An energy conversion system may include a stationary structure, a rotatable structure configured to rotate relative to the stationary structure, wherein the rotatable structure defines an axis of rotation. The system may further include at least one blade member mounted to and extending radially outward from the rotatable structure, the at least one blade member being configured to interact with fluid currents flowing in a direction substantially parallel to the axis of rotation to cause the rotatable structure to rotate about the axis of rotation, and at least one bearing mechanism disposed to provide at least one of a radial and axial bearing between the rotatable structure and the stationary structure as the rotatable structure rotates about the stationary structure. The system may be configured to convert rotation of the rotatable structure to at least one of electricity and hydrogen production.