A thermal energy storage (TES) system that uses an elemental material (e.g., elemental sulfur) as an energy storage material is disclosed. The energy storage material is separately stored from a heat transfer fluid. For example, the energy storage material can be sealed within one or more corrosion-resistant containers that are further contained within an outer shell. A heat transfer fluid flows through the shell via an inlet and an outlet, over and around the containers. A TES system may include an energy source that receives thermal energy intermittently, and a steam generator.
STATEMENT OF GOVERNMENT LICENSE RIGHTS
 This invention was made with Government support under Contract DE-AR0000140, awarded by the United States Department of Energy, Advanced Research Projects Administration--Energy. The Government has certain rights in the invention.