Washington Post: With great fanfare, an Arizona-based energy company signed a preliminary agreement with China last fall to build the world’s largest solar-power plant in the Mongolian desert. The deal was hailed as the first major example of the United States and China cooperating on a big-ticket energy project, and the largest foray by a U.S. company into Asia’s fast-growing alternative- energy market. The agreement became a centerpiece achievement of President Obama’s visit to China last …