An interesting source for a perpetual supply of electricity is now being discussed:
Physicists at Yale University have made the first definitive measurements of “persistent current,” a small but perpetual electric current that flows naturally through tiny rings of metal wire even without an external power source.(Science Daily). Whether or not this technology could help to meet the Tenet 3(b) necessity of developing space craft that will travel exceedingly fast, it does show that there are sources of power we have not explored yet.
The counterintuitive current is the result of a quantum mechanical effect that influences how electrons travel through metals, and arises from the same kind of motion that allows the electrons inside an atom to orbit the nucleus forever. “These are ordinary, non-superconducting metal rings, which we typically think of as resistors,” Harris said. “Yet these currents will flow forever, even in the absence of an applied voltage.”