From a presentation by Michael Vickerman to the Wisconsin Association of Energy Engineers, April 29, 2009:

Why Promote Windpower?
Clean = Environmental
Non-depleting = Energy Security
Fixed Price = Risk Management
Creates Wealth = Economic Development
Scalable to Utilities = Practicality

The current Renewable Energy Standard (RES) will yield an additional ~4.2 billion kWh/yr of qualifying renewable electricity by 2015, assuming no load growth.

Assuming that windpower generates 90% of that quantity, about 1,600 MW of wind capacity must come on line between 2004 and 2015 to satisfy the RES.