The difference between heat and thermal energy is that thermal energy is not in the process of being transferred; it is not in transit, but remains as part of the internal energy of the system; heat, on the other hand, is energy in transit, i.e. energy in the process of being transferred from a hotter system towards another colder system (Engel & Reid. 2006. Pp.16 and 17). In summary, the thermal energy is energy within the system; heat is energy outside the system.
The thermal energy is continuously converted into gravitational energy and vice verse (Maoz. 2007. Page 48). For example, when we lift an object at rest on the floor, the thermal energy of our body is transferred to the object lifted. As we lift the object, our thermal energy is stored as gravitational energy in the gravity field. There, the energy will remain until the object acquires movement.
Consequently, the thermal energy in the gravity field is always negative, and therefore the gravity field constitutes a stable deposit of thermal energy. (Guth. 1999. Pp. 335-339)
Thermal energy units are Watts*second (W*s), Joules (J) or calories (cal). Notice the difference between the heat units (W, J/s, calories/s) and the thermal energy units (W*s, J, calories).
Suplee, Curt. The Plasma Universe. 2009. Cambridge University Press, New York. Pp. 27-39.
Guth, Alan H. The Inflationary Universe: The Quest for a New Theory of Cosmic Origins. Perseus Books Group, 1999, New York, New York. Pp. 29-31.
Van Ness, Hendrick C. Understanding Thermodynamics. PAGE 17.
Thomas Engel and Philip Reid. Thermodynamics, Statistical, Thermodynamics & Kinetics. 2006. Pearson Education, Inc. Pp. 13, 16, 355.
Maoz, Dan. Astrophysics. 2007. Princeton University Press. New Jersey. Pp. 48-49.
Potter, Merle C. and Somerton, Craig W. Thermodynamics for Engineers. Mc Graw-Hill. 1993. PAGE 40.
Pitts, Donald and Sissom, Leighton. Heat Transfer. 1998. McGraw-Hill.
Sutton, David B., Harmon, N. Paul. Ecology: Selected Concepts. 2000. John Wiley & Sons, Inc. New York. Pp. 49-57.
Wilson, Jerry D. College Physics-2nd Edition; Prentice Hall Inc. 1994.