The effectiveness of heat transfer to and from a thermal energy storage medium, for example a phase change medium, is enhanced by the inclusion of thermally-conductive elements within the thermal energy storage medium. The thermally-conductive elements may be filler shapes placed in a self-supporting stacking arrangement, which may be a random stacking arrangement. The effective thermal conductivity of the matrix that includes the thermal energy storage medium and the thermally-conductive elements is higher than the thermal conductivity of the thermal energy storage medium itself. Other thermally-conductive elements may be used, for example thermally-conductive sheets.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
 This invention was made with government support under contract GO18156 awarded by the United States Department of Energy. The Government of the United States of America may have certain rights in the invention.