itch.io

When you load the generator into the rover for the first time, the log tells you that it fills the compartment. If you try to install the generator, it warns you that it's permanent and that it'll prevent you installing other bulky equipment.

That being said, I do agree, which is why this is listed as a known issue.

"There are one or two places where actions which the player is aware of and may have performed before aren't available due to other actions that you have/haven't performed, and it might not be obvious why unless you've read and remember all the story messages."

Anyway, yeah, not obvious.