Welcome back.
Energy/month is just that, energy collected for the current month. The relevance being tied to clan monthly energy and the associated end-of-month rankings for trophies. Just energy would be the lifelong total sum one has collected on the bot, but this will reset to 0 if you leave your clan, as will the monthly energy if any was had.
The energy generation is currently a range of 20-60 per hour. Things that affect the amount include level, total wins, ratio, and the offset representing how much energy you've taken in the current month vs generated which is shown in parenthesis next to monthly energy. The upper cap of 60 EPH (energy per hour) generated used to go a lot higher, so this is in some ways a remnant of the system in an older state.
It's very trivial to hit 60 EPH if you aren't an extremely low level, I think it's near impossible to hit the cap without being at least level 30 or upper 20's. But once you're closer to level 60 you will get the full EPH just from holding a half decent ratio. You can take a look at the monthly HoF or look in random clan rosters to get a feel for how much each thing affects it.
The only main thing that's changed (currently anyway, hope it gets removed) is that each day we progress into the month, the amount of energy that gets taken/given from fights goes up by 5%. Day 1 starts at +0% though, so as of now on day 11 in the month, we're at a +50% energy rate shown by the Monthly Crescendo buff in the top left.