Designing a hybrid power generation system is a complicated task due to a number of variables that needs to be considered in design configuration. Relying on only one performance index to assess the hybrid system performance may lead to wrong selection of the system configuration. In the present work, a new approach of assessing a hybrid PV-wind power generation system using the concept of overall performance index (OPI) is presented. The overall performance index can involve any number of indicators that are important for assessment of the hybrid system with capability to assign each one of them a weight depending on its importance on the overall performance. As a case study, sizing and optimizing the hybrid PV-wind power generation system is carried out using (OPI) concept. Traditionally the loss of power supply probability (LPSP) or cost of energy (COE) was used individually for hybrid system performance assessment; however, in the present study, the (OPI) concept is used to combine (LPSP), energy excess percentage (EXC) and (COE) in one overall performance index. (C) 2015 Elsevier Ltd. All rights reserved.