At the April 30, 2025, Southeastern Regional Transmission Planning (SERTP) stakeholder meeting on Long-Term Scenario Development, Southeast utilities took a small but important step toward updating their planning methods. But, with load forecasts surging, reliability risks mounting, and economic opportunities on the line, the Southeast needs more than compliance checkboxes—it needs leadership and vision.

Scenario-based planning is essential for long-term regional transmission planning because it enables utilities and planners to prepare for a range of plausible futures rather than betting on a single forecast. By modeling diverse scenarios—such as varying levels of electrification, clean energy adoption, expected power plant retirements, or economic growth—planners can identify transmission investments that perform well across multiple outcomes like high-impact extreme weather events over time. This reduces the risk of overbuilding or underbuilding and ensures that the grid remains reliable, affordable, and adaptable under changing conditions. Scenario planning supports strategic ‘least regrets’ decision-making, enhances resilience, and aligns transmission development with evolving public policies and market forces. Multi-scenario transmission planning helps “future proof” the grid.

Go Long!

Much of the discussion at the SERTP meeting focused on baseline scenarios; however, all scenarios are expected to only evaluate 20-years worth of forecasts. While this is a significant improvement over SERTP’s current 10-year outlook, it falls well short of the useful lifespan of a transmission project, which can range from 40-60 years. By only evaluating 20 years worth of transmission needs, utilities may miss opportunities to future-proof the grid. FERC’s Order 1920 sets a floor of 20 years for transmission planning horizons—but not a ceiling. Meanwhile, the Southwest Power Pool (SPP) currently uses a 40-year time horizon that recognizes the importance of long-term planning and the useful lifespan of transmission assets.

Longer horizons better capture the full spectrum of benefits identified in Order 1920, including reduced generation capacity investments, avoided reliability upgrades, reduced congestion, and resilience to extreme weather impacts on the energy system. They also allow for multi-value projects that have the flexibility to serve both today’s and tomorrow’s customers across a range of possible outcomes over a long term time horizon. Failing to plan beyond 2045 locks in a cycle of reactive, piecemeal transmission that leads to higher costs and lower reliability. FERC Order 1920 is flexible enough to allow the states to decide whether 20-years, 40-years or some other timeframe is appropriate for evaluation, or perhaps simply as a side sensitivity.

Scenarios Should Plausibly Cover a Range of Outcomes

SERTP's current proposal includes three scenarios, the minimum required under Order 1920. The ‘Base Case’ is that which the Southeast utilities frame as the most likely; however, this case will rely on utility IRPs in the footprint. Not all utilities have robust IRP processes that occur on a regular basis, potentially creating an outdated base case. SREA recommends that IRPs be incorporated as much as reasonable, but if, for instance, a utility makes major announcements around generation additions, retirements, or load growth projections, the Base Case should be flexible enough to include those more firm decisions, even if those decisions are not reflected in a utility’s latest IRP. Similarly, state mandates or corporate goals should be recognized in this base case. As a hedge, MISO considers only 85% of these goals are met in the base case, and 100% of IRPs are met for instance.

Beyond the Base Case, SERTP utilities propose evaluating two additional scenarios, for a total of three. Many utilities across the southeast already incorporate potentially dozens of scenarios in their IRPs. TVA, for instance, includes thirty different generation-based scenarios in its IRP. The most important element of scenario development is that it captures a range of outcomes driven by consistent factors that change the energy mix across a number of scenarios. Whether it is 3 or 5 scenarios SERTP should be considering corporate goals, state laws, trends in fuel prices and generation performance, assumed power plant retirements, trends in interconnection queues including drop-outs of requests, and other credible inputs that FERC Order 1920 requires will provide a more robust foundation for all scenarios to be more plausible. It’s also possible that by limiting the number of scenarios SERTP evaluates, that the utilities will effectively need to discard and ignore significant IRP-related data and work. Again, FERC Order 1920 requires a minimum of three scenarios, and regions can choose to have more analysis.

If SERTP utilities plan transmission only for the base case, they’ll likely under-build the system, leading to costly local upgrades. At the upper end of the scenarios utilities may or may not overplan, but the important thing is that stakeholders at least get to see how transmission solutions perform. Modeling consistent and plausible factors across a range of scenarios will provide a more robust foundation for identifying cost-effective and resilient transmission solutions that perform well across multiple future circumstances.

Reforming the Regional Planning Stakeholder Group (RPSG)

In the regular annual SERTP process, participants annually form the RPSG to identify five transmission studies. Order 1920 does not replace Order 1000 or Order 890, which are the genesis of the RPSG. SREA has participated in the RPSG for the past four years, but some sectors have been vacant or non-participants for over a decade. No current state public service commissioner has ever attended a SERTP meeting, a key constituency that we need to do a better job incorporating, regardless of Order 1920.

Transparency Still Lags Behind

Stakeholder involvement depends on transparency, and on this front, SERTP continues to struggle. At the latest SERTP meeting, meeting materials were not made available until about a week after the meeting occurred, robbing stakeholders of the ability to prepare for a multi-hour, highly technical meeting. Planning-grade cost data, while now nominally available, remains gated behind confidentiality agreements​. Data regarding scenarios, load, generation, costs, and other assumptions are necessary prior to meetings to ensure meeting efficiency, and maximizing positive contributions from stakeholders. Stakeholders should be fully engaged in scenario selection, benefit metric development, and project evaluation criteria—with published minutes, meeting recordings, and draft materials circulated at least a week in advance.

Let’s Not Forget the Economic Stakes

SREA’s recent Brattle-commissioned report showed that the Southeast faces up to 20 GW of new load and 80 GW of new generation by 2035, yet the region hasn’t approved a single regionally-planned transmission project in more than a decade​.

Transmission inaction is already imposing real costs. Delayed and higher cost interconnection needs, higher cost local transmission upgrades, and constrained access to low-cost resources are pushing rates higher and deterring investment. Proactive, scenario-based transmission planning isn’t a bureaucratic requirement—it’s an economic imperative. We will pay for our electric grid one way or another. Transmission lines can take a long time to construct, and the sooner that multi-value focused transmission is planned, the sooner it is constructed and the multitude of benefits related to projects are shared by consumers. We can either be proactive and plan for the future, or we will pay for the system with economic losses and power outages.

The Bottom Line

SERTP’s adoption of Order 1920 will vastly improve the current planning process in the region. That being said, the region has the opportunity to be a leader in transmission planning, incorporating best practices from across the country. Moving beyond bare-minimum compliance and embracing the spirit of Order 1920 includes:

• A 40-year planning horizon,
• A stakeholder-developed additional scenario
• Transparent and inclusive stakeholder processes, and
• Serious consideration of multi-value regional projects.

The Southeast deserves a modern, cost-effective, and resilient grid. FERC has given the region the tools. Now it’s time for SERTP to use them.