Solar power seems to fulfill those conditions, but it is not constant and requires a huge land mass to collect energy, taking that land out of food and other production.  It also requires very extensive manufacturing of the equipment used.

Solving the limits to be overcome in the future for both sources - more efficient solar panels and regenerating nuclear "waste" in used uranium rods - is likely to happen, but re-using the expended rods in nuclear power is more efficient than replacing solar panels continuously.

But all in all, the key is in eliminating the internal combustion engine as quickly as we can.

Des Emery