This work reviews autonomous buildings that have been designed to cover electricity requirements by Renewable Energy Source (RES). Not only naturally installed systems but also theoretical presentations (simulations) are included in this study in order to clarify their feasibility and their general behaviour under different weather conditions in several locations. Authors judge on- and off- grid connection, while energy buffering with or without eco-friendly character is also discussed. Finally, the necessity of a relative optimization process is presented, in order to assure the feasibility of off-grid projects, implemented in remote areas with totally “green” technologies