This book provides readers with an overview of recent theories and methods for studying complex mechanical systems used in energy production. The emphasis is put on strategies for increasing energy efficiency, and on recent industrial applications. Topics cover: design, modeling and control of hybrid energy systems, dynamic behaviour of composites, structural vibration, multiphysics dynamic systems, fault diagnosis and robust design. Based on peer-review contributions and invited talks presented at the second International Workshop on MOdelling and Simulation of COmplex Systems for Sustainable Energy Efficiency, MOSCOSSEE 2024, held on November 2-3, 2024, in Matmata, Gabes, Tunisia, this book offers timely information on methods and tools for application in renewable energy production. It provides a valuable resource to both academics and professionals, and a bridge to facilitate communication between the two groups. The conference was organised by The LAboratory of Mechanics, Modelling and Production (LA2MP) at the National School of Engineers of Sfax from University of Sfax, Tunisia, the department of Mechanical Engineering at the National School of Engineers of Gabes from the University of Gabes and the Applied Research Unit for Renewable Energy, Water and the Environment from University of Nouakchott, Mauritania.