What is the most efficient process of making electricity from heat?

Question

In comparison, how efficient is the magnetism-to-electricity ratio?

Nuclear is a process used to CREATE heat. MY question is about the most efficient process of converting existing heat to electricity.

Answer 1

The "Stirling engine" is theoretically the most efficient heat engine possible, and it can be very closely approached in practice.

The mechanical power, which the engine produces from its heat source, can be made into electricity as efficiently as it could from any other engine.

Answer 2

The steam turbine is the most efficient machine we have; the best ones approach 50% efficiency. Theoretical efficiency depends on the ratio of temperature drop through the turbine divided by the inlet temperature. The practical limitations are the strength of the materials at high temperature, and the unavoidable reality that the exhaust must be significantly hotter than ambient.

The mechanical efficiency of the generators (is that what you mean by "magnetism-to-electricity ratio"?) can approach 99% for large systems.

Answer 3

Probably nuclear.