The conversion of kinetic to potential and back to kinetic energy is a form of energy storage, but not creation.
Harnessing gravity could occur in the form of the "slingshot" orbits, where a spacecraft steals a small amount of the stored orbital energy of the moon or planet from it's parent plant or sun, but due to the relative masses and speeds the impact is real, but practically negligible - steal too much energy from the orbiting body and and there will be a noticeable impact to the orbit.
Harnessing gravity could occur in the form of the "slingshot" orbits, where a spacecraft steals a small amount of the stored orbital energy of the moon or planet from it's parent plant or sun, but due to the relative masses and speeds the impact is real, but practically negligible - steal too much energy from the orbiting body and and there will be a noticeable impact to the orbit.