[srean]

Nitpick on nitpick -- you absolutely can convert heat energy into electric energy. A dynamo on a heat engine does exactly that. What suffices is temperature differential.

It is a terrible analogy, a modern physicist would prefer being caught dead rather than using it, but one can think of heat as a liquid (traditionally called caloric ) stored in a vessel. Temperature is the level of the liquid. For flow you need another vessel where the level is low, that would allow flow of heat from a vessel with higher level to a lower one and one can then convert that flow into power of a form one desires. Its possible to go in the opposite direction also, that's called a heat pump. Charge and voltage would be another (incorrect) way of thinking about heat and temperature.