Generating energy from the difference between extremely hot and slightly hot is cheap and efficient using turbines. Going from slightly hot to cold, as in the

Generating energy from the difference between extremely hot and slightly hot is cheap and efficient using turbines. Going from slightly hot to cold, as in the case of geothermal and capturing residual heat in the stack of a natural gas plant, is thermodynamically inefficient and quite expensive. Since fusion energy is extremely hot, it is efficient. Other sources of "extremely hot" include: combustion (typically from fossil fuels) and solar thermal.