Yesterday saw DC Comics reveal Superman's new power: Super Flare.
Now Superman #38 is out today revealing the full story.
I'm actually surprised JMS didn't think of this, but as a result of Superman using his Super Flare power, his cells are completely depleted of solar energy.
It takes 24 hours for his cells to recharge, which leaves Superman completely powerless aka a regular ol' human.
More spoilers from the issue include the Superman's heat vision was a precursor to the new Super Flare ability; that using the Super Flare destroyed Superman's New 52 costume, so Batman and Alfred create the new one, and Superman reveals his secret identity to Jimmy Olsen (via Newsarama).