The Slug lacks solar panels and takes its power from a nuclear generator. This allows the ship to stay powered, but still narrow enough to fit through high security docking bay doors. This narrow profile means it can dock at stations where larger ships cannot fit.
A big thanks goes to CommanderOz who created the SVG Station Planner Kit for Space Agency. As well as Benoit13 and ISAAC who contributed to the kit. The kit made it easy to quickly try out different arrangements of modules to see how they looked without actually having to build it in the game. If you are designing stations or ships, I highly recommend you try it out.