Hey, we're of one mind on this one, RedSunofKrypton. I too get a charge out of trying to make S.F. and comics work in the real world. It reduces that 'suspension of disbelief' factor considerably if we can at least theoretically have a way for these characters and situations really exist.
Good call on solar neutrinos, though it must be noted that this is a partial fix at best. The proportion of solar energy in the neutrinos is only 5% or 1/20th of the total solar energy received. While that power level would remain pretty constant even at nighttime, it does considerably reduce the power available. Thus, it makes it even more necessary for solar energy to catalyze a higher-order energy process of some sort since even full solar power is insufficient to even power mobile plants let alone a superhuman being.
For feats like OWAW where Superman moves Warworld -- esp. against its own world moving engines empowered by Imperiex energies! -- it would take power levels on the par with hundreds of galaxies to achieve which far outbalance the measly power of Earth's Sun by a factor of hundreds of billions.
We could fall back on established Genesis continuity and suggest that Superman's power is more truly somehow connected to the Source, the ultimate origin of everything. This is not entirely unreasonable. He not only produces mass/energy in excess of what he evidently takes in, but he can produce assymmetric matter from that energy in his body mass without a proportionate amount of antimatter. The only known mechanisms that could do this are the Big Bang itself and the theoretical assymmetry possible at the quantum scale for gravitational collapse in black holes and singularities. Hey, those sound suspiciously like what the Source resembles.