WindWings on cargo ships - How to they work?

I've just seen and read the 'Big Picture' feature in the latest E+T Magazine about the cargo ship fitted with WindWings in a bid to cut emissions (article on E+T digital below) 


I'm intrigued as to how they work, or more precisely, what happens to them in really stormy weather? With normal canvas sails they're taken in during storms but these look like pretty solid objects? So if there's high/storm winds around, how do  they prevent the ship from swaying or rolling too much?  

Are they not as solid as they look and perhaps fold and collapse downwards?