China could be the largest market for grid energy storage technology, and now, according to battery maker BYD and China's State Grid utility, the country's potentially got the world's largest battery energy storage station in Zhangbei, Hebei Province. See photo above of the building with rows (bigger than a football field) of BYD's Iron-Phosphate batteries that make up the 36 MW-hours of energy storage along with what looks like rooftop solar panels. A lot of companies have been trying to break into China's grid energy storage market including lithium ion battery maker A123 Systems , flow battery marker ZBB Energy, and even U.S. power producer Duke Energy. China is expected to embrace grid energy storage, as a way to more reliably install the 100 GW of variable clean power that the country wants.