Energy Harvesting (EH) is now becoming popular due to promising long lasting life time of communication system. Some of the communication systems use EH device as their energy source. However, EH also has a limitation that is shown in its characteristics as random arrival and scarce of energy. Both of limitation is very influencing the system performance and the number of transmitted data. As we know the more energy is harvested, the longer system can operate. Because of EH limitation, the system with EH device needs to adjust to get the maximal channel capacity. This paper proposes the cooperative communication system with modified decode and forward (DF) method and EH device as a source energy. The modified DF method incorporate adaptive modulation at relay node to transmit data to the destination node. To test the proposed system, in this paper, three different scenarios are simulated, i.e. the non cooperative communication system with EH device as source energy, the cooperative communication system with DF method but fixed modulation level and EH device as a source energy and the proposed system. The simulation result shows the channel capacity of the proposed system is better than two other scenarios.