as with most fluff articles.. no hard numbers.
Its easy to say x cost y with wind and make it look good if you take installed CAPACITY / COST
The problem is that well... CAPACITY / COST = LIE
GENERATION / COST = TRUE COST
Example
http://en.wikipedia.org/wiki/Wind_power_in_Texas
Texas has 12355 MW-Capacity so at max cap = 148260 (2013) per year (Cap x 12 months)
actual generation 35874 (2013)
meaning that the Generation is 112386 MW per year Less than Capacity.
if my math is correct that means a Capacity is 3.13x generation.
and is not scalable nor on demand.
The last part of your phrase is absolutely crucial for stability on the modern grid. Generating assets have to be dispatchable, and wind and solar are not. You either have them or you don't. And demand-side management isn't going to cut it in a large, geographically dispersed, modern industrialized country like the US and others.
Keeping the modern electric grid running reliably and stable over an incredibly dynamic range of loads and generating sources is an amazingly complex and sophisticated process. It is a true miracle of state-of-the-art technology that few understand and even fewer appreciate. It delivers a vital product to almost everyone who wants and needs it, literally at the flip of a switch. And when large numbers of people are forced to do without it for very long, even as short as a day, it makes headlines across the country.