The only energy source that is not in any way related to the Sun is:

Concept

Energy sources can be classified by the physical process that ultimately drives them.

Solar heating powers the water cycle and atmospheric circulation, while ocean tides arise from gravitational interactions and geothermal energy comes from heat within Earth.

Application

• Hydropower follows the water cycle: solar heating causes evaporation, which leads to precipitation and replenishes flowing water.

• Wind follows atmospheric circulation: unequal solar heating creates pressure differences that move air.

• Tidal energy follows gravitational forcing: the Moon is the dominant influence, and the Sun also contributes to ocean tides.

• Geothermal energy follows Earth’s internal heat, chiefly residual heat from planetary formation and heat released by radioactive decay.

Cross-check and result

Hydro, wind, and tidal energy each have a solar link. Geothermal energy is driven by heat within Earth, so Geothermal is the only offered source not related to the Sun.