A robotic rover can afford to shut down during the night but humans aren't able to do that. So you need to average out the power generated over the day night cycle and add mass for enough batteries to store daytime power for use at night. Last I did the calculations that roughly doubled the weight. So more like a factor of 8 than 2. But still, power generation won't be the majority of the mission weight so it's not a slam dunk.

On the moon it would be. Half-month long nights mean you'd need a lot more batteries if you're making a permanent settlement and aren't at one of those spots on the south pole where you can always see the sun traveling along the horizon.

EDIT:

I think solar panels have gotten a lot lighter since the ISS went up and when I last did the math nuclear and solar were a lot closer.