That's because there's not much load in that area. America's best wind power belt is north from the Texas panhandle up to Canada.[1] But there are no big cities in that region.
The US thus needs more long DC power lines. The technology is already in use in China. The Zhundong-Sichuan power line goes 2600km. It's a DC line at 1.1 megavolts carrying 10 gigawatts. That technology could easily carry power from the wind belt to the rest of the US.
Right, and places like Texas, Colorado, Oklahoma, and Montana are not included in the Midwest. The point isn't that the wind belt region makes up exactly 1/5 of the population, but that there are many people there that shouldn't be dismissed because they aren't in the most densely populated cities.
The wind farms in SW Minnesota/the eastern Dakotas/ NW Iowa (http://www.nrel.gov/gis/images/30m_US_Wind.jpg) are relatively close to the larger urban areas in the region and I suspect some of it might even feed into Chicago.
There's not much overlap between the wind belt and where people live. But there are many round farms in the wind belt. The unused corners of round farms would be good places for windmills. There's road access in place. Extra revenue for farmers. Won't bother the crops.
Collecting up the power and shipping it somewhere useful is a problem. That requires new high voltage transmission lines and collection at substations for conversion to DC and long distance transmission.
Agreed on the HVDC lines. They end up reducing the cost of electricity too, because they let us use all of the really cheap wind on the plains, and sun from the southwest.
This is of course expected, and not a knock on the achievement at all. Wind is in its early days, and growing quickly. There's only so much installed capacity, so it's going to reach it's peak percentage of the energy mix when the demand is lowest. And it will only do that if its the cheapest available energy.
Also, wind tends to be higher at night-time, which makes them a good complement to solar. Getting to >50% is something that many many many people have doubted is possible at all.
The US thus needs more long DC power lines. The technology is already in use in China. The Zhundong-Sichuan power line goes 2600km. It's a DC line at 1.1 megavolts carrying 10 gigawatts. That technology could easily carry power from the wind belt to the rest of the US.
[1] http://www.nrel.gov/gis/images/80m_wind/USwind300dpe4-11.jpg