Current power systems on remote islands use diesel generators (DG) that have high operational and maintenance costs, and emit excessive amounts of carbon dioxide. In this respect, power systems based on renewable energy are currently gaining research attention, with the aim of improving the economic performance and reducing greenhouse gas emissions. However, as the output of renewable energy fluctuates and varies depending on weather conditions, a battery energy storage system (BESS) and DG are required to stabilize the renewable energy output. Then the capacity balances of renewable energy, BESS and DG and these operation methods are main issues. In this paper, several output control methods were proposed for DG and the appropriate generators capacity were evaluated. The effectiveness of the methods was then verified by conducting economic and environmental evaluations. This study conducted a numerical simulation using real data, measured in a power system on an existing island in Japan.