This paper presents the work performed within the project entitled "Design and Development of an Autonomous Desalination System with Photovoltaics and Wind Generator". The project is partially financed by the Greek Ministry of Development within the Operational Programme for Competitiveness, Measure 4.3, PAVET 2000, Third Community Support Framework. The project started in October 2001 and has 24 month duration. The aim of this project is the design and development of an autonomous hybrid power supply system to drive seawater reverse osmosis (RO) desalination unit for the production of potable water. Measurements of basic parameters are taken into account in order to examine the performance, reliability of the system and its potentiality in autonomous operation.