The ultimate source of energy is the sun. It sustains virtually every aspect of life on Earth. Other sources of energy, both renewable and nonrenewable, either directly or indirectly depend on the sun.
Fossil fuels, such as gas, oil and coal, are transformed forms of animal and plants which were once sustained by the sun's energy. Biomass is a by-product of photosynthesis, which is a process that heavily relies on the sun. Hydropower relies on the water cycle which also depends on solar radiation. Wave power, tidal power and wind energy all rely on the sun in one way or another. The continuous thermo-nuclear reaction taking place in the sun produces large quantities of energy in the form of heat and light.