Same Power: Flats vs. Hills

I've been experimenting with bikecalculator.com, an awesome resource for folks who like numbers. One question I had was "Is a hill, with the difficulty of the uphill and ease of the downhill, equivalent to a flat portion".

Short answer: No

Long answer: No. I was suprised. Take someone generating 150 watts, riding on the hoods over the course of a mile. On a 2% grade, it will take him 31 seconds longer to do a half mile up and half mile down over the time it would take him if it was a flat mile (3:28). If it was a 4% grade, it would take him 1:47 longer.

A note on grade: 4% seems relatively small but it is the grade of the steep roads most people know of. I used this site to calculate grade and google earth to look and distance and elevation.