You know those little blue potions we have next to our health that will restore our mana and health fully? What if we had one for potions? We wouldn't be able to fill it with gold or crowns, but our own energy! It could have a cap, let's say 200, and if you don't use all your energy you can transfer it into this potion.
Example: I just finished gardening and I have 159 energy left, I click the button and, poof! I have 0 energy but a 159/200 energy potion. When I finish gardening the next day, I have 10 energy left but now I want to train my pet. Instead of spending crowns I click my potion and, poof! Now I have 169 energy and 0/200 potion.
Yes, I think there should be a way to generate/preserve energy somehow. I think we should get our energy filled when we level up in gardening (like we do with health and mana when leveling up in PVE). Or maybe when reaching a new fishing level should fill it as well?
I like your idea - a 'mini bank' for unused energy.
Honestly, I love this idea, probably due to the simple fact that this is incredibly helpful and useful tool, but I also believe it makes things too easy. I can't speak on behalf of everyone, but I harvest couch potatoes in order to train my pet, because they offer mega snacks after the final harvest. To put things into perspective, if you were able to do this with mega snacks or even level 8 snacks which can be easily purchased, the amount you could train your pet would be simply too much. You are expected to put time and effort into your pet and garden, which of course makes it all the more rewarding when you get what you want. Now I know it may seem like a pretty minor boost of energy, but do the math and you will be surprised how big the impact would be.