Why do you think prices will go down? That's not at all what's been happening lately or the consensus estimate by analysts.
Coupled with increasing efficiency that reduces demand, and energy prices should go down, not up. (Adjusting for inflation.)
In comparison inflation has raised prices by 19% over that same period [1]
I think it's also not obvious that the natural gas glut is a long term trend. It's a complex issue for sure, but here are some perspectives: http://www.businessinsider.com/arthur-berman-shale-is-magica...
[0] http://www.eia.gov/electricity/data/browser/#/topic/7?geo=g&...