Hmmm - I've no good evaluation of this page's accuracy, but the first graph here says a 90kg bike/rider needs 250W to maintain 20kmh up only a 4% gradient hill. That's not very "steep". 20kmh up a 10% grade (which _is_ a "steep" hill) requires ~600W.

http://theclimbingcyclist.com/gradients-and-cycling-how-much...