I think they got the measurements and units wrong. The article says that the power would not be generated like a windmill but from a wire. Then it says that the wire would be relatively short and the sail impossibly huge. Chances are the article got it wrong and the reality is that a small sail would be used to tow out a long 5,000 mile spool of wire. As the solarwind particles cross over the wire it will create the electricity just like passing a wire through a magnetic field creates electricity. I would like to read the original source rather than this typical example of science journalism.
"Ninety percent of baseball is half mental." -- Yogi Berra