A direct current power transmission system comprising: a first plurality of series connected power collection systems; and at least one superconducting DC conductor coupled to said first plurality of series connected power collection systems and configured to transmit power generated by said first plurality of power collection systems to a remote load; wherein each power collection system of said first plurality of series connected power collection systems comprises a power source and an alternating current to DC converter, and wherein said AC to DC converters are controlled to output a substantially constant current to said at least one superconducting DC conductor; and further comprising a superconducting direct current conductor connector; and wherein the first plurality of power collection systems is coupled to the superconducting DC conductor connector by a first conductor and at least a second plurality of power collection systems is coupled to connector by a second conductor; and wherein superconducting DC conductor connector is coupled to at least one high temperature superconducting DC conductor for transmission of the power generated by systems (12, 14) to a remote location and wherein superconducting DC conductor connector couples the conductors (32, 34) to superconducting DC conductor; and wherein the at least one superconducting DC conductor is included within a superconducting DC cable that includes a plurality of electrically isolated superconducting DC conductors; and wherein superconducting DC cable includes a first set of conductors and a second set of conductors wherein conductors in the first set of conductors are coupled to the power collection systems (12, 14), and configured to transmit power to a remote AC grid and conductors in the second set of conductors are a return path between the AC grid and the power collection systems (12, 14); and wherein the power transmission system is configured such that power is transmitted at a substantially constant current and wherein the superconducting DC cable is current optimized, so that currents within each sub-cable of said first and second set of conductors and are controlled to be substantially constant and identical at all times. a first plurality of series connected power collection systems; and at least one superconducting DC conductor coupled to said first plurality of series connected power collection systems and configured to transmit power generated by said first plurality of power collection systems to a remote load; wherein each power collection system of said first plurality of series connected power collection systems comprises a power source and an alternating current to DC converter, and wherein said AC to DC converters are controlled to output a substantially constant current to said at least one superconducting DC conductor; and further comprising a superconducting direct current conductor connector; and wherein the first plurality of power collection systems is coupled to the superconducting DC conductor connector by a first conductor and at least a second plurality of power collection systems is coupled to connector by a second conductor; and wherein superconducting DC conductor connector is coupled to at least one high temperature superconducting DC conductor for transmission of the power generated by systems (12, 14) to a remote location and wherein superconducting DC conductor connector couples the conductors (32, 34) to superconducting DC conductor; and wherein the at least one superconducting DC conductor is included within a superconducting DC cable that includes a plurality of electrically isolated superconducting DC conductors; and wherein superconducting DC cable includes a first set of conductors and a second set of conductors wherein conductors in the first set of conductors are coupled to the power collection systems (12, 14), and configured to transmit power to a remote AC grid and conductors in the second set of conductors are a return path between the AC grid and the power collection systems (12, 14); and wherein the power transmission system is configured such that power is transmitted at a substantially constant current and wherein the superconducting DC cable is current optimized, so that currents within each sub-cable of said first and second set of conductors and are controlled to be substantially constant and identical at all times.