I haven't done any detailed calculations but from what I remember it isn't worth it - you have to use such large conductors to compensate for voltage drop it becomes too costly. I faintly remember an eco-nut who built his own house off-grid in the late 90s and ran 24 V lighting (or maybe it was 12 V) throughout a rather average single-family home. He used 6 mm2 wire! Don't ask me how he connected that to light switches!
