Harnessed Lightning

If a spell or ability with one or more targets states that you "may pay" some amount of energy , and each permanent that it targets has become an illegal target, the spell or ability won't resolve. You can't pay any energy even if you want to.

Energy counters aren't mana. They don't go away as steps, phases, and turns end, and effects that add mana "of any type" can't give you energy counters.

Keep track of how many energy counters each player has. Potential ways to track this include writing theme down on paper or using dice, but any method that is clear and mutually agreeable is fine. (At higher levels of tournament play, dice may not be allowed for tracking counters that players have.)