Seems that in a single swipe Amazon would more than double the total USA’s wind generation capacity when this goes into production in 2017. A really fantastic achievement (or am I missing something in the data?).
Total US wind energy in 2015: 73,992 megawatts [1]
Amazon’s Scurry County Texas capacity: 1 million megawatts
Nothing strange at all about MWh/year. A MWh is just 1000 kWh, which is a very standard unit of energy.
With wind farms it makes more sense to talk about it's production in MWh rather than it's capacity in MW. The actual energy produced by a 253 MW array will vary significantly based on where it is sited, etc.
The watt (and hence kW and MW) are measurements of power, not energy. kWh (and MWh) are common, internationally accepted units for measuring energy.
Wind (and solar) energy production tends to vary seasonally, so it makes sense to use a year rather than some other time unit when discussing how much energy these things can produce.
That's one million megawatt hours. Watt-hours are the most confusing unit ever, and measure energy, not power. (A watt-hour is the amount of energy produced by one watt for an hour.)
1e6 MW hours = 3.6e15 joules. The power plant generates this over a year, so that 3.6e15 joules / year = 114 MW on average.
They imply 45 cap factor with the 1,000,000 MWh which is expected for Scurry Co and the newer turbines. 1000000/(253*8760) ...rounded ignoring leap year.
Total US wind energy in 2015: 73,992 megawatts [1]
Amazon’s Scurry County Texas capacity: 1 million megawatts
[1] http://www.greentechmedia.com/articles/read/7-Charts-That-Sh...
Edit..
From the replies it seems it would be at best ~0.3% of total wind generation capacity in USA.