The sun's energy drives various processes on earth. One of these processes is photosynthesis in plants whereby light energy is converted into chemical energy by forming carbohydrates from carbon dioxide plus water, which is a process which usually gives off oxygen which animals need to breathe. Another process driven by the sun's energy could be evaporation of water into the air to form water vapour and clouds which then precipitate when cooled off over mountains so is involved in the water cycle.
It is a fact that nuclear energy is converted into thermal energy in the core of a nuclear reactor. This is because it is part of a power plant fission act, where nuclear energy heats up water in a nearby vicinity.
