Last summer, Brattle Group Principal Michael Hagerty testified on CCEBA’s behalf before the South Carolina Public Service Commission (PSC). He delivered a clear message: the path to a reliable and affordable power system doesn’t require choosing between traditional and renewable resources—it demands both. Hagerty, whose work spans resource and transmission planning across the electric sector, pointed to Duke Energy’s 2023 Integrated Resource Plan (IRP), making the case that large-scale additions of solar photovoltaic (PV) and battery storage are essential components of a least-cost portfolio. And when paired with proactive transmission planning, they help keep customer bills down and the grid secure.
In the 2023 IRP, the preferred portfolio—P3 Fall Base—included 12,600 megawatts (MW) of solar and 5,100 MW of battery storage by 2035. These additions were selected because they can help meet future energy needs at the lowest cost and at the lowest risk to ratepayers. Hagerty noted that Duke’s IRP modeling placed an artificial cap on annual solar buildout based on assumptions about the utility’s ability to interconnect those resources. If these constraints were lifted, the model would in fact have selected even more solar.
Increasing battery storage would also help keep the lights on during periods of high demand. By 2035, battery storage is expected to provide 4,745 MW (in winter) and 10,441 MW (in summer) toward meeting Duke’s reserve margins. These resources are fast, flexible, and can respond to disturbances and peak load requirements in ways traditional power plants cannot—especially during emergencies.
Proactive Transmission Planning Lowers Costs and Increases Reliability
Hagerty’s testimony underscored the importance of coordinating transmission planning with resource planning. Currently, Duke Energy does not look at the future resource mix in conjunction with modeling for its planning studies, and transmission constraints limit how much new clean energy can be interconnected each year. The utility has begun to improve its approach with initiatives like the Red Zone Expansion Plan (RZEP) and the Multi-Value Strategic Transmission (MVST) process, but more work is needed. More proactive, scenario-based planning would create necessary headroom on the system in advance of interconnection requests, help foresee what the system will eventually need, and allow cost effective resources to quickly come online. Without these strategies, the system will remain bottlenecked and Duke will always have to play catch-up. That means higher costs, longer timelines, delays in serving new loads, and fewer clean energy options for customers.
Hagerty also recommended that Duke examine best practices from the Southern Power Pool (SPP) and Midcontinent Independent System Operator (MISO), where transmission planners use scenario planning, economic and policy driver analysis, and multi-value assessments to determine optimal long-term upgrades.These actions help ensure that transmission investments align with both reliability and affordability goals.
What Happens if We Ditch Carbon Goals?
Recent legislative proposals and talking points suggest that both North and South Carolina should abandon carbon reduction goals entirely and bet big on natural gas under the assumption that it will save customers money. But Duke Energy already ran this scenario as part of its IRP modeling—specifically to comply with a request from the South Carolina PSC, since South Carolina has no statutory carbon limits—and it didn’t hold up under scrutiny. In the “no carbon constraints” scenario, solar PV was reduced by 12 to 13 gigawatts (GW), and battery storage, wind, and nuclear were also scaled back or eliminated. Gas-fired capacity, however, increased by five to seven GW over the Company’s preferred portfolio.
On the cost front, the “no carbon” plan’s cost savings were less than one billion dollars through 2038 compared to the P3 Fall Base—a figure that is well within the margin of uncertainty for a 15-year forecast. In return, that plan would dramatically increase reliance on natural gas, leaving ratepayers vulnerable to fuel price volatility, potential pipeline capacity shortages, and future regulations.
Duke put it this way in its own filing:
The No Carbon Constraint scenario] “results in a PVRR [present value of revenue requirements] within $1B of the preferred portfolio through 2038, while failing to mitigate commodity price and future regulatory risk or capture the benefits of resource diversity, subjecting customers to over-reliance on natural gas supply and deliverability to the region, in addition to being non-compliant with applicable laws. For these reasons, this informational portfolio cannot be the most reasonable and prudent means of meeting the Companies’ resource planning requirements.”
(Duke Energy Carolinas IRP, Appendix C, p. 100)
In plain terms: you might save one billion dollars without additional clean energy resources—but if gas prices spike even once in the next 15 years, ratepayers could end up paying far more than that. Portfolios with more renewables, on the other hand, not only reduce carbon emissions, but also act as a hedge against price shocks. The South Carolina PSC eventually concluded that Duke Energy’s chosen plan with a portfolio of new gas, solar, wind and battery storage capacity was the most balanced, least-risk option, and rejected the “no carbon constraint” portfolio.
The Bottom Line: Reliable, Affordable Power Takes Balance
Hagerty’s testimony reinforces what Duke’s own modeling, the PSC’s final order, and years of experience have demonstrated: a diverse, balanced resource mix is a surefire way to deliver affordable and reliable power to the Carolinas. The choice isn’t between renewables and reliability—it’s between building for the future, or gambling on it. With comprehensive, coordinated planning, transparent stakeholder engagement, and smarter investments in grid-enhancing technologies, we can meet growing energy demand, protect customers from price shocks, and support a thriving economy.