Shen's E should cost less energy as you rank it up, 180 is too much in late game extended fights.
I find it strange that even though Shen has 400 energy and his skills cost over twice as much as some other champions, he still only gets the same amount of energy regen as other champions. With that said the fact that his Q will return more energy in total than it costs (assuming you get all 3 procs off) makes it's somewhat manageable, but once you get around 20% CDR I find myself running out of energy despite my best efforts to keep an eye on it.
Since his late game is already his strong point I wouldn't want to buff it TOO much, but bringing his E down to around 140 would be enough to make it more manageable. Either that or give him more base energy regen, or bump the energy return on his Q & E by 10.
Also I know most people think Shen is super weak right now, but I've actually had a ton of success with him in the Jungle... it feels like that's where he belongs now.