Electricity is the most important power supply in urban areas but the huge difference between peak and trough demands still remain a serious problem which has led to a conspicuous decline of efficiency in electricity use and a waste of renewable energy such as wind power and solar power. Recently the development of DC-power supply systems and distributed storage provides a new solution for peak-load shifting and with a better capacity of renewable power uptake. In this paper, a DC-building in the low-carbon city of Shenzhen is used as a case-study and the battery capacity has been calculated and optimised with the simulation. The main conclusions are that the battery capacity determined by discarding a little part of solar power can be reduced by a significant degree and the distributed battery deployment by floor prevails over the centralised battery deployment.