Sure, but if humans are going into deep space (beyond Mars in this case) then we're talking about nuclear propulsion at least which means you've got lots of power.

When people designing real spaceships say "deep space" they mean "beyond Earth orbit", but usually not past Mars.

In sci-fi deep space, yes, you'd have next to no solar power. (In fact, it's minimally useful in the solar system past Jupiter.) But if you can get there at all, you're probably not worried about that.