Hybrid energy systems have attracted significant attention to supply the power requirements of stand-alone areas. Among different configurations, photovoltaic-diesel (PV/diesel) power generation systems are one of the most promising ones for their good performance. Owing to the complexity of the hybrid PV/diesel system, optimal balance between these two sources needs particular attention to find a good engineering solution. This paper focuses on optimal sizing of a PV/diesel power generation system by harmony search (HS) algorithm. Three new pitch adjustment mechanisms are introduced to enhance the diversification and intensification capabilities of HS. The results are compared with the results obtained by original HS, particle swarm optimization (PSO) and genetic algorithm (GA). Simulation results show that HS-II which focuses on intensification, finds more promising results than the other investigated methods. Moreover, hybridization of PV and diesel generator reduces the system costs and pollutant emissions. (C) 2017 Elsevier Ltd. All rights