I didn't vote because my preferred response isn't available - both. Why rely on a single power source? You need redundancy on a long term base far more than under other space flight circumstances. As for the day/night argument and solar, if you have sufficient solar power to split water into hydrogen and oxygen, you have fuel and a means of recycling water. I would think for safety reasons, at least three power sources should be used such as nuclear, solar and stored energy such as fuel cells, batteries or O2/H2 gas. We should finally look at recycling the air using plants to get O2 from CO2. I can't see how a moon base would be sustainable unless they can make O2 from CO2. Plants can also be used for food. You really need to establish a mini-ecosystem.