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Generation and Transmission Expansion Planning with BESS-Based Virtual Transmission Lines

Qiushi Wang, Xingpeng Li

arXiv:2610.02674v1eess.SYcs.SY

TL;DR

Rapid renewable and integrated data-center growth creates planning and congestion challenges, while physical transmission expansion can take years to deploy. The paper incorporates relaxed VTL-paired BESS coordination into long-term GTEP; in the base case, it reduces multiple congestion measures relative to standalone BESS with a small increase in total cost.

  • Problem

    The system-level effects of massive integrated data-center clustering on GTEP and congestion remain little studied, while physical transmission projects can take a decade to permit and build.

    Source: §I · p. 3

  • Method

    The paper adds relaxed VTL-paired BESS coordination to long-term GTEP, preventing paired units from charging or discharging simultaneously.

    Source: §I · p. 4, C. BESS Model · p. 6, D. Virtual Transmission Model · p. 6

  • Results

    Compared with GTEP-BESS, GTEP-VTL reduces weighted congested line-hours by 12.3%, total congestion rent by 2.8%, and weighted N-1 violation instances by 8.6%, with a 0.3% increase in total cost.

    Source: GTEP-VTL · pp. 8–9

  • Takeaways & Limitations

    On the revised IEEE 24-bus system, VTL provides congestion-mitigation benefits complementary to standalone BESS.

    Source: §IV · pp. 9–10

Abstract

from arXiv · show

This paper proposes a mathematical model for long-term Generation and Transmission Expansion Planning (GTEP) that integrates a relaxed Virtual Transmission Line (VTL) as a Storage in Place of Transmission Asset (SIPTA) strategy to address challenges posed by transmission capacity shortages and system congestion in deregulated power markets, particularly under the rapid growth of renewable energy resources and integrated data centers. The proposed VTL formulation coordinates the operation of the two battery energy storage systems (BESSs) forming a VTL pair by preventing them from charging or discharging simultaneously, thereby providing additional congestion relief without introducing an explicit congestion cost into the objective function. Base case studies on a revised IEEE 24-bus system demonstrate that VTL reduces system congestion compared with the standalone BESS case, achieving a 12.3% reduction in weighted total congestion and up to approximately 67% reduction in congestion on individual transmission branches, with only a 0.3% increase in total planning cost. Furthermore, improvements across multiple congestion metrics indicate that the benefits of VTL extend beyond reducing congested line-hours to reducing congestion rent and N-1 transmission violations in the base case. These results demonstrate the potential of VTL to provide congestion mitigation that complements standalone BESS applications.

I. INTRODUCTION

Deregulated-market cost minimization and rapid renewable and data-center growth leave the congestion effects of expansion uncertain, while physical transmission projects can take years to deploy. This paper addresses the untested long-term GTEP application of relaxed VTL as SIPTA.

I. INTRODUCTION

  • In deregulated markets, cost-minimizing GTEP may not alleviate congestion, as renewable growth changes operations and makes transmission investment financial analysis uncertain.The traditional congestion-mitigation goal of transmission planning has shifted toward cost-based investment optimization.Source: §I · pp. 2–3
  • System-level effects of massive integrated data-center clustering on GTEP and congestion have received little attention, while physical line permitting and construction can take a decade.ERCOT forecasts data-center and crypto loads adding approximately 32.7 GW to 2025–2031 system peak, about 22.5% of projected 2031 peak demand.Source: §I · p. 3
  • BESS can serve as a non-wire congestion alternative, but regulatory and market barriers have hindered storage deployment and have often been overlooked in energy modeling.The passage describes Germany’s 2019 SATA exception allowing TSO-owned or operated BESS for secure and reliable system operation.Source: §I · p. 3
  • Grid Boosters support N-1 security during line outages but do not join daily energy scheduling; conventional VTL pairs can be infeasible under equal-rate absorption and injection.The relaxed VTL strategy addresses that constraint by preventing paired BESSs from charging or discharging simultaneously without requiring equal exchange rates.Source: §I · p. 3
  • Prior relaxed-VTL studies assess short-term operation, leaving its investment costs and capacity planning in a long-term expansion framework unevaluated.Earlier work reports congestion relief and operational-cost benefits, including under renewable uncertainty.Source: §I · p. 3
  • The paper integrates relaxed VTL-paired BESS investment into long-term GTEP and evaluates its cost and congestion effects alongside standalone BESS and physical transmission expansion.The revised IEEE 24-bus case also examines data-center load growth, BESS investment timing, and physical transmission investment decisions.Source: §I · p. 4

II. METHODOLOGIES

The methodology compares three progressively broader GTEP configurations under a shared multi-year planning and operating framework. A common cost objective accounts for operations, investment, residual asset value, renewable curtailment, and load shedding.

II. METHODOLOGIES

  • GTEP-PT includes generation and physical transmission expansion, GTEP-BESS adds standalone storage, and GTEP-VTL adds mandatory coordination for installed paired BESSs.The three configurations share the same underlying GTEP formulation and progressively add BESS and VTL options and constraints.Source: §II · p. 4
  • All configurations use the same horizon, operating constraints, data-center and load-growth assumptions, representative-day profiles, and curtailment, shedding, and residual-value formulations.Their differences arise from the available expansion and coordination options.Source: §II · p. 4
  • The shared objective minimizes expected operating and infrastructure investment costs over the planning horizon while accounting for residual value, renewable curtailment, and load shedding.Residual value is subtracted to avoid penalizing assets that retain economic value at the horizon’s end.Source: §II · pp. 4–5
  • Gas operating costs are weighted across representative days, while new gas, solar, and wind generation and physical lines incur capital costs in the planning formulation.Solar and wind operating costs are neglected because they do not incur fuel costs.Source: §II · p. 4
  • GTEP-VTL uses the GTEP-BESS objective and adds coordination constraints, with no separate VTL investment cost because selected BESS pairs implement it through coordinated operation.BESS investment cost is proportional to installed energy capacity.Source: §II · p. 4

B. Generation and Transmission Expansion Planning

The planning model couples network operation with generation, renewable, and load expansion across years. It represents data-center demand as a phased-in, utilization-dependent load and carries commissioned assets forward through the horizon.

B. Generation and Transmission Expansion Planning

  • The model enforces nodal power balance, generator operating limits, DC power flow, and thermal limits, with candidate-line flow allowed only after construction.Once commissioned, candidate transmission lines remain in service for the rest of the planning horizon.Source: B. Generation and Transmission… · p. 5
  • New gas generators, once built, remain in service through the horizon, with output limited by invested capacity.Equations (18)–(22) define their investment and hourly operating constraints.Source: B. Generation and Transmission… · p. 5
  • New solar and wind output plus curtailment are limited by invested capacity and their respective production capacity factors; existing renewable curtailment is also constrained.The passage identifies separate constraints for new solar, new wind, and existing solar and wind resources.Source: B. Generation and Transmission… · pp. 5–6
  • Data-center demand is phased in over the planning horizon and modeled as a linear function of IT utilization, combining idle baseline consumption with workload-dependent power.The workload factor varies by time and represents projected data-center utilization profiles.Source: B. Generation and Transmission… · p. 6
  • Each investment’s residual value is proportional to its useful life remaining at the planning horizon’s end and is bounded by asset-specific constraints.The passage specifies constraint equations (40)–(47).Source: B. Generation and Transmission… · p. 6

C. BESS Model

The BESS model links storage operation to investment decisions and constrains charging, discharging, energy state, and residual value.

C. BESS Model

  • BESS residual value is bounded by constraints that assume linearized capital-cost depreciation.Source: C. BESS Model · p. 6
  • Discharging BESS power enters nodal balance as an injection, while charging power is treated as a load.BESS operation status is tied to investment status.Source: C. BESS Model · p. 6
  • BESS charging and discharging are limited by installed capacity and their respective durations, while stored energy is bounded and follows a cyclic daily boundary condition.Mode indicators are available only if the BESS is installed by the operation year, and a BESS cannot charge and discharge simultaneously.Source: C. BESS Model · p. 6

D. Virtual Transmission Model

The relaxed VTL is modeled as a SIPTA project using paired BESS candidates subject to BESS constraints. Its coordination rules restrict simultaneous operation and tie activation to both batteries’ investment and operational status.

D. Virtual Transmission Model

  • The relaxed VTL is a SIPTA project formed from paired BESS candidates, which are a subset of the new BESS set and follow the BESS constraints.Source: D. Virtual Transmission Model · p. 6
  • When activated, a VTL pair cannot charge simultaneously or discharge simultaneously, coordinating the paired batteries’ operation.Source: D. Virtual Transmission Model · p. 6
  • VTL activation requires both paired BESSs to be invested and operational in the year, and the VTL mode is forced once both are operational.The VTL activation status indicator is tied to its yearly operational status indicator.Source: D. Virtual Transmission Model · p. 6

III. CASE STUDIES

The revised IEEE 24-bus case compares physical transmission expansion, standalone BESS, and coordinated VTL planning over a 10-year horizon. VTL lowers multiple congestion measures relative to standalone BESS with a small increase in planning cost, while its effects vary across branches.

III. CASE STUDIES

  • The revised IEEE 24-bus case models a 10-year horizon with 2,600 MW of added data-center load and 4% annual growth in other demand.Peak load reaches 9,860 MW by the horizon’s end; six representative days are selected from daily profiles.Source: §III · p. 7
  • GTEP-VTL activates one VTL pair in Year 3 and requires about 19% less BESS investment capacity than GTEP-BESS.The reported BESS investments are 5,359 MWh for GTEP-VTL and 6,635 MWh for GTEP-BESS.Source: §III · p. 7
  • In GTEP-VTL, the BESSs at buses 10 and 14 do not charge simultaneously or discharge simultaneously, changing power injections and withdrawals across the network.This coordination changes power-flow patterns and provides a congestion-reduction mechanism without adding explicit congestion constraints or objectives.Source: §III · p. 8, Figure 4 · p. 8

GTEP-VTL

  • 12.3% lower weighted congested line-hours, 2.8% lower total congestion rent, and 8.6% fewer weighted N-1 violation instances accompany a 0.3% total-cost increase for GTEP-VTL versus GTEP-BESS.GTEP-BESS is the normalization baseline; the three reported congestion measures capture line-hours, congestion rent, and screened N-1 violations.Source: GTEP-VTL · pp. 8–9
  • Four branches have congestion reductions above 14%, with one reaching 67.76%; the largest gains need not occur on branches connected to the VTL buses.The optimized solution activates one VTL pair at buses 10–14.Source: Table 4 · p. 9, GTEP-VTL · p. 9
  • VTL’s branch-level response is heterogeneous: some of the five most congested GTEP-BESS branches improve substantially, while others change little or become slightly more congested.The paper therefore recommends evaluating VTL locations through system-wide optimization rather than selecting pairs only by individual-branch congestion.Source: GTEP-VTL · p. 9, Table 5 · p. 9

C. Sensitivity Analysis – BESS Capital Cost

The sensitivity analyses examine VTL under higher BESS capital costs and when new physical transmission lines are unavailable. VTL provides additional congestion relief in these settings, with trade-offs that depend on storage deployment timing.

C. Sensitivity Analysis – BESS Capital Cost

Sensitivity Analysis – Unavailability of new Physical Transmission Line

  • Without new physical line options, GTEP-VTL achieves lower system-wide congestion and fewer N-1 violations than GTEP-BESS, but higher total congestion rent.The comparison is summarized in Table 7.Source: C. Sensitivity Analysis – BESS Capital… · p. 9, Table 7 · p. 9
  • In Year 1 without new line options, GTEP-VTL congestion rent is $176 MM higher than GTEP-BESS ($271 MM vs. $95 MM), mainly due to storage deployment timing.VTL delays BESS deployment at buses 10 and 14; over Years 2–10, it reduces congestion rent by $89 MM relative to GTEP-BESS.Source: C. Sensitivity Analysis – BESS Capital… · p. 9
  • Branch 6–10 accounts for $116 MM of the Year 1 congestion-rent excess, as peak demand at bus 10 must pass through it without BESS buffering.The VTL coordination constraint reduces the marginal value of BESS at bus 10, resulting in about 60% less capacity there and deployment delayed from Year 1 to Year 4.Source: C. Sensitivity Analysis – BESS Capital… · p. 9

IV. CONCLUSION

The paper incorporates a practical relaxed VTL as a SIPTA strategy into long-term GTEP planning. On the revised IEEE 24-bus system, VTL complements standalone BESS with congestion benefits and only a marginal change in total planning cost.

IV. CONCLUSION

  • The paper develops long-term GTEP models incorporating a practical relaxed VTL strategy as Storage in Place of Transmission Asset (SIPTA).The study frames VTL as relevant where physical transmission expansion faces long permitting and construction timelines.Source: §IV · pp. 9–10
  • Compared with standalone BESS, VTL yields fewer congested line-hours and N-1 violations, with only a marginal change in total planning cost.Both options help alleviate near-term transmission investment needs and reduce renewable curtailment and load shedding; VTL also reduces congestion rent in the base case and BESS cost sensitivity study.Source: §IV · p. 10
  • By changing the spatial coordination of BESS charging and discharging, VTL changes power-flow patterns and can alleviate congestion on neighboring branches.The conclusion characterizes this congestion mitigation as complementary to standalone BESS.Source: §IV · p. 10
  • Future work will test VTL on larger, more diverse power-system cases and with more detailed operational and investment assumptions.Source: §IV · p. 10
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