In this article, we present a brief survey on green 5G cellular networks, and explore some research issues and challenges of the enabling techniques for green broadband wireless networks. The trend of achieving green power in cellular networks is driving network operators and standardization authorities to work together to reduce carbon footprint of their products in order to bring eco friendly 5G green radio cellular base stations. We will first provide an overview on 5G wireless system architecture and the corresponding new protocol stacks. Next, hybrid multiple access schemes, such as combining orthogonal (OFDMA) and non-orthogonal (CDMA) approaches, aiming at improving the both capacity and coverage performances simultaneously are discussed. Since base stations consume the maximum portion of the total energy in current cellular systems, we explore important renewable energy techniques for green base stations, We will provide a comprehensive survey on how to generate renewable energy, such as solar, wind and fuel cells, for green base stations in 5G green cellular networks.