In this paper, a four-port DC-DC converter is proposed for applications in a grid-connected integrated solar PV and energy storage system. The four ports of the converter are one input source, one bidirectional port, and two output ports. The bidirectional port can be used to integrate the energy storage system to the solar PV generation system, while the two outputs provide the flexibility to supply either two loads or a single load. The detailed analysis and two applications of the four-port DC-DC converter are given in this paper. All of the theoretical analyses are verified by the simulation results.