The exhaust gas emission from marine diesel engines is one of the major environmental issues. The authors have been studying the use of photovoltaic energy for the electric power system on ships. This paper proposes an operation control of a photovoltaic/diesel hybrid generating system for a small ship in consideration of the fluctuating photovoltaic power due to solar radiation. The aim of the control is to minimize the fuel consumption and storage capacity of the battery. The validity of the proposed control method is shown by the numerical simulation based on the experimental data of a photovoltaic system. (C) 2001 Published by Elsevier Science B.V. All rights reserved.