Maybe some survival elements then, like food? Another random idea is being able to leave your tank if it runs out of energy. Seeing as how the area seems to be a desert, you could have limited time as a person before you die(food stored in tank to heal you?), but maybe if you're lucky, enough to fetch energy and bring it back.(probably not a full refill though) Would give you a use for the old human sprite, too
Could also make crossing cracked tiles easier, a person wouldn't break it, so could run across and drag a crystal to the tank.
Also, have the charging station have a "short range teleport" or something, once you collect enough crystals you can go to a new area. That way you can continue gameplay, maybe eventually go to different more unique area types, looking for some "oasis"/"paradise", which could be a goal.
If these are varying from your goals for the game, what are they? (if you have any, I know this was a random weekend project originally)