Hello, and thanks for reaching out!
Once you have restored power to the plant, in order to open the loading bay doors, you'll need to use the panel in Master Control, which is actually the small grey building straight south of the loading bay doors. There's a small "path" of cobblestones leading off the main road that will help you find the doorway (see the picture attached). I apologize for the lack of clarity, and hope that you are enjoying your time with VoltAge:Genesis.
