgeneration storage transmissionelectricity system costsreliability constraintsclimate policies
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The pith

Co-optimizing generation, storage, and transmission reduces estimated transmission upgrade needs by 67 percent compared to sequential planning.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper tests whether planning electricity investments in one integrated step captures interactions better than the common practice of first choosing generation and storage then adding transmission to fix resulting problems. In a detailed 20-zone model of the PJM region that already includes reliability rules and state policies, the integrated approach requires far less new transmission. This produces modestly lower total costs while meeting the same reliability and climate targets. A reader would care because current U.S. planning processes may be committing to unnecessary and costly transmission lines.

Core claim

The multistage, multi-locational planning model that co-optimizes generation, storage, and transmission investments while respecting reliability constraints and state energy and climate policies estimates 67% lower transmission upgrade needs than the sequential model in the most conservative specification, leading to total system costs that are 0.6% lower and similar reliability and climate outcomes.

What carries the argument

A multistage, multi-locational planning model that simultaneously optimizes investments in generation, storage, and transmission.

If this is right

  • Co-optimized planning achieves the same reliability and climate goals with substantially less new transmission infrastructure.
  • Total system costs are 0.6 percent lower when generation, storage, and transmission decisions are made jointly rather than sequentially.
  • Sensitivity cases show even larger reductions in transmission needs and costs plus improved reliability and climate performance under co-optimization.
  • The sequential approach overestimates transmission needs because it does not account for how generation and storage can be located to relieve transmission pressure.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The same co-optimization logic could be applied to other U.S. regions that currently use sequential planning.
  • Regulators could require co-optimized models in future compliance filings to avoid over-procurement of transmission.
  • Generation siting decisions made under a copper-plate assumption systematically inflate later transmission requirements.

Load-bearing premise

The 20-zone stakeholder-informed model of the PJM region sufficiently captures the interactions among generation, storage, and transmission investments as well as all relevant reliability constraints and state policies.

What would settle it

Compare the actual transmission upgrades built in PJM over the next decade against the amounts predicted by each planning method when both are run on the same starting assumptions and updated with observed demand and policy changes.

Figures

Figures reproduced from arXiv: 2509.24959 by Bur\c{c}in \"Unel, Christoph Graf, Maya Domeshek.

Figure 1
Figure 1. Figure 1: Baseline Topology and Transmission Corridor Limits [PITH_FULL_IMAGE:figures/full_fig_p006_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Cumulative Added Transmission 2045 [GW] Capacity build-out is similar for the co-optimized and se￾quential cases [PITH_FULL_IMAGE:figures/full_fig_p007_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Cumulative Renewable and Gas Capacity Additions by 2045 [GW] [PITH_FULL_IMAGE:figures/full_fig_p008_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Average Hourly Net Load 2045 [GW] 2) Impact on Costs, Reliability, and Emissions We find that in our main specification (‘ELCC Queue Limits’) the net present value system cost over the whole planning period is 0.6% lower in the co-optimized planning model compared the the sequential planning model which amounts to approximately $3 billion (2024$) over the planning horizon (see Table IV). While this may see… view at source ↗
read the original abstract

Coordinated planning of generation, storage, and transmission more accurately captures the interactions among these three capacity types necessary to meet electricity demand, at least in theory. However, in practice, U.S. system operators typically follow a sequential planning approach: They first determine future generation and storage additions based on an assumed unconstrained (`copper plate') system. Next, they perform dispatch simulations of this projected generation and storage capacity mix on the existing transmission grid to identify transmission constraint violations. These violations indicate the need for transmission upgrades. We describe a multistage, multi-locational planning model that co-optimizes generation, storage, and transmission investments. The model respects reliability constraints as well as state energy and climate policies. We test the two planning approaches using a current stakeholder-informed 20-zone model of the PJM region, developed for the current FERC Order No. 1920 compliance filing process. In our most conservative model specification, we find that the co-optimized approach estimates 67% lower transmission upgrade needs than the sequential model, leading to total system costs that are .6% lower and similar reliability and climate outcomes. Our sensitivities show larger transmission and cost savings and reliability and climate benefits from co-optimized planning.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript compares sequential transmission planning (first optimizing generation/storage under a copper-plate assumption, then identifying upgrades via dispatch on the existing grid) against a multistage co-optimized model that jointly plans generation, storage, and transmission while respecting reliability constraints and state policies. Using a stakeholder-informed 20-zone representation of PJM developed for FERC Order No. 1920 compliance, the authors report that co-optimization yields 67% lower transmission upgrade needs, 0.6% lower total system costs, and comparable reliability and climate outcomes in the most conservative specification, with sensitivities showing larger benefits.

Significance. If robust, the quantitative comparison would supply concrete evidence on the value of coordinated planning for FERC 1920 processes and similar regulatory filings. The stakeholder-informed dataset and inclusion of policy constraints lend practical relevance; the reported sensitivities provide some indication of result stability.

major comments (2)
  1. [Model description and results sections] The central numerical result (67% lower transmission upgrades) rests on the 20-zone PJM model. No resolution-sensitivity analysis is presented to test whether intra-zonal constraints, which are invisible at this aggregation, materially alter upgrade volumes in the sequential path or the siting flexibility in the co-optimized path. A finer zonal or nodal check would be required to establish that the reported gap is not inflated by the chosen spatial resolution.
  2. [Results and sensitivity analysis] The phrase 'most conservative model specification' is used to qualify the headline 67% and 0.6% figures, yet the manuscript does not enumerate which parameter settings or constraint tightenings define this case relative to the sensitivities. Without an explicit mapping, it is difficult to assess whether the conservative case truly bounds the comparison or simply reflects one point in a broader parameter space.
minor comments (2)
  1. [Abstract] The abstract writes '.6%' instead of '0.6%'; this should be standardized for readability.
  2. [Figures and tables] Figure captions and table footnotes should explicitly state the exact reliability and policy constraints enforced in both planning formulations so readers can verify they are identical.

Simulated Author's Rebuttal

2 responses · 0 unresolved

Thank you for the detailed and constructive feedback on our manuscript. We have carefully considered each major comment and provide point-by-point responses below. Where revisions are warranted, we indicate the changes to be made in the revised version.

read point-by-point responses

  1. Referee: [Model description and results sections] The central numerical result (67% lower transmission upgrades) rests on the 20-zone PJM model. No resolution-sensitivity analysis is presented to test whether intra-zonal constraints, which are invisible at this aggregation, materially alter upgrade volumes in the sequential path or the siting flexibility in the co-optimized path. A finer zonal or nodal check would be required to establish that the reported gap is not inflated by the chosen spatial resolution.

    Authors: We recognize the importance of spatial resolution in transmission planning models. The 20-zone representation was specifically developed through stakeholder engagement for the FERC Order No. 1920 compliance filing, providing a balance between detail and computational feasibility for policy analysis. Both the sequential and co-optimized approaches use the same zonal structure, so the comparison remains internally consistent. However, we agree that intra-zonal effects could influence the results. In the revised manuscript, we will expand the model description section to discuss the limitations of zonal aggregation and include a qualitative assessment of how finer resolution might affect the findings. A full nodal sensitivity is beyond the scope of the current study due to data and computational constraints, but we will note this as an area for future research. revision: partial

  2. Referee: [Results and sensitivity analysis] The phrase 'most conservative model specification' is used to qualify the headline 67% and 0.6% figures, yet the manuscript does not enumerate which parameter settings or constraint tightenings define this case relative to the sensitivities. Without an explicit mapping, it is difficult to assess whether the conservative case truly bounds the comparison or simply reflects one point in a broader parameter space.

    Authors: We appreciate this observation and agree that greater clarity is needed. The 'most conservative' specification refers to the base case with the tightest reliability constraints and the most stringent policy requirements among the scenarios considered. In the revised manuscript, we will add an explicit description in the results section, including a table that maps the key parameters (such as reserve margins, transmission loss factors, and policy targets) for the conservative case versus the sensitivity runs. This will help readers understand how it bounds the comparison. revision: yes

Circularity Check

0 steps flagged

No circularity: independent model comparison on shared inputs

full rationale

The paper defines and solves two separate optimization problems (sequential planning versus co-optimized generation-storage-transmission planning) on the identical 20-zone PJM dataset and constraint set. The 67% transmission reduction and 0.6% cost difference are direct numerical outputs of these distinct formulations rather than any quantity fitted from one run to the other or defined in terms of itself. No self-citation, ansatz, or uniqueness theorem is invoked to force the result; the derivation chain remains self-contained against the external benchmark of the stakeholder-informed zonal model.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central comparison depends on the accuracy of the 20-zone PJM representation and the formulation of reliability and policy constraints; these are treated as given inputs from the stakeholder process rather than derived within the paper.

axioms (1)
  • domain assumption The 20-zone model developed for FERC Order No. 1920 compliance accurately represents PJM transmission, generation, and policy constraints.
    Invoked when both planning approaches are tested on this model.

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Reference graph

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