Tesla has inked its first deal to build a grid-scale battery power plant in China amid a strained trading relationship between Beijing and Washington. The U.S. company posted on the Chinese social media service Weibo that the project would be the largest of its kind in China when completed. Utility-scale battery energy storage systems help electricity grids keep supply and demand in balance. They are increasingly needed to bridge the supply-demand mismatch caused by intermittent energy sources such as solar and wind. Chinese media outlet Yicai first reported that the deal, worth 4 billion yuan ($556 million), had been signed by Tesla, the local government of Shanghai and financing firm China Kangfu International Leasing, according to the Reuters news agency. Tesla said its battery factory in Shanghai had produced more than 100 Megapacks — the battery designed for utility-scale deployment — in the first quarter of this year. One Megapack can provide up to 1 megawatt of power for four hours. "The grid-side energy storage power station is a 'smart regulator' for urban electricity, which can flexibly adjust grid resources," Tesla said on Weibo, according to a Google translation. This would "effectively solve the pressure of urban power supply and ensure the safe, stable and efficient electricity demand of the city," it added. "After completion, this project is expected to become the largest grid-side energy storage project in China."