Earth's internal heat budget

Earth's internal heat budget is about heat that comes from the Earth itself, not heat from the Sun. 
The flow of heat from Earth's interior to the surface is estimated at 47±2 terawatts (TW). It comes from two main sources in roughly equal amounts. There is the "radiogenic heat" produced by the radioactive decay of isotopes in the mantle and crust. Secondly, there is the "primordial heat" left over from the formation of Earth.
As many people know, the deeper down you go, the hotter the Earth gets. Mine shafts are a good example of this.
Radiogenic heat.
This is still being produced. but its amount reduces very slowly as time passes. Remember, these radioactive elements are produced in supernovae, and are quite different from the Sun, which is mostly hydrogen. The planets are completely different from the Sun, historically and in their make-up.
Primordial heat.
Primordial heat is the heat lost by the Earth as it continues to cool from its original formation, in contrast to its still actively-produced radiogenic heat. 
The Earth core's heat flow—heat leaving the core and flowing into the overlying mantle is thought to be due to primordial heat. It is estimated as 5–15 TW.