Since we're talking about energy consumption, you can get the same result without involving dozens of servers by typing this in your Unix terminal:

  $ units -v "15 TWh/year" "GW"
         15 TWh/year = 1.7111933 GW
         15 TWh/year = (1 / 0.58438752) GW

I've always suspected such a tool must exist in a typical *nix environment but never bothered to search for it. This is very helpful. Thanks for the simple example!

There's also an interactive mode if you leave out the positional arguments. That's my go-to CLI calculator, it knows enough arithmetic and the understanding of units is a nice bonus.

Wolfram Alpha did ok for me on my first try: http://www.wolframalpha.com/input/?i=15+TWh%2Fyr+in+GW

That might be why. I typed it out as 15 terawatt hours per year to gigawatts

This actually work as well: https://www.wolframalpha.com/input/?i=15+terawatthour+per+ye...