Smart grids are the networks which are having intelligence in the generation stage to the after distribution ones. These networks Have very high power efficiency. Moreover, they are applicable stages to the green energy as they depend on green sources as well as intelligence in operation. They may be fully automated. Really, the communication system can connect among different parts of a smart grid. In addition, the communication system performance is governed by the channel performance. In this manuscript, we try to develop a new path loss model for a communication channel in these grids. Moreover, the deduced equation is applied to predict the overall system performance. The received signal strength RSS is measured and there are trials to improve it by applying space time block codes STBC. The simulation results show that the application of STBC codes, inside smart grids, can greatly improve the performance of a smart grid.