The rated peak power of the Vulcano plant is about 80 kW. The main feature of the plant lies in its dual operating mode: either stand-alone or grid-connected. The plant, commissioned half-way through 1984, has always worked uninterruptedly and satisfactorily and, for this reason, it is expected to keep on operating in the coming years. Beginning from 1987, it has been considered worth carrying out research on a number of specific points not so far dealt with in sufficient detail in literature, as follows: experimental research on the deterioration, over a period of time, of the characteristics of the modules of the plant; theoretical and experimental research on the plant`s electrochemical storage system. The research on the second of the above subjects has a number of aims: to improve methods of checking the state of charge of batteries in newly-designed photovoltaic plants; to improve the ways in which the Vulcano battery storage system is operated; and to monitor and make a careful diagnosis of the condition of the plant`s battery.