My friends at China's Green Beat did a podcast (click image on right) on solar thermal heating last month. According to the self-dubbed "Green Brothers" of China's Green Beat, China has 40 million solar water heating systems covering 90 million square meters and accounting for two-thirds of the world's market share. The Chinese government intends to more than triple such surface area to 300 million square meters by 2020. The podcast takes a closer look at the city of Rizhao (日照）(which literally means "sunshine") in the northeast province of Shandong, the producer of 15% of China's solar water heating systems. According to Worldchanging, solar water heaters are currently installed in 99% of all buildings in Rizhao’s urban area, and in more than 30% of residences in rural areas.
Often mentioned in the same breath as Rizhao is the city of Kunming in the southern province of Yunnan, as this Worldwatch Institute story describes.
Solar water heating systems in Kunming, Yunnan.
Source: Worlwatch Institute