U.S. Department of Energy

Innovative Thermal Energy Storage for Baseload Solar Power Generation

University of South Florida logo Illustration of a clear cylinder filled with yellow balls.

Proposed TES system with packed-bed configuration.

The University of South Florida, under the Baseload CSP FOA, is researching and developing a thermal energy storage system based on encapsulated phase change materials (PCM) that can meet the utility-scale baseload CSP plant requirements at significantly lower system costs.


Existing thermal energy storage (TES) concepts cost about $27 per kilowatt hour thermal (kWht). The University of South Florida proposes a TES system concept that can reduce the cost to as low as $3.54/kWht to make it competitive with fossil fuels and allow for a capacity factor increase to 75% or greater. Specific objectives include:

  • Developing an encapsulated PCM for thermal energy storage in the temperature range of 300°–450°C with a cyclic performance (charge/discharge heat transfer) capability of at least 1,000 cycles
  • Designing a one-tank storage system using spherical (or other shape) PCM capsules immersed in synthetic oil with an integrated heat exchanger for charge/discharge testing.


The University of South Florida's project employs a latent heat storage system that uses a phase change material (salt) encapsulated by a shell (metal) to overcome the barrier of low thermal conductivity. Capsules will be placed in direct contact with the heat transfer fluid to achieve the highest heat transfer rates. There are two major challenges to the success of this concept:

  • Forming porous macrospheres of the PCM material at optimum size and pore volume to account for the volume change from solid to liquid phase
  • Encapsulating the macrospheres of PCM in a higher melting temperature material, preferably a metal, at low cost.

The research team is developing a two-dimensional numerical model to look at diffusion-natural, convection controlled heat transfer in an encapsulated sphere.

Publications, Patents, and Awards

  • S. Kuravi, J. Trahan, M.M. Rahman, D.Y. Goswami, and E.K. Stefanakos, "Analysis of Transient Heat Transfer in a Thermal Energy Storage Module for Baseload Solar Power," Paper No. IMECE2010-40773, in Proceedings of the ASME 2010 International Mechanical Engineering Congress & Exposition, Vancouver, BC, Canada, November 12-18, 2010, ISBN 978-0-7918-3891-4.
  • A. Ramos, C.A. Asselineau, J. Gonzalez-Aguilar, M.M. Rahman, M. Romero, D.Y. Goswami, and E.K. Stefanakos, "Transient Numerical Analysis of PCM-Contained Spherical Capsules for Heat Storage in Concentrating Solar Power Plants," in Proceedings of the 12th International Conference on Energy Storage (Innostock 2012), Lleida, Spain, May 16-19, 2012.
  • J. Trahan, S. Kuravi, D.Y. Goswami, M.M. Rahman, E.K. Stefanakos, "Thermal Characterization of High Temperature Inorganic Phase Change Materials for Thermal Energy Storage Applications," Paper No. ESFuelCell2012-91475, in Proceedings of the ASME 2012 6th International Conference of Energy Sustainability, San Diego, CA, July 23-26, 2012.
  • S. Pendyala, P. Sridharan, S. Kuravi, C.K. Jotshi, M.K. Ram, M. Rahman, E.K. Stefanakos, and D.Y. Goswami, "Macroencapsulation of Sodium Nitrate for Thermal Energy Storage in Solar Thermal Power," Paper No. ESFuelCell2012-91447, in Proceedings of the ASME 2012 6th International Conference of Energy Sustainability, San Diego, CA, July 23-26, 2012.
  • A. Ramos, M.M. Rahman, D.Y. Goswami, and E.K. Stefanakos, "Parametric Investigation of the Melting and Solidification Process in an Encapsulated Spherical Container," Paper No. ESFuelCell2012-91435, in Proceedings of the ASME 2012 6th International Conference of Energy Sustainability, San Diego, CA, July 23-26, 2012.
SunShot logo

Learn about other DOE competitive awards for concentrating solar power research that are in progress.