Steady Heat, Flexible Power: Flexibility by Proxy in Nuclear-Thermal Energy Storage Systems

Nicolas Trosino, John E. Parsons, Ruaridh Macdonald, Charles Forsberg, and Yannick Perez

May 2026

We use a capacity expansion and dispatch model to study the value of integrating a Thermal Energy Storage (TES) system into a fusion power plant. Storage enables the plant to run the fusion reactor at very high capacity factors, while generation of electricity fluctuates significantly. TES enables penetration of fusion even at relatively high capital costs. Our model optimally sizes both the power and the energy capacity of the TES, and we find that it chooses very long durations. The TES has a lower turnover than grid batteries, but a higher utilization. The TES captures a higher spread on its turnovers than grid batteries, and its operating profitability is more concentrated in a fewer number of hours.

Keywords: Thermal Energy Storage, Capacity Expansion and Dispatch Modeling, Electric System Flexibility, Next-generation Nuclear Energy, Fusion Energy, Cost Minimization.