Wireless networks have experienced fast development in the past decades. Various advancing wireless technologies have been proposed. To catch up with the ever-increasing diverse communication needs, cloud-radio access networks (C-RAN), which decouples the baseband processing unit (BBU) from the remote radio head (RRH), has been proposed. On the other hand, it has been widely recognized that huge energy consumption has been raised due to the massive deployment of cellular networks. Lowering the network energy consumption therefore becomes a widely concerned topic. To combat the limitations in traditional power grid, smart grid, with the emphasis on distributed energy resource (DER) and bidirectional energy sharing, is advocated to power the wireless networks. In this paper, we are motivated to investigate a joint RRH-BBU association and energy sharing problem towards brown energy usage minimization in green energy powered C-RAN. The problem is formulated into a mixed integer linear programming (MILP) form. To address the computation complexity of solving MILP, a two-phase heuristic polynomial-time algorithm is proposed and evaluated via extensive simulation based studies.