This number only talks about the potential energy available from wind, not how practical it is to produce it. For example, the US uses about 20% of the world's total energy (see
https://en.wikipedia.org/wiki/World_energy_consumption ). Scientists involved in another study of wind power (see
http://spectrum.ieee.org/green-tech/wind/little-limit-to-the-amount-of-wind-energy ) say that it would require 4 million windmills to produce half of the planet's current total energy requirements. That means the US would need about 800,000 large windmills to produce half of its total power from wind. In 2009, the US installed 5700 windmills (see
http://www.awea.org/issues/supply_chain/Anatomy-of-a-Wind-Turbine.cfm ), so at that rate it would take 140 years to build the windmills needed to replace half the US energy requirements *today*.
We could build windmills faster, but there are other restrictions. Building such a large number of windmills requires enormous amounts of concrete (1.7 million cubic yards of concrete for the 5700 windmills built in 2009, enough for more than 7,630 miles of 4-foot wide sidewalk), rebar, as well as other materials. And we have to build an electric grid that could collect the electricity from remote windmills and deliver it to cities.
This is not to say it's impossible. The US currently has around 540,000 active oil wells, and each of them is roughly the same investment as one windmill ($4 million for an oil well vs. $3 to $3.5 million for a windmill, see
http://www.petrostrategies.org/Learning_Center/drilling_operations.htm and
http://www.windustry.org/resources/how-much-do-wind-turbines-cost ). But it took us 150 years to build that kind of an oil infrastructure, even though there were enormous rewards for companies that did so. Building 800,000 windmills would require well over $2 trillion, plus the costs of building the associated electric infrastructure. We would also need to come up with some kind of energy storage system (completely unknown at this point) for when the wind isn't blowing hard enough to meet our immediate needs, as well as convert most of our cars to electric. It's not something that's going to happen overnight.
