U.S. Treasury Secretary Janet Yellen has wrapped up a five-day visit to China where she met with top Chinese academic, political and financial leaders in Guangzhou and Beijing. High on her list of topics was an accusation of China's production overcapacity in green technology and U.S. fears that Chinese exports could harm its interests. What is behind this overcapacity claim? Is the U.S. over-reacting to China’s successful green technological development?