Efficiency was measured by dividing each state’s Gross Domestic Product (GDP) (total value of all goods and services produced) by the kilowatt hours of electricity it consumed. That’s basically how much money a state could put into the economy for each unit of energy consumed.
Nice stat, but I’d bet if these states made more money per unit of energy, their lifestyle would see more spending and with it, more energy. That would reduce the “efficiency”.
However, the information is still neat to look at how widely states vary for how much they make per unit of energy spent.
New York was at the top with $7.18 for each kilowatt hour of electricity (a 15W compact fluorescent light burning for 66 hours 40 minutes, 66.7 hrs), while Mississippi was at the bottom, by far, at just over $3 per kilowatt hour.
See how other states did in comparison with this really cool interactive map!
Sources:
Rocky Mountain Institute (original source)
Yahoo! Green for additional statistical comparisons for context