Time Machine Problems

[Will_32]

Ok, I'm having some very frustrating and reoccurring issues with Time Machine. I have an early 2015 13" rMBP base model that I just got at the end of July brand new for college and my external HD that I'm backing up my computer on is a Seagate Slim Plus 1TB model. At night I plug my computer in to charge and I plug in my external HD to backup overnight. I have power nap enabled so that I can close my computer and it will (theoretically) still backup. But when I wake up in the morning and check Time Machine, it says it only performed one backup while it was sleeping and that was after the first hour that I put the computer to sleep. Is this what is supposed to happen? Or is it supposed to backup every hour? Because from my understanding of Time Machine, its supposed to backup every hour. Also, am I misunderstanding Power Nap? Does power nap only work when the laptop screen is open and sleeping? Anybody who could help me out that would be much appreciated!