The sun produces energy by converting gravitational potential energy into radiation via quantum processes in the nucleus of the atoms.
Since the mass of the sun and it's temperature are not quite enough to generate nuclear FUSION on their own, quantum tunneling is the primary process by which nuclear fusion occurs in our sun, SOL. FISSION also occurs as a result of this fusion.
Additionally, gravitational potential energy is also the reason that supernovae are so bright. Cool!
