Assessing the Reliability Benefits of Energy Storage as a Transmission Asset

TL;DR

This paper introduces a two-stage framework that couples expansion planning for transmission and energy storage (via JHSMINE) with a probabilistic reliability assessment (A-LEAF) to quantify the reliability value of using storage as a transmission asset (SATOA) versus traditional transmission upgrades. Through a case study on a simplified, Texas-like system, it analyzes three investment scenarios—transmission expansion (TEP), battery expansion (BEP), and joint expansion (BTEP)—under weather-dependent outages to compute reliability metrics such as EUE and LOLH. The findings show that while transmission upgrades deliver the largest reliability gains, large-scale storage can achieve substantial improvements, with smaller storage deployments offering favorable cost-per-unit improvements; however, storage generally does not outperform the transmission upgrade in this scenario. The work emphasizes the need to couple least-cost planning with reliability analysis to properly evaluate the economic and reliability trade-offs between storage-as-transmission and traditional wires investments, and suggests future work on market participation, higher-resolution networks, and weather-dependent transmission outages.

Abstract

Utilizing energy storage solutions to reduce the need for traditional transmission investments has been recognized by system planners and supported by federal policies in recent years. This work demonstrates the need for detailed reliability assessment for quantitative comparison of the reliability benefits of energy storage and traditional transmission investments. First, a mixed-integer linear programming expansion planning model considering candidate transmission lines and storage technologies is solved to find the least-cost investment decisions. Next, operations under the resulting system configuration are simulated in a probabilistic reliability assessment which accounts for weather-dependent forced outages. The outcome of this work, when applied to TPPs, is to further equalize the consideration of energy storage compared to traditional transmission assets by capturing the value of storage for system reliability.

Figures (8)

• Figure 1: Overview of the analysis framework. The expansion planning process, described in subsection \ref{['sec:btep']}, selects optimal size and location of storage and transmission assets, and the probabilistic reliability assessment, described in subsection \ref{['sec:ra']}, simulates operations under random generation outage scenarios and computes reliability metrics.
• Figure 2: Overview of the Monte Carlo simulation in the reliability assessment model. The black box represents the steady-state system operation for each hour, while the red box illustrates the post-contingency system re-dispatch phase
• Figure 3: The network used in the case study, an aggregated ERCOT system which preserves individual generator units.
• Figure 4: Annual expected unserved energy (EUE) in each zone under the Transmission Expansion (TEP), Battery Expansion (BEP, by zone in which the battery is installed), and Reference cases.
• Figure 5: Annual loss of load hours (LOLH) in each zone under the Transmission Expansion (TEP), Battery Expansion (BEP, by zone in which the battery is installed), and Reference cases.