In this paper, the problem of the use of dispersed generation (DG) for providing ancillary services in electrical distribution systems is addressed. Fuel cell-based, photovoltaic cell-based, and wind generation systems are connected to the distribution network through power electronic interfaces, each with a proper storage system for the optimal grid operation. Thanks also to the storage system, the DG units are able to provide ancillary services such as load following, back-up, peak shaving, reactive power support and power quality disturbance compensation. A centralized control system coordinates the DG units. Time domain simulations on an actual distribution system are reported and discussed.