[vdondeti]

Well, it depends on how far back you want to go. All elements come from nuclear reactions in suns/stars which occur partly due to gravity. Some elements are unstable making them radioactive, some of which we use for nuclear fission. Big chunks of stars form planets and the associated geothermal energy. So, solar reactions and gravity account for all energy either directly or indirectly. Gravity is also the cause of tidal energy.

[jhales]

Those don't count as we can't access them directly. The idea with solar is we can access it directly, but we are using indirect methods.